Hydroboration of carbon dioxide with catechol- and pinacolborane using an Ir–CNP* pincer complex. Water influence on the catalytic activity

Jou nal Name ARTICLE This jou nal is © The Royal Socie y o Chemis y 20xx J. Name., 2013, 00, 1-3 | 1 Please do no adjus ma gins Please do no adjus ma gins a. Ins i u o de In es igaciones Químicas (IIQ), Depa amen o de Química Ino gánica and Cen o de Inno ación en Química A anzada (ORFEO-CINQA). CSIC and Uni e sidad de Se illa. A da. Amé ico Vespucio 49, 41092, Se illa (Spain). E-mails : nu [email protected]; and es.sua [email protected] † Dedica ed o P o . E nes o Ca mona on occasion o his 70 h anni e sa y. Elec onic Supplemen a y In o ma ion (ESI) a ailable: [NMR and ESI-MS spec a o selec ed de i a i es and ca aly ic eac ions, and X- ay c ys allog aphy da a o CCDC 1856145]. See DOI: 10.1039/x0xx00000x Recei ed 00 h Janua y 20xx, Accep ed 00 h Janua y 20xx DOI: 10.1039/x0xx00000x www. sc.o g/ Hyd obo a ion o ca bon dioxide wi h ca echol- and pinacolbo ane using an I -CNP* pince complex. Wa e in luence on he ca aly ic ac i i y P áxedes Sánchez, Ma ín He nández-Juá ez, Nu ia Rendón,* Joaquín López-Se ano, Eleu e io Ál a ez, Ma ga i a Paneque, and And és Suá ez* I idium complexes based on dep o ona ed lu idine-de i ed CNP* pince s 2a/2b selec i ely ca alyze he hyd obo a ion o CO2 unde mild condi ions (1-2 ba CO2, 30 oC) o me hoxybo ane using HBca (TOF up o 56 h-1) and o he o ma e le el wi h HBpin (TOF up o 1245 h-1). In e es ingly, an in iguing, posi i e wa e e ec on he eac ion a es has been obse ed. NMR spec oscopy and ESI-MS analysis o he hyd obo a ion eac ions ha e shown he o ma ion o ligand-p o ona ed [I (CNP)(CO)(BR2)H][B(R2)2] (R2 = ca echola e, pinacola e) de i a i es unde ca aly ic condi ions. Con ol expe imen s, howe e , ha e demons a ed ha hese de i a i es a e no ca aly ically compe en species in he hyd obo a ion o CO2. In oduc ion Ca bon dioxide is he C1 ca bon sou ce pa excellence o chemicals and uels p oduc ion due o i s abundan , enewable and non- oxic na u e. 1 Howe e , he chemical ans o ma ion o CO 2 is signi ican ly hampe ed by i s high he modynamic and kine ic s abili y. While con e sion o CO 2 by non- edox p ocesses such as he p oduc ion o ca bona es, ca bama es and u e hanes a e ela i ely well-es ablished p ocesses, 1 he educ ion o CO 2 o syn he ically and ene ge ically ele an p oduc s such as o mic acid de i a i es and me hanol s ill ep esen s an impo an challenge. 2 Among po en ial educ an s, dihyd ogen p o ides he mos a om-economical al e na i e, and consequen ly i is no su p ising ha hyd ogena ion o CO 2 o o ma es and, o a lesse ex en , o MeOH has been p o usely s udied. 2 Since hyd ogena ion o CO 2 usually in ol es he use o high empe a u es and p essu es, o he educing agen s such as hyd osilanes 3 o hyd obo anes 4 ha e also ecei ed a signi ican a en ion due o he milde eac ion condi ions ha can be employed wi h hese species. Fu he mo e, hei eac i i y can be adjus ed by a ying he silane o bo ane subs i uen s acili a ing access o di e en C1 p oduc s including CO, CH 2 O, MeOH and CH 4 . 3,4 In his ein, pa icula ly appealing o syn he ic pu poses is he educ ion o CO 2 o o ma e and ace al de i a i es ha se e o he de elopmen o educ i e unc ionaliza ions o CO 2 . 5 Reduc ion o ca bon dioxide can be accomplished in he absence o a ca alys wi h me al bo ohyd ides. 6 On he con a y, he hyd obo a ion o CO 2 wi h e en e y eac i e BH 3 adduc s should be ca ied ou in he p esence o a ca alys . 7,8 Since he seminal wo k o Guan e al. epo ing he educ ion o CO 2 wi h HBca (ca echolbo ane) o me hanol media ed by pince nickel complexes, 9 he e has been an in ense impe us o he de elopmen o non-me al, 8,10 main g oup me al, 11 and ansi ion me al ca alys s o CO 2 hyd obo a ion. 12-21 Among hese ca aly ic sys ems, hiola e nickel 12 and palladium 13 pince complexes ha e p o ided he highes TOFs, in he ange o 1780 o 2400 h -1 , o he educ ion o CO 2 o me hoxybo ane using HBca as educ an . Also, while hyd obo a ion o CO 2 wi h BH 3 and HBca p oceeds o he me hoxide le el, he educ ion p ocess can be con olled o some ex en by he use o less eac i e bo anes such as HBpin (pinacolbo ane). Thus, selec i e educ ion o CO 2 o o moxybo ane, which has been p o en o se e as a o ma e sou ce o syn he ic pu poses, 14 has been achie ed wi h HBpin and a me al ca alys . 11c,14-17 I is also wo h men ioning a emp s o gene a e ace al de i a i es ha can be employed as me hylene ans e eagen s. 18-20 I is in e es ing o no e ha al hough ca alys s o he hyd obo a ion o CO 2 based on di e en me als, including mos o g oups 8-11 elemen s, ha e been epo ed, i is su p ising ha i idium complexes, which ha e been equen ly employed in hyd obo a ion eac ions, 22-24 ha e no been in es iga ed in he educ ion o CO 2 by hyd obo anes. While being less a ac i e in e ms o cos and en i onmen al aspec s, noble me al ca alys s should no be igno ed since highe ca aly ic e iciencies and s abili ies may compensa e o ARTICLE Jou nal Name 2 | J. Name., 2012, 00, 1-3 This jou nal is © The Royal Socie y o Chemis y 20xx Please do no adjus ma gins Please do no adjus ma gins hei inc ease p ice and be use ul o small scale applica ions. He ein, we epo an I ca alys p ecu so based on a dep o ona ed lu idine-de i ed N-he e ocyclic ca bene/phosphine CNP* pince ha selec i ely ca alyzes he hyd obo a ion o CO 2 o me hoxy- o o moxybo ane depending on he employed hyd obo ane (HBca o HBpin). In e es ingly, an unexpec ed posi i e in luence o he p esence o small amoun s o wa e in he eac ion a es has been obse ed. Finally, i idium species o med unde ca aly ic condi ions ha e been in es iga ed and hei pa icipa ion in he ca aly ic cycle has been e alua ed. Resul s and discussion Syn hesis o he ca alys p ecu so Reac ion o he ca bonyl i idium complex 1(Cl) 25 wi h KO Bu in THF yielded he o ma ion o a mix u e o he dep o ona ed “ au ome ic” species 2a and 2b (Scheme 1). The a io, as de e mined by 1 H NMR spec oscopy, be ween hese species depends on he sol en . In he 1 H NMR spec um egis e ed in THF-d 8 , 2a and 2b appea in a 9:1 a io, whe eas a 2a / 2b a io o 4 was obse ed in C 6 D 6 . In he o me sol en , he CH 2 N b idge o he pince o 2a p oduces in he 1 H NMR spec um a single signal a 4.72 ppm (2H) and he me hyne CHP a m gi es ise o a double esonance a 3.84 ppm ( 2 J HP = 1.9 Hz, 1H), meanwhile 2b exhibi s a single peak a 6.17 ppm (1H) o he CHN pince a m and a double signal a 3.51 ppm ( 2 J HP = 11.4 Hz, 2H) o he hyd ogens o he me hylene CH 2 P moie y. Fo bo h complexes, he esonances co esponding o he py idine de i ed agmen s appea signi ican ly shi ed up ield (6.30- 5.37 ppm) in compa ison o 1(Cl) , in ag eemen wi h he p esence o dea oma ized cen al ings. In he 13 C{ 1 H} NMR spec um, de i a i e 2a exhibi s he esonance p oduced by he ca benic ca bon a om as a double a 182.8 ppm (J CP = 92 Hz) and ha o he CO ligand a 182.0 ppm (d, J CP = 10 Hz). Fu he suppo o he in e ed s uc u e o 2a was ob ained by a X- ay di ac ion s udy o a single c ys al o he complex (Fig. 1). 26 Dep o ona ion o he me hylene P-a m is e lec ed in sho C(19)-P(1) and C(19)-C(18) bond leng hs o 1.743 and 1.370 Å, espec i ely. Fu he mo e, al e na ing C-C dis ances in he py idine moie y e idence ing dea oma iza ion as shown by he elonga ed C(18)-C(17) and C(16)-C(15) dis ances o 1.460 and 1.396 Å, and sho en C(17)-C(16) and C(15)-C(14) bond leng hs o 1.343 and 1.378 Å, espec i ely (a e age C-C bond in he py idine molecule: 1.38 Å). As in e ed om he di e en 2a / 2b a ios obse ed in dis inc sol en s, complexes 2a and 2b a e in equilib ium in solu ion. This obse a ion is u he mani es ed in he 1 H, 1 H- exchange spec oscopy (EXSY) spec um (mixing ime = 0.8 s) o he 2a / 2b mix u e in we THF-d 8 egis e ed a 25 o C, whe e in ense exchange c oss-peaks a e obse ed be ween: i) signals co esponding o he me hyne and me hylene b idges o 2a , ii) esonances caused by he CHP and CH 2 N moie ies o 2a wi h hose o he CH 2 P and CHN b idges o 2b , espec i ely, and iii) he signals o he me hyne and me hylene agmen s o 2a and 2b wi h hose o wa e (Fig. S1). These obse a ions suppo ha he iden a e ligand b idges can ge in ol ed in e e sible p o ona ion/dep o ona ion media ed by wa e molecules ac ing as p o on ans e assis an s. 27 Scheme 1 Syn hesis o complexes 2a and 2b . Fig. 1 ORTEP d awing a 30% ellipsoid p obabili y o complex 2a. Mos hyd ogen a oms and sol en molecule (THF) ha e been omi ed o cla i y. Selec ed bond leng hs [Å] and angles [o]: I (1)-C(1) 2.034(8), I (1)-N(3) 2.127(5), I (1)-P(1) 2.285(2), I (1)-C(32) 1.818(8), C(1)-I (1)-P(1) 168.3(2), C(1)-I (1)-C(32) 97.2(3), C(32)-I (1)-N(3) 172.9(3), C(1)- I (1)-N(3) 89.7(2), P(1)-I (1)-N(3) 82.64(16). Ca aly ic hyd obo a ion o CO2 Hyd obo a ion o CO 2 ca alyzed by he mix u e o complexes 2a / 2b was in es iga ed. Ini ial eac ions we e ca ied ou wi h HBca in THF-d 8 (2 ba CO 2 , 30 o C) using 1.0 mol% o 2a / 2b . Selec i e CO 2 educ ion o he co esponding me hoxybo ane (CH 3 OBca ) was es ablished by 1 H NMR spec oscopy a e he obse a ion o a single esonance a 3.81 ppm, and he appea ance o a b oad signal in he 11 B NMR spec um a 22.5 ppm. Also, he expec ed concomi an o ma ion o dibo oxane (ca BOBca ) was con i med by he appea ance o a whi e p ecipi a e a e emo al o THF-d 8 unde acuum and addi ion o C 6 H 6 (  H (THF-d 8 ) = 6.83, 6.93 ppm;  B (THF-d 8 ) = 16.5 ppm). 28 Al hough signi ican ca e was exe cised in he se -up o he ca aly ic expe imen s, hese eac ions we e ini ially ound di icul o ep oduce. Howe e , a e sc upulous con ol o he eac ion pa ame e s, a ma ked in luence o he p esence o wa e in he hyd obo a ion eac ion was no iced. 29 The e o e, ca aly ic eac ions we e pe o med in he p esence o a iable amoun s o wa e (Table 1). Reac ions we e ollowed up by 1 H{ 11 B} NMR spec oscopy, and o a meaning ul compa ison o he ca aly ic ac i i y, TON alues we e de e mined a e 1.5 h Jou nal Name ARTICLE This jou nal is © The Royal Socie y o Chemis y 20xx J. Name., 2013, 00, 1-3 | 3 Please do no adjus ma gins Please do no adjus ma gins al hough upon ex ended eac ion imes all he eac ions p oceeded o comple ion. Thus, when he ca aly ic eac ion was pe o med in he p esence o 1 mol% o wa e , o ma ion o 18% o me hoxybo ane was obse ed (TON = 54; TOF = 36 h - 1 ) (en y 1). By inc easing he wa e con en , as e ans o ma ion o CO 2 o me hoxybo ane was e idenced, p o iding up o 28% con e sion o me hoxybo ane in he p esence o 5 mol% o wa e (TON = 84; TOF = 56 h -1 ) (en ies 2 and 3). I should be no ed ha o he la e eac ion he maximum yield is 30% a e conside ing he amoun o bo ane ha is hyd olyzed o ca BOBca . Fu he inc ease in he wa e con en o he eac ion o 6 mol% somewha dec eased he ca aly ic ac i i y (TOF = 50 h -1 ) (en y 4). In e es ingly, complex 1(Cl) was ound a poo e ca alys han 2a / 2b p o iding 78 u no e s a e 16 h (TOF = 4.9 h -1 ) (en y 5). Con ol expe imen s showed ha 2a / 2b ca alyzes he hyd olysis o HBca o yield ca BOBca as he sole p oduc . Table 1 Ca aly ic hyd obo a ion o CO2 wi h HBca En y Ca alys H 2 O (mol%) Yield (%) TON 1 2a/2b 1 18 54 2 3 24 72 3 5 28 84 4 6 25 75 5a 1(Cl) 3 26 78 Reac ion condi ions: 1.0 mol% [I ], 2 ba CO2, 30 oC, THF-d8, [HBca ] = 0.5 M. Reac ion ime: 1.5 h, unless o he wise no ed. Yields we e de e mined by 1H{11B} NMR spec oscopy using hexame hylbenzene as in e nal s anda d. TON alues based on moles o B-H bonds eac ed pe mole ca alys : (mmol me hoxybo ane x 3)/(mmol ca ). a Reac ion ime: 16 h. Nex , he ca aly ic pe o mance o 2a / 2b in he hyd obo a ion o CO 2 wi h HBpin was examined unde 1 ba o CO 2 a 30 o C (Table 2). These eac ions we e ca ied ou wi h low ca alys loadings o 0.2 mol%. While p e ious epo s ha e shown ha educ ion o CO 2 wi h pinacolbo ane may yield o ma e (HCO 2 Bpin), ace al (H 2 C(OBpin) 2 ) and me hoxy (CH 3 OBpin) de i a i es, o mix u es he eo , eac ions wi h 2a / 2b ga e solely o moxybo ane. Mo eo e , as in he case o he eac ions wi h HBca , he p esence o small amoun s o wa e signi ican ly inc eases he eac ion a e. All eac ions p oceeded o con e sions o HBpin highe han 90%, al hough TON alues we e compa ed a e a eac ion ime o 20 min. Fo example, eac ion in he p esence o 1 mol% o wa e p o ided he o moxybo ane de i a i e in 30% yield (TOF = 450 h -1 , en y 1), whe eas upon addi ion o inc easing amoun s o wa e up o 7 mol% a ca. h ee- old ise o he ca aly ic ac i i y (TOF = 1245 h -1 ) was obse ed (en ies 2-5). Mo eo e , when he ca alys loading was u he educed o 0.1 mol%, o moxybo ane was ob ained in 74% yield a e 1 h, wha ep esen s a no able TOF o 740 h -1 . Among he ew ca alys s ha selec i ely p oduces o moxybo ane, 11c,14-17 only he palladium pince complex epo ed by Haza i e al. p o ides as e eac ion a es wi h low ca alys loadings (TOF = 8500 h -1 , 0.01 mol% ca alys ). 15 Table 2 Ca aly ic hyd obo a ion o CO2 wi h HBpin En y H2O (mol%) Yield (%) TON 1 1 30 150 2 2 72 360 3 3 79 395 4 6 80 400 5 7 83 415 6a 3 74 740 Reac ion condi ions, unless o he wise no ed: 0.2 mol% 2a/2b, 1 ba CO2, 30 oC, THF-d8, [HBpin] = 0.4 M. Reac ion ime: 20 min. Yields we e de e mined by 1H{11B} NMR spec oscopy using hexame hylbenzene as in e nal s anda d. TON alues as de e mined by (mmol o moxybo ane)/(mmol ca ). a 0.1 mol% 2a/2b. Reac ion ime: 1.0 h. S udy o me al species o med unde ca aly ic condi ions To shed ligh on he me al species o med unde ca aly ic condi ions, he hyd obo a ion o CO 2 (2 ba ) wi h HBca was ca ied ou using 20 mol% o 2a / 2b in THF-d 8 . Upon eac ion comple ion only a single signal is obse ed in he 31 P{ 1 H} NMR spec um a 16.9 ppm ha co esponds o a dihyd ide species, as deduced by he appea ance o wo double s o double s signals appea ing a 17.5 ( 2 J HP = 12 Hz, 2 J HH = 2 Hz) and 8.3 ppm ( 2 J HP = 22 Hz, 2 J HH = 2 Hz) in he 1 H NMR spec oscopy expe imen . The e o e, we hypo hesized whe he he species obse ed a e eac ion comple ion was a dihyd ide I complex based on a p o ona ed CNP ( 3 + , Scheme 2) o dep o ona ed CNP* ( 4 , Scheme 3) ligand, and consequen ly an independen syn hesis o bo h complexes was pu sued. Fo he s udy o complex 3(Cl) , a CD 2 Cl 2 solu ion o 1(Cl) was exposed o 1 ba o H 2 (Scheme 2). The 1 H NMR spec um o he newly o med species showed a double o double s a 17.45 ppm ( 2 J HP = 11.7 Hz, 2 J HH = 1.6 Hz) a ibu able o he I H ans o he py idine moie y, and a double o double s o double s appea ing a 8.32 ppm ( 2 J HP = 22.2 Hz, 2 J HH = 1.6 Hz, 4 J HH = 1.6 Hz) caused by he hyd ide ligand placed cis o he N-dono agmen ha couples wi h he o he I H hyd ogen and one o he hyd ogens o he CH 2 P b idge. 30 Meanwhile, he 31 P{ 1 H} NMR spec um displays a single signal a 16.9 ppm. These da a ag ee well wi h he obse ed signals a he end o he ca aly ic eac ion and demons a es ha ligand p o ona ion occu s unde ca alysis. Complex 3(Cl) could no be isola ed since i s a emp ed pu i ica ion yielded mix u es o 3(Cl) and 1(Cl) , indica ing ha he dihyd ido complex loses H 2 unde acuum. ARTICLE Jou nal Name 4 | J. Name., 2012, 00, 1-3 This jou nal is © The Royal Socie y o Chemis y 20xx Please do no adjus ma gins Please do no adjus ma gins Scheme 2 Reac ion wi h H2 o complex 1(Cl). Scheme 3 Reac ion wi h H2 o complexes 2a / 2b . Addi ionally, o ma ion o a dep o ona ed dihyd ide complex 4 was uled ou since exposu e o he 2a / 2b mix u e o H 2 (5 ba ) in THF-d 8 p oduced in he 31 P{ 1 H} NMR spec um a single a 8.8 ppm. Fu he mo e, in he 1 H NMR spec um de i a i e 4 showed wo double o double s appea ing a 8.64 ( 2 J HP = 20.8 Hz, 2 J HH = 1.5 Hz) and 16.59 ( 2 J HP = 11.3 Hz, 2 J HH = 1.5 Hz), 30 whe eas he signals o he dea oma ized py idine ing a e signi ican ly shi ed o high ield appea ing in he ange be ween 6.56 and 5.71 ppm. Complex 4 also eadily loses H 2 unde acuum leading o he egene a ion o he 2a / 2b mix u e. Fu he mo e, analysis by ESI-MS (posi i e mode) o he ca aly ic eac ion be ween CO 2 and HBca in he p esence o 20 mol% o 2a / 2b p o ided a peak a m/z 698 a ibu able o he ca ionic agmen [I H 2 (CNP)(CO)] + ( 3 + ), while in he nega i e mode a peak a m/z 227 was obse ed ha has been assigned o he a ylspi obo ona e es e [Bca 2 ] . Deg ada ion o HBca p omo ed by nucleophiles, including complexes con aining anionic ligands, ha e been shown o p o ide he abo e anion along wi h o he bo on species such as B 2 ca 3 and BH 3 . 23,24,31 Howe e , o ma ion o hese, o o he , bo on de i a i es could no be unequi ocally de ec ed by MS o NMR spec oscopy. Mo eo e , al hough HBpin has been shown o be less p one o deg ada ion han HBca , 22d,32 ESI-MS analysis o a ca aly ic eac ion wi h HBpin using 20 mol% o 2a / 2b allowed o he de ec ion o he ca ionic agmen 1 + and he anion [Bpin 2 ] (m/z 243). 33 We specula e ha o ma ion o [Bca 2 ] and [Bpin 2 ] anions migh ini ially in ol e nucleophilic a ack o he hyd obo ane by he me hyne ca bon o he dep o ona ed CNP* ligand, 27 and ligand-assis ed B-H ac i a ion, as shown by Mils ein e al. o ela ed Ru complexes. 34 Howe e , di ec e idence o hese p ocesses has emained elusi e in ou sys em. Since he hyd obo a ion eac ion is signi ican ly as e using HBpin han wi h HBca , he la e p ocess was chosen o ge insigh in o he o ma ion o o he me al species du ing he ca aly ic eac ion. Hyd obo a ion o CO 2 (2 ba ) wi h HBca using 10 mol% o 2a / 2b in THF-d 8 was moni o ed by 1 H NMR spec oscopy, showing he o ma ion o a hyd ide complex ha p oduces a double esonance a 6.9 ppm ( 2 J HP = 21 Hz), and which could be he esul o he oxida i e addi ion o HBca o 1 + . In o de o unequi ocally de e mine he s uc u e o his de i a i e, complex 1(Bca 2 ) was eadily isola ed a e anion exchange o 1(Cl) wi h Li[Bca 2 ] 35 and made eac wi h HBca (Scheme 4). Addi ion o a sligh excess o HBca (1.5 equi ) o a THF-d 8 solu ion o 1(Bca 2 ) p oduced he decolo ing o he ini ially yellow solu ion o yield he bo yli idium hyd ide complex 5(Bca 2 ) . 24,36 This de i a i e was spec oscopically cha ac e ized since a emp s o isola e 5(Bca 2 ) yielded mix u es o 1(Bca 2 ) and 3(Bca 2 ) . Diagnos ic signals o complex 5(Bca 2 ) in he 1 H NMR and 13 C{ 1 H} NMR spec a egis e ed in THF-d 8 include he p esence o a double esonance a 6.90 ppm ( 2 J HP = 21.1 Hz) a ibu able o he hyd ido ligand, and a double a 154.3 ppm (J CP = 96 Hz) due o he ca benic ca bon, espec i ely. The p esence o he ca bonyl ligand is mani es ed in he 13 C{ 1 H} NMR spec um by a b oad esonance a 176.8 ppm, and in he IR spec um by an abso p ion a 2005 cm -1 . Mo eo e , in addi ion o he HBca and bisca echolbo a e esonances appea ing in he 11 B NMR spec um a 22.5 (d, J BH = 189 Hz) and 15.1 ppm espec i ely, a b oad signal a 12.9 ppm is also obse ed, which ha e been assigned o he bo yl ligand. Also, while hese spec oscopic da a do no allow o a s aigh o wa d di e en ia ion be ween he wo possible isome s esul ing om he oxida i e addi ion o HBca o 1(Bca 2 ) , i.e. ans ( 5-I ) o cis ( 5-II ) coo dina ion o he bo yl ligand o he py idine agmen (Fig. 2), compa ison o he chemical shi o he esonance o he hyd ido ligand wi h hose o complex 3(Cl) sugges s a cis coo dina ion o he Bca moie y o he ca bonyl ligand. This ligand disposi ion p e en s he ans coo dina ion o he wo po en ially  -accep ing bo yl and ca bonyl ligands. 36b,37 Mo eo e , DFT calcula ions (B3LYP-D3, 6-31g(d,p)/SDD) o 5-I and 5-II indica e ha he o me ca ionic species is mo e s able by 3.2 kcal/mol (Fig. 2). Also o no e, in he 1 H, 1 H-exchange spec oscopy (EXSY) spec um o he eac ion mix u e o 1(Bca 2 ) and HBca in THF-d 8 egis e ed a 25 o C, exchange c oss peaks a e obse ed be ween he signal o he a oma ic hyd ogens co esponding o HBca and hose o he [Bca 2 ] anion indica i e o he exis ence o a bo on subs i uen sc ambling p ocess. Upon egis e ing he same expe imen a 50 o C, a c oss-peak signal caused by he exchange be ween ee HBca and he hyd ido ligand is also obse ed poin ing ou o he e e sibili y o he B-H oxida i e addi ion. Cl N PPh2 NNMes I CO H2, CD2Cl2 Cl N PPh2 NNMes I H CO H 1(Cl) 3(Cl) acuum Jou nal Name ARTICLE This jou nal is © The Royal Socie y o Chemis y 20xx J. Name., 2013, 00, 1-3 | 5 Please do no adjus ma gins Please do no adjus ma gins Scheme 4 Syn hesis o 1(Bca 2) and 1(BA F), and eac ions wi h bo anes. Fig. 2 Rela i e he modynamic s abili y o ca ionic agmen s 5-I and 5-II, and 6-I and 6- II. Da a in pa en hesis a e G in THF (kcal mol-1). To es he o ma ion o analogous species o 5(Bca 2 ) wi h HBpin, complex 1(BA F ) , p e iously p epa ed by anion exchange o 1(Cl) wi h NaBA F , was eac ed wi h an excess o HBpin (2.4 equi ) (Scheme 4). The newly o med species 6(BA F ) p o ided compa able NMR spec a o hose o 5(Bca 2 ) , wi h he logical di e ences o he signals due o he [BA F ] - anion and he bo yl ligand, e incing he cis a angemen o he bo yl and CO ligands. Howe e , DFT calcula ions (B3LYP- D3, 6-31g(d,p)/SDD) shows ha he isome 6-I is 3.5 kcal/mol less s able han 6-II , wha can be asc ibed o he p esence o non-s abilizing in e ac ions in 6-I be ween he mo e s e ically demanding pinacol moie y wi h he subs i uen s o he NHC and phosphino agmen s (Fig. 2). Also o in e es , exchange c oss-peaks be ween he esonances o he ee bo ane and he hyd ido ligand o 6(BA F ) a e obse ed in he 1 H, 1 H-EXSY spec um. NMR spec a o he eac ion o complexes 5(Bca 2 ) and 6(BA F ) wi h CO 2 did no show any no iceable changes, i.e. inse ion o CO 2 in o he I -H bond o yield a o ma o complex was no obse ed. The e o e, in o de o de e mine whe he species 5(Bca 2 ) and 6(BA F ) pa icipa e in he educ ion o CO 2 wi h bo anes, complexes 1(Bca 2 ) and 1(BA F ) we e employed as p e-ca alys in lieu o 2a / 2b in he hyd obo a ion o CO 2 wi h HBca and HBpin, espec i ely. Unde he eac ion condi ions o Table 1, en y 5, 1(Bca 2 ) p o ided a signi ican ly lowe TOF o 6.8 h -1 (89% con . a e 13 h). Simila ly, complex 1(BA F ) was also ound a poo e ca alys p ecu so han 2a / 2b in he educ ion o CO 2 since negligible o ma ion o o moxypinacolbo ane was obse ed (<5% con . a e 21 h). O e all, hese esul s suppo ha 5(Bca 2 ) and 6(BA F ) a e no signi ican ly in ol ed in he hyd obo a ion o CO 2 using 2a / 2b as ca aly ic p ecu so s. Ma de , Bake e al. ha e simila ly obse ed ha while [I (Cl)(COE) 2 ] 2 /PPh 3 mix u es p omo e HBca deg ada ion and a e ac i e in alkene hyd obo a ions, isola ed i idium bo yl compounds gene a ed om he eac ion o his ca aly ic sys em and hyd obo anes p oduce inne ec i e ca alys s. 24 Simila ly, o hiola e Ni and Pd pince complexes, which a e e y ac i e ca aly ic p ecu so s in he hyd obo a ion o CO 2 o CH 3 OBca , i has been shown ha he co esponding hyd ide species a e p obably no in ol ed in he ca aly ic p ocess. 12,13 As p e iously epo ed, ca aly ic hyd obo a ion o CO 2 wi h HBpin can p oceed o he me hoxide le el (CH 3 OBpin), 4 al hough wi h a p ope choice o he ca alys pa ially educed p oduc s including he co esponding o moxybo ane de i a i e can be ob ained. 14-20 Guan e al. ha e compu a ionally s udied he educ ion o CO 2 wi h HBca o CH 3 OBca media ed by a pince nickel hyd ide complex. 9b The delinea ed mechanism is composed o h ee successi e cycles. The i s cycle in ol es CO 2 inse ion in o he Ni-H bond o yield a Ni- o ma e in e media e ha upon in e ac ion wi h HBpin yields HCO 2 Bca . The subsequen educ ion o o moxybo ane implies he inse ion in o a Ni-H bond o p oduce o maldehyde, which is inally educed o CH 3 OBca by a hi d molecule o HBca . Analogous s eps ha e also been p oposed o he hyd obo a ion o CO 2 wi h HBpin ca alyzed by a Ru complex. 38 Based on he mechanism p oposed by he Guan g oup, Haza i e al. ha e assumed ha he high selec i i y p o ided by a pince Pd complex in he hyd obo a ion o CO 2 wi h HBpin o he o ma e le el is de e mined by he la ge size o he pinacol agmen ha p e en s u he educ ion o HCO 2 Bpin. 15 Fu he mo e, selec i e educ ion o CO 2 o o moxybo ane wi h HBpin has only been achie ed wi h me al based ca alys s. 14-17 The e o e, since a highly selec i e CO 2 hyd obo a ion wi h HBpin o o moxybo ane akes place using 2a / 2b , i can be expec ed ha me al species should be in ol ed in he ca aly ic eac ions. Fu he mo e, conside ing he deg ada ion o he hyd obo anes as well as he obse ed in luence o wa e , i can be p oposed ha he ca aly ically ac i e species a e i idium de i a i es o med by eac ion o 2a / 2b wi h he hyd obo anes and wa e . Howe e , since in addi ion o us a ed Lewis pai s con aining bo on-based moie ies capable o ca alyzing he hyd obo a ion o CO 2 , 8a,8b,8g o he bo on species ha e been shown o ca alyze hyd obo a ion eac ions, as epo ed o he ca aly ic addi ion o hyd obo anes o alkenes and alkynes, 39 educ ion o CO 2 media ed by bo on species de i ed om hyd obo ane deg ada ion p omo ed by 2a / 2b , o hei pa icipa ion in accele a ing an I -ca alyzed eac ion, 40 canno be ully uled ou . Conclusions The i idium complexes suppo ed by dep o ona ed lu idine- de i ed CNP* pince s 2a / 2b ca alyze he hyd obo a ion o CO 2 . A ma ked in luence o he hyd obo ane is obse ed in he selec i i y and a e o he eac ions. Mo e in e es ingly, ARTICLE Jou nal Name 6 | J. Name., 2012, 00, 1-3 This jou nal is © The Royal Socie y o Chemis y 20xx Please do no adjus ma gins Please do no adjus ma gins signi ican eac ion a e accele a ions ha e been obse ed a e op imiza ion o he wa e con en o he eac ions, sugges ing ha wa e is in ol ed in he o ma ion o he ca aly ically ac i e species. Thus, upon using HBca selec i e educ ion o CO 2 o he me hanol equi alen is obse ed (TOF up o 58 h -1 ), whe eas he mos s e ically demanding HBpin yields he co esponding o moxybo ane as he sole p oduc wi h no able ca aly ic ac i i ies (TOF up o 1245 h -1 ). Unde ca aly ic condi ions, i idium species esul ing om he oxida i e addi ion o he hyd obo ane o ligand- p o ona ed [I (CNP)(CO)][B(R 2 ) 2 ] (R 2 = ca echol, pinacol) complexes has been obse ed. Howe e , con ol expe imen s indica e ha hese species a e ine icien ca alys s in he hyd obo a ion o CO 2 . Taking in o accoun he obse ed wa e e ec , he hyd obo ane deg ada ion leading o he o ma ion o [B(R 2 ) 2 ] - anions, and he di e en selec i i y obse ed in he educ ion o CO 2 wi h HBca and HBpin, we eel inclined o conside ha he hyd obo a ion eac ions a e ca alyzed by I - con aining species o med a e eac ion o 2a / 2b wi h he hyd obo ane in he p esence o wa e . Un o una ely, we ha e been unable o de ec such as species by NMR spec oscopy o MS, sugges ing ha hey a e o med in low concen a ions. Expe imen al Gene al p ocedu es All eac ions and manipula ions we e pe o med unde ni ogen o a gon, ei he in a B aun Labmas e 100 glo ebox o using s anda d Schlenk- ype echniques. All sol en s we e dis illed unde ni ogen wi h he ollowing desiccan s: sodium-benzophenone-ke yl o die hyl e he (E 2O) and e ahyd o u an (THF); sodium o pen ane and oluene; CaH2 o dichlo ome hane and ace oni ile (CH2Cl2, CH3CN); and NaOMe o me hanol (MeOH). Fo he p epa a ion o we THF-d8 solu ions, comme cial THF-d8 (Eu iso op, <0.05% wa e ) was d ied wi h sodium-benzophenone-ke yl and dis illed unde a gon, and known amoun s o wa e we e added. Wa e con en in he hus p epa ed solu ions was con i med by 1H NMR spec oscopy using hexame hylbenzene as in e nal s anda d. Complex 1(Cl),25 Li[Bca 2]35 and Na[BA F]41 we e syn he ized ollowing p e iously epo ed me hods. All o he eagen s we e pu chased om comme cial supplie s and used as ecei ed. NMR spec a we e ob ained on B uke DPX-300, DRX-400, AVANCEIII/ASCEND 400R o DRX-500 spec ome e s. 31P{1H} and 11B NMR shi s we e e e enced o ex e nal 85% H3PO4 and BF3E 2O espec i ely, while 13C{1H} and 1H shi s we e e e enced o he esidual signals o deu e a ed sol en s. All da a a e epo ed in ppm down ield om Me4Si. All NMR measu emen s we e ca ied ou a 25 °C, unless o he wise s a ed. NMR signal assigna ions we e con i med by 2D NMR spec oscopy (1H-1H COSY, 1H-1H NOESY, 1H-13C HSQC and 1H- 13C HMBC) and 1H{31P} and 1H{11B} NMR expe imen s. HRMS da a we e ob ained on a JEOL JMS-SX 102A mass spec ome e a he Ins umen al Se ices o Uni e sidad de Se illa (CITIUS). ESI-MS expe imen s we e ca ied ou in a B uke 6000 appa a us by he Mass Spec ome y Se ice o he Ins i u o de In es igaciones Químicas. Elemen al analyses we e un by he Analy ical Se ice o he Ins i u o de In es igaciones Químicas in a Leco T ueSpec CHN elemen al analyze . IR spec a we e acqui ed on a B uke Tenso 27 ins umen . Syn hesis o complexes Complexes 2a/2b. To a solu ion o 1(Cl) (0.075 g, 0.10 mmol) in THF (5 mL) was added a solu ion o KO Bu (0.013 g, 0.11 mmol) in THF (5 mL) gi ing ise o a ed solu ion. The esul ing solu ion was s i ed o 2 h, and sol en was e apo a ed unde educed p essu e. The esidue was ex ac ed wi h oluene (2  10 mL), and ola iles we e emo ed unde acuum. The solid ob ained was washed wi h pen ane (2  10 mL) and d ied unde acuum o gi e he mix u e o complexes 2a and 2b as a ed solid (0.050 g, 70%). C ys als o 2a sui able o X- ay di ac ion analysis we e g own om a sa u a ed solu ion o he complexes 2a/2b in THF. Anal. calcd (%) o C32H29I N3OP: C 55.32, H 4.21, N 6.05; ound: C 55.10, H 4.56, N 6.09. IR (nujol): 1938 (CO) cm-1. NMR spec oscopy da a o 2a: 1H NMR (500 MHz, THF-d8):  7.57 (m, 4H, 4 H a om PPh), 7.41 (s, 1H, H a om NHC), 7.20 (m, 6H, 6 H a om PPh), 7.09 (s, 1H, H a om NHC), 6.92 (s, 2H, 2 H a om Mes), 6.30 (m, 2H, Hb + Hc), 5.37 (dd, 3JHH = 3.7 Hz, 3JHH = 3.7 Hz, 1H, Hd), 4.72 (s, 2H, CH2N), 3.84 (d, 2JHP = 1.9 Hz, 1H, Ha), 2.28 (s, 3H, CH3), 2.09 (s, 6H, 2 CH3). 31P{1H} NMR (202 MHz, THF-d8):  28.3. 13C{1H} NMR (125 MHz, THF-d8):  182.8 (d, JCP = 92 Hz, C-2 NHC), 182.0 (d, JCP = 10 Hz, CO), 156.3 (d, JCP = 24 Hz, Cq a om), 150.8 (d, JCP = 1 Hz, Cq a om), 140.6 (d, JCP = 58 Hz, 2 Cq a om), 139.6 (Cq a om), 137.5 (Cq a om), 136.9 (2 Cq a om), 132.9 (d, JCP = 11 Hz, 4 CH a om), 131.9 (d, JCP = 2 Hz, Cc), 129.4 (2 CH a om), 129.3 (d, JCP = 2 Hz, 2 CH a om), 128.3 (d, JCP = 10 Hz, 4 CH a om), 121.8 (d, JCP = 3 Hz, CH a om), 121.1 (d, JCP = 3 Hz, CH a om), 117.8 (d, JCP = 19 Hz, Cb), 101.7 (Cd), 69.1 (d, JCP = 69 Hz, Ca), 57.3 (CH2N), 21.2 (CH3), 18.6 (2 CH3). NMR spec oscopy da a o 2b: 1H NMR (500 MHz, THF-d8):  7.64 (m, 4H, 4 H a om PPh), 7.49 (s, 1H, H a om NHC), 7.32 (m, 6H, 6 H a om PPh), 7.06 (s, 1H, H a om NHC), 6.91 (s, 2H, 2 H a om Mes), 6.17 (s, 1H, He), 6.17 (d, 3JHH = 8.7 Hz, 3JHH = 6.3 Hz, 1H, Hc), 6.05 (d, 3JHH = 8.9 Hz, 1H, Hd), 5.53 (d, 3JHH = 6.1 Hz, 1H, Hb), 3.51 (d, 2JHP = 11.4 Hz, 1H, CH2P), 2.25 (s, 3H, CH3), 2.12 (s, 6H, 2 CH3). 31P{1H} NMR (202 MHz, THF-d8):  33.3. Complex 1(Bca 2). A solu ion o 1(Cl) (0.100 g, 0.14 mmol) and Li[Bca 2] (0.035 g, 0.15 mmol) in MeCN (8 mL) was s i ed o 1 h. The esul ing suspension was il e ed, and sol en was emo ed unde educed p essu e. The esidue was ex ac ed wi h CH2Cl2 (2  10 mL), and he solu ion was b ough o d yness. The esul ing solid was washed wi h pen ane (2  8 mL) and d ied unde acuum. Complex 1(Bca 2) was ob ained as an o ange solid (0.073 g, 58%). IR (nujol): 1973 cm-1 (CO). 1H NMR (500 MHz, CD2Cl2):  7.79 (dd, 3JHH = 7.7 Hz, 3JHH = 7.7 Hz, 1H, H a om Py), 7.65 (d, 3JHH = 7.7 Hz, 1H, H a om Py), 7.59 (m, 6H, 6 H a om), 7.52 (m, 2H, 2 H a om), 7.44 (m, 4H, 4 H a om), 7.04 (s, 2H, 2 H a om Mes), 7.01 (s, 1H, H a om NHC), 6.55 (m, 8H, Bca 2), 5.42 (s, 2H, CH2N), 4.09 (d, 2JHP = 10.1 Hz, 2H, Jou nal Name ARTICLE This jou nal is © The Royal Socie y o Chemis y 20xx J. Name., 2013, 00, 1-3 | 7 Please do no adjus ma gins Please do no adjus ma gins CH2P), 2.36 (s, 3H, CH3), 2.13 (s, 6H, 2 CH3). 31P{1H} NMR (202 MHz, CD2Cl2):  45.4. 11B{1H} NMR (96 MHz, CD2Cl2):  14.4. 13C{1H} NMR (125 MHz, CD2Cl2):  178.6 (d, JCP = 98 Hz, C-2 NHC), 177.1 (d, JCP = 9 Hz, CO), 165.0 (d, JCP = 7 Hz, Cq a om), 155.3 (Cq a om), 152.3 (4 Cq a om Bca 2), 141.5 (CH a om), 140.3 (Cq a om), 136.3 (2 Cq a om), 135.6 (Cq a om), 133.2 (d, JCP = 12 Hz, 4 CH a om), 132.0 (2 CH a om), 130.2 (d, JCP = 54 Hz, 2 Cq a om), 129.5 (d, JCP = 11 Hz, 4 CH a om), 129.3 (2 CH a om), 124.7 (d, JCP = 10 Hz, CH a om), 124.6 (CH a om), 122.8 (CH a om), 122.5 (CH a om), 118.2 (4 CH a om Bca 2), 108.7 (4 CH a om Bca 2), 55.5 (CH2N), 42.6 (d, JCP = 31 Hz, CH2P), 21.3 (CH3), 18.5 (2 CH3). HRMS (ESI): m/z 696.1743 [(MBca 2)+] (exac mass calcula ed o C32H30I N3OP: 696.1750). Complex 1(BA F). A solu ion o 1(Cl) (0.096 g, 0.13 mmol) and Na[BA F] (0.116 g, 0.13 mmol) in CH2Cl2 (7 mL) was s i ed o 2 h. The esul ing suspension was il e ed, and sol en was emo ed unde educed p essu e. The esul ing solid was washed wi h pen ane (2  10 mL) and d ied unde acuum. Complex 1(BA F) was isola ed as an o ange solid (0.186 g, 91%). Anal. calcd (%) o C64H42BF24I N3OP: C 49.31; H 2.72; N 2.70; ound: C 49.20; H 2.92; N 2.78. IR (nujol): 1979 (CO) cm-1. 1H NMR (500 MHz, CD2Cl2):  7.95 (dd, 3JHH = 7.7 Hz, 3JHH = 7.7 Hz, 1H, H a om Py), 7.76 (s, 8H, 8 H a om BA F), 7.72 (d, 3JHH = 7.8 Hz, 1H, H a om Py), 7.63 (m, 4H, 4 H a om), 7.59 (s, 4H, 4 H a om BA F), 7.51 (m, 7H, 7 H a om), 7.44 (dd, 3JHH = 1.8 Hz, 5JHP = 0.8 Hz, 1H, H a om NHC), 7.17 (d, 3JHH = 1.8 Hz, 1H, H a om NHC), 7.09 (s, 2H, 2 H a om Mes), 5.39 (s, 2H, CH2N), 4.14 (d, 2JHP = 10.1 Hz, 2H, CH2P), 2.40 (s, 3H, CH3), 2.16 (s, 6H, 2 CH3). 31P{1H} NMR (202 MHz, CD2Cl2):  45.6. 11B{1H} NMR (96 MHz, CD2Cl2):  6.6. 13C{1H} NMR (125 MHz, CD2Cl2):  179.3 (d, JCP = 99 Hz, C-2 NHC), 176.4 (d, JCP = 10 Hz, CO), 165.9 (d, JCP = 7 Hz, Cq a om), 162.2 (q, JCB = 50 Hz, 4 BCq a om BA F), 154.9 (Cq a om), 141.5 (CH a om), 140.8 (Cq a om), 136.1 (2 Cq a om), 135.2 (m, 8 CH a om BA F), 133.2 (d, JCP = 12 Hz, 4 CH a om), 132.3 (2 CH a om), 129.6 (o e lapped, 2 Cq a om), 129.6 (d, JCP = 11 Hz, 4 CH a om), 129.5 (2 CH a om), 129.3 (q, JCF = 32 Hz, 8 Cq a om BA F), 125.0 (q, JCF = 272 Hz, 8 CF3), 124.9 (d, JCP = 10 Hz, CH a om), 123.9 (CH a om), 123.3 (CH a om), 121.8 (CH a om), 117.9 (m, 4 CH a om BA F), 56.3 (CH2N), 43.1 (d, JCP = 31 Hz, CH2P), 21.3 (CH3), 18.5 (2 CH3); signal o one qua e na y a oma ic ca bon could no be iden i ied. Complex 3(Cl). In a J.Young- al ed NMR ube, a solu ion o 1(Cl) (0.050 g, 0.07 mmol) in CD2Cl2 (0.5 mL) was cha ged wi h 1 ba o H2. The esul ing solu ion was immedia ely analyzed by NMR spec oscopy indica ing comple e o ma ion o 3(Cl). Complex 3(Cl) loses hyd ogen upon exposu e o acuum. IR (CD2Cl2): 2338 (I H), 2085 (I H), 1987 (CO) cm-1. 1H NMR (500 MHz, CD2Cl2):  8.45 (s, 1H, H a om NHC), 8.29 (d, 3JHH = 6.4 Hz, 1H, H a om Py), 7.99 (dd, 3JHH = 7.3 Hz, 3JHH = 6.6 Hz, 1H, H a om Py), 7.82 (d, 3JHH = 6.4 Hz, 1H, H a om Py), 7.60 (dd, 3JHP = 12.8 Hz, 3JHH = 7.7 Hz, 2H, 2 H a om PPh), 7.51 (dd, 3JHH = 7.6 Hz, JHP = 6.3 Hz, 1H, H a om PPh), 7.40 (m, 5H, 5 H a om PPh), 7.27 (m, 2H, 2 H a om PPh), 7.12 (d, 2JHH = 15.4 Hz, 1H, CHHN), 7.07 (s, 1H, H a om NHC), 7.05 (s, 2H, 2 H a om Xyl), 4.89 (d, 2JHH = 15.3 Hz, 1H, CHHN), 4.82 (dd, 2JHH = 17.1 Hz, 2JHP = 12.5 Hz, 1H, CHHP), 3.63 (dd, 2JHH = 17.1 Hz, 2JHP = 10.2 Hz, 1H, CHHP), 2.42 (s, 3H, CH3), 2.01 (s, 3H, CH3), 1.86 (s, 3H, CH3), 8.32 (ddd, 2JHP = 22.2 Hz, 2JHH = 1.6 Hz, 4JHH = 1.6 Hz, 1H, I H cis o Py), 17.45 (dd, 2JHP = 11.7 Hz, 2JHH = 1.6 Hz, 1H, I H ans o Py). 31P{1H} NMR (202 MHz, CD2Cl2):  16.9. 13C{1H} NMR (125 MHz, CD2Cl2):  175.0 (CO), 163.4 (d, JCP = 3 Hz, Cq a om), 156.9 (d, JCP = 100 Hz, C-2 NHC), 155.8 (Cq a om), 140.3 (CH a om), 139.6 (Cq a om), 136.8 (Cq a om), 135.7 (Cq a om), 135.5 (Cq a om), 134.9 (d, JCP = 12 Hz, 2 CH a om), 134.4 (d, JCP = 49 Hz, Cq a om), 132.3 (d, JCP = 2 Hz, CH a om), 131.3 (d, JCP = 2 Hz, CH a om), 130.4 (d, JCP = 11 Hz, 2 CH a om), 130.1 (d, JCP = 63 Hz, Cq a om), 129.5 (d, JCP = 10 Hz, 2 CH a om), 129.4 (CH a om), 129.2 (CH a om), 129.1 (d, JCP = 12 Hz, 2 CH a om), 125.7 (CH a om), 124.1 (d, JCP = 3 Hz, CH a om), 123.4 (d, JCP = 10 Hz, CH a om), 121.8 (d, JCP = 3 Hz, CH a om), 58.1 (CH2N), 46.1 (d, JCP = 37 Hz, CH2P), 21.3 (CH3), 18.4 (CH3), 18.2 (CH3). MS (ESI, CH2Cl2/MeCN): m/z (%): 698 (100) [(MCl)+]. Complex 4. In a J.Young- al ed NMR ube, a solu ion o 2a/2b (0.010 g, 0.014 mmol) in THF-d8 (0.5 mL) was cha ged wi h 5 ba o H2. The esul ing solu ion was immedia ely analyzed by NMR spec oscopy showing comple e o ma ion o 4. Complex 4 eadily loses hyd ogen upon emo al o he H2 a mosphe e. 1 H NMR (500 MHz, THF-d 8 ):  7.58 (m, 3H, 3 H a om), 7.41 (dd, J HP = 10.1 Hz, 3 J HH = 7.6 Hz, 2H, 2 H a om), 7.19 (m, 7H, 7 H a om), 7.06 (m, 2H, 2 H a om), 6.56 (dd, 3 J HH = 8.8 Hz, 3 J HH = 6.2 Hz, 1H, H c ), 6.43 (d, 3 J HH = 8.8 Hz, 1H, H b ), 5.71 (d, 3 J HH = 6.2 Hz, 1H, H d ), 5.01 (d, 2 J HH = 14.1 Hz, 1H, CHHN), 4.70 (d, 2 J HH = 14.3 Hz, 1H, CHHN), 3.93 (d, 2 J HP = 2.7 Hz, 1H, H a ), 2.43 (s, 3H, CH 3 ), 2.03 (s, 3H, CH 3 ), 1.95 (s, 3H, CH 3 ), 8.64 (dd, 2 J HP = 20.8 Hz, 2 J HH = 1.5 Hz, 1H, I H), 16.59 (dd, 2 J HP = 11.3 Hz, 2 J HH = 1.6 Hz, 1H, I H). 31 P{ 1 H} NMR (202 MHz, THF-d 8 ):  8.8. 13 C{ 1 H} NMR (125 MHz, THF-d 8 ):  176.5 (b m, CO), 174.7 (d, J CP = 19 Hz, C q a om), 162.7 (d, J CP = 92 Hz, C-2 NHC), 150.3 (C q a om), 145.0 (d, J CP = 50 Hz, C q a om), 140.7 (d, J CP = 71 Hz, C q a om), 139.2 (C q a om), 138.4 (C q a om), 136.7 (C q a om), 136.0 (C q a om), 134.7 (d, J CP = 11 Hz, 2 CH a om), 132.0 (d, J CP = 2 Hz, C c ), 131.4 (d, J CP = 12 Hz, 2 CH a om), 129.5 (CH a om), 129.3 (CH a om), 129.0 (CH a om), 128.6 (CH a om), 128.0 (d, J CP = 10 Hz, 2 CH a om), 127.8 (d, J CP = 11 Hz, 2 CH a om), 122.0 (CH a om), 121.8 (d, J CP = 3 Hz, CH a om), 115.3 (d, J CP = 18 Hz, C b ), 102.0 (C d ), 66.6 (d, J CP = 78 Hz, C a ), 60.3 (CH 2 N), 21.2 (CH 3 ), 18.7 (CH 3 ), 18.4 (CH 3 ). Complex 5(Bca 2 ). In a J.Young- al ed NMR ube, a solu ion o 1(Bca 2 ) (0.035 g, 0.04 mmol) in THF-d 8 (0.5 mL) was ea ed wi h HBca (5.0  L, 0.05 mmol). Comple e con e sion o 1(Bca 2 ) o 5(Bca 2 ) was de e mined by NMR spec oscopy. IR (CH 2 Cl 2 ): 2101 (  I H ), 2005 (  CO ) cm -1 . 1 H NMR (500 MHz, THF-d 8 ):  7.91 (d, 3 J HH = 1.1 Hz, 1H, H a om NHC), 7.86 (d, 3 J HH = 7.9 Hz, 1H, H a om Py), 7.82 (dd, 3 J HH = 7.8 Hz, 3 J HH = 7.8 Hz, 1H, H a om Py), 7.74 (d, 3 J HH = 7.4 Hz, 1H, H a om Py), 7.48 (m, 4H, 4 H a om), 7.36 (m, 4H, 4 H a om), 7.24 (m, 2H, 2 H a om), 7.11 (b , H a om HBca ), 7.05 (d, 3 J HH = 1.1 Hz, 1H, H a om NHC), 6.97 (b , H a om HBca ), 6.82 (s, 1H, H a om Mes), 6.76 (m, 2H, 2 H a om I Bca ), 6.70 (m, 2H, 2 H a om ARTICLE Jou nal Name 8 | J. Name., 2012, 00, 1-3 This jou nal is © The Royal Socie y o Chemis y 20xx Please do no adjus ma gins Please do no adjus ma gins I Bca ), 6.39 (b m, 8H, 8 H a om Bca 2 ), 6.00 (d, 2 J HH = 15.7 Hz, 1H, NCHH), 5.97 (s, 1H, H a om Mes), 5.01 (dd, 2 J HH = 17.3 Hz, 2 J HP = 12.5 Hz, 1H, PCHH), 5.00 (d, 2 J HH = 15.7 Hz, 1H, NCHH), 4.37 (q, 1 J HB = 190 Hz, HBca ), 3.98 (dd, 2 J HH = 17.1 Hz, 2 J HP = 10.2 Hz, 1H, PCHH), 2.01 (s, 3H, CH 3 ), 1.86 (s, 3H, CH 3 ), 1.81 (s, 3H, CH 3 ), 6.90 (d, 2 J HP = 21.1 Hz, 1H, I H). 31 P{ 1 H} NMR (202 MHz, THF-d 8 ):  15.7. 11 B NMR (96 MHz, THF-d 8 ):  22.5 (d, J BH = 189 Hz, HBca ), 15.1 (b , Bca 2 ), 12.9 (I Bca ). 13 C{ 1 H} NMR (101 MHz, THF-d 8 ):  176.8 (b , CO), 162.0 (C q a om), 155.1 (C q a om), 154.3 (d, J CP = 96 Hz, C-2 NHC), 153.3 (4 C q a om Bca 2 ), 151.0 (2 C q a om I Bca ), 149.5 (2 C q a om HBca ), 141.3 (CH a om), 140.1 (C q a om), 136.2 (C q a om), 135.8 (C q a om), 135.2 (C q a om), 133.7 (d, J CP = 11 Hz, 2 CH a om), 132.4 (d, J CP = 11 Hz, 2 CH a om), 132.2 (CH a om), 131.9 (CH a om), 131.8 (d, J CP = 50 Hz, C q a om), 130.0 (d, J CP = 11 Hz, 2 CH a om), 129.9 (CH a om), 129.4 (CH a om), 129.2 (d, J CP = 62 Hz, C q a om), 129.1 (d, J CP = 12 Hz, 2 CH a om), 125.0 (CH a om), 124.9 (CH a om), 124.7 (d, J CP = 10 Hz, CH a om), 123.9 (CH a om), 122.6 (b , 2 CH a om HBca ), 121.4 (2 CH a om I Bca ), 118.0 (4 CH a om Bca 2 ), 112.4 (b , 2 CH a om HBca ), 111.3 (2 CH a om I Bca ), 108.7 (4 CH a om Bca 2 ), 59.1 (CH 2 N), 46.1 (d, J CP = 39 Hz, CH 2 P), 21.3 (CH 3 ), 18.6 (CH 3 ), 17.6 (CH 3 ). Complex 6(BA F ). In a J.Young- al ed NMR ube, a solu ion o 1(BA F ) (0.023 g, 0.015 mmol) in THF-d 8 (0.5 mL) was ea ed wi h pinBH (5.3  L, 0.036 mmol). Comple e con e sion o 1(BA F ) o 6(BA F ) was de e mined by NMR spec oscopy. IR (CH 2 Cl 2 ): 2089 (  I H ), 1993 (  CO ) cm -1 . 1 H NMR (400 MHz, THF- d 8 ):  8.03 (dd, 3 J HH = 7.7 Hz, 3 J HH = 7.7 Hz, 1H, H a om Py), 7.79 (s, 8H, 8 H a om BA F ), 7.73 (m, 2H, 2 H a om), 7.68 (d, 3 J HH = 7.7 Hz, 1H, H a om Py), 7.61 (m, 2H, 2 H a om), 7.57 (s, 4H, 4 H a om BA F ), 7.45 (m, 8H, 8 H a om), 7.25 (s, 1H, H a om), 7.06 (s, 1H, H a om), 7.01 (s, 1H, H a om), 5.79 (d, 2 J HH = 15.8 Hz, 1H, NCHH), 5.19 (d, 2 J HH = 15.8 Hz, 1H, NCHH), 4.86 (dd, 2 J HH = 16.9 Hz, 2 J HP = 12.5 Hz, 1H, PCHH), 3.83 (dd, 2 J HH = 17.1 Hz, 2 J HP = 10.4 Hz, 1H, PCHH), 3.75 (q, 1 J HB = 172 Hz, HBpin), 2.33 (s, 3H, CH 3 ), 2.12 (s, 3H, CH 3 ), 2.05 (s, 3H, CH 3 ), 1.22 (s, 4 CH 3 HBpin), 0.74 (s, 6H, 2 CH 3 I Bpin), 0.71 (s, 6H, 2 CH 3 I Bpin), 6.81 (d, 2 J HP = 22.1 Hz, 1H, I H). 31 P{ 1 H} NMR (162 MHz, THF-d 8 ):  18.1. 11 B NMR (128 MHz, THF-d 8 ):  30.1 (d, J BH = 173 Hz, HBpin), 23.2 (b , I Bpin), 4.6 ppm (BA F ). 13 C{ 1 H} NMR (101 MHz, THF- d 8 ):  178.0 (b , CO), 162.6 (q, J CB = 50 Hz, 4 BC q a om BA F ), 162.4 (C q a om), 156.8 (d, J CP = 102 Hz, C-2 NHC), 155.6 (C q a om), 140.8 (CH a om), 139.8 (C q a om), 137.2 (C q a om), 135.9 (C q a om), 135.4 (m, 8 CH a om BA F ), 133.8 (d, J CP = 11 Hz, 2 CH a om), 132.1 (m, 2 CH a om), 132.0 (CH a om), 131.8 (CH a om), 129.8 (m, 4 CH a om + 8 C q a om BA F ), 128.8 (d, J CP = 11 Hz, 2 CH a om), 125.2 (q, J CF = 272 Hz, 8 CF 3 ), 125.0 (CH a om), 123.6 (CH a om), 123.4 (CH a om), 123.3 (CH a om), 118.0 (m, 4 CH a om BA F ), 83.6 (2 C q HBpin), 82.8 (2 C q I Bpin), 59.7 (CH 2 N), 47.3 (d, J CP = 37 Hz, CH 2 P), 25.0 (4 CH 3 HBpin), 24.9 (o e lapped wi h sol en signal, 2 CH 3 I Bpin), 24.2 (2 CH 3 I Bpin), 20.9 (CH 3 ), 18.9 (CH 3 ), 18.8 (CH 3 ); signals o h ee qua e na y a oma ic ca bons could no be de ec ed due o signi ican spec um complexi y. Rep esen a i e p ocedu e o CO 2 hyd obo a ion wi h HBca In a glo ebox, a J.Young- al ed NMR ube was cha ged wi h a solu ion o 2a / 2b (1.6 mg, 2.3  mol) and hexame hylbenzene (3.8 mg, 0.023 mmol) in THF-d 8 con aining 0.2% o wa e (0.5 mL) ( o al wa e con en : 5 mol%), and ca echolbo ane (25  L, 0.23 mmol) was added. The NMR ube was submi ed o acuum o emo e he N 2 a mosphe e, cha ged wi h CO 2 (2 ba ) and hea ed o 30 o C. Reac ion p og ess was moni o ed by 1 H{ 11 B} and 11 B NMR spec oscopies. Rep esen a i e p ocedu e o CO 2 hyd obo a ion wi h HBpin In a glo ebox, a J.Young- al ed NMR ube was cha ged wi h 300  L o a eshly p epa ed 1.3 mM s ock solu ion o 2a / 2b (0.4  mol) in THF-d 8 con aining 0.2% o wa e , hexame hylbenzene (3.8 mg, 0.023 mmol) and THF-d 8 (0.2 mL) con aining 0.2% o wa e ( o al wa e con en : 5 mol%). Pinacolbo ane (32  L, 0.22 mmol) was added, and he NMR ube was submi ed o acuum o emo e he N 2 a mosphe e, cha ged wi h CO 2 (1 ba ) and hea ed o 30 o C. Reac ion p og ess was moni o ed by 1 H{ 11 B} and 11 B NMR spec oscopies. DFT calcula ions DFT calcula ions we e ca ied ou wi h he Gaussian 09 p og am. 42 The hyb id unc ional B3LYP 43 was used, wi h dispe sion e ec s aken in o accoun by adding he D3 e sion o G imme’s empi ical dispe sion. 44 C, H, N, B, O and P a oms we e ep esen ed by he 6-31g(d,p) basis se , 45 whe eas I was desc ibed using he S u ga /D esden E ec i e Co e Po en ial and i s associa ed basis se SDD. 46 All geome y op imiza ions we e pe o med wi hou es ic ions in THF (bulk sol en e ec s modelled wi h he SMD con inuum model). 47 Con lic s o in e es The e a e no con lic s o decla e. Acknowledgemen s Financial suppo (FEDER con ibu ion) om he Spanish MINECO (CTQ2016-80814-R and CTQ2016-81797-REDC) is g a e ully acknowledged. M.H.J. hanks SECITI-DF o a pos doc o al ellowship and CONACyT Mexico o pos doc o al unding (263719). 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