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Ca bonyl Hypoiodi es as Ex emely S ong Halogen Bond Dono s
© 2021 The Au ho s. Angewand e Chemie In e na ional Edi ion published by Wiley-VCH GmbH
Published e sion
Yu, Shilin; Wa d, Jas S.; T uong, Khai-Nghi; Rissanen, Ka i
Yu, S., Wa d, J. S., T uong, K.-N., & Rissanen, K. (2021). Ca bonyl Hypoiodi es as Ex emely
S ong Halogen Bond Dono s. Angewand e Chemie, 60(38), 20739-20743.
h ps://doi.o g/10.1002/anie.202108126
2021
Halogen Bonding
Ca bonyl Hypoiodi es as Ex emely S ong Halogen Bond Dono s
Shilin Yu, Jas S. Wa d, Khai-Nghi T uong, and Ka i Rissanen*
Abs ac : Neu al halogen-bonded OIN complexes we e
p epa ed om in si u o med ca bonyl hypoiodi es and
a oma ic o ganic bases. The ca bonyl hypoiodi es ha e
a s ongly pola ized iodine a om wi h la ge s-holes han any
known uncha ged halogen bond dono . Modula ing he Lewis
basici y o he selec ed py idine de i a i es and ca boxyla es
leads o halogen-bonded complexes whe e he classical OI···N
halogen bond ans o ms mo e in o a halogen-bonded
COO···IN+ion-pai (sal ) wi h an asymme ic OIN
moie y. X- ay analyses, NMR s udies, and calcula ions e eal
he halogen bonding geome ies o he ca bonyl hypoiodi e-
based OIN complexes, con i ming ha in he solid-s a e he
iodine a om is much close o he N-a om o he py idine
de i a i es han i s o iginal posi ion a he ca boxyla e O-a om.
Halogen bonding (XB) has become one o he mos s udied
non-co alen in e ac ions, mo e speci ically elec ophile-
nucleophile in e ac ions, as demons a ed by he apid
inc ease o publica ions since 2007.[1–8] Halogen bonding has
ecen ly been de ined o occu be ween halogens being
elec ophilic and neu al o anionic nucleophiles.[9]
Despi e ongoing deba e abou he ue na u e o he
halogen bonding,[10–13] i is equen ly used as a non-co alen
in e ac ion o cons uc sup amolecula complexes. Owing o
he simila i y o he bonding geome ies and di ec ionali y i s
kinship wi h hyd ogen bonding is mo e han e iden . Halogen
bonding has been success ully applied o con ol he sel -
assembly o a mul i ude o hos –gues sys ems (ion-pai
ecogni ion, biomolecula /chemical sepa a ions), as well as
he syn hesis o unc ional ma e ials (po ous, magne ic,
phospho escen , liquid c ys als).[1,2] C ys al enginee ing,[1–4,14]
he o igin o halogen bonding, es ablished he di ec ionali y,
and speci ici y esul ing in complex s uc u es wi h appealing
a chi ec u es. Owing o he demand o e y p ecise design
p inciples, hollow capsula molecula assemblies solely based
on halogen bonding ha e only e y ecen ly been p e-
pa ed.[15,16] Owing o i s na u e, halogen bonding is mo e
di ec ional han hyd ogen bonding,[17] ye i is much mo e
di icul o s udy in solu ion and has he e o e been demon-
s a ed mos ly in he solid-s a e.[18–21]
When an elec on is emo ed om he halogen a om, i
becomes a posi i ely cha ged ee ion, a halenium ion X+
(X=I, B o Cl). These ca ions can be ega ded as e y s ong
bis- unc ional XB dono s, hough he eac i i y o he ee
halenium ion e ec i ely p e en s hei use as such. Howe e ,
by applying sui able Lewis bases in he syn hesis, he
halenium ions can be apped in o a [LXL]+complex
exhibi ing a h ee-cen e - ou -elec on (3c-4e) bond. Fi s o
hese, namely he iodonium bis(py idine) complexes wi h
a[N
IN]+3c-4e bond, we e epo ed in he 1960s by Hassel
e al.,[22] C ich on e al.,[23] and Hague e al.[24] They ha e
a ac ed a lo o a en ion, especially wi hin he halogen
bonding communi y and ha e ecen ly been e iewed.[25,26]
The iconic example, bis(py idine)iodonium(I) e a luo obo-
a e, Ba luengas eagen ,[27] is a mild iodina ion eagen and
an oxidan . Ba luengas eagen is a ela i ely s able whi e
solid and is soluble in bo h o ganic and aqueous solu ions, and
i s applicabili y in o ganic syn hesis has been widely demon-
s a ed.[28] E dlyi[29–34] has demons a ed ha he [NIN]+
halogen bond by e y p ecise and comp ehensi e s udies in
solu ion, supplemen ed wi h compu a ional calcula ions con-
i ming ha he [NIN]+halogen bond is symme ic wi h he
iodine a om loca ed in he cen e be ween he N-a oms. The
anionic analogue [OIO], iz. dioxoiodane compounds,
ha e ecen ly applied as eagen s in o ganic syn hesis.[35]
The mos s udied o he Ba luenga- ype halonium ion
complexes[36–39] a e he symme ical [NXN]+(X =B o I)
complexes.[24,27] Asymme ic he e olep ic halonium com-
plexes ha e been p epa ed by E dlyi and co-wo ke s,[30]
wi h he help o molecula cle s. Only e y ecen ly he
i s un es ained he e olep ic [N1IN2]+complexes ha e
been epo ed in he solid-s a e[40] and solu ion.[41]
Apa om he abo e men ioned cha ged XB complexes,
also neu al NI···N and NI···ON XB complexes a e easily
p epa ed om sui able haloimides and halosul onimides as
he XB dono s and py idine de i a i es o py idine-N-oxides
as he XB accep o s, ex ensi ely s udied by Fou migu[42,43]
and Rissanen.[19–21,44]
Inspi ed by he abo e-men ioned wo k, we sough o
p obe he RCOOI molecules, namely ca bonyl hypoio-
di es, as a po en ial new mo i o halogen bond dono s. To he
bes o ou knowledge, ca bonyl hypoiodi es which we e
s abilized by py idine we e i s s udied by Ca lsohn in his
habili a ion in 1932.[45] In 1940s, Kleinbe g, Zinga o and co-
wo ke s epo ed he p epa a ion o a se ies o iodine(I) sal s
by he eac ion o di e en sil e ca boxyla es and iodine in
he p esence o py idine, 2-picoline o 4-picoline as he
s abilizing ligand.[46–49] Some o hese sal s we e e ec i ely
u ilized as iodina ion eagen s wi h in e es ing an ibac e ial
p ope ies.[43] Fu he mo e, he wo known single c ys al
[*] D . S. Yu, D . J. S. Wa d, D . K.-N. T uong, P o . K. Rissanen
Depa men o Chemis y, Uni e si y o Jy askyla
Su on ie 9 B, 40014 Jy skyl (Finland)
E-mail: ka i. . issan[email p o ec ed]
Suppo ing in o ma ion and he ORCID iden i ica ion numbe (s) o
he au ho (s) o his a icle can be ound unde :
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 2021 The Au ho s. Angewand e Chemie In e na ional Edi ion
published by Wiley-VCH GmbH. This is an open access a icle unde
he e ms o he C ea i e Commons A ibu ion Non-Comme cial
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s uc u es mani es ing py idine
benzoyl hypoiodi e 1b [named as
benzoa o-py idine-iodine(I)] and
bis-py idine ph haloyl hypoiodi e
[ph hala o-bis(py idine-iodine(I)],
we e epo ed 40 yea s ago by
Ha l.[50] In addi ion o hei syn-
hesis,[27] use o s uc u ally ela ed
anionic complexes [RCOOI
OOCR], which should be con-
side ed as he anionic- ype 3c-4e
XB complexes wi h wo oxygen
a oms as XB accep o s,[25] ha e
been u ilized as dynamic axles in
he cons uc ion o o axanes.[51]
He ein, we epo he in es i-
ga ions on neu al OIN com-
plexes, ea ed as new examples o
halogen-bonded complexes, whe e he ca bonyl hypoiodi es
ac as XB dono s. The esul s clea ly show ha ca bonyl
hypoiodi es a e e y p omising as s ong halogen bond
dono s, gi ing unambiguous NMR spec a and mani es ing
e y s ong sal -like cha ac e (a leas in he solid-s a e)
whe e he iodine has jumped om he ca boxyl oxygen o he
N-a om o he py idine de i a i e o ming a e y s ongly
halogen-bonded [RCOO][+IN(py)] ion-pai .
The syn hesis ou e o he neu al hypoiodi e OIN
complexes is illus a ed in Scheme 1.[47,49] Cha ac e iza ion
and de ails o he syn hesis and he NMR s udies o all wel e
hypoiodi e complexes (1b,1d,2a–2d,3a,3b,3d,4a,4band
4d) om py idine and i s selec ed de i a i es, sil e ca box-
yla es, and elemen al iodine a e p esen ed in he Suppo ing
In o ma ion (SI).
The 15N NMR chemical shi alues based on he 1H-15N
HMBC measu emen s (SI) o he py idinic ni ogen o 2a–2d
and ee ligand 2a e summa ized in he Table 1. The
complexa ion-induced chemical shi change, DdN, de ined
as d(15NOIN)d(15NL), wi h OIN as he halogen-bonded
complexes and Las ee 1–4, is e y la ge and mani es s
a d ama ic change in he chemical en i onmen o he
py idinic N-a om du ing he complexa ion. Wi h inc easing
Lewis basici y o he ca boxyla es he DdNinc eases. The
s able N-me hyl-DMAP ca ion [2CH3]+, as he PF6sal , has
aDdNbe ween 2c and 2d (Table 1). Compa ed wi h he
co esponding i luo oace a e sal o DMAP ([2H]TFAc),
he hypoiodi e complex 2dhas a much la ge DdN(129.4 s.
85.6 ppm, Table S1), which indica es a bigge inc ease o he
elec on densi y a ound py idinic ni ogen in 2d.[52,53]
The DdNo h ee benzoa e-based OIN complexes (1b,
2band 3b) was also compa ed, as shown in Table 1. When he
nucleophilici y o he used base inc eases, he la ge he 15N
NMR chemical shi change. The complex 1bhas he smalles
15N NMR chemical shi change alue, which is s ill bigge
han ha o py idinium i luo oace a e ([1H]TFAc) (81.0
s. 70.0 ppm, Table S1).
The single c ys als o he complexes 1b,2a,2b,2c,2d,3b,
3d,4a and 4d we e g own ei he om dichlo ome hane o
chlo o o m upon slow e apo a ion o by apo di usion o
pen ane, die hyl e he o pe oleum e he in o dichlo o-
me hane, chlo o o m o ace oni ile. The c ys allog aphic
de ails a e p esen ed in he SI (Table S1). The DMAP- (2a,
2b,2c, and 2d) and benzoa e-based (1b,2b, and 3b)O
IN
complexes will be discussed as wo di ec ly compa able se ies
o complexes. The OI bonds o 2a,2b and 2c (Table 1,
Figu e 1) a e e y simila o each o he (ca. 2.21 ) and
iden ical o he OIO bonds (c . 2.20 ) in he anionic
dioxoiodane complexes.[35] The IN bond dis ances (Table 1)
o 2a,2b, and 2c a e all equal (ca. 2.23 ) and e y much
esemble hose obse ed o p e iously epo ed 3c-4e [NI
N]+halogen-bonded iodonium complexes.[22,37,40,54,55] A no a-
ble excep ion is he 2d whe e he IN bond leng h o
2.173(4)  is much oo sho o be a con en ional 3c-4e
halogen bond. The iodine is abou 0.08  close o he
py idinic ni ogen in 2d han in a ypical halonium ion [NI
N]+complex and 0.04  close han in he NISac-DMAP (2-
NISac) (inne )-sal complex epo ed by Fou migu (c .
2.218(2) ).[34]
Apa om he sho IN bond in 2d, he OI bond is
elonga ed by 0.323  om he 1.989  ob ained om he
DFT calcula ions o he hypoiodi e d(SI, Table S1) e sus
2.312(4)  om he SCXRD. This alue is analogous o he
s onges I···O halogen bonds obse ed in N-iodosaccha in-
py idine-N’-oxide halogen-bonded complexes,[19–21,44] and hus
he OI bond in 2d is be e desc ibed as an I···O halogen
Scheme 1. Syn hesis o he OIN complexes, wi h DMAP (2) and Ag-
benzoa e gi en as an example (2b).
Table 1: The OI and IN dis ances om SCXRD and DFTs udies and he 15N NMR chemical shi s o
1b,2,2a–2d,3b,[2CH3]PF6,[2I2]PF6, and 2-NISac.
Complex d(OI) []
(XRD/DFT)
d(IN) []
(XRD/DFT)
d15N[b]
[ppm]
Dd[c]
[ppm]
1b 2.159(5)/2.133 2.299(7)/2.301 148.7 81.0
2––108.6 –
2a 2.203(11)/2.15 2.234(14)/2.27 204.7 96.1
2b 2.210(3)/2.171 2.241(3)/2.247 209.5 100.9
2c 2.21(1)[a]/2.18 2.22(1)[a]/2.24 212.2 103.6
2d 2.312(4)/2.248 2.173(4)/2.189 238.0 129.4
[2CH3]PF6––224.0 115.4
[2I2]PF6––216.1 107.5
2-NISac[42] 2.292(2)[d]/2.314 2.218(2)/2.247 200.8 92.2
3b 2.230(4)/2.164 2.232(4)/2.2.257 202.1 102.5
[a] A e age o ou c ys allog aphically independen complexes in he asymme ic uni . [b] The 1H-15N
HMBC NMR chemical shi o py idinic ni ogen in [OIN] complexes o ee ligands in CD2Cl2. [c] The
15N NMR chemical shi change upon complexa ion. [d] (Sac)NI bond leng h.
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bond. The OIN bond leng hs in he solid-s a e o 2d
suppo i s desc ip ion as an ion-pai o he N-iodo-N’,N’-
dime hylaminopy idinium ca ion, and a i luo oace a e
anion, s abilized by a e y s ong N+I···OC halogen
bond. The sho es IN bond o 2.167(4)  was obse ed
o complex 4d, and simila ly, he longes IO bond leng h
was o 2das p e iously s a ed, hough i ually he same as in
4d(c . 2.308(4) ).
Consis en wi h he gene al linea i y o halogen bonds, he
angles o he OIN moie ies in all hypoiodi e complexes all
wi hin he ange o 172.9(5)–178.1(1)
8
and a e close o he
halogen bond angles obse ed o he N-iodosaccha in-
py idine-N’-oxide halogen-bonded complexes[19–21,44] han o
he s ic ly linea 3c-4e [NIN]+halogen bonds.[22,37,40,54,55]
The SCXRD da a o 2a–2d demons a es he dynamic
bonding si ua ion o he OIN moie y, wi h sho e IN
bond leng hs e lec ing an inc ease in he N-iodopy idinium
cha ac e o he py idine de i a i e, concomi an ly wi h an
elonga ion o he OI bond leng h e lec ing an inc ease in
he anionic cha ac e o he ca boxyla e componen . As
expec ed, subs i u ed py idines such as DMAP (2) and 4-
pipe idinopy idine (4), ha a e s onge nucleophiles, a e
be e able o induce his inc eased N-iodopy idinium cha -
ac e in he OIN complexes desc ibed he ein. Es ima ion
o he N-iodopy idinium cha ac e is di icul as no N-
iodopy idinium ca ion X- ay s uc u e is known (only he
N- luo opy idinium ca ion is known).[56] In he 3c-4e [NI
N]+halogen-bonded symme ic halonium complex [2I
2]PF6, he ela i e N-iodopy idinium cha ac e can be con-
side ed o be 50% (NI: 2.250 , NN: 4.500 ),[36,40,57] while
o he [2I]+ca ion he IN bond dis ance can only be
ob ained wi h compu a ional me hods (SI, sec ion 3). The
DFT compu ed alue o he IN bond dis ance in [2I]+is
2.042 . Using hese wo alues and he SCXRD measu ed I
N dis ances, he ela i e N-iodopy idinium cha ac e can be
es ima ed o he Fou migu epo ed 2-NISac complex[34]
(56.5%), 2d (67.6%), 3d (62.4%) and 4d (69.1%) in he
solid-s a e. Due o he dynamic na u e[51] o he OIN
moie y in solu ion, no clea co ela ion abou he N-iodopy -
idinium cha ac e in he solid-s a e and in solu ion can be
gi en.
When keeping he i luo oace yl hypoiodi e moie y
cons an bu changing he py idine moie y, namely complexes
2d,3d, and 4d, no appa en di e ences in he halogen
bonding geome ies we e obse ed, as in all complexes he
OI(2d: 2.312(4) , 3d: 2.282(5) , 4d: 2.308(4)) , he IN
bond dis ances (2d: 2.173(4) , 3d: 2.194(5) , 4d: 2.167-
(4) ) and he OIN angles (2d: 175.5(2)
8
,3d: 172.1(2)
8
,
4d: 175.0(1)
8
) a e e y simila . This is e y likely due o he
ac ha all 2,3and 4a e e y s ong Lewis bases and ac as
e y s ong XB dono s enhancing he ion-pai o ma ion in
he solid-s a e.
Fo compa ison o he halogen bonding geome ies om
he SCXRD and DFT calcula ions (SPARTAN’18,[58] M06-
2X, de 2-TZVP) wi h non-pola sol en model (DCM) we e
pe o med. The de ailed expe imen al SCXRD and calcu-
la ed DFT geome ies a e gi en in SI (Table S1). The DFT
calcula ed bond geome ies a e ex emely close o hose
expe imen ally de e mined by SCXRD. This is a con incing
p oo ha he compu a ional alues ob ained o he non-
single c ys alline complexes a e easible and can be used o
discuss he dynamic bonding beha io o he OIN sys em.
The hypoiodi es a–dshowed no end on he OI bond
dis ance as in all cases i is 1.99  (DFT, Table S1). D as ic
elonga ion o he OI bond occu s du ing he OIN
complex o ma ion as he OI bond ge longe by 0.17–
0.34 , and co espondingly he IN bonds sho en
(Table S1). The N···O dis ance in all OIN complexes also
emains i ually unchanged (4.43–4.48 ).
The molecula elec os a ic su ace po en ial maps
(MEPS, Figu e 2) o he hypoiodi es a–d e eal e y la ge
s-holes, anging om +170.41 kJmol1(a) o
+234.55 kJmol1(d). Due o he s ong pola izing powe o
he ca boxyla e moie y hese alues a e la ge when compa ed
o some common s ong halogen bond dono s like i luo -
oiodome hane (+139.50 kJmol1), iodoace ylene
(+165.47 kJmol1), ICl (+182.41 kJmol1) and N-iodosac-
cha in (+226.36 kJmol1) (SI, Figu e S75).
Figu e 1. The X- ay c ys al s uc u es o 2a,2b,2c and 2d ( op o
bo om; he mal ellipsoids a 50% p obabili y).[59]
Figu e 2. The elec os a ic po en ial su aces and he Vs,max (kJmol1)
alues calcula ed a he M06-2X/6–311+G(3d ,2p) le el on he
0.001 a.u. molecula su aces o a–d.
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While he asymme ic OIN halogen-bonded hypoiodi e
complexes a e s able (wi h a ew excep ions) unde no mal
condi ions, hey can be p one o exchange eac ions o he
co esponding posi i ely cha ged [LIL]+(L =Lewis base)
halonium complex in he p esence o excess Lewis base,
depending on he s eng h o he Lewis base and he
ca boxyla e used. This is unambiguously p o en by a i a ion
expe imen moni o ed by 1H NMR in d2-DCM (Figu e 3).
The OIN hypoiodi e complex 2d (Figu e 3a) was i a ed
wi h DMAP o p obe he displacemen o he TFAc anion.
Gi en ha DMAP is a s ong nucleophile, i would be
expec ed o eplace he TFAc anion o o m he [2I2]+
halonium complex. This indeed happens as, wi h he inc eas-
ing amoun o DMAP, he signals o DMAP in 2d (g een
colo ) g adually diminish, while new peaks (blue colo )
eme ge o he symme ic [2I2]+halonium complex (Fig-
u e 3b– ). The 1H NMR spec um o a sepa a ely p epa ed
[2I2]PF6halonium complex is shown in Figu e 3h o
e e ence. A wo equi alen s o 2(Figu e 3g), i was
obse ed ha he signals o 2d had nea ly comple ely
disappea ed.
In conclusion, a se ies o halogen-bonded OIN hypo-
iodi e complexes ha e been syn hesized, and hei solid-s a e
s uc u es in es iga ed, o p obe he dependency be ween he
OI and IN bond leng hs and he Lewis basici y o he N-
dono . The solid-s a e s udies e ealed ha hese OIN
complexes can be desc ibed as a new class o halogen-bonded
complexes, namely as a e y s ongly bound ion-pai com-
p ised om an iodopy idinium ca ion and an anion de i ed
om he espec i e acid used. The 1H–15N HMBC NMR
s udies e eal a d as ic change in he chemical shi o he
py idinic ni ogen a om in he complexes, especially hose
om s ong acids, esul ing in a s able halogen-bonded
complex. The compu a ional calcula ions suppo hei cha -
ac e iza ion, e ealing e y la ge s-holes o he pa en
hypoiodi es. The Vs,max alue (+234.55 kJmol1) o he
i luo oace yl hypoiodi e su passed ha o he p e iously
s onges neu al halogen bond dono molecule, N-iodosac-
cha in (+226.36 kJmol1). The exchange eac ions o he
hypoiodi e complex 2d (COOIN(2)) wi h excess o 2
esul s in he co esponding posi i ely cha ged [2I2]+
halonium complex, wi h COOas he anion. Fu he mo e,
he esul s p o ide use ul knowledge o he de elopmen o
XB based ma e ials and OIN based an ibac e ial agen s.
Acknowledgemen s
We a e g a e ul o inancial suppo om he Academy o
Finland (K.R.: g an no. 317259), he Finnish Cul u al
Founda ion Cen al Fund (J.S.W.: g an no. 00201148), he
Magnus Eh n oo h Founda ion (J.S.W.), and he Uni e si y o
Jy skyl.
Con lic o In e es
The au ho s decla e no con lic o in e es .
Keywo ds: halogen bonding · hypoiodi e · NMR spec oscopy ·
py idine · sup amolecula chemis y
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Accep ed manusc ip online: July 16, 2021
Ve sion o eco d online: && &&,&&&&
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Communica ions
Halogen Bonding
S. Yu, J. S. Wa d, K.-N. T uong,
K. Rissanen*
&&&& —&&&&
Ca bonyl Hypoiodi es as Ex emely
S ong Halogen Bond Dono s
Ca bonyl hypoiodi es possess e y
s ongly pola ized iodine a oms, includ-
ing wha is now he la ges known s-hole
o a neu al compound, and ac as s ong
halogen bond dono s. When s ong Lewis
bases, o example DMAP, a e used as
halogen bond accep o s, he iodine a om,
o all in en s and pu poses, ans e s
om he oxygen o ni ogen a om o gi e
an ion-pai o he gene al o m [RCOO]-
[I+N(DMAP)] wi h an O···IN halogen
bond.
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