Dal on
T ansac ions
PAPER
Ci e his: Dal on T ans., 2013, 42, 3533
Recei ed 27 h Sep embe 2012,
Accep ed 4 h Decembe 2012
DOI: 10.1039/c2d 32273k
www. sc.o g/dal on
Ca aly ic amine-bo ane dehyd ogena ion by
a PCP-pince palladium complex: a combined
expe imen al and DFT analysis o he
eac ion mechanism†‡
And ea Rossin,*
a
Gio anni Bo a i,
b
Ana M. Lozano-Vila,
b
Ma ga i a Paneque,*
b
Mau izio Pe uzzini,*
a
And ea Rossi
a
and Fab izio Zanobini
a
Ca aly ic dehyd ogena ion o ammonia-bo ane (NH
3
·BH
3
, AB) and dime hylamine bo ane (NHMe
2
·BH
3
,
DMAB) by he Pd
II
complex [(
Bu
PCP)Pd(H
2
O)]PF
6
[
Bu
PCP = 2,6-C
6
H
3
(CH
2
P
Bu
2
)
2
] leads o oligome iza ion
and o ma ion o spen uels o gene al o mula cyclo-[BH
2
–NR
2
]
n
(n= 2,3; R = H, Me) as eac ion
byp oduc s, while one equi alen o H
2
is eleased pe amine-bo ane equi alen . The p ocesses we e
ollowed h ough mul inuclea (
31
P,
1
H,
11
B) a iable empe a u e NMR spec oscopy; kine ic measu e-
men s on he hyd ogen p oduc ion a e and he ela i e a e cons an s we e also ca ied ou . One non-
hyd idic in e media e could be de ec ed a low empe a u e, whose chemical na u e was explo ed
h ough a DFT modeling o he eac ion mechanism, a he M06//6-31+G(d,p) compu a ional le el. The
compu a ional ou pu was o help o p opose a eliable mechanis ic pic u e o he p ocess.
In oduc ion
The inc easing ques o efficien and sa e hyd ogen ese oi s
o p ac ical applica ions in uel-cells echnology wi hin he
ame o he so-called “hyd ogen economy”
1
has led o an
eno mous g ow h o he ela ed hyd ogen s o age esea ch
ield in ecen yea s.
2
As a as chemical s o age is conce ned,
one o he mos p omising ma e ials ha can sa is y all he
a o emen ioned equi emen s is ammonia-bo ane (AB).
3
In
ac , AB is an easy- o-handle solid, i is he mally s able and
wi h a ela i ely high hyd ogen con en (19.3% w H). Homo-
geneously-ca alyzed AB dehyd ogena ion/hyd olysis is he pa h
ha he ino ganic chemis can ollow o exploi AB as hyd o-
gen s o age ma e ial. A numbe o li e a u e examples a e
known, whe e H
2
e olu ion is mainly ca alyzed by u henium,
4
hodium,
5
and i idium
6
o ganome allics. Pince - ype me al
complexes in pa icula ha e been p o ed o be ex emely
efficien as alkane dehyd ogena ion ca alys s.
7
Gi en he iso-
lobal analogy be ween AB and e hane, some I -based pince
sys ems ha e been also exploi ed o AB dehyd ogena ion.
6
G oup 10 ansi ion me al complexes ha e been sca cely
exploi ed o achie e his a ge ; o he bes o ou knowledge,
he only li e a u e s udies o da e a e ep esen ed by he
Ni
0
-Ende s’NHC (1,3,4- iphenyl-4,5-dihyd o-1H-1,2,4- iazol-5-
ylidene) complex
8
ha can elease mo e han 2.5 equi alen s
o H
2
pe equi alen o AB wi hin 4 h a 60 °C and by he Pd
II
complex [Pd(MeCN)
4
][BF
4
]
2
,
9
eleasing up o 2 equi alen s o
H
2
pe equi alen o AB wi hin 60 s a oom empe a u e. Some
nanos uc u ed Pd
0
he e ogeneous sys ems ha e been also
examined o AB dehyd ogena ion,
10
wi h compa able esul s.
He e, amine-bo ane dehyd ogena ion/oligome iza ion by an
ai -s able obus PCP-pince Pd
II
complex [(
Bu
PCP)Pd(H
2
O)]-
PF
6
[2,
Bu
PCP = 2,6-C
6
H
3
(CH
2
P
Bu
2
)
2
] is desc ibed. The
expec ed compound has been gene a ed om he co espond-
ing chlo o complex (
Bu
PCP)Pd(Cl) (1) a e halide abs ac ion
Scheme 1 Syn hesis o complex 2.
†In memo y o D S e ano Midollini, in ecogni ion o his ema kable scien i ic
con ibu ions o he g ow h o he I alian o ganome allic chemis y.
‡Elec onic supplemen a y in o ma ion (ESI) a ailable: Fig. S1–S5, comple e
c ys allog aphic da a and ables o 2, Ca esian xyz coo dina es and ela ed
absolu e G
THF
ene gy alues o 2
H
_AB,2
H
_AB2,2
H
_BNBN,2
H
_cyc and [(
H
PCP)-
Pd(η
2
-H
2
)]
+
. CCDC 891104. Fo ESI and c ys allog aphic da a in CIF o o he elec-
onic o ma see DOI: 10.1039/c2d 32273k
a
Consiglio Nazionale delle Rice che, Is i u o di Chimica dei Compos i
O ganome allici (ICCOM-CNR), Via Madonna del Piano 10, 50019 Ses o Fio en ino
(Fi enze), I aly. E-mail: [email p o ec ed]
b
Ins i u o de In es igaciones Químicas, CSIC and Uni e sidad de Se illa,
A . Amé ico Vespucio 49, 41092 Se illa, Spain
This jou nal is © The Royal Socie y o Chemis y 2013 Dal on T ans., 2013, 42, 3533–3541 | 3533
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online
View Jou nal
| View Issue
wi h AgPF
6
in we THF (Scheme 1). The [(
Bu
PCP)Pd]
+
agmen ,
wi h a coo dina ion acancy on he me al cen e, is a he
eac i e, and he emp y si e is easily occupied by wa e
molecules, hus o ming he ela ed aquo complex.
Expe imen al sec ion
All eac ions we e pe o med using he s anda d Schlenk p o-
cedu es unde a d y ni ogen a mosphe e, unless speci ied. All
sol en s employed we e pu ged wi h ni ogen o 10 min
be o e use. The
Bu
PCP(H) ligand (STREM Chemicals L d), sil e
hexa luo ophospha e (STREM Chemicals L d), ammonium
e achlo opallada e(II) (Ald ich), ammonia-bo ane complex
(Ald ich), dime hylamine-bo ane complex (Ald ich) and i-
e hylamine-bo ane complex (Ald ich) we e used as pu chased,
wi hou u he ea men . Deu e a ed sol en s (Ald ich) we e
degassed by h ee eeze–pump– haw cycles be o e use. NMR
spec a we e eco ded on a BRUKER AVANCE II 300 MHz spec-
ome e , equipped wi h a low- empe a u e measu emen ool.
1
H and
13
C{
1
H} chemical shi s a e epo ed in pa s pe
million (ppm) down ield o e ame hylsilane (TMS) and we e
calib a ed agains he esidual p o ia ed esonance o he
deu e a ed sol en (
1
H) o he deu e a ed sol en esonance
(
13
C{
1
H}), espec i ely, while
31
P{
1
H} was e e enced o 85%
H
3
PO
4
wi h down ield shi aken as posi i e.
11
B chemical
shi s we e e e enced o BF
3
·OE
2
. In a ed spec a we e
eco ded wi h a Pe kin-Elme Spec um BX FT-IR spec o-
pho ome e . The C, H elemen al analyses we e made a
ICCOM-CNR using a The mo FlashEA 1112 Se ies CHNS-O
elemen al analyze wi h an accep ed ole ance o ±0.4 uni s on
ca bon (C) and hyd ogen (H).
Syn hesis o (
Bu
PCP)Pd(Cl) (1)
This compound has al eady been epo ed in he li e a u e;
11
in he e, an imp o emen o he o iginal p epa a ion is
epo ed. Ammonium e achlo opallada e(II) (NH
4
)
2
PdCl
4
(0.14 g, 0.5 mmol) was dissol ed in 20 mL 2-me hoxye hanol a
oom empe a u e. The ee ligand
Bu
PCP(H) (0.2 g, 0.5 mmol,
1 equi .) was added o his solu ion, and he esul ing mix u e
was hea ed a 100 °C o 40 min. A e ha ime, he colou less
solu ion was b ough o oom empe a u e, and a whi e c ys al-
line p ecipi a e o pu e 1(0.2 g; yield: 80%) was ob ained a e
concen a ion o ca. 5 mL and addi ion o 15 mL H
2
O. The p e-
cipi a e was il e ed, washed wi h small po ions (3 × 10 mL) o
an E OH–H
2
O mix u e (4 : 1) and inally d ied unde a b isk
ni ogen s eam.
31
P{
1
H}-NMR (121.49 MHz, ppm, CDCl
3
):
72.1 (s).
Syn hesis o [(
Bu
PCP)Pd(H
2
O)]PF
6
(2)
0.1 g (0.19 mmol) o 1we e dissol ed in 15 mL THF and
0.1 mL H
2
O. To his solu ion, 0.06 g (0.22 mmol, 1.2 equi .) o
solid AgPF
6
we e added in one po ion. Immedia e o ma ion
o a whi e AgCl p ecipi a e was obse ed. The suspension was
le o s i igo ously o e nigh a ambien empe a u e, in he
da k. A e ha ime, he colou less supe na an was il e ed
and concen a ed o ca. 5 mL unde a b isk ni ogen lux.
n-Pen ane addi ion (10 mL) led o p ecipi a ion o 2as a whi e
c ys alline solid, ha was washed wi h small pen ane po ions
(3 × 10 mL) and d ied unde a ni ogen s eam (0.12 g; quan i-
a i e yield). Single c ys als sui able o X- ay analysis we e
g own om THF–n-pen ane solu ions a ambien empe a u e.
Anal. Calcd o 2,C
24
H
45
F
6
OP
3
Pd (662.91): C, 43.48; H, 6.84.
Found: C, 43.25; H, 7.01. IR (298 K, KB , cm
−1
): 3312 w [ν(O–
H)], 2960 m, 2900 m, 2870 m [ν(C–H)], 1627 w [ν(C C)],
1472 m, 1370 m, 1265 m, 1178 m, 1021 m, 963 w, 843 s
[γ(C–H)], 557 s [ν(P–F)].
1
H-NMR (300.13 MHz, ppm, THF-d
8
,
298 K): 6.95 (A H, 3H, m), 5.12 (H
2
O, 2H, s), 3.33 (PCH
2
, 4H, ,
*
J
H–P
= 4.1 Hz), 1.40 (CH
3
, 36H, ,
*
J
H–P
= 6.9 Hz).
13
C{
1
H}
NMR (75.46 MHz, ppm, THF-d
8
,298K):149.7(C
a -ipso
, ,
*
J
C–P
=
9.8 Hz), 146.4 (C
a -p
, s), 124.0 (C
a -m
, s), 121.0 (C
a -o
, ,
*
J
C–P
=
10.4 Hz), 32.9 (PCH
2
, ,
*
J
C–P
= 7.6 Hz), 29.4 [PC(CH
3
)
3
, ,
*
J
C–P
= 11.2 Hz], 26.6 (PC(CH
3
)
3
, s).
31
P{
1
H}-NMR (121.49 MHz,
ppm, THF-d
8
, 298 K): 76.7 (PCP, s), −148.0 (PF
6
, sep ., J
P–F
=
710.5 Hz).
X- ay da a collec ion
X- ay da a o 2we e collec ed a low empe a u e (120 K) on
an Ox o d Diff ac ion XCALIBUR 3 diff ac ome e equipped
wi h a CCD a ea de ec o using Mo K
α
adia ion (λ= 0.7107 Å).
The p og am used o he da a collec ions was C ysAlis CCD
1.171.
12
Da a educ ions we e ca ied ou wi h he p og am
C ysAlis RED 1.171
13
and he abso p ion co ec ions we e
applied wi h he p og am ABSPACK 1.17.13. Di ec me hods
implemen ed in Si 97
14
we e used o sol e he s uc u es and
he e inemen s we e pe o med by ull-ma ix leas -squa es
agains F
2
implemen ed in SHELX97.
15
All he non-hyd ogen
a oms we e e ined aniso opically while he hyd ogen a oms
we e ixed in calcula ed posi ion and e ined iso opically wi h
he he mal ac o depending on ha o he a om o which
hey a e bound. A diffe en ea men was used o he hyd o-
gen a oms o he aquo ligand: hey we e ound in he Fou ie
densi y map, he coo dina es we e ee o e ine and hei
he mal ac o s we e bound o ha o oxygen. Geome ical cal-
cula ions we e pe o med by PARST97
16
and molecula plo s
we e p oduced by he p og am ORTEP3.
17
VT-NMR moni o ing o he eac ion o 2 wi h excess BH
3
·L
(L = NH
3
, NHMe
2
, NE
3
)
Only he eac ion o 2wi h BH
3
·NH
3
is desc ibed, as he o he
bo ane adduc s we e eac ed wi h 2in an analogous manne .
In a ypical expe imen , 2(0.040 g, 0.06 mmol) was placed in a
5 mm qua z NMR ube unde an ine a mosphe e. THF-d
8
(0.5 mL) was ans e ed in o he ube ia a cannula, and he
esul ing solu ion was b ough o 190 K using a d y ice–
ace one ba h. 5 equi . BH
3
·NH
3
(0.0093 g, 0.3 mmol) we e dis-
sol ed in he minimum amoun (0.5 mL) o THF-d
8
in o a sepa-
a e Schlenk lask unde ni ogen, and he esul ing solu ion
was sy inged in o he cold NMR ube. The ube was hen
inse ed in o he NMR spec ome e p obe head p e-cooled
a 190 K. Subsequen ly, he p obe was wa med slowly o
oom empe a u e in s eps o 20 K each, and new se s o
Pape Dal on T ansac ions
3534 |Dal on T ans., 2013, 42, 3533–3541 This jou nal is © The Royal Socie y o Chemis y 2013
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online
mul inuclea NMR da a we e collec ed a each s ep. In he case
o (nea ) liquid amine-bo ane eagen s, he equi ed numbe
o equi alen s we e di ec ly sy inged in o he p e-cooled NMR
ube, always kep a 190 K.
Kine ic measu emen s
(a) H
2
e olu ion a e. The kine ic uns we e ca ied ou
wi h he Man o he Moon X102 ki (see Fig. S1‡ o de ails).
Unde an ine a mosphe e, 0.010 g o AB (0.32 mmol) we e
placed in a wo-necked ound-bo omed 30 mL lask connec ed
o a swi chable h ee-way al e h ough a To ion sc ew. AB was
dissol ed in 1 mL dioxane, s i ed a 303 K in an oil ba h, hen
he al e was swi ched o he p essu e ansduce which is con-
nec ed ia wi eless o he so wa e eco ding he kine ic p o ile
on-line. A s ock solu ion o 2in he same sol en was added o
each he desi ed 2: AB ela i e s oichiome y (see below) and
he eac ion was s i ed o 18–24 hou s. The esul ing kine ic
da a we e co ec ed by he injec ed olume o ca alys solu ion:
he p essu e inc ease caused by he injec ion was measu ed on
a blank solu ion and used o calcula e he co ec numbe o
eleased H
2
equi alen s. A he end o he eac ion, he supe -
na an was ans e ed o an NMR ube and analyzed h ough
31
P{
1
H} and
11
B NMR spec oscopy, o iden i y he soluble eac-
ion by-p oduc s.
(b) Moni o ing con e sion o AB o DMAB o de e mi-
na ion o he eac ion a e u ilizing
11
B NMR spec oscopy.
The a ia ion o AB/DMAB concen a ion du ing he eac ion
wi h 2a 303 K in THF-d
8
was moni o ed h ough he in e-
g a ion o he ela ed
11
B NMR signals. A coaxial ex e nal s an-
da d o BF
3
·E
2
O was employed, o ha e a e e ence signal o
he peaks in eg a ion. The NMR ubes we e p epa ed in he
same manne as ha desc ibed abo e o he VT expe imen s.
In o de o a oid sample decomposi ion, addi ion o he
excess amine-bo ane (5 equi alen s) was made a 190 K and
he mix u e wa med slowly o 303 K wi hin he p obe head o
he NMR spec ome e .
Compu a ional de ails
Densi y Func ional Theo y (DFT) calcula ions we e pe o med
o he AB case only o he sake o simplici y, using he Gaus-
sian09 p og am ( e ision A.02).
18
Model s uc u es we e op i-
mized wi h an M06 unc ional
19
(al eady employed
success ully in o he cases o he ea men o molecules con-
aining da i e bonds
20
) using he LANL2DZ pseudopo en ial
21
and ela ed basis se
22
on he palladium and phospho us
a oms, a 6-31G* basis se on all he o he pince a oms and a
6-31+G(d,p) basis se on BH
3
·NH
3
. In oduc ion o diffuse
unc ions is essen ial o well- ep oduce con o ma ional equili-
b ia and expe imen al elec on affini ies.
23
An ex a p- ype
pola iza ion unc ion o P and an ex a - ype unc ion o Pd
we e added o he s anda d se .
22
Gibbs ene gy calcula ions o
in e ela i e he modynamic s abili ies we e ca ied ou on a
model sys em, wi h he e -bu yl g oups on he pince ligand
eplaced by H a oms (
H
PCP), in o de o each a sa is ac o y
comp omise be ween model sys em accu acy and sho compu-
a ional imes. E alua ion o he sol en effec s was pe o med
h ough a con inuum modelling o he eac ion medium. Bulk
sol en effec s (THF, ε= 7.42) we e exp essed h ough he SMD
Con inuum Model,
24
wi h he same basis se used o he gas
phase op imiza ions. Gibbs ene gy in solu ion was calcula ed
acco ding o he ollowing simpli ied equa ion:
GTHF ¼Ggas þðETHF EgasÞ
Resul s and discussion
Syn hesis and cha ac e iza ion o he ca aly ic species
The syn hesis o he chlo o complex (
Bu
PCP)Pd(Cl) 1was
ca ied ou h ough he di ec eac ion o ammonium e a-
chlo opallada e(II) (NH
4
)
2
PdCl
4
and he comme cially a ailable
Bu
PCP(H) in 2-me hoxye hanol, wi h concomi an in si u C–H
bond ac i a ion and HCl/NH
4
Cl elimina ion. The eac ion
yield has been sligh ly imp o ed ( om 75 o 80%) wi h espec
o he o iginal li e a u e epo ,
11
whe e he benzoni ile
adduc cis-PdCl
2
(PhCN)
2
as a Pd
II
sou ce was employed
ins ead. Halide abs ac ion om 1wi h AgPF
6
in we THF led
o he isola ion o he ai -s able compound [(
Bu
PCP)Pd(H
2
O)]-
PF
6
(2); he aquo ligand hough is a he labile and i can be
easily eplaced by o he small molecules ha en e he me al
coo dina ion sphe e. Ne e heless, no eplacemen o he co-
o dina ed wa e molecule wi h o he neu al coo dina ing
species (ace oni ile, ca bon monoxide
25
) was a emp ed, since
hese species may be eac i e owa ds amine-bo anes, while
wa e is kine ically and he modynamically ine unde he eac-
ion condi ions employed in ou s udy ( ide in a); his has
also been con i med by he compu a ional esul s.
26
2has
been ho oughly cha ac e ized h ough mul inuclea (
31
P,
1
H,
13
C) NMR and IR spec oscopy; single c ys als sui able o
X- ay diff ac ion we e g own om THF–n-pen ane solu ions.
The compound c ys allizes in he monoclinic P2
1
space g oup
(Fig. 1); he coo dina ion geome y a he Pd
II
cen e is (dis-
o ed) squa e plana {[α(P(1)–Pd–P(2)] = 166.02(3)°; α[P(1)–Pd–
O(1)] = 96.86(9)°; α[P(1)–Pd–C(1)] = 83.48(9)°}; he s uc u al
pa ame e s {d[Pd–C(1)] = 2.026(3) Å; d[Pd–P(1)] = 2.314(1) Å;
Fig. 1 ORTEP diag am ( he mal ellipsoids a 50% p obabili y) o he asym-
me ic uni in he c ys al la ice o 2. Hyd ogen a oms on he ligand omi ed o
cla i y. Hyd ogen bonds depic ed as yellow do ed lines. See he ESI‡ o he
comple e se o c ys allog aphic pa ame e s and ables.
Dal on T ansac ions Pape
This jou nal is © The Royal Socie y o Chemis y 2013 Dal on T ans., 2013, 42, 3533–3541 | 3535
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online
d[Pd–O(1)] = 2.157(3) Å} a e e y simila o hose o o he
species con aining he [(
Bu
PCP)Pd]
+
agmen .
27
The PF
6
−
coun e ion is hyd ogen-bonded o he coo dina ed aquo ligand
{d[F(2)⋯H(1B)] = 2.51(5) Å; d[F(3)⋯H(1A)] = 2.24(5) Å; α[F(2)-
⋯H(1B)–O(1)] = 109(3)°; α[F(3)⋯H(1A)–O(1)] = 142(4)°}.
Va iable empe a u e mul inuclea NMR analysis
The eac ion o 2wi h 5 equi alen s o AB in THF-d
8
was ol-
lowed ia mul inuclea
31
P,
1
H and
11
B a iable- empe a u e
(VT) NMR spec oscopy in he 190–298 K empe a u e ange.
A 190 K he only species p esen in he
31
P{
1
H} NMR spec a
besides he s a ing ma e ial is a non-hyd idic in e media e a
δ
P
= 81 ppm (Fig. 2); abo e 230 K, a slow con e sion o
his species in o he hyd ide compound (
Bu
PCP)Pd(H) (δ
P
=
94.4 ppm; δ
H
=−4.2 ppm,
1
J
H–P
= 13.7 Hz)
11,28
occu ed.
Du ing he same eac ion ime, an off-whi e polyme ic p ecipi-
a e was also o med a he bo om o he NMR ube. The
soluble dehyd ogena ion by-p oduc s a e en a i ely assigned
o oligome ic species o gene al o mula [BH
2
–NH
2
]
n
(n=2–3),
29
as sugges ed by he
11
B-NMR peak cen e ed a δ
B
=−12.1 ppm
eco ded in he supe na an solu ion (Fig. 3). I appea s as a
e y b oad pseudo-qua e , esul ing om he o e lapping o
wo iple s alling a close chemical shi s ( his has been con-
i med by he
11
B{
1
H} spec a, whe e wo b oad single s a e
obse ed a δ
B
=−11.6 and δ
B
=−12.7 ppm. The p esence o
wo peaks is likely o be ela ed o he diffe en chain size,
since ea ly li e a u e epo s
29b
s a ed ha he cyclic and linea
isome s a e indis inguishable in he
11
B-NMR spec a). Un o -
una ely, all he a emp s made o isola e he pu e p oduc s
ailed. The solid p ecipi a e has been in es iga ed by IR spec-
oscopy: i p obably consis s o a mix u e o uniden i ied
longe -chain [BH
2
–NH
2
]
n
oligome s o he same ype as hose
p esen in solu ion [ he adso p ion bands ela ed o he
ν(BH
2
), ν(NH
2
) and ν(B–N) no mal modes we e obse ed a
3284, 2425 and 1458 cm
−1
, espec i ely;
30
he exac chemical
composi ion hough could no be de e mined]. A e 18 h a
ambien empe a u e, no all he excess o AB was con e ed
in o oligome s; a comple e con e sion could no be achie ed,
while he s a ing ca alys u ned in o he he modynamically
s able hyd ide species (
Bu
PCP)Pd(H) quan i a i ely. This is
also in ag eemen wi h he kine ic esul s ( ide in a). I is
likely ha he monohyd ide species ep esen s he “spen ca a-
lys ”, as con i med by i s di ec eac i i y wi h AB (1 : 5), which
did no lead o any H
2
p oduc ion and/o AB oligome iza ion.
The eac ion wi h he N-subs i u ed amine-bo ane DMAB
(in he same 1 : 5 s oichiome ic a io) p oceeded h ough a
eac ion mechanism ha seems o be he same as ha o AB;
again, a low empe a u es a peak alling a δ
P
= 82.0 ppm was
de ec ed in he
31
P{
1
H} NMR spec um, ha slowly disappea s
u ning in o he (
Bu
PCP)Pd(H) complex (Fig. S2‡); a he end
o he ca alysis, he cyclic dime cyclo-[BH
2
–NMe
2
]
2
was he
main species obse ed in he
11
B NMR spec um as a iple a
δ
B
= 5.9 ppm (
1
J
B–H
= 113.4 Hz, Fig. S3‡).
31
No un eac ed
DMAB was de ec ed a oom empe a u e a e 18 h; a odds
wi h wha was ound o AB, comple e con e sion o DMAB o
Fig. 2
31
P{
1
H} VT-NMR spec a o he 2: AB mix u e (1 : 5 s oichiome y, THF-
d
8
). The ed box highligh s he signal o he eac ion in e media e de ec ed
be ween 190 and 230 K.
Fig. 3
11
B VT-NMR spec a o he 2: AB mix u e (1 : 5 s oichiome y, THF-d
8
).
The ed box highligh s he signal o he oligome ic p oduc ob ained du ing he
dehyd ogena ion p ocess.
Pape Dal on T ansac ions
3536 |Dal on T ans., 2013, 42, 3533–3541 This jou nal is © The Royal Socie y o Chemis y 2013
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online
oligome s was achie ed. No e idence o o ma ion o he e hyl-
ene analogue BH
2
NMe
2
was ound, ei he coo dina ed o he
me al cen e o ee in solu ion (a odds wi h o he li e a u e
cases
4d, ,5a,b,i,l
), p esumably because o he as dime iza ion
p ocess.
No eac ion occu ed be ween 2and ie hylamine bo ane
NE
3
·BH
3
(always in a 1 : 5 a io); only he un eac ed s a ing
ma e ials we e obse ed in he NMR spec a, a all empe a-
u es. This con i ms ha hyd ogen is di ec ly p oduced om
he amine-bo ane dehyd ogena ion.
Quan i a i e H
2
de e mina ion
The kine ic p o iles a 303 K o he AB dehyd ogena ion eac-
ion we e also de e mined, o diffe en (2: AB) s oichiome ic
a ios (Fig. 4). In he (1 : 5) case, he eac ion was comple ed
a e ca. 22 h, and one H
2
equi alen pe AB equi alen was
eleased. Analysis h ough
11
B NMR o he supe na an solu-
ion a he end o he eac ion did no show un eac ed AB, in
con as wi h he obse a ion made in he VT NMR expe i-
men ; his is p obably due o he diffe en hyd ogen concen-
a ion in he wo expe imen s. Indeed, unde hese
expe imen al condi ions, ca. 50% o 2is s ill p esen a he
end o he p ocess. In ag eemen wi h ha , he inc ease o AB
concen a ion in he eac ion causes a elease o less H
2
equi alen s and a mo e apid ca alys deac i a ion [i.e. o -
ma ion o (
Bu
PCP)Pd(H)]. Thus, wi h a (1 : 20) a io, a ound 0.9
H
2
equi alen s pe AB equi alen a e eleased be o e all he
me al complex has been ans o med in o (
Bu
PCP)Pd(H), wi h
some AB being un eac ed in he inal solu ion. In con as ,
unning he eac ion wi h a (1 : 50) a io, he amoun o H
2
equi alen s eleased is ne e highe han 0.4–0.5, wi h
un eac ed monome in he inal solu ion, his indica ing a
quicke ca alys deac i a ion.
The measu emen o he amoun o H
2
eleased in he eac-
ion wi h DMAB ollowing his app oach was p o ed o be no
easible. The ola ili y o he co esponding spen uel cyclo-
[BH
2
–NMe
2
]
232
p o ided an exceedingly high alue o he o al
gas p essu e eco ded; i was no possible o quan i y he con-
ibu ion gi en by each o he wo species. None heless, i is
easonable o assume ha a maximum o one H
2
equi alen
pe monome equi alen is eleased also in his case, acco d-
ing o he
11
B NMR analysis o he spen uel (see p e ious
pa ag aph and Fig. S3‡).
Kine ic measu emen s and e alua ion o he eac ion a e
h ough
11
B NMR spec oscopy
Fo he sake o compa ison, he kine ic a e cons an (k
obs
)
alues o he dehyd ogena ion o AB and DMAB by 2a
303 K we e de e mined h ough
11
B NMR moni o ing. The com-
pe i i e eac ion o nascen H
2
wi h he palladium agmen o
p oduce he “spen o m”(
Bu
PCP)Pd(H) is esponsible o he
a ia ion o he ac i e ca alys concen a ion in ime; conse-
quen ly, o a mo e eliable e alua ion o he a e cons an s,
only he da a poin s collec ed wi hin he ini ial 3 h we e aken
in o accoun o he i ing, assuming ha he ca alys concen-
a ion is cons an wi hin his ime ange. The esul s we e
plo ed as a 1/[AB] s. g aph (Fig. 5), assuming a second o de
kine ic a e law wi h espec o AB: −d[AB]/d =k
obs
[AB]
2
. The
assump ion comes om he esul s o he DFT mechanis ic
analysis ( ide in a), whe e he only eac ion s ep showing a
posi i e ΔG alue is ha ela ed o he adduc be ween he
[(
H
PCP)Pd]
+
agmen and wo molecules o AB. In o de
o e i y his hypo hesis, an ini ial a e expe imen was
Fig. 4 H
2
e olu ion in he AB dehyd ogena ion p ocess ca alyzed by 2(303 K,
dioxane) o diffe en 2: AB a ios (◆,1:5;▲, 1 : 20).
Fig. 5 (a) Linea [AB] s. and (b) no malized 1/[AB] s. plo s (second o de
a e law) o he AB dehyd ogena ion eac ion ca alyzed by 2(303 K, THF-d
8
).
Dal on T ansac ions Pape
This jou nal is © The Royal Socie y o Chemis y 2013 Dal on T ans., 2013, 42, 3533–3541 | 3537
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online

pe o med on he eac ion be ween 2and AB (see ESI‡ o
de ails). The esul s con i med he second o de in subs a e
concen a ion. Following he second o de da a i ing, a inal
k
obs
alue o 4.31(11) × 10
−4
M
−1
s
−1
is ob ained o AB. As o
DMAB, he same app oxima ion led o a k
obs
alue o 2.67(5) ×
10
−4
M
−1
s
−1
(Fig. S4‡). The eac ion a e is highe o AB han
o DMAB, p obably because o a p edominan s e ic hin-
d ance o he seconda y amine wi h espec o ammonia ha
easonably makes dime iza ion slowe .
DFT modeling o he AB dime iza ion mechanism
The esul s coming om he VT-NMR s udies p omp ed us o
cas ligh on he eac ion mechanism h ough DFT modeling,
a he M06//6-31+G(d,p) compu a ional le el. Fo he sake o
simplici y, only he o ma ion o cyclo-(BH
2
–NH
2
)
n
(n=2)was
aken in o accoun in he compu a ional modeling o he eac-
ion mechanism. To his aim, a simpli ied s uc u e o 2was
aken in o accoun o he he modynamics calcula ions,
whe e he bulky e -bu yl g oups we e eplaced wi h hyd ogen
a oms, o achie e he bes comp omise be ween model sys em
accu acy and compu a ional ime.
33
The esul ing [(
H
PCP)Pd-
(H
2
O)]
+
ca ion 2
H
was assumed o be he s a ing complex. The
o e all p oposed ca aly ic cycle o he AB dime iza ion eac-
ion wi h o ma ion o he ino ganic cyclobu ane analogue
[BH
2
–NH
2
]
2
and wo equi alen s o H
2
(ΔG=−12.0 kcal mol
−1
,
Scheme 2) is epo ed in Scheme 3. Due o he complex na u e
o he mechanis ic s eps in ol ed in his p ocess, no ansi ion
s a es could be ound along he eac ion coo dina e; he e o e,
only he ΔG alues ( he modynamics) o each s ep ha e been
assessed in THF.
The aquo complex 2
H
eadily unde goes ligand exchange
wi h one molecule o AB, o o m an η
1
-BH-bonded adduc
2
H
_AB (Fig. 6).
26
The in e ac ion o AB wi h he [(
H
PCP)Pd]
+
agmen is weak, bu he exchange p ocess is he modynami-
cally downhill, wi h a ΔGo −7.5 kcal mol
−1
. No s abilizing
in e ac ion o he ammonia-bo ane N–H bonds wi h he
[(
H
PCP)Pd]
+
agmen was ound, in line wi h wha was al eady
obse ed in o he cases o ca ionic ansi ion me al moie-
ies.
9,6c
I is p oposed ha he labile in e media e obse ed in
he
31
P{
1
H} NMR spec a in he a iable- empe a u e expe i-
men s could be ep esen ed by he simple adduc be ween
[(
Bu
PCP)Pd]
+
and AB, wi h he same s uc u e as 2
H
_AB.
In e ac ion o 2
H
_AB wi h an addi ional AB molecule leads
o he adduc 2
H
_AB2 (Fig. 7), wi h a posi i e Gibbs ene gy a i-
a ion o +4.9 kcal mol
−1
. The en opy educ ion while passing
om (2
H
_AB + AB) o 2
H
_AB2 is a plausible eason o his s ep
o be endoe gonic. The p esence o he second AB molecule
a o s he coo dina ion slippage o he Pd-bound AB om
Scheme 2 Cyclo-dime iza ion o AB.
Scheme 3 P oposed ca aly ic cycle o AB cyclo-dime iza ion in he p esence
o 2. The dihyd ogen bonding be ween hyd idic and p o onic H a oms is shown
in ed. Reac an s and p oduc s a e d awn in blue.
Fig. 6 Op imized geome y o [(
H
PCP)Pd(η
1
-AB)]
+
(2
H
_AB). Selec ed op imized
bond leng hs epo ed (Å). H a oms on he pince ligand omi ed o cla i y.
A om colo code: whi e, H; g ay, C; pu ple, P; blue, N; pink, B; ligh blue, Pd.
Fig. 7 Op imized geome y o [(
H
PCP)Pd(σ-BH-AB)⋯AB]
+
(2
H
_AB2). Selec ed
op imized bond leng hs epo ed (Å). H a oms on he pince ligand omi ed o
cla i y. A om colo code: see Fig. 6. N–H⋯H–B dihyd ogen bonds and σ-BH
agos ic in e ac ions d awn as yellow do ed lines.
Pape Dal on T ansac ions
3538 |Dal on T ans., 2013, 42, 3533–3541 This jou nal is © The Royal Socie y o Chemis y 2013
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online
η
1
-BH o σ-BH agos ic. This e eals ha bo h coo dina ion
modes a he Pd
II
ca ion a e possible, and he σ-agos ic geome-
y can be conside ed a so o “ ansi ion s a e”be ween
diffe en η
1
-BH modes o he luxional AB “ligand”.
34
Dihyd o-
gen B–H⋯H–N bonding be ween he wo monome s is p esen
[op imized d(B–H⋯H–N) = 1.83 Å]. A weak N–H in e ac ion o
he non-coo dina ed monome wi h he me al cen e is also
p esen [op imized d(N–H⋯Pd) = 2.67 Å].
A his s age, a me al-media ed AB dime iza ion may occu ,
wi h o ma ion o one equi alen o H
2
and he linea BH
3
–
NH
2
–BH
2
–NH
3
dime ( he ino ganic bu ane analogue, which
was also independen ly p epa ed and cha ac e ized)
35
coo di-
na ed o palladium, i.e. he [(
H
PCP)Pd(η
1
-BH–BH
3
–NH
2
–BH
2
–
NH
3
)]
+
adduc (2
H
_BNBN, Fig. 8). The ΔG o his s ep equals
−13.5 kcal mol
−1
.
Fu he in amolecula dehyd ogena ion (p omo ed by he
exis ence o an in amolecula dihyd ogen bonding in
2
H
_BNBN, as e idenced in Fig. 8) leads o [(
H
PCP)Pd(η
1
-BH-
cyclo-(BH
2
–NH
2
)
2
]
+
(2
H
_cyc, Fig. 9), whe e he s abilizing σ-BH
agos ic in e ac ion p o ides ΔG=−1.1 kcal mol
−1
. A his
s age, eplacemen o he cyclic dime by ano he AB
“monome ”(ΔG=−2.2 kcal mol
−1
) egene a es he s a ing
ac i e species 2
H
_AB o ano he ca aly ic un. Du ing he eac-
ion cou se ca alys deac i a ion p og essi ely occu s, h ough
di ec in e ac ion o 2
H
wi h nascen H
2
and subsequen o -
ma ion o he non-classical hyd ide [(
H
PCP)Pd(η
2
-H
2
)]
+
(Fig. S5‡). This eac ion is almos he moneu al (ΔG=+
0.8 kcal mol
−1
). Despi e he lack o expe imen al e idence o
he exis ence o such an uns able and eac i e dihyd ogen
compound {only he pla inum(II) analogue [(
Bu
PCP)P (η
2
-H
2
)]
+
was expe imen ally syn hesized h ough p o ona ion o he
classical (
Bu
PCP)P (H) and de ec ed in he
1
H NMR spec um
a e y low empe a u es (180 K)
36
} and he sca ci y o genuine
non-classical Pd molecula hyd ogen complexes, i can be
possibly in oked as he ansien p ecu so o he inal classi-
cal monohyd ide.
Conclusions
In summa y, amine-bo ane dehyd ogena ion/oligome iza ion
media ed by he obus palladium (PCP)-pince complex
[(
Bu
PCP)Pd(H
2
O)]PF
6
has been s udied h ough a combina ion
o expe imen al (VT-NMR, kine ic p o iles) and compu a ional
(DFT) echniques, wi h he aim o un a eling eac ion in e -
media es and he amoun o H
2
p oduced unde he applied
expe imen al condi ions. A odds wi h o he Pd
II
-based
sys ems,
9
he pince compound examined p oduces only one
H
2
equi alen pe AB equi alen . This e eals a limi ed de-
hyd ogena ion abili y ha leads o “alipha ic” a he han “a o-
ma ic”(bo azine-like) oligome s as a spen uel. A he same
ime, his inding can be seen as an ad an age om an engin-
ee ing poin o iew, since in hyd ogen uel cells echnology
signi ican effo s a e being made o educe o elimina e bo a-
zine as a de imen al side-p oduc . Besides, hese mechanis ic
s udies a e o undamen al impo ance in ligh o he de elop-
men o be e -pe o ming homogeneous ca alys s o an
efficien AB dehyd ogena ion. No el pince - ype ansi ion
me al o ganome allics a e cu en ly being p epa ed in ou lab-
o a o ies, wi h he aim o es ing hem as no el amine-bo ane
dehyd ogena ion ca alys s.
Acknowledgemen s
The PIRODE p ojec o he I alian Minis y o he En i on-
men , he EFOR p ojec o he I alian Na ional Resea ch
Council, he Spanish Minis y o Science (p ojec s CTQ2010-
17476 and Consolide -Ingenio 2010 CSD2007-00006) and he
Jun a de Andalucía (p ojec P09-FQM-4832) (FEDER suppo )
a e acknowledged o inancial suppo . The CNR–CSIC bila -
e al ag eemen is acknowledged o mobili y unding h ough
he “Chemical hyd ogen s o age: amino bo anes ac i a ion
wi h ansi ion me al o ganome allics”p ojec (CSIC
2010IT0036, CNR 11544). A. M. L.-V. hanks he CSIC and ESF
o suppo h ough he JAE-doc p og am. The use o he com-
pu a ional acili ies o he Cen e de Se eis Cien í ics i Aca-
dèmics de Ca alunya (CESCA) is g ea ly app ecia ed. Thanks a e
also gi en o he p ojec Fi enze Hyd olab-2 suppo ed by ECRF.
No es and e e ences
1(a) R. Lan, J. T. S. I ine and S. Tao, In . J. Hyd ogen Ene gy,
2012, 37, 1482–1494; (b) T. Umegaki, J.-M. Yan,
Fig. 8 Op imized geome y o [(
H
PCP)Pd(σ-BH–BH
3
–NH
2
–BH
2
–NH
3
)]
+
(2
H
_BNBN). Selec ed op imized bond leng hs epo ed (Å). H a oms on he
pince ligand omi ed o cla i y. A om colo code: see Fig. 6. N–H⋯H–B dihyd o-
gen bonds and σ-BH agos ic in e ac ions d awn as yellow do ed lines.
Fig. 9 Op imized geome y o {(
H
PCP)Pd[σ-BH-cyclo-(BH
2
NH
2
)
2
]}
+
(2
H
_cyc).
Selec ed op imized bond leng hs epo ed (Å). H a oms on he pince ligand
omi ed o cla i y. A om colo code: see Fig. 6. σ-BH agos ic in e ac ions d awn
as yellow do ed lines.
Dal on T ansac ions Pape
This jou nal is © The Royal Socie y o Chemis y 2013 Dal on T ans., 2013, 42, 3533–3541 | 3539
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online
X.-B. Zhang, H. Shioyama, N. Ku iyama and Q. Xu,
In . J. Hyd ogen Ene gy, 2009, 34, 2303–2311; (c) D. Wenge ,
W. Poli ke, E. Schmid -Ihn, T. Abdel-Base and S. Maus,
In . J. Hyd ogen Ene gy, 2009, 34, 6265–6270.
2 U. Ebe le, M. Fede hoffand F. Schue h, Angew. Chem., In .
Ed., 2009, 48, 6608–6630 and e e ences he ein.
3(a) S. Udishnu, U. B. Demi ci, B. R. Jagi da and P. Miele,
ChemSusChem, 2011, 4, 1731–1739; (b) T. Hügle, M. Ha l
and D. Len z, Chem.–Eu . J., 2011, 17, 10184–10207;
(c) A. S aubi z, A. P. M. Robe son and I. Manne s, Chem.
Re ., 2010, 110, 4079–4124; (d) N. C. Smy he and
J. C. Go don, Eu . J. Ino g. Chem., 2010, 509–521;
(e) F. H. S ephens, V. P. Pons and R. T. Bake , Dal on T ans.,
2007, 2613–2626; ( ) T. B. Ma de , Angew. Chem., In . Ed.,
2007, 46, 8116–8118.
4(a) C. J. Wallis, H. Dye , L. Vendie , G. Alca az and S. Sabo-
E ienne, Angew. Chem., In . Ed., 2012, 51, 3646–3648;
(b) B. L. Conley, D. Guess and T. J. Williams, J. Am. Chem.
Soc., 2011, 133, 14212–14215; (c) G. Alca az and S. Sabo-
E ienne, Angew. Chem., In . Ed., 2010, 49, 7170–7179;
(d) G. Alca az, L. Vendie , E. Clo and S. Sabo-E ienne,
Angew. Chem., In . Ed., 2010, 49, 918–920; (e)M.Käβ,
A. F ied ich, M. D ees and S. Schneide , Angew. Chem., In .
Ed., 2009, 48, 905–907; ( ) A. F iede ich, M. D ees and
S. Schneide , Chem.–Eu . J., 2009, 15, 10339–10342;
(g) N. Blacquie e, S. Diallo-Ga cia, S. I. Go elsky, D. A. Black
and K. Fagnou, J. Am. Chem. Soc., 2008, 130, 14034–14035.
5(a) L. J. Sewell, G. C. Lloyd-Jones and A. S. Welle , J. Am.
Chem. Soc., 2012, 134, 3598–3610; (b) C. Y. Tang,
N. Phillips, J. I. Ba es, A. L. Thompson, M. J. Gu mann and
S. Ald idge, Chem. Commun., 2012, 48, 8096–8098;
(c) C. Y. Tang, A. L. Thompson and S. Ald idge, Angew.
Chem., In . Ed., 2010, 49, 921–925; (d) G. Alca az,
A. B. Chaplin, C. J. S e ens, E. Clo , L. Vendie , A. S. Welle
and S. Sabo-E ienne, O ganome allics, 2010, 29, 5591–5595;
(e) A. B. Chaplin and A. S. Welle , Ino g. Chem., 2010, 49,
1111–1121; ( ) A. B. Chaplin and A. S. Welle , Angew.
Chem., In . Ed., 2010, 49, 581–584; (g) R. Dallaneg a,
A. B. Chaplin and A. S. Welle , Angew. Chem., In . Ed., 2009,
48, 6875–6878; (h) T. M. Douglas, A. B. Chaplin,
A. S. Welle , X. Yang and M. B. Hall, J. Am. Chem. Soc.,
2009, 131, 15440–15456; (i) M. E. Sloan, T. J. Cla k and
I. Manne s, Ino g. Chem., 2009, 48, 2429–2435;
(j) T. M. Douglas, A. B. Chaplin and A. S. Welle , J. Am.
Chem. Soc., 2008, 130, 14432–14433; (k) T. J. Cla k,
G. R. Whi ell and I. Manne s, Ino g. Chem., 2007, 46,
7522–7527; (l) Y. Chen, J. L. Ful on, J. C. Linehan and
T. Au ey, J. Am. Chem. Soc., 2005, 127, 3254–3255.
6(a) H. C. Johnson, A. P. M. Robe son, A. B. Chaplin,
L. J. Sewell, A. L. Thompson, M. F. Haddow, I. A. Manne s
and A. S. Welle , J. Am. Chem. Soc., 2011, 133, 11076–11079;
(b) R. Ciganda, M. A. Ga alda, L. Iba lucea, E. Pinilla and
M. Rosa io To es, Dal on T ans., 2010, 39, 7226–7229;
(c) T. W. G aham, C.-W. Tsang, X. Chen, R. Guo, W. Jia,
S.-M. Lu, C. Sui-Seng, C. B. Ewa , A. Lough, D. Amo oso
and K. Abdu -Rashid, Angew. Chem., In . Ed., 2010, 49,
8708–8711; (d) A. Rossin, M. Capo ali, L. Gonsal i,
A. Gue i, A. Lledós, M. Pe uzzini and F. Zanobini,
Eu . J. Ino g. Chem., 2009, 3055–3059; (e) A. Paul and
C. B. Musg a e, Angew. Chem., In . Ed., 2007, 46,
8153–8156; ( ) M. C. Denney, V. Pons, T. J. Hebden,
M. Heinekey and K. I. Goldbe g, J. Am. Chem. Soc., 2006,
128, 12048–12049.
7(a)The Chemis y o Pince Compounds, ed. D. Mo ales-
Mo ales and C. M. Jensen, Else ie , Ams e dam NL, 2007;
(b) I. Gö ke -Schne mann, P. Whi e and M. B ookha ,
J. Am. Chem. Soc., 2004, 126, 1804–1811; (c) K. K ogh-Jespe -
sen, M. Cze w, N. Summa, K. B. Renkema, P. D. Acho d
and A. S. Goldman, J. Am. Chem. Soc., 2002, 124,
11404–11416.
8(a) X. Yang and M. B. Hall, J. Am. Chem. Soc., 2008, 130,
1798–1799; (b) R. J. Kea on, J. M. Blacquie e and
R. T. Bake , J. Am. Chem. Soc., 2007, 129, 1844–1845.
9 S.-K. Kim, W.-S. Han, T.-J. Kim, T.-Y. Kim, S. W. Nam,
M. Mi o aj, Ł. Piekoś, A. Michalak, S.-J. Hwang and
S. O. Kang, J. Am. Chem. Soc., 2010, 132, 9954–9955.
10 (a) Ö. Me in, S. Duman, M. Dinç and S. Özka , J. Phys.
Chem. C, 2011, 115, 10736–10743; (b) R. P. Sh es ha,
H. V. K. Diyabalanage, T. A. Semelsbe ge , K. C. O and
A. K. Bu ell, In . J. Hyd ogen Ene gy, 2009, 34, 2616–2621.
11 C. J. Moul on and B. L. Shaw, J. Chem. Soc., Dal on T ans.,
1976, 1020–1024.
12 C ysAlisCCD 1.171.31.2 ( elease 07-07-2006), C ysAlis171.
NET, Ox o d Diff ac ion L d.
13 C ysAlis RED 1.171.31.2 ( elease 07-07-2006), C ysAlis171.
NET, Ox o d Diff ac ion L d.
14 A. Al oma e, M. C. Bu la, M. Camalli, G. L. Casca ano,
C. Giaco azzo, A. Guaglia di, A. G. G. Moli e ni, G. Polido i
and R. Spagna, J. Appl. C ys allog ., 1999, 32, 115.
15 G. M. Sheld ick, SHELXL, 1997.
16 M. Na delli, Compu . Chem., 1993, 7, 95.
17 L. J. Fa ugia, J. Appl. Chem., 1999, 32, 837.
18 M. J. F isch, e al.,GAUSSIAN 09 (Re ision A.02), Gaussian
Inc., Walling o d CT, 2009.
19 Y. Zhao and D. G. T uhla , Theo . Chem. Acc., 2008, 120,
215–241.
20 Y. Zhao and D. G. T uhla , Acc. Chem. Res., 2008, 41,
157–167.
21 (a) P. J. Hay and W. R. Wad , J. Chem. Phys., 1985, 82,
270–283; (b) W. R. Wad and P. J. Hay, J. Chem. Phys., 1985,
82, 284–298.
22 (a) A. Höllwa h, M. Böhme, S. Dapp ich, A. W. Ehle s,
A. Gobbi, V. Jonas, K. F. Köhle , R. S egmann, A. Veldkamp
and G. F enking, Chem. Phys. Le ., 1993, 208, 237–240;
(b) A. W. Ehle s, M. Böhme, S. Dapp ich, A. Gobbi,
A. Höllwa h, V. Jonas, K. F. Köhle , R. S egmann,
A. Veldkamp and G. F enking, Chem. Phys. Le ., 1993, 208,
111–114.
23 B. J. Lynch, Y. Zhao and D. G. T uhla , J. Phys. Chem. A,
2003, 107, 1384–1388.
24 A. V. Ma enich, C. J. C ame and D. G. T uhla , J. Phys.
Chem. B, 2009, 113, 6378–6396.
Pape Dal on T ansac ions
3540 |Dal on T ans., 2013, 42, 3533–3541 This jou nal is © The Royal Socie y o Chemis y 2013
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online
25 Li e a u e examples con aining he [(
Bu
PCP)M(L)]
+
ca ionic
agmen a e: (a)[(
Bu
PCP)Ni(MeCN)]
+
: V. A. Le ina,
A. Rossin, N. V. Belko a, M. R. Chie o i, L. M. Eps ein,
O. A. Filippo , R. Gobe o, L. Gonsal i, A. Lledòs,
E. S. Shubina, F. Zanobini and M. Pe uzzini, Angew. Chem.,
In . Ed., 2011, 50, 1367–1370; (b)[(
Bu
PCP)P (CO)]
+
:
D. Vuzman, E. Po e eno , Y. Diskin-Posne , G. Lei us,
L. W. Y. Shimon and D. Mils ein, Dal on T ans., 2007,
5692–5700.
26 The di ec eac ion o AB wi h he coo dina ed wa e mol-
ecule did no lead o easonable ΔG alues in some s eps
o he (supposed) ca aly ic cycle, p o iding a e y un a o -
able o e all he modynamics. Indeed, no expe imen al e i-
dence o eac ion be ween AB o DMAB and H
2
Owas
ound, unde he applied expe imen al condi ions
[i.e. absence o
11
B NMR signals ypical o bo ic acid-
like hyd olysis p oduc s ( o be expec ed a ound δ
B
=
+18.0 ppm)]. F om all hese indings, his hypo hesis was
disca ded.
27 [(
Bu
PCP)Pd(H
2
O)]BF
4
: B. F. M. Kimmich, W. J. Ma shall,
P. J. Fagan, E. Haup man and R. M. Bullock, Ino g. Chim.
Ac a, 2002, 330,52–58. (
Bu
PCP)Pd(NO
2
)/(
Bu
PCP)Pd(NO
3
):
R. Johansson, L. Oh s om and O. F. Wend , C ys . G ow h
Des., 2007, 7, 1974–1979. (
Bu
PCP)Pd(CH
3
): R. Johansson,
M. Ja enma k and O. F. Wend , O ganome allics, 2005, 24,
4500–4502. (
Bu
PCP)Pd(OCOCF
3
): M. T. Johnson, M. Ce ina,
K. Rissansen and O. F. Wend , Ac a C ys allog ., Sec . E:
S uc . Rep. Online, 2010, 66, m675.
28 M. C. Denney, N. A. Smy he, K. L. Ce o, R. A. Kemp and
K. I. Goldbe g, J. Am. Chem. Soc., 2006, 128, 2508–2509.
29 (a) W. J. Shaw, J. C. Linehan, N. K. Szymczak,
D. J. Heldeb an , C. Yonke , D. M. Camaioni, R. T. Bake
and T. Au ey, Angew. Chem., In . Ed., 2008, 47, 7493–7496;
(b) J. S. Wang and R. A. Geanangel, Ino g. Chim. Ac a, 1988,
148, 185–190.
30 K. W. Böddeke , S. G. Sho e and R. K. Bun ing, J. Am.
Chem. Soc., 1966, 88, 4396–4401.
31 (a) H. J. Cowley, M. S. Hol , R. L. Melen, J. M. Rawson and
D. S. W igh , Chem. Commun., 2011, 47, 2682–2684;
(b) T. Bewe ies, J. Thomas, M. Klahn, A. Schulz,
D. Helle and U. Rosen hal, ChemCa Chem, 2011, 3,
1865–1868.
32 C. A. Jaska, K. Temple, A. J. Lough and I. Manne s, Chem.
Commun., 2011, 962–963.
33 An assessmen o he compu a ional e o made when
passing om he eal o he model sys em was made on
he gas phase ΔE alues o he exchange eac ion [(
R
PCP)
Pd(H
2
O)]
+
+AB→[(
R
PCP)Pd(AB)]
+
+H
2
O. The esul s we e
he ollowing: R =
Bu, ΔE=−8.3 kcal mol
−1
;R=H,ΔE=
−11.5 kcal mol
−1
. Thus, he same o de o magni ude o
he he modynamic eac ion pa ame e s is calcula ed when
eplacing he ( eal) e -bu yl subs i uen s on phospho us
wi h hyd ogen a oms.
34 This kind o luxional coo dina ion hap ici y ( ha ans-
la es in o magne ically equi alen H a oms in he
1
H NMR
spec a) has also been obse ed o ansi ion me al bo ohy-
d ide complexes, such as: (a) (PPh
3
)
2
Cu(BH
4
): I. E. Golub,
O. A. Filippo , E. I. Gu sul, N. V. Belko a, L. M. Eps ein,
A. Rossin, M. Pe uzzini and E. S. Shubina, Ino g. Chem.,
2012, 51, 6486–6497; (b)(
Bu
PCP)Ni(BH
4
): A. Rossin,
M. Pe uzzini and F. Zanobini, Dal on T ans., 2011, 40,
4447–4452.
35 X. Chen, J.-C. Zhao and S. G. Sho e, J. Am. Chem. Soc.,
2010, 132, 10658–10659.
36 B. F. M. Kimmich and R. M. Bullock, O ganome allics, 2002,
21, 1504–1507.
Dal on T ansac ions Pape
This jou nal is © The Royal Socie y o Chemis y 2013 Dal on T ans., 2013, 42, 3533–3541 | 3541
Published on 04 Decembe 2012. Downloaded by Cen o de In es igaciones Cien i icas Isla de la Ca uja (CICIC) on 23/05/2014 12:22:29.
View A icle Online