N-heterocyclic carbenes in Lewis acid/base stabilised phosphanylboranes

Article abstract of DOI:10.1002/ejic.200800305

The reactions of 2-borane-1,3,4,5-tetramethylimidazoline (BH ₃·NHC^Me) with selected phosphane adducts of the Lewis acids B(C₆F₅)₃ and Ga(C₆F ₅)₃ are studied. Among others, adducts (C ₆F₅)₃Ga·PH₂Cp* (1a) and (C₆F₅)₃B·PH₂Cp* (2) are used as starting materials. When the (C₆F₅) ₃Ga-phosphane adducts 1a and (C₆F₅) ₃Ga·PPhH₂ are treated with BH₃· NHC^Me, the Lewis acid/base stabilised phosphanylboranes (C ₆F₅)₃Ga·P(Cp*)HBH ₂·NHC^Me (3a) and (C₆F₅) ₃Ga· P(Ph)HBH₂·NHC^Me (3b) are formed, respectively, by a hydrogen elimination reaction. In contrast, the reaction of BH₃·NHC^Me with the (C₆F ₅)₃B-phosphane adducts (C₆F₅) ₃B· PH₂R [R = H, R = Cp* (2) and R = Ph] in CH₂Cl₂ at room temperature leads to the formation of a salt with the general formula [(C₆F₅)₃BH] [RPH₂·BH₂·NHC^Me] (4a: R = H, 4b: R = Cp*, 4c: R = Ph). To synthesise the Lewis acid/base stabilised phosphanylborane with (C₆F₅)₃B as a Lewis acid and 1,3,4,5-tetramethylimidazolylidene (NHC^Me) as a Lewis base, a different synthetic pathway was applied: the replacement reaction of the Lewis base. At room temperature, NHC^Me displaced the amine in (C ₆F₅)₃B·P(Ph)HBH₂· NMe₃ to yield (C₆F₅)₃B·P(Ph) HBH₂·NHC^Me (5). All compounds were comprehensively characterised by spectroscopic methods. Compounds 1a, 1b, 2, 3a, 3b and 5 were additionally characterised by X-ray crystallographic analysis. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800305

FULL PAPER
DOI: 10.1002/ejic.200800305
N-Heterocyclic Carbenes in Lewis Acid/Base Stabilised Phosphanylboranes
Ariane Adolf,[a] Ulf Vogel,[a] Manfred Zabel,[a] Alexey Y. Timoshkin,[b] and
Manfred Scheer*[a]
Dedicated to Professor Heinrich Nöth on the occasion of his 80th birthday
Keywords: Boron / Phosphorus / Gallium / Carbenes / Lewis acids / Lewis bases
The reactions of 2-borane-1,3,4,5-tetramethylimidazoline
(BH3·NHCMe) with selected phosphane adducts of the Lewis
acids B(C6F5)3 and Ga(C6F5)3 are studied. Among others, ad-
ducts (C6F5)3Ga·PH2Cp* (1a) and (C6F5)3B·PH2Cp* (2) are
used as starting materials. When the (C6F5)3Ga–phosphane
adducts 1a and (C6F5)3Ga·PPhH2 are treated with
formula [(C6F5)3BH][RPH2·BH2·NHCMe] (4a: R = H, 4b: R =
Cp*, 4c: R = Ph). To synthesise the Lewis acid/base stabilised
phosphanylborane with (C6F5)3B as a Lewis acid and 1,3,4,5-
tetramethylimidazolylidene (NHCMe) as a Lewis base, a dif-
ferent synthetic pathway was applied: the replacement reac-
tion of the Lewis base. At room temperature, NHCMe dis-
BH3·NHCMe, the Lewis acid/base stabilised phosphanylbor- placed the amine in (C6F5)3B·P(Ph)HBH2·NMe3 to yield
anes (C6F5)3Ga·P(Cp*)HBH2·NHCMe (3a) and (C6F5)3Ga·
P(Ph)HBH2·NHCMe (3b) are formed, respectively, by a hydro-
gen elimination reaction. In contrast, the reaction of
BH3·NHCMe with the (C6F5)3B–phosphane adducts (C6F5)3B·
PH2R [R = H, R = Cp* (2) and R = Ph] in CH2Cl2 at room
temperature leads to the formation of a salt with the general
(C6F5)3B·P(Ph)HBH2·NHCMe (5). All compounds were com-
prehensively characterised by spectroscopic methods. Com-
pounds 1a, 1b, 2, 3a, 3b and 5 were additionally character-
ised by X-ray crystallographic analysis.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
the group 13) can be activated by thermal or catalytic meth-
ods to liberate H2. Oligophosphanylboranes [HRP–BH2]n
(n = 3, 4; R = Ph) were synthesised by a dehydrocoupling
reaction at elevated temperatures[9,10] or catalysed by RhI
complexes as Manners et al. have demonstrated.[11,12] Denis
et al. described the synthesis of the polymeric phosphanyl-
borane [H2P–BH2]n by a dehydrocoupling reaction cata-
lysed by B(C6F5)3.[13] However, so far all attempts to isolate
the parent monomeric compound of this class [H2P–BH2]
were to no avail and only theoretical investigations on the
compound have been performed.[14–16] Our approach to the
parent compounds of phosphanylboranes was to stabilise
them by the coordination of Lewis acids and Lewis bases
of type A compounds (Scheme 1). In these instances, the
lone pair of electrons of the phosphorus atom is occupied
by a Lewis acid (LA) and the boron atom is coordinated
by a Lewis base (LB).[17–20] Furthermore, we were able to
synthesise the first hydrogen-substituted phosphanylborane
that is only stabilised by the Lewis base NMe3 (B).[21]
Introduction
In the last years, much attention has been given to hydro-
gen activation because of its importance for hydrogen stor-
age applications. Next to metal hydrides as storage media,
main group compounds such as amine–borane[1,2] were
studied, because of their high potential for hydrogen storage
capacity (i.e., H3N·BH3 contains 19.6 wt.-% hydrogen[1]). In
contrast, the well-known phosphane–borane compounds
synthesised in the groups of Nöth and Paine,[3,4] Power[5,6]
and others have not been considered in this specific context
until Stephan et al. discovered the first reversible, metal-free
hydrogen activation with the compound (C6H2Me3)2P-
(C6F4)B(C6F5)2.[7] Furthermore, it has been realised that
simple phosphane–borane mixtures can be used for H2 acti-
vation under mild conditions.[8]
The group 13/15 compounds of the general formula
H3E–EЈH3 (E = element of the group 15, EЈ = element of
[a] Institut für Anorganische Chemie der Universität Regensburg
93049 Regensburg, Germany
Fax: +49-941-9434439
E-mail: manfred.scheer@chemie.uni-regensburg.de
[b] St. Petersburg State University, Department of Chemistry, Uni-
versity pr. 26,
198504 Old Peterhoff, St. Petersburg, Russia
E-mail: alextim@AT11692.spb.edu
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Scheme 1. LA = W(CO)5, Cr(CO)5, B(C6F5)3, Ga(C6F5)3; LB =
NMe3.
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N-Heterocyclic Carbenes in Lewis Acid/Base Stabilised Phosphanylboranes
Whereas the LA/LB-stabilised phosphanylalanes and Cp* protons arise at different chemical shifts with an inte-
-gallanes are accessible by a hydrogen elimination reac- gration ratio of 3:6:6 indicating no fluxional behaviour of
tion,[19,20] this synthetic pathway fails when H3B·NMe3 is the Cp* moiety. The 31P NMR spectra reveal triplets (1a: δ
1
1
used as the starting material [Equation (1)].
= –65.3 ppm, JP,H = 347 Hz; 2: δ = –38.3 ppm, JP,H =
394 Hz). Whereas in the FD-MS spectrum of 1a the molec-
ular ion peak was observed, for 2 only the fragments
[B(C6F5)3]+ and [Cp*PH2]+ are detected.
Figure 1 shows the X-ray structure of 1a in the crystal.
The Ga–P bond length in 1a [2.442(1) Å] is within the nor-
mal range for dative Ga–P single bonds, which may vary
from 2.40 to 2.46 Å.[5,22,23] The B–P bond length in com-
pound 2 [2.040(2) Å] (Figure 2) is in good agreement with
the B–P bond lengths found for (C6F5)3B·PH3 [2.044(8),
2.046(8), 2.048(8) Å], whose unit cell contains three inde-
pendent molecules.[24]
(1)
The LA/LB-stabilised phosphanylboranes are available
salt elimination reaction as shown in Equa-
tion (2).[17,18]
by
a
(2)
Herein we report the synthesis and characterisation of
LA/LB-stabilised phosphanylboranes with 1,3,4,5-tetra-
methylimidazolylidene (NHCMe) as a Lewis base and
Ga(C6F5)3 as a Lewis acid by a hydrogen elimination reac-
tion. Furthermore, we observed different reaction behav-
iour depending on the Lewis acid: by using B(C6F5)3 as
Lewis acid and NHCMe as Lewis base, the salts [(C6F5)3-
BH][RPH2·BH2·NHCMe] are formed [R = H, Cp*(C5Me5),
Ph].
Figure 1. Molecular structure of 1a in the crystal. Selected bond
lengths [Å] and angles [°]: Ga–P 2.442(1), P–C(Cp*) 1.856(3), Ga–
P–C(Cp*) 121.0(1); 2: B–P 2.040(2), P–C(Cp*) 1.871(2), B–P–
C(Cp*) 123.9(1).
Results and Discussion
Synthesis and Characterisation of the Starting Materials
The synthesis of the starting materials is described for
those compounds which have not yet been published in the
literature. The Lewis acid/base adducts (C6F5)3Ga·PH2Cp*
(1) and (C6F5)3B·PH2Cp* (2) (Cp* = C5Me5, pentameth-
ylcyclopentadienyl) were prepared by the reaction of the
Lewis acid {1: (C6F5)3Ga·Et2O [Equation (3)], 2: (C6F5)3B
[Equation (4)]} with PH2Cp* at room temperature in tolu-
ene.
Figure 2. Molecular structure of 2 in the crystal. The hydrogen
atoms of the Cp* ring are omitted for clarity. Selected bond lengths
[Å] and angles [°]: B–P 2.040(2), P–C(Cp*) 1.871(2), B–P–C(Cp*)
123.9(1).
(3)
Initial attempts to synthesise (C6F5)3Ga·PH2Cp* pro-
duced the compound (C6F5)3Ga·OPH2Cp* (1b).[25] We as-
sume that 1b is a decomposition product of 1a, most likely
formed through the unintended presence of air.
(4)
1
The H NMR spectra of the products show a doublet
As a second starting material, 2-borane-1,3,4,5-tetra-
1
1
(1a: δ = 4.08 ppm, JP,H = 348 Hz; 2: δ = 4.71 ppm, JP,H
=
methylimidazoline (BH3·NHCMe) was used. This com-
394 Hz) attributable to the PH2 protons. The signals for the pound was first synthesised and published by Kuhn et al.
Eur. J. Inorg. Chem. 2008, 3482–3492
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FULL PAPER
in 1993, but was so far not characterised by X-ray structural
analysis.[26] We obtained single crystals of BH3·NHCMe
from a hexanes solution at –25 °C.[25]
Synthesis of Lewis Acid/Base Stabilised Phosphanylboranes
(5)
In general, B–P bonds can be formed by hydrogen elimi-
nation when a catalyst and/or elevated temperatures are
used. Often, most methods need the combination of
both.[11–13] For the first time, we have found now that the
synthesis of LA/LB-stabilised phosphanylboranes with
Ga(C6F5)3 as the Lewis acid and NHCMe as Lewis base is
performed by an uncatalysed H2 elimination reaction at
room temperature.
Computational Studies of the Reaction Mechanism
As a reaction mechanism of the formation of ionic com-
pounds 4 one can postulate the dissociation of the
(C6F5)3B–phosphane adduct in the first step [Equation (6)].
A reversible adduct formation between phosphanes and flu-
orinated triarylboron compounds such as (C6F5)3B·PH3
was also described by Bradley et al.[28] As a second step,
the free Lewis acid (C6F5)3B abstracts a hydride from the
BH3 group, which results in the formation of a boronium
cation stabilised by a PH2R moiety (4a: R = H, 4b: R =
Cp*, 4c: R = Ph) [Equation (7)].
When (C6F5)3Ga·PCp*H2 (1a) or (C6F5)3Ga·PPhH2[18] is
treated with BH3·NHCMe in nonpolar solvents at room
temperature, LA/LB-stabilised phosphanylboranes 3a or 3b,
respectively, are formed (Scheme 2). At room temperature,
the formation of 3a does not occur quantitatively, so the
reaction was heated at reflux overnight to improve the
yields.
(6)
(7)
To support the postulated reaction mechanism, density
functional theory (DFT) calculations were applied on the
single steps of the model reaction between (C6F5)3B·PH3
Scheme 2. Reaction of LA–phosphane adducts with BH3·NHCMe
.
and BH3·NHCMe [25,29]
.
The results of the calculated reac-
tion energies are listed in Table 1. Scheme 3 illustrates the
In contrast to Ga compounds 3a and 3b, very different changes in energy between the single steps.[30] When com-
results were obtained upon treatment of the (C6F5)3B– paring the energies of reactions (1) and (2), we notice that
phosphane adducts (C6F5)3B·PH3,[24] (C6F5)3B·PH2Cp* (2) the formation of a LA/LB-stabilised phosphanylborane by
or (C6F5)3B·PH2Ph[13] with BH3·NHCMe at room tempera- a hydrogen elimination reaction is slightly favoured [reac-
ture in CH2Cl2. In this case, no formation of LA/LB-stabi- tion (2)] relative to the formation of the ionic species
lised phosphanylboranes is observed; rather, the salts [(C6F5)3BH][PH3·BH2·NHCMe] [reaction (1)], although the
[(C6F5)3BH][RPH2·BH2·NHCMe] (4a: R = H, 4b: R = Cp*, H2 elimination reaction could not be observed experimen-
4c: R = Ph) are obtained as colourless viscous oils tally. The dissociation of (C6F5)3B and PH3 [reaction (3)]
(Scheme 2). Similar cations can be found in the salt possesses an activation barrier of 20.6 kJmol–1 (Scheme 3,
[PH3·BH2·NMe3]+[(CO)5W·SnCl3]– synthesised by Schwan left). The following hydride abstraction reaction [reac-
in our group and in [(R3P)2BH2]+[B(cat)2]– (R = Me, Et; cat tion (4)] is clearly favoured by 50.2 kJmol–1. This step com-
= 1,2-O2C6H4) synthesised by Marder and Baker et al.[27] pensates the dissociation energy of the adducts. The stabili-
To synthesise LA/LB-stabilised phosphanylboranes with sation of the boronium cation by PH3 [reaction (5)] leads to
(C6F5)3B as Lewis acid and NHCMe as Lewis base, another a further gain in energy by 29.6 kJmol–1. It is not clarified
synthetic pathway was used. The reaction of (C6F5)3B· yet if the hydride abstraction reaction and the coordination
P(Ph)HBH2·NMe3[18] with NHCMe in toluene at room tem- of PH3 proceed in two separate steps or if the reaction fol-
perature leads to a substitution of the Lewis base. NMe3 is lows a concerted mechanism. The formation of 4a from
liberated and the compound (C6F5)3B·P(Ph)HBH2·NHCMe (C6F5)3B·PH3 and BH3·NHCMe results in a total energy
(5) is formed as a colourless crystalline compound [Equa- gain of 64.6 kJmol–1. Reaction (1) is also thermodynami-
tion (5)].
cally allowed by ∆G°298 = –1.4 kJmol–1.
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Eur. J. Inorg. Chem. 2008, 3482–3492

N-Heterocyclic Carbenes in Lewis Acid/Base Stabilised Phosphanylboranes
Table 1. Calculated energies, standard enthalpies and standard Gibbs energies (kJmol–1; gas-phase reaction) at 298 K (B3LYP/6-31G*).
BArF = B(C6F5)3, NHCMe = 1,3,4,5-tetramethylimidazolylidene. Compounds in curly brackets identify a contact ion pair.
Reaction
∆E°0
∆H°298
∆G°298
(1)
(2)
BArF·PH3 + BH3·NHCMe = {BArFH···PH3BH2·NHCMe
}
–64.6
–73.4
–55.2
–80.1
–1.4
–53.4
BArF·PH3 + BH3·NHCMe = BArF·PH2BH2·NHCMe + H2
(3)
(4)
BArF·PH3 = BArF + PH3
20.6
–50.2
11.5
–43.3
–23.4
–39.2
22.1
15.6
BArF + BH3·NHCMe = {BArFH···BH2·NHCMe
{BArFH···BH2·NHCMe} + PH3 =
}
(5)
–35.1
{BArFH···PH3BH2·NHCMe
}
(6)
(7)
(8)
(9)
BArF·PH3 + BH3·NMe3 = {BArFH···PH3BH2·NMe3}
BArF·PH3 + BH3·NMe3 = BArF·PH2BH2·NMe3 + H2
BArF + BH3·NMe3 = {BArFH···BH2·NMe3}
8.8
–26.6
–4.2
–7.6
18.1
–34.8
1.9
60.5
–24.3
54.7
{BArFH···BH2·NMe3} + PH3 = {BArFH···PH3BH2·NMe3}
4.7
45.0
Scheme 3. Change in energies in the systems (C6F5)3B·PH3 + BH3·NHCMe (left) and (C6F5)3B·PH3 + BH3·NMe3 (right). Compounds in
curly brackets identify a contact ion pair.
For the system (C6F5)3B·PH3 and BH3·NMe3, experi-
mentally neither the hydrogen elimination [reaction (7)] re-
action nor the formation of an ionic product [reaction (6)]
is observed. In calculations we found that reaction (6) in
Table 1 with ∆G°298 = 60.5 kJmol–1 is strongly prohibited.
The right part in Scheme 3 shows the changes in energies
for the partial steps of the reaction leading to the salt for-
mation [reactions (6) to (9), Table 1]. What attracts atten-
tion is that the initial energy for the dissociation of
(C6F5)3B and PH3 cannot be compensated by the following
reaction steps, which gives an explanation for the experi-
Scheme 4. Possibilities of delocalisation of the positive charge in
mental fact that ionic products are not formed in these reac-
tions. An explanation of the different reactivities could be
the fact that the positive charge of the boronium cation can
be delocalised with the carbene ligand, which thus stabilises
the system (Scheme 4).
the [PH3·BH2·NHCMe +
] cation.
Computations predict that the H2 elimination reac-
tions (10) and (11) (Table 2) between Ga(C6F5)3–phosphane
According to Mulliken population analysis, the partial adducts and BH3·NHCMe are exothermic by 58 and
charge on the NMe3 moiety in [PH3·BH2·NMe3]+ is +0.50, 68 kJmol–1, respectively, whereas the ion-pair formation re-
whereas on the NHCMe unit in [PH3·BH2·NHCMe +
] it is actions (12) and (13) (Table 2) are only slightly exothermic
+0.76. This observation supports larger delocalisation of by 8 and 12 kJmol–1, respectively. Furthermore the stan-
the positive charge on the carbene ligand like that proposed dard Gibbs energies for reactions (10) and (11) are negative
in Scheme 4.[28,30]
at 298 K so these reactions are allowed thermodynamically.
Eur. J. Inorg. Chem. 2008, 3482–3492
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FULL PAPER
Table 2. Calculated energies, standard enthalpies and standard Gibbs energies (kJmol–1; gas-phase reaction) at 298 K (B3LYP/6-31G*).
GaArF = Ga(C6F5)3, NHCMe = 1,3,4,5-tetramethylimidazolylidene. Compounds in curly brackets identify a contact ion pair.
Reaction
∆E°0
∆H°298
∆G°298
(10)
(11)
GaArF·P(Ph)H2 + BH3·NHCMe = GaArF·P(Ph)HBH2·NHCMe + H2
GaArF·P(Cp*)H2 + BH3·NHCMe = GaArF·P(Cp*)HBH2·NHCMe + H2
–62.2
–53.5
–68.4
–58.7
–41.2
–32.1
(12)
(13)
GaArF·P(Ph)H2 + BH3·NHCMe = {GaArFH···P(Ph)H2BH2·NHCMe
GaArF·P(Cp*)H2 + BH3·NHCMe = {GaArFH···P(Cp*)H2BH2·NHCMe
}
–15.7
–12.3
–11.7
–7.8
55.1
66.8
}
In contrast, Gibbs energy values for reactions (12) and (13) three signals at δ = 1.36, 1.81, 1.82 ppm; 4c: R = Ph, two
are positive; thus, these reactions are thermodynamically multiplets at δ = 7.51–7.57, 7.59–7.69 ppm) are detected.
forbidden at 298 K.[32]
Compound 4a shows a doublet of triplets at δ = 4.60 ppm
3
(1JP,H = 401 Hz, JH,H = 8 Hz) for the PH3 protons. The
signal for the PH2 unit in 4b arises at δ = 4.69 ppm as a
Spectroscopic Characterisation of Lewis Acid/Base
Stabilised Phosphanylboranes
3
doublet of triplets (1JP,H = 374 Hz, JH,H = 7 Hz), and for
4c the PH2 group is detected as a doublet of triplets at δ =
3
1
5.79 ppm (1JP,H = 398 Hz, JH,H = 7.5 Hz). The known H
In the 1H NMR spectra of 3a,b, two singlets [3a: δ = 1.15
(CCH3), 2.63 ppm (NCH3); 3b: δ = 1.13 (CCH3), 2.64 ppm
(NCH3)] for the methyl groups of the N-heterocyclic carb-
enes are detected. Furthermore, three signals of three dif-
ferent methyl groups of the Cp* substituent are observed,
which is characteristic for a η1 bonding mode of each Cp*
ring. The PH protons can be detected as corresponding
NMR signal of the [(C6F5)3BH]– anion could only be de-
tected in the H NMR spectrum of 4b.[27]
1
The 31P NMR spectrum of 4a shows a broad quartet at
δ = –119.2 ppm (1JP,H = 401 Hz). This is in close agreement
with the 31P NMR spectroscopic data found for
[PH3·BH2·NMe3][(CO)5W·SnCl3].[27] This compound shows
a quartet at δ = –117.8 ppm with a similar hydrogen–phos-
1
doublets (3a: δ = 4.42 ppm, JP,H = 313 Hz; 3b: δ =
1
4.76 ppm, 1JP,H = 325 Hz). In addition to the 1JP,H coupling
phorus coupling constant of JP,H = 418 Hz. In case of 4b
and 4c, respectively, a broad triplet is detected in the 31P
3
for 3b, a small JH,H coupling constant (3JH,H = 7 Hz) is
1
detected. In the 31P NMR spectra, broad doublets are ob-
NMR spectra (4b: δ = –40.8 ppm, JP,H = 374 Hz; 4c: δ =
–57.9 ppm, JP,H = 398 Hz). The signals are broadened be-
1
1
served (3a: δ = –72.2 ppm, JP,H = 314 Hz; 3b: δ =
1
cause of the phosphorus–boron coupling. Comparison of
the 31P NMR spectroscopic data of 4c (δ = –57.9 ppm, 1JP,H
= 398 Hz) with that of (C6F5)3B·P(Ph)HBH2·NHCMe (5; δ
–71.8 ppm, JP,H = 326 Hz).
Both compounds 3a and 3b show similar chemical shifts
in their 11B NMR spectra (3a: δ = –35.3 ppm, 3b: δ =
–32.8 ppm), and the signal of the H3B·NHCMe starting ma-
terial occurs in the same region (δ = –35.0 ppm).[26] In both
cases, no B–H coupling can be observed due to the broad-
ness of the signals. No molecular ion peak is detected in
the MS (EI) spectra of either 3a or 3b and only the
1
= –43.8 ppm, JP,H = 351 Hz) shows that the phosphorus
signal of the cation is shifted upfield and shows a larger
hydrogen–phosphorus coupling constant.
The BH2 units of the cations are always detected as very
broad signals in the 11B NMR spectra. Compound 4a
1
[BH2·NHCMe +
] fragment is found. In the IR spectrum of
both compounds the corresponding P–H and B–H stretch-
ing modes are detected.
shows a doublet of triplets (δ = –37.6 ppm, JB,H = 92 Hz,
1JB,P = 37 Hz), which is the best-resolved signal for the BH2
unit in the row 4a–c. The 11B NMR signal of cation 4b is
detected as a broad doublet at δ = –37.8 ppm, where only
The MS (ESI) spectra of 4a–c show the anion peak
[(C6F5)3BH]– with 100% relative abundance as a single sig-
nal in the anion subspectrum and the corresponding molec-
ular ion peak of the cations of 4b and 4c in the cation
subspectrum. The cation subspectrum of 4a shows a
[PH2(BH2·NHCMe)2]+ fragment as the most intense signal,
1
the JB,P coupling constant (48 Hz) can be observed. The
11B NMR spectra of 4c shows a very broad signal for the
BH2 group at δ = –35.6 ppm. In comparison to the chemical
shift of the BH3·NHCMe starting material (δ = –34.9 ppm),
compound 3a (δ = –35.3 ppm) or 3b (δ = –32.8 ppm), the
shift of the signals for the BH2 units in 4a–c support the
coordination of the NHCMe Lewis base. The 11B NMR
spectroscopic data of [(C6F5)3BH]– were already described
by Shore et al.[33] and the 19F NMR spectroscopic data were
discussed by Santini et al.[34]
but the [PH3BH2·NHCMe +
] cation could not be detected.
The IR spectra of compounds 4a–c reveal absorptions in
the range from 2030 to 2349 cm–1 for the P–H stretching
modes and the B–H stretching modes appear between 2445
and 2380 cm–1. The MS (ESI) spectra of 5 show the corre-
sponding molecular ion peak. The IR spectrum of 5 shows
The 31P NMR spectrum of 5 shows a doublet at δ =
B–H stretching modes in a characteristic region (2460, –43.8 ppm (1JP,H = 351 Hz). Whereas the 11B NMR spec-
2419 cm–1) and a signal for the P–H vibration at 2316 cm–1. trum of the starting material shows a broad signal at δ =
The H NMR spectra of 4a–c show the signals for the –10.8 ppm arising for the BH2 unit,[18] the BH2 group in 5
1
NHCMe moiety at very similar chemical shifts (4a: δ = 2.15, can be detected as a broad singlet at δ = –33.2 ppm. The
3.63 ppm; 4b: δ = 2.14, 3.50 ppm; 4c: δ = 2.16, 3.60 ppm). 19F NMR signals detected for 5 (δ = –128.1, –158.8,
In addition, the signals for the R substituent (4b: R = Cp*, –164.6 ppm) are clearly shifted downfield relative to those
3486
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3482–3492

N-Heterocyclic Carbenes in Lewis Acid/Base Stabilised Phosphanylboranes
found for compounds 4a–c. The influence of the different
Lewis bases NMe3 and NHCMe is responsible for the dif-
ferent chemical shifts.
X-ray Structural Characterisation of LA/LB-Stabilised
Phosphanylboranes 3a, 3b and 5
The structures of 3a,b and 5 were confirmed by X-ray
diffraction studies (Table 4). Selected bond lengths and
angles for compounds 3a,b are listed in Table 3 and those
for compound 5 in Figure 4. Compound 3a crystallises in
the monoclinic space group P21/c with two independent
molecules (A and B) in the unit cell. Compound 3b crystal-
Figure 4. Molecular structure of 5 in the crystal. The hydrogen
lises in the monoclinic space group P21/n and 5 crystallises
in the monoclinic space group C2/c. Compounds 3a,b (Fig-
ure 3) and 5 (Figure 4) show the same HRP–BH2 structural
motif (3a: R = Cp*, 3b and 5: R = Ph) in the solid state.
The phosphorus atom of the HRP–BH2 fragment coordi-
nates the Lewis acid [3a, 3b: Ga(C6F5)3; 5: B(C6F5)3] and
the NHCMe Lewis base coordinates to the boron atom of
this fragment so that the boron and the phosphorus atoms
are surrounded by four substituents. The substituents
around the P–B bond adopt a slightly staggered conforma-
tion, whereas the Lewis acid and the Lewis base in 3b adopt
an antiperiplanar geometry [Ga–P–B–CNHC torsion angle:
176.26(1)°]. In 3a and 5, a synclinal arrangement of the
Lewis acid and the Lewis base for 3b [67.9(3) and 82.0(3)°]
and 5 [80.2(4)°] is found.[35]
atoms of the phenyl group are omitted for clarity. Selected bond
lengths [Å] and angles [°]: B(1)–P 2.035(2), P–B(2) 1.979(2), B(2)–
CNHC 1.607(3), CNHC–N(1) 1.353(2), CNHC–N(2) 1.353(2), B(1)–P–
B(2) 119.54(8), P–B(2)–CNHC 110.1(1), N(1)–CNHC–N(2) 105.2(2),
B(1)–P–B(2)–CNHC 80.2(4).
The Ga–P bond lengths found in 3a [A: 2.392(1) Å, B:
2.407(1) Å] and 3b [2.405(1) Å] are slightly shorter than the
corresponding bond found in starting material
1
[2.442(1) Å] and (C6F5)3Ga·P(Ph)H2 [2.477(1) Å], respec-
tively.[18] A good agreement is found when comparing the
Ga–P bond lengths with the respective bond length in the
LA/LB-stabilised phosphanylboranes (C6F5)3Ga·PH2BH2·
NMe3 [2.393(1) Å] and (C6F5)3Ga·P(Ph)HBH2·NMe3
[2.424(1) Å].[18] Compound 5 reveals a dative B(1)–P bond
length of 2.035(2) Å, which is close to the B–P bond length
found in (C6F5)3B·PPhH2 (2.039 Å)[13] and (C6F5)3B·PH3
[2.046(8) Å].[24] The central P–B bond lengths of 3a
[1.982(4) and 1.978(4) Å], 3b [1.982(6) Å] and 5 [P–B(2):
1.979(2) Å] agree well with usual P–B single bond lengths,
which range from 1.90 to 2.0 Å.[3–5] Especially, the compari-
son with other LA/LB-stabilised phosphanylboranes show
a good agreement in the P–B bond length [(C6F5)3B·
PH2BH2·NMe3: 1.989(4) Å, (C6F5)3B·P(Ph)HBH2·NMe3:
1.974(3) Å or (C6F5)3Ga·PH2BH2·NMe3: 1.992(2) Å]. Al-
though the B–CNHC bond of 3b [1.588(7) Å] reveals the
same length as the B–CNHC bond in starting material 1a
[1.588(4) Å], the corresponding bonds in 3a [1.610(5) and
1.596(5) Å] and 5 [1.607(3) Å] are slightly elongated.
Table 3. Selected bond lengths [Å] and angles [°] of 3a (molecules
A and B) and 3b.
3a: A
3a: B
3b
Ga–P
P–B
B–CNHC
CNHC–N(1)
CNHC–N(2)
Ga–P–B
P–B–CNHC
N(1)–CNHC–N(2)
Ga–P–B–CNHC
2.392(1)
1.982(4)
1.610(5)
1.359(4)
1.349(4)
118.37(13)
111.1(2)
105.2(3)
67.9(3)
2.407(1)
1.978(4)
1.596(5)
1.360(4)
1.349(5)
118.65(13)
112.1(2)
105.6(3)
82.0(3)
2.405(1)
1.982(6)
1.588(7)
1.344(5)
1.344(5)
122.3(2)
104.0(4)
104.3(5)
176.26(1)
Figure 3. Molecular structure of 3a (left, hydrogen atoms of the Cp* ring are omitted for clarity) and 3b (right) in the crystal.
Eur. J. Inorg. Chem. 2008, 3482–3492
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3487

A. Adolf, U. Vogel, M. Zabel, A. Y. Timoshkin, M. Scheer
FULL PAPER
(C6D6, 25 °C): δ = –121.8 (m, 6 F, o-F), –152.5 (t, 3JF,F = 19.1 Hz,
Conclusions
3 F, p-F), –160.9 (m, 6 F, m-F) ppm. 13C{1H} NMR (C6D6, 25 °C):
2
The results reported herein have shown that depending δ = 9.5 (s, CCH3, Cp*), 10.6 (s, CCH3, Cp*), 20.9 (d, JC,P
=
1
5.9 Hz, PCCH3, Cp*), 50.9 (d, JC,P = 14.5 Hz, PC, Cp*), 113.6 [t,
2JC,F = 45.5 Hz, GaC, Ga(C6F5)3], 134.9 (s, PCC, Cp*), 137.3 [dm,
1JC,F = 254.3 Hz, m-C, Ga(C6F5)3], 140.3 (s, PCCC, Cp*), 141.8
on the chosen Lewis acid (C6F5)3B or (C6F5)3Ga the reac-
tion between (C6F5)3E·PH2R and BH3·NHCMe (E = Ga or
B, R = H, Cp*, Ph) leads to different products. The reaction
of (C6F5)3Ga·PH2R [R = Cp* (1a), Ph] with BH3·NHCMe
proceeds at room temperature by a hydrogen elimination
reaction to form the LA/LB-stabilised phosphanylboranes
3a and 3b. Thus, for the first time, a P–B bond can be
formed by a hydrogen elimination reaction under the ap-
plied mild conditions. By using (C6F5)3B·PH2R [R = H,
1
1
[dm, JC,F = 252.4 Hz, p-C, Ga(C6F5)3], 149.0 [dm, JC,F
=
233.8 Hz, o-C, Ga(C6F5)3] ppm. MS (FD, toluene): m/z (%) = 739
(15) [M]+, 570 (33), 335 (34) [(C6F5)2H]+, 168 (100) [M – Ga
(C F ) ]+. IR (KBr): ν = 2971 (vs, CH), 2918 (vs, CH), 2862 (s,
˜
6
5 3
CH), 2747 (m), 2635 (m), 2577 (m), 2541 (m), 2400 (w, PH), 2372
(s, PH), 2329 (m, br.), 2223 (w), 2091 (w), 2049 (w), 1918 (w, br.),
1860 (w, br.), 1640 (vs), 1513(vs), 1469 (vs, br.), 1377 (m), 1367 (m),
Cp* (2), Ph], the reaction with BH3·NHCMe leads to vis- 1268 (vs), 1235 (m), 1132 (m), 1115 (w, sh.), 1080 (vs), 1055 (s, sh.),
1010 (m), 961 (vs), 855 (m), 837 (s), 795 (s), 744 (m), 721 (s), 616
(s), 610 (m, sh.), 591 (s), 518 (w), 491 (m) cm–1. C28H17F15GaP
(739.1): calcd. C 45.50, H 2.32; found C 45.41, H 2.30. Data for
cous oils of ionic products of the formula [(C6F5)3BH]-
[RPH2·BH2·NHCMe] (4a: R = H, 4b: R = Cp*, 4c: R =
Ph). DFT calculations give some insight into the preferred
type of the corresponding experimentally observed reac-
tion. However, the synthesis of the LA/LB-stabilised phos-
phanylborane (5) with (C6F5)3B as the LA and NHCMe as
the LB was achieved by a Lewis base substitution reaction.
In the solid state, the substituents around the P–B core of
the phosphanylboranes 3a,b and 5 show a staggered confor-
1
3
1b: H NMR (C6D6, 25 °C): δ = 0.89 (d, JP,H = 21 Hz, PCCH3, 3
1
H, Cp*), 2.35 (s, 12 H, Cp*), 5.57 (d, JP,H = 512 Hz, 2 H, PH2)
1
ppm. 31P NMR (C6D6, 25 °C): δ = 34.5 (t, JP,H = 512 Hz, PH2)
ppm. 31P{1H} NMR (C6D6, 25 °C): δ = 34.5 (s, PH2) ppm. 19F
3
NMR (C6D6, 25 °C): δ = –124.9 (m, 6 F, o-F), –153.0 (t, JF,F
=
20 Hz, 3F p-F), –161.2 (m, 6 F, m-F) ppm. 13C{1H} NMR (C6D6,
1
25 °C): δ = 9.0 (s, CCH3, Cp*), 9.7 (s, CCH3, Cp*), 55.1 (d, JP,C
mation. The LA and the LB in 3b adopt an antiperiplanar = 54 Hz, PC, Cp*), 113.7 [t, 2JC,F = 46 Hz, GaC, Ga(C6F5)3], 130.7
1
(s, PCC, Cp*), 136.1 [dm, JC,F = 256 Hz, m-C, Ga(C6F5)3], 140.5
[dm, 1JC,F = 254 Hz, p-C, Ga(C6F5)3], 142.7 (s, PCCC, Cp*), 147.9
[dm, 1JC,F = 234 Hz, o-C, Ga(C6F5)3] ppm. MS (FD, toluene): m/z
geometry, whereas the LA and the LB in 3a and 5 show a
synclinal arrangement.
(%) = 754 (100) [M]+, 1508.5 (5) [2M]+. IR (KBr): ν = 2975 (s,
˜
CH), 2924 (s, CH), 2872 (s, CH), 2750 (w), 2635 (w), 2575 (w),
2539 (w), 2471 (w), 2420 (m, sh., PH), 2399 (s, PH), 2324 (m), 2223
(w), 2082 (w), 2041 (w), 1917 (w), 1860 (w), 1712 (m), 1640 (vs),
1578 (m), 1510 (vs), 1461 (vs, br.), 1379 (s), 1365 (vs), 1271 (vs),
1221 (w), 1149 (vs, POGa), 1068 (vs, br.), 1011 (vs), 962 (vs), 888
(w), 799 (s), 743 (m), 721 (m), 696 (m), 611 (s), 569 (m), 538 (w),
522 (w), 491 (m), 435 (m) cm–1. C28H17F15GaOP (755): calcd. C
44.54, H 2.27; found C 44.35, H 1.94.
Experimental Section
General Techniques: All manipulations were performed under an
atmosphere of dry nitrogen by using standard glove box and
Schlenk techniques. Solvents were degassed and purified by stan-
dard procedures. The compounds (C6F5)3B,[36] (C6F5)3Ga·Et2O,[36]
Cp*PH2 (Cp* = C10H15),[37] (C6F5)3B·PH3,[24] (C6F5)3B·PH2Ph,[13]
(C6F5)3Ga·PH2Ph,[18]
(NHCMe),[38]
1,3,4,5-tetramethylimodazol-2-ylidene
2-boran-1,3,4,5-tetramethylimodazoline
H3B·
were prepared ac-
(C6F5)3B·PH2Cp* (2): A mixture of B(C6F5)3 (2.9 g, 5.66 mmol)
and Cp*PH2 (0.954 g, 5.67 mmol) in toluene (40 mL) was stirred
for 18 h at room temperature. After removal of the solvent in
vacuo, the residue was washed with n-hexane (3ϫ10 mL). Single
crystals of 2 were obtained by recrystallisation from n-hexane at
–25 °C as colourless plates. Yield: 3.52 g (91.4%). 1H NMR (C6D6,
25 °C): δ = 0.51 (d, 3JP,H = 17 Hz, 3 H, Cp*), 1.33 (d, 5JP,H = 3 Hz,
[18]
NHCMe[26] and (C6F5)3B·PHPh–BH2·NMe3
cording to the literature procedures or former published methods
of our research group. The NMR spectra were recorded with either
an Avance 300 (1H: 300.132 MHz, 31P: 121.468 MHz, 19F:
282.404 MHz) or Avance 400 spectrometer [1H: 400.13 MHz, 31P:
161.976 MHz, 11B: 128.378 MHz, 13C(1H): 100.623 MHz] with δ
[ppm] referenced to external SiMe4 (1H, 13C), H3PO4 (31P),
BF3·Et2O (11B) or CFCl3 (19F). IR spectra were measured with a
DIGILAB (FTS 800) FTIR spectrometer. All mass spectra were
recorded with a ThermoQuest Finnigan TSQ 7000 (ESI MS) or a
Finnigan MAT 95 (FD MS and EI MS). The C, H, N analyses
were measured with an Elementar Vario EL III apparatus.
1
6 H, Cp*), 1.37 (s, 6 H, Cp*), 4.71 (d, JP,H = 394 Hz, 2 H, PH2)
1
ppm. 31P NMR (C6D6, 25 °C): δ = –38.3 (t, JP,H = 394 Hz, PH2)
ppm. 31P{1H} NMR (C6D6, 25 °C): δ = –38.3 (s, PH2) ppm. 19F
NMR (C6D6, 25 °C): δ = –129.5 (m, 6 F, o-F), –155.6 (br. s, 3 F,
3
p-F), –163.1 (m, JF,F = 19 Hz, 6 F, m-F) ppm. 11B NMR (C6D6,
25 °C): δ = –15.5 [br. s, B(C6F5)3] ppm. 13C{1H} NMR (C6D6,
(C6F5)3Ga·PH2Cp* (1a): A mixture of (C6F5)3Ga·Et2O (3.55 g, 25 °C): δ = 9.7 (s, CCH3, Cp*), 10.8 (s, CCH3, Cp*), 21.6 (s,
1
5.5 mmol) and Cp*PH2 (0.926 g, 5.5 mmol) in toluene (50 mL) was
stirred for 18 h at room temperature. After removal of the solvent
in vacuo, the residue was dried at 10–3 bar until a fine, white powder
of 1a was obtained. Recrystallisation of the residue from n-hexane
at –25 °C yielded colourless crystals of 1a. Yield: 3.6 g (88.7%). On
one occasion we obtained colourless crystals of 1b, presumably by
decomposition of 1a. The crystals grew in a Schlenk tube that was
stored for several weeks at 4 °C. Data for 1a: 1H NMR (C6D6,
PCCH3, Cp*), 51.6 (d, JC,P = 23.5 Hz, PC), 155.5 [br. m, BC,
1
B(C6F5)3], 135.4 (s, PCC, Cp*), 137.5 [dm, JC,F = 253 Hz, m-C,
B(C6F5)3], 139.8 (d, JC,P = 7 Hz, PCCC, Cp*), 140.6 [dm, JC,F
3
1
=
1
250 Hz, p-C, B(C6F5)3], 148.5 [dm, JC,F = 242 Hz, o-C, B(C6F5)3]
ppm. MS (FD, toluene): m/z (%) = 512 (100) [M – PH2Cp*]+, 335
(5) [(C F ) H]+, 168 (50) [M – B(C F ) ]+. IR (KBr): ν = 2965 (s,
˜
6
5 2
6 5 3
CH), 2942 (s, CH), 2922 (s, CH), 2863 (s, CH), 2745 (m, br.), 2567,
(w, br.), 2454 (m), 2409 (m, PH), 2349 (w, PH), 2227 (w), 2096 (w,
br.), 2045 (w, br.), 1869 (w, br.), 1647 (vs), 1596 (m), 1522 (vs), 1471
(vs, br.), 1453 (s, sh.), 1386 (s), 1377 (s), 1285 (s), 1234 (m), 1093
(vs, br.), 1022 (w, sh.), 980 (vs), 931 (w), 899 (m), 859 (m), 800 (m,
sh.), 786 (s), 773 (s), 761 (s), 741 (s), 683 (s), 670 (s), 657 (m), 632
3
25 °C): δ = 0.6 (d, JP,H = 15 Hz, 3 H, Cp*), 1.25 (s, 6 H, Cp*),
1
1.28 (s, 6 H, Cp*), 4.08 (d, JP,H = 348 Hz, 2 H, PH2) ppm. 31P
1
NMR (C6D6, 25 °C): δ = –65.3 (t, JP,H = 348 Hz, PH2) ppm.
31P{1H} NMR (C6D6, 25 °C): δ = –65.3 (s, PH) ppm. 19F NMR
3488
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3482–3492

N-Heterocyclic Carbenes in Lewis Acid/Base Stabilised Phosphanylboranes
(m), 611 (w), 593 (m), 570 (m), 512 (w) cm–1. C28H17BF15P (680.2): 443 (m), 694 (m), 608 (m), 504 (vs), 491 (vs) cm–1.
calcd. C 49.44, H 2.52; found C 49.29, H 2.56.
C31H20BF15GaN2P (817): calcd. C 45.57, H 2.47, N 3.43; found C
44.98, H 2.18, N 3.49.
(C6F5)3Ga·P(Cp*)HBH2·NHCMe (3a): A mixture of 1 (250 mg,
0.34 mmol) and H3B·NHCMe (47 mg, 0.34 mmol) in toluene
(30 mL) was heated at reflux for 18 h. The slightly yellow solution
was cooled to room temperature, concentrated to 1–2 mL in vacuo
and layered with n-hexane (2–3 mL). From this mixture, colourless
plates of 3a were obtained, which were separated and washed with
n-hexane (3ϫ5 mL). Yield: 213 mg (72%). 1H NMR (C6D6,
[(C6F5)3BH]–[PH3·BH2·NHCMe +
]
(4a): H3B·NHCMe (121 mg,
0.88 mmol) was added to a solution of (C6F5)3B·PH3 (480 mg,
0.88 mmol) in CH2Cl2 (10 mL). After stirring the solution for 5 h
at room temperature the solvent was removed in vacuo and 4a was
obtained as a colourless, viscous oil. Yield: 427 mg (71%). 1H
NMR (CD2Cl2, 25 °C): δ = 2.15 (s, CCH3, 6 H, NHCMe), 3.63 (s,
25 °C): δ = 1.15 (s, 6 H, NHCMe, CCH3), 1.37 (d, JP,H = 16 Hz,
3
1
3
NCH3, 6 H, NHCMe), 4.6 (dt, JP,H = 401 Hz, JH,H = 8 Hz, PH3,
PCCH3, 3.5 H, Cp*), 1.47 (s, CCH3, 3 H, Cp*), 1.60 (s, CCH3, 6
H, Cp*), 1.90 (s, CCH3, 3 H, Cp*), 2.63 (s, NCH3, 6 H, NHCMe),
4.42 (dd, 1JP,H = 313 Hz, 3JH,H = 16 Hz, 1 H, PH) ppm. 31P NMR
3 H) ppm. 31P NMR (CD2Cl2, 25 °C): δ = –119.2 (q, JP,H
=
1
401 Hz, PH3) ppm. 31P{1H} NMR (CD2Cl2, 25 °C): δ = –119.2 (s,
PH3) ppm. 11B NMR (CD2Cl2, 25 °C): δ = –25.6 {d, 1JB,H = 93 Hz,
1
(C6D6, 25 °C): δ = –72.2 (d, JP,H = 314 Hz, PH) ppm. 31P{1H}
BH, [(C6F5)3BH]–}, –37.6 (br. dt, JB,H = 92 Hz, JB,P = 37 Hz,
1
1
NMR (C6D6, 25 °C): δ = –72.2 (s, PH) ppm. 11B NMR (C6D6,
25 °C): δ = –35.3 (br. s, BH2) ppm. 11B{1H} NMR (C6D6, 25 °C):
δ = –35.3 (br. s, BH2) ppm. 19F NMR (C6D6, 25 °C): δ = –121.0 [m,
o-F, 6 F, Ga(C6F5)3], –155.5 [t, 3JF,F = 20 Hz, p-F, 3 F, Ga(C6F5)3],
–162.0 [m, m-F, 6 F, Ga(C6F5)3] ppm. 13C{1H} NMR (C6D6,
BH2) ppm. 11B{1H} NMR (CD2Cl2, 25 °C): δ = –25.6 {s, BH,
[(C6F5)3BH]–}, –37.7 (br. d, JB,P = 45 Hz, BH2) ppm. 19F NMR
1
(CD2Cl2, 25 °C): δ = –133.9 {m, o-F, 6 F, [(C6F5)3BH]–}, –164.3 {t,
3JF,F = 20 Hz, p-F, 3 F, [(C6F5)3BH]–}, –167.3 {m, m-F, 6 F, [(C6F5)3-
BH]–} ppm. 13C{1H} NMR (CD2Cl2, 25 °C): δ = 8.7 (s, CCH3,
NHCMe), 33.3 (s, NCH3, NHCMe), 125.5 {br. m, BC, [(C6F5)3-
25 °C): δ = 7.5 (s, CCH3, NHCMe), 10.9 (d, JC,P = 24 Hz,
3
4
PCCCH3, Cp*), 10.4 (d, JC,P = 14 Hz, PCCCCH3), 20.4 (s,
1
BH]–}, 127.8 (s, C=C, NHCMe), 136.8 {dm, JC,F = 243 Hz, m-C,
PCCH3, Cp*), 31.6 (s, NCH3, NHCMe), 52.7 (d, 1JC,P = 14 Hz, PC,
1
[(C6F5)3BH]–}, 138.2 {dm, JC,F = 244 Hz, p-C, [(C6F5)3BH]–},
2
Cp*), 117.9 [t, JC,F = 50 Hz, GaC, Ga(C6F5)3], 124.7 (s, C=C,
1
148.5 {dm, JC,F = 241 Hz, o-C, [(C6F5)3BH]–} ppm. MS (ESI–,
2
1
NHCMe), 137.05 (d, JC,P = 7 Hz, PCC, Cp*), 137.1 [dm, JC,F
=
CHCN): m/z (%) = 513 (100) [(C6F5)3BH]–. MS (ESI+, CHCN):
1
259 Hz, m-C, Ga(C6F5)3], 138.4 (s, PCCC, Cp*), 140.9 [dm, JC,F
m/z (%)
=
307 (100) [PH2(BH2·NHCMe)2]+, 261 (4) [BH2·
1
= 249 Hz, p-C, Ga(C6F5)3], 149.2 [dm, JC,F = 234 Hz, o-C,
(NHCMe)2]+, 139 (5) [BH3·NHCMe + H]+, 125 (67) [NHCMe
+
Ga(C6F5)3], 159.3 (br. m, BC, NHCMe) ppm. MS (EI, 70 eV, tolu-
H]+. IR (THF): ν = 2612 (w, br.), 2576 (w, br.), 2436 (m, vbr., BH),
˜
ene): m/z (%) = 570 (6) [(C6F5)3Ga]+, 403 (13) [(C6F5)2Ga]+, 304
2398 (m, vbr., BH), 2349 (w, PH), 2285 (w, PH), 2029 (w), 1640
(s), 1548 (w), 1508 (vs), 1465 (vs), 1376 (m), 1273 (s), 1224 (m),
1103 (s, br.), 1016 (m, br.), 970 (vs), 807 (m), 765 (m), 735 (m), 661
(w), 646 (w), 601 (w), 567 (m) cm–1.
(14) [(C6F5)BH2·NHCMe]+, 137 (100) [BH2·NHCMe]+. IR (KBr): ν
˜
= 2959 (m, CH), 2924 (s, br., CH), 2861 (m, br., CH), 2426 (m,
BH), 2399 (m, BH), 2349 (w, PH), 1639 (s), 1609 (w), 1509 (vs),
1378 (m), 1268 (s), 1232 (m), 1159 (w), 1128 (m), 1076 (s, br.), 1024
(m), 960 (vs), 898 (m, br.), 856 (w), 790 (s), 721 (m), 665 (w), 610
(m), 489 (m) cm–1.
(C6F5)3Ga·P(Ph)HBH2·NHCMe (3b): H3B·NHCMe (61 mg, CH2Cl2 (5 mL). After stirring the solution for 4 h at room tempera-
0.44 mmol) was added to a solution of (C6F5)3Ga·PPhH2 (300 mg, ture the solvent was removed in vacuo and 4b was obtained as a
0.44 mmol) in C6D6 (5 mL) and stirred for 18 h at room tempera-
ture. The formation of H2 was observed, and the colour of the
solution turned to light yellow. After concentration of the the solu-
tion to a volume of 1–2 mL, it was layered with n-hexane (2–3 mL).
Colourless, cubic crystals were formed that were separated and
[(C6F5)3BH]–[PH2Cp*·BH2·NHCMe + (4b): H3B·NHCMe (61 mg,
]
0.44 mmol) was added to a solution of 2 (300 mg, 0.44 mmol) in
colourless, viscous oil. Yield: 284 mg (79%). 1H NMR (CD2Cl2,
3
25 °C): δ = 1.36 (d, JP,H = 17 Hz, PCCH3, 3 H, Cp*), 1.81 (d,
5JP,H = 4 Hz, CCH3, 6 H, Cp*), 1.82 (s, CCH3, 6 H, Cp*), 2.14 (s,
CCH3, 6 H, NHCMe), 3.50 (s, NCH3, 6 H, NHCMe), 3.58 {br. q,
1
3
1JH,B = 91 Hz, 1 H, [(C6F5)3BH]–}, 4.69 (dt, JP,H = 374 Hz, JH,H
= 7 Hz, 2 H, PH2) ppm. 31P NMR (CD2Cl2, 25 °C): δ = –40.8 (t,
1JP,H = 374 Hz, PH2) ppm. 31P{1H} NMR (CD2Cl2, 25 °C): δ =
1
washed with n-hexane (3ϫ3 mL). Yield: 194 mg (54%). H NMR
(C6D6, 25 °C): δ = 1.13 (s, CCH3, 6 H, NHCMe), 2.64 (s, NCH3, 6
1
3
H, NHCMe), 4.76 (dt, JP,H = 325 Hz, JH,H = 7 Hz, 1 H, PH), 6.9
–40.8 (s, PH2) ppm. 11B NMR (CD2Cl2, 25 °C): δ = –25.6 {d, 1JB,H
(m, 3 H, Ph), 7.4 (m, 2 H, Ph) ppm. 31P NMR (C6D6, 25 °C): δ = = 90 Hz, BH, [(C6F5)3BH]–}, –37.8 (br. td, JB,P = 48 Hz, BH2)
1
–71.8 (d, JP,H = 326 Hz, PH) ppm. 31P{1H} NMR (C6D6, 25 °C): ppm. 11B{1H} NMR (CD2Cl2, 25 °C): δ = –25.6 {s, [(C6F5)3BH]–},
1
δ = –71.8 (s, PH) ppm. 11B NMR (C6D6, 25 °C): δ = –32.8 (br. s,
BH2) ppm. 11B{1H} NMR (C6D6, 25 °C): δ = –32.8 (br. s, BH2)
–37.8 (br. d, JB,P = 41.5 Hz, BH2) ppm. 19F NMR (CD2Cl2,
1
3
25 °C): δ = –133.8 {m, o-F, 6 F, [(C6F5)3BH]–}, –164.4 {t, JF,F
=
ppm. 19F NMR (C6D6, 25 °C): δ = –121.8 [m, 6 F, o-F, Ga-
20 Hz, p-F, 3 F, [(C6F5)3BH]–}, –167.4 {m, m-F, 6 F, [(C6F5)3-
(C6F5)3], –155.0 [t, JF,F = 20 Hz, 3 F, p-F, Ga(C6F5)3], –162.1 [m, BH]–} ppm. 13C{1H} NMR (CD2Cl2, 25 °C): δ = 8.8 (s, CCH3,
3
6 F, m-F, Ga(C6F5)3] ppm. 13C{1H} NMR (C6D6, 25 °C): δ = 7.5
NHCMe), 10.1 (s, CCH3, Cp*), 11.4 (s, CCH3, Cp*), 19.0 (d, JC,P
2
(s, CCH3, NHCMe), 31.9 (s, NCH3, NHCMe), 116.3 [m, GaC, = 5 Hz, PCCH3, Cp*), 33.3 (s, NCH3, NHCMe), 50.6 (d, JC,P
=
1
Ga(C6F5)3], 125.0 (s, C=C, NHCMe), 128.7 (d, JC,P = 9 Hz, m-C,
25 Hz, PC, Cp*), 125.0 {br. m, BC, [(C6F5)3BH]–}, 127.1 (s, C=C,
2
4
3
1
Ph), 129.7 (d, JC,P = 3 Hz, p-C, Ph), 132.8 (d, JC,P = 8 Hz, o-C,
Ph), 137.1 [dm, JC,F = 257 Hz, m-C, Ga(C6F5)3], 141.1 [dm, JC,F
= 249 Hz, p-C, Ga(C6F5)3], 149.2 [dm, JC,F = 236 Hz, o-C,
NHCMe), 134.4 (s, PCC, Cp*), 136.8 {dm, JC,P = 250 Hz, m-C,
1
1
1
[(C6F5)3BH]–}, 138.1 {dm, JC,P = 239 Hz, p-C, [(C6F5)3BH]–},
1
141.3 (d, 3JC,P = 7 Hz, PCCC, Cp*), 148.5 {dm, 1JC,P = 233 Hz, o-
C, [(C6F5)3BH]–} ppm. MS (ESI–, CHCN): m/z (%) = 513 (100)
Ga(C6F5)3] ppm. MS (EI, 70 eV, CH2Cl2): m/z (%) = 570 (14)
[(C6F5)3Ga]+, 403 (34) [(C6F5)BH·NHCMe]+, 168 (35) [C6F5H]+, [(C6F5)3BH]–. MS (ESI+, CHCN): m/z (%)
=
441 (10.5)
137 (100) [BH2·NHCMe]+. IR (C D ): ν = 2958 (s, br., CH), 2928
[Cp*PH(BH2·NHCMe)2]+, 305 (100) [PH2Cp*·BH2·NHCMe]+, 125
˜
6
6
(m, CH), 2867 (m, CH), 2630 (w), 2572 (w), 2536 (w), 2428 (s, BH), (15) [NHCMe + H]+. IR (THF): ν = 2741 (m, br.), 2661 (w), 2612
˜
2398 (s, BH), 2349 (w, sh., PH), 2220 (w), 1638 (s), 1580 (w), 1555
(m), 1509 (vs), 1463 (vs, br.), 1360 (m), 1330 (s), 1268 (m), 1158
(w), 1074 (vs, br.), 1023 (m, br.), 960 (vs), 886 (m), 811 (s), 793 (m),
(w), 2574 (m), 2445 (s, vbr., BH, K+), 2380 (s, vbr., BH, K+), 2346
(sh., BH, A–), 2279 (m, PH), 2171 (w, PH), 2030 (w), 1640 (s), 1603
(w), 1580 (w), 1547 (w), 1509 (vs), 1467 (vs), 1456 (vs), 1376 (m),
Eur. J. Inorg. Chem. 2008, 3482–3492
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3489

A. Adolf, U. Vogel, M. Zabel, A. Y. Timoshkin, M. Scheer
FULL PAPER
1273 (s), 1104 (vs, br.), 1030 (m), 969 (vs), 922 (vs, br.), 805 (w),
765 (m), 735 (s), 660 (m), 601 (w), 567 (m), 468 (w) cm–1.
1438 (w), 1376 (m), 1261 (s), 1114 (s, br.), 1012 (m), 970 (vs), 807
(s, br.), 711 (s), 678 (m), 567 (m), 467 (w) cm–1.
[(C6F5)3BH]–[PH2Ph·BH2·NHCMe +
]
(4c): H3B·NHCMe (136 mg,
(C6F5)3B·P(Ph)HBH2·NHCMe
(5):
H3B·NHCMe
(55 mg,
0.987 mmol) was added to a solution of (C6F5)3B·PH2Ph (614 mg,
0.987 mmol) in CH2Cl2 (20 mL). After stirring the solution for 5 h
at room temperature the solvent was removed in vacuo and 4c was
obtained as a colourless, viscous oil. Yield: 601 mg (80%). 1H
0.44 mmol) was added to a solution of (C6F5)3B·PPhHBH2·NMe3
(0.304 g, 0.44 mmol) in toluene (10 mL). Incipiently showing a red
colour, the solution turned light yellow after stirring for 18 h at
room temperature. After concentration of the solution to a volume
NMR (CD2Cl2, 25 °C): δ = 2.16 (s, CCH3, 6 H, NHCMe), 3.60 (s, of 0.5–1 mL, it was layered with n-hexane (2–3 mL). After 3 weeks
1
3
NCH3, 6 H, NHCMe), 5.79 (dt, JP,H = 398 Hz, JH,H = 7.5 Hz, 2 at 8 °C colourless prisms were formed, which were separated and
H, PH), 7.51–7.57 (m, 2 H, Ph), 7.59–7.69 (m, 3 H, Ph) ppm. 31P
washed with n-hexane (2ϫ5 mL). Yield: 123 mg (37%) H NMR
1
1
NMR (CD2Cl2, 25 °C): δ = –57.9 (t, JP,H = 398 Hz, PH2) ppm.
(C6D6, 25 °C): δ = 1.08 (s, CCH3, 6 H, NHCMe), 2.62 (s, NCH3, 6
31P{1H} NMR (CD2Cl2, 25 °C): δ = –57.9 (s, PH2) ppm. 11B NMR
H, NHCMe), 5.66 (d, JP,H = 351 Hz, 1 H, PH), 6.8–7.4 (m, Ph)
1
(CD2Cl2, 25 °C): δ = –25.5 {d, JB,H = 92 Hz, BH, [(C6F5)3BH]–},
ppm. 31P NMR (C6D6, 25 °C): δ = –43.8 (d, JP,H = 351 Hz, PH)
1
1
–35.6 (br. s, BH2) ppm. 11B{1H} NMR (CD2Cl2, 25 °C): δ = –25.5 ppm. 31P{1H} NMR (C6D6, 25 °C): δ = –43.8 (s, PH) ppm. 11B
{s, BH, [(C6F5)3BH]–}, –35.5 (s, BH2) ppm. 19F NMR (CD2Cl2, NMR (C6D6, 25 °C): δ = –14.4 [br. s, B(C6F5)3], –33.2 (br. s, BH2)
25 °C): δ = –133.7 {m, o-F, 6 F, [(C6F5)3BH]–}, –164.3 {t, JF,F
=
ppm. 11B{1H} NMR (C6D6, 25 °C): δ = –14.4 [br. s, B(C6F5)3],
3
20 Hz, p-F, 3 F, [(C6F5)3BH]–}, –167.3 {m, m-F, 6 F, [(C6F5)3-
–33.2 (br. s, BH2) ppm. 19F NMR (C6D6, 25 °C): δ = –128.1 [s, o-
BH]–} ppm. 13C{1H} NMR (CD2Cl2, 25 °C): δ = 8.6 (s, CCH3, F, 6 F, B(C6F5)3], –158.8 [t, JF,F = 21 Hz, p-F, 3 F, B(C6F5)3],
3
NHCMe), 33.3 (s, NCH3, NHCMe), 115.8 (d, JC,P = 64 Hz, PC,
–164.6 [m, m-F, 6 F, B(C6F5)3] ppm. 13C{1H} NMR (C6D6, 25 °C):
1
Ph), 125.6 {br. s, BC, [(C6F5)3BH]–}, 126.1 (s, C=C, NHCMe), 127.7 δ = 7.6 (s, CCH3, NHCMe), 31.9 (s, NCH3, NHCMe), 119.4 [m, BC,
3
2
(s, m-C, Ph), 130.3 (d, JC,P = 11 Hz, p-C, Ph), 133.7 (d, JC,P
=
B(C6F5)3], 124.9 (s, C=C, NHCMe), 128.5 (s, m-C, Ph), 130.2 (s, p-
10 Hz, o-C, Ph), 136.9 {dm, JC,F = 250 Hz, m-C, [(C6F5)3BH]–}, C, Ph), 133.3 (d, 2JC,P = 6 Hz, o-C, Ph), 137.4 [dm, 1JC,F = 244 Hz,
1
138.3 {dm, JC,F = 244 Hz, p-C, [(C6F5)3BH]–}, 148.7 {dm, JC,F m-C, B(C6F5)3], 139.8 [dm, JC,F = 231 Hz, p-C, B(C6F5)3], 148.7
1
1
1
= 236 Hz, o-C, [(C6F5)3BH]–}, 153.3 (br. s, BC, NHCMe) ppm. MS
[dm, JC,F
=
232 Hz, o-C, B(C6F5)3] ppm. MS (ESI–,
1
(ESI–, CHOH, CH3COO–NH4+): m/z (%) = 513 (100) [(C6F5)3- CHCOOC2H5, CH3OH, CH3COO–NH4+): m/z (%) = 757 (100)
BH]–. MS (ESI+, CH3OH, CH3COO–NH4+): m/z (%) = 383 (100) [M – H]–, 529 (31) [B(C6F5)3·NH3]–. MS (ESI+, CHCOOC2H5,
[PPhH(BH2·NHCMe
)
2
+ 2H]+, 247 (12) [PH2Ph·BH2·NHCMe]+, CH3OH, CH3COO–NH4+): m/z (%) = 776 (100) [M + NH4]+,
137 (51) [BH2·NHCMe]+, 125 (13) [NHCMe + H]+. IR (THF): ν = 383 (17) [PPhH(BH2·NHCMe
)
+ 2H]+, 247 (28) [PPhH2·BH2·
2
˜
2446 (w, vbr., BH, K+), 2401 (m, vbr., BH, K+), 2356 (sh., BH, NHCMe]+. IR (KBr): ν = 2957 (m, CH), 2925 (s CH), 2859 (m, br.,
˜
A–), 2302 (m, PH), 2189 (w, PH), 1639 (m), 1508 (vs), 1470 (s),
CH), 2460 (m, br., BH), 2419 (m, br., BH), 2316 (w, br., PH), 1644
Table 4. Crystallographic data for BH3·NHCMe and compounds 1a, 1b, 2, 3a,b and 5.
BH3·NHCMe 1a
1b 3a
C28H17F15GaP C28H17F15GaPO C28H17F15BP C35F15H30N2GaPB· C31H20F15N2GaPB C31H20F15N2B2P·
2
3b
5
Empirical formula
C7H15N2B
0.25C7H7·0.25C6H14
875.11
0.71073
Monoclinic
123(1)
0.5C7H8
800.11
0.71073
Monoclinic
123(1)
Formula mass
λ [Å]
Crystal system
T [K]
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
138.02
739.11
0.71073
Monoclinic
173(1)
P 21/n
10.127(2)
15.930(3)
18.515(4)
90
105.15(3)
90
2883.0(10)
4
755.1
680.2
816.99
1.54178
Monoclinic
123(1)
0.71073
Triclinic
203(2)
0.71073
Monoclinic
123(1)
1.54178
Monoclinic
123(2)
¯
P1
P 21/c
P 21/n
P 21/c
P 21/n
C 2/c
10.392(2)
10.463(2)
14.033(3)
97.94(3)
102.25(3)
97.23(3)
1457(5)
2
8.8220(18)
19.650(4)
16.408(3)
90
105.31(3)
90
2743.4(10)
4
1.647
23.493(2)
16.7946(12)
25.162(2)
90
114.338(10)
90
9045.5(14)
8
1.285
13.5347(3)
10.0972(2)
23.9708(5)
90
92.223(2)
90
3273.45(12)
4
1.658
30.027(3)
14.3337(12)
16.9845(14)
90
109.829(10)
90
6876.7(11)
8
1.546
16.912(5)
10.313(5)
90
90.411(5)
90
1714.8(13)
8
1.069
γ [°]
V [Å3]
Z
Dcalcd [mgm–3
]
1.703
1.126
1464
1.720
0.118
748
µ [mm]–1
F (000)
0.479
608
0.222
1360
0.730
3520
2.655
1624
0.191
3240
2θ range
Index ranges
8.58–102.65
–9 Յ h Յ 9
3.42–51.9
–11 Յ h Յ 12 –11 Յ h Յ 11
3.98–48.04
5.22–51.74
3.8–51.76
4.99–124.21
–13 Յ h Յ 13
–10 Յ k Յ 6
–24 Յ l Յ 24
8813
3543
0.784
0.0416
473
4.38–51.82
–36 Յ h Յ 36
–17 Յ k Յ 17
–20 Յ l Յ 20
35140
6654
1.081
0.0359
523
–10 Յ h Յ 10 –28 Յ h Յ 28
–23 Յ k Յ 23 –20 Յ k Յ 20
–20 Յ l Յ 19 –30 Յ l Յ 30
14639
4976
1.041
0.0558
419
–17 Յ k Յ 16 –19 Յ k Յ 19 –11 Յ k Յ 11
–10 Յ l Յ 10 –22 Յ l Յ 22 –16 Յ l Յ 15
9110
Reflections collected
19826
5477
1.025
0.0855
419
0.0418
0.1177
0.908/–0.989
9314
4272
1.141
0.1297
428
0.0718
0.1977
0.379/–0.549
83936
17250
0.824
0.1040
999
0.0437
0.1026
0.823/–0.306
Independent reflections 1823
Goodness-of-fit on F2
Rint
0.921
0.087
213
0.0460
0.1215
0.22/–0.27
Parameters
[a]
R1 [I Ͼ 2s(I)]
0.0375
0.1075
0.366/–0.281
0.0352
0.0582
0.334/–0.252
0.0422
0.1246
0.569/–0.324
[b]
wR2 (all data)
Max/min ∆ρ [eÅ–3
]
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = √Σ[w(Fo – Fc ) ]/√Σ[w(Fo2)2].
2
2 2
3490
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3482–3492

N-Heterocyclic Carbenes in Lewis Acid/Base Stabilised Phosphanylboranes
[14]
M. B. Coolidge, W. T. Borden, J. Am. Chem. Soc. 1990, 112,
1704–1706.
T. L. Allen, A. C. Scheiner, H. F. Schäfer, Inorg. Chem. 1990,
29, 1930–1936.
(m), 1558 (w), 1516 (vs), 1464 (vs, br.), 1375 (w), 1279 (m), 1090
(s, br.), 1028 (w), 980 (s, br.), 857 (w), 804 (w, br.), 788 (m), 771
(w), 745 (w), 696 (w), 670 (m), 574 (m) cm–1.
[15]
Crystal-Structure Analysis: The crystal structure analysis of 1, 2,
3a and 5 was performed with a STOE IPDS diffractometer with
Mo-Kα radiation (λ = 0.71073 Å). The crystal structure analysis of
3b was performed with an Oxford Gemini Ultra diffractometer
with Cu-Kα (λ = 1.54178 Å). The structures were solved by direct
methods with the SHELXS-97 program, and full-matrix least-
squares refinement on F2 in SHELXL-97 was performed with an-
isotropic displacements for non-H atoms.[39] Hydrogen atoms at
the carbon atoms were located in idealised positions and refined
isotropically according to the riding model. The hydrogen atoms at
the phosphorus and boron atoms were localised by residual elec-
tron density and freely refined. These results are summarised in
Table 4. Compound 5 crystallises with 0.5 molecules of toluene per
molecular unit, which was considered by solving the structure.
When solving structure 3a, it was not possible to adjust the other
disordered solvent molecules in the unit cell into the structural
model. Because of the volume expansion of the found electron den-
sity, we assume that 3a crystallises with two molecules of n-hexane
and two molecules of toluene in the unit cell. Subsequently, for
solving the structure 3a the program SQUEZZE[40] was used.
[16]
[17]
T. L. Allen, W. H. Fink, Inorg. Chem. 1992, 31, 1703–1705.
U. Vogel, P. Hoemensch, K.-C. Schwan, A. Y. Timoshkin, M.
Scheer, Chem. Eur. J. 2003, 9, 515–519.
A. Adolf, M. Zabel, M. Scheer, Eur. J. Inorg. Chem. 2007, 15,
2136–2143.
U. Vogel, A. Y. Timoshkin, M. Scheer, Angew. Chem. Int. Ed.
2001, 40, 4409–4412.
U. Vogel, A. Y. Timoshkin, K.-C. Schwan, M. Bodensteiner,
M. Scheer, J. Organomet. Chem. 2006, 691, 4556–4564.
K.-C. Schwan, A. Y. Timoshkin, M. Zabel, M. Scheer, Chem.
Eur. J. 2006, 12, 4900–4908.
[18]
[19]
[20]
[21]
[22]
[23]
N. C. Norman, N. L. Pickett, Coord. Chem. Rev. 1995, 145, 27–
54.
J. L. Atwood, F. R. Bennett, F. M. Elms, G. A. Koutsantonis,
C. L. Raston, K. D. Robinson, D. J. Young, Inorg. Chem. 1992,
31, 2673–2674.
D. C. Bradley, M. B. Hursthouse, M. Motevalli, Z. Dao-Hong,
J. Chem. Soc., Chem. Commun. 1991, 1, 7–8.
For details see the Supporting Information.
N. Kuhn, G. Henkel, T. Kratz, J. Kreutzberg, R. Boese, A. H.
Maulitz, Chem. Ber. 1993, 126, 2041–2045.
[24]
[25]
[26]
[27]
a) K.-C. Schwan, PhD Thesis, University of Regensburg, Re-
gensburg, 2006; b) S. A. Westcott, H. P. Blom, T. B. Marder,
R. T. Baker, J. C. Calabrese, Inorg. Chem. 1993, 32, 2175–2182.
D. C. Bradley, I. S. Harding, A. D. Keefe, M. Motevalli, D. H.
Zeng, J. Chem. Soc., Dalton Trans. 1996, 3931–3936.
DFT calculations were performed by using the standard
Gaussian 03 program suite [M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A.
Montgomery Jr, T. Vreven, K. N. Kudin, J. C. Burant, J. M.
Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M.
Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M.
Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene,
X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C.
Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yaz-
yev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannen-
berg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavach-
ari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clif-
ford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A.
Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe,
P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez,
J. A. Pople, Gaussian 03 (Revision D.01), Gaussian, Inc., Wall-
ingford CT, 2004]. B3LYP functional (A. D. Becke, J. Chem.
Phys. 1993, 98, 5648–5652; C. Lee, W. Yang, R. G. Parr, Phys.
Rev. B 1988, 37, 785–789) was used together with the standard
6-31G* basis set for H, B, C, N, F, P and Ga atoms. All struc-
tures were fully optimised with subsequent vibrational analysis
and correspond to the minimum on the potential energy sur-
face.
CCDC-679314 (for BH3·NHCMe), -679315 (for 1a), -679316 (for
1b), -679317 (for 2), -679318 (for 3a), -679319 (for 3b) and -679320
(for 5) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[28]
[29]
Supporting Information (see footnote on the first page of this arti-
cle): Experimental, analytical and crystallographic details of com-
pound 1b; crystallographic data of BH3·NHCMe; optimised geome-
tries of {BArFH···BH2·NHCMe}, PH3BH2·NHCMe {BArFH···
,
PH3BH2·NHCMe} and {BArFH···PH3BH2·NMe3}.
Acknowledgments
This work was comprehensively supported by the Deutsche For-
schungsgemeinschaft and the Fonds der Chemischen Industrie.
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We discuss ∆E°0 values because we are primarily concerned
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+
[31]
[32]
Mulliken partial charges: [PH3·BH2·NMe3] : PH3 (0.476) BH2
(0.025) NMe3 (0.499); [PH3·BH2·NHCMe]+: PH3 (0.4556) BH2
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Eur. J. Inorg. Chem. 2008, 3482–3492
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3491

A. Adolf, U. Vogel, M. Zabel, A. Y. Timoshkin, M. Scheer
FULL PAPER
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[37]
[38]
[39]
[40]
Received: March 25, 2008
Published Online: July 4, 2008
3492
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3482–3492