Preparation and structures of group 12 and 14 element halide-carbene complexes

Article abstract of DOI:10.1071/CH13209

The synthesis of a series of N-heterocyclic carbene (NHC) complexes involving zinc, cadmium, and the heavy Group 14 elements germanium, tin, and lead is reported. The direct reaction between the bulky carbene IPr (IPr≤(HCNDipp)2C:, Dipp≤2,6-iPr2C6H3) and the Group 14 halide reagents GeCl4 and SnCl4 afforded the 1:1 complexes IPr·ECl4 (E≤Ge and Sn) in high yield; similarly, ZnI2 interacted with IPr in THF to give the THF-bound complex IPr·ZnI2·THF. CdCl2 underwent divergent chemistry with IPr and the major product isolated was the imidazolium salt [IPrH] [IPr·CdCl3], which could be converted into IPr·CdCl2·THF upon treatment with Tl[OTf]. In addition, the stable PbII amide adduct, IPr·PbBr(NHDipp), was prepared. Each of the new carbene-element halide adducts was treated with the hydride sources Li[BH4] and Li[HBEt3] in order to potentially access new element hydride adducts and/or clusters. In most instances scission of the element-carbene bonds transpired, except in the case of IPr·ZnI2·THF, which reacted with two equivalents of Li[BH4] to yield the thermally stable bis(borohydride) zinc complex IPr·Zn(BH4)2.

Full text of DOI:10.1071/CH13209

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2013, 66, 1235–1245
Full Paper
http://dx.doi.org/10.1071/CH13209
Preparation and Structures of Group 12 and 14
Element Halide Carbene Complexes
]
A
A
A
S. M. Ibrahim Al-Rafia, Paul A. Lummis, Anindya K. Swarnakar,
A
A
A
Kelsey C. Deutsch, Michael J. Ferguson, Robert McDonald,
A B
,
and Eric Rivard
A
Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive,
Edmonton, Alberta, T6G 2G2, Canada.
B
Corresponding author. Email: erivard@ualberta.ca
The synthesis of a series of N-heterocyclic carbene (NHC) complexes involving zinc, cadmium, and the heavy Group 14
elements germanium, tin, and lead is reported. The direct reaction between the bulky carbene IPr (IPr ¼ (HCNDipp)2C:,
Dipp ¼ 2,6-iPr2C6H3) and the Group 14 halide reagents GeCl4 and SnCl4 afforded the 1 : 1 complexes IPrꢀECl4 (E ¼ Ge
and Sn) in high yield; similarly, ZnI2 interacted with IPr in THF to give the THF-bound complex IPrꢀZnI2ꢀTHF. CdCl2
underwent divergent chemistry with IPr and the major product isolated was the imidazolium salt [IPrH][IPrꢀCdCl3], which
could be converted into IPrꢀCdCl2ꢀTHF upon treatment with Tl[OTf]. In addition, the stable PbII amide adduct, IPrꢀPbBr
(NHDipp), was prepared. Each of the new carbene–element halide adducts was treated with the hydride sources Li[BH4]
and Li[HBEt3] in order to potentially access new element hydride adducts and/or clusters. In most instances scission of the
element–carbene bonds transpired, except in the case of IPrꢀZnI2ꢀTHF, which reacted with two equivalents of Li[BH4] to
yield the thermally stable bis(borohydride) zinc complex IPrꢀZn(BH4)2.
Manuscript received: 26 April 2013.
Manuscript accepted: 11 June 2013.
Published online: 1 August 2013.
Introduction
precursors to new clusters and/or nanomaterials by thermolysis
chemistry.[15]
Since the discovery that N-heterocyclic carbenes (NHC) could
be synthesised in large quantities as thermally stable materi-
als,[1] researchers have sought to explore this versatile ligand
class within the context of catalysis[2] and to intercept novel
bonding environments within the main group.[3] In relation to
the latter concept, the generation/stabilisation of reactive main
group element allotropes such as the tetrylone dimers E2 (E ¼ Si,
Ge, and Sn),[4–6] the diboron species B2,[7] and the parent
methylene and ethylene analogues (EH2 and H2EEH2)[8–11] in
the form of stable NHC adducts, represent interesting additions
to the chemical literature.[12]
In general, the preparation of the above-mentioned reactive
species necessitates the use of main group element halide
adducts of NHCs as starting reagents. In line with this concept,
we report the synthesis of new Group 12 and 14 element halide
adducts containing the readily prepared hindered carbene IPr
(IPr ¼ (HCNDipp)2C:, Dipp ¼ 2,6-iPr2C6H3) as a donor.[13]
Added interest for this research endeavour stems from the
reports that various NHC–zinc adducts (including those of
ZnBr2) can act as catalysts for a variety of transformations
ranging from the ring-opening polymerization of lactides, to the
synthesis of value added products from CO2.[14] Our ultimate
goal for preparing Group 12 and 14 element halide complexes is
to convert these species into new hydride analogues using
productive halide/hydride substitution chemistry; such species
could yield novel chemistry with CO[214] and might be useful
Results and Discussion
Carbene Complexes of Group 12 Element Dihalides
The use of NHC as ligands with Group 12 elements is not a new
concept, as illustrated by the report of a stable NHC–mercury
complex by Wanzlick in 1970.[16,17] The primary motivation for
our exploration of carbene coordination chemistry involving
Group 12 element halides is the future synthesis of novel hydride
species by halide metathesis chemistry;[18] it should be men-
tioned that one of our original synthetic targets from this study,
[IPrꢀZnH(m-H)]2, was recently prepared by Okuda and
coworkers.[18e]
As depicted in Scheme 1, the thermally stable zinc iodide
adduct IPrꢀZnI2ꢀTHF (1) (mp ¼ 150–1528C) was prepared in
1
high yield by combining IPr with ZnI2 in THF. The H NMR
spectrum of 1 gave expected features for a mono-adduct of IPr
including a diagnostic pair of doublet resonances due to the
presence of diasterotopically inequivalent Me groups within
the peripheral isopropyl groups of the carbene donor.
Additional structural authentication of 1 was achieved by
single-crystal X-ray crystallography and the refined structure
of 1 is shown in Fig. 1.
As expected, the Zn centre in 1 adopts a slightly distorted
˚
tetrahedral geometrywitha CIPr–Zn bondlengthof2.0419(19) A.
Journal compilation Ó CSIRO 2013
www.publish.csiro.au/journals/ajc

1236
S. M. I. Al-Rafia et al.
For comparison, the CIPr–Zn distances in the recently
˚
average) has the same value within experimental error as 1,[19]
the monomeric THF-free adduct IPrꢀZnI2 were obtained.[21] Of
particular note, Jones and coworkers have recently reported the
analogous bromide adduct [IPrꢀZnBr(m-Br)]2 whereby the
replacement of iodide with bromide groups at zinc led to
the formation of a centrosymmetric dimer.[22]
reported zinc dichloride adduct IPrꢀZnCl2ꢀTHF (2.045(6) A
˚
while the Zn–O distance in 1 (2.1252(16) A) is lengthened in
˚
relation to the Zn–O bond length in IPrꢀZnCl2ꢀTHF (2.093(4) A
average).[19,20] Attempts to bind an additional equivalent of
IPr to the Zn centre in 1 (to form IPrꢀZnI2ꢀIPr) did not yield
any appreciable coordination chemistry, but rather crystals of
Our attempts to extend carbene complexation to cadmium
dichloride proved to be more of a challenge.[22,23] When IPr was
directly combined with CdCl2 in a THF/dioxane solvent mixture,
a new Cd-containing product was obtained after crystallizing the
resulting crude material from THF/hexanes at ꢁ358C. Interest-
ingly, this product contained 1H NMR spectroscopic resonances
consistent with the presence of two distinct IPr environments.
For example, a singlet resonance was present at 6.57 ppm (in
C6D6) due to backbone-positioned C–H groups of the central
five-membered ring in IPr; this signal was also accompanied by
adjoining satellites resonances resulting from long-range cou-
pling (,4J ¼ 5.6 Hz) to NMR active 111Cd and 113Cd nuclei
(I ¼ 1/2; 12.8 and 12.2 % abundances, respectively).[24] Thus it
appeared that one of the IPr units was bound to a Cd centre.
A second set of IPr resonances was also detected and gave
diagnostic resonances for the known imidazolium cation
[IPrH]þ (e.g. the backbone C–H groups of the imidazolium
heterocycle were located at 9.21 ppm). The composition of the
isolated Cd product was corroborated by X-ray crystallography,
whichidentifiedtheproductas[IPrH][IPrꢀCdCl3] (2)(Scheme2,
Fig. 2).
iPr
I
iPr
I
iPr
iPr
Zn
iPr
N
N
THF
N
ZnI2
ꢀ
O
N
iPr
iPr
iPr
1
IPr
Scheme 1.
The formation of 2 suggests that C–H bond activation of one
equivalent of carbene likely transpired[25] to form the imidazo-
lium salt 2; at this time we are unsure about the fate of the other
product(s) generated in this transformation. In chemistry
reported by the Jones group, IPr and Cl2Geꢀdioxane combine
in THF to give crystals of [IPrH]GeCl3,[5a,26] whereas when
the same reaction is conducted in either Et2O[5a] or toluene[8] the
production of IPrꢀGeCl2 occurs in high yield. Therefore the
stronger donating ability of the THF and dioxane appear to assist
in the C–H activation/deprotonation chemistry leading to HCl
production and the subsequent formation of 2. Unfortunately,
our attempts to react CdCl2 with IPr in less polar solvents (Et2O
and toluene) gave no reaction, presumably due to the low
solubility of CdCl2 in these solvents. In contrast to our studies,
the Jones group reports clean adduct formation between CdI2
and IPr in toluene, to form [IPrꢀCdI(m-I)]2, adding support to the
notion that polar solvents accelerate the production of HCl in the
reaction between CdCl2 and IPr.[22]
N(1)
I(1)
O
Zn
C(1)
N(2)
I(2)
As depicted in Fig. 2, compound 2 consists of discrete
cationic [IPrH]þ and anionic [IPr–CdCl3]ꢁ units in the solid
˚
state. The CIPr–Cd interaction in 2 is 2.246(3) A and is consid-
Fig. 1. Thermal ellipsoid plot (30 % probability level) for IPrꢀZnI2ꢀTHF
(1). All hydrogen atoms have been omitted for clarity. Selected bond lengths
˚
[A] and angles [deg.]: Zn––C(1) 2.0419(19), Zn––I(1) 2.6120(3), Zn–I(2)
erably shorter than the CNHC–Cd distances noted within various
[23]
˚
NHC adducts of CdMe2 (2.327(2) to 2.406(4) A).
The Cd
centre within the [IPr–CdCl3]ꢁ anion has a distorted tetrahedral
geometry with bond angles at Cd in the range of 103.59(3)8 to
2.5580(3), Zn–O 2.1252(16); I(1)–Zn–I(2) 112.701(10), C(1)–Zn–I(1)
108.10(6), C(1)–Zn–I(2) 120.21(5), C(1)–Zn–O 110.49(7).
iPr
iPr
Cl
i
Cl
iPr
iPr
Pr
iPr
iPr
H
iPr
iPr
ꢀ
TI[OTf]
THF
N
N
N
ꢀ
Cd
iPr
ꢁ
CdCl3
N
N
N
THF/dioxane
O
CdCl2
N
N
iPr
iPr
ꢁ ??
ꢁ TICI
ꢁ [IPrH]OTf
iPr
iPr
iPr
iPr
2
3
Scheme 2.

Group 12 and 14 Element Carbene Complexes
1237
114.76(7)8, while the metrical parameters for the remaining
[IPrH]þ cation match those found in related imidazolium salts
present in the literature.[5a,27]
underwent loss of THF under vacuum to yield IPrꢀCdCl2, which
1
was characterized by H and 13C{1H} NMR spectroscopy and
elemental analysis (C, H, and N).
As part of our attempts to induce HCl elimination from
[IPrH][IPrꢀCdCl3] (2) and generate a well defined neutral
cadmium dihalide adduct, we treated 2 with thallium triflate,
Tl[OTf], in THF. Upon adding Tl[OTf] to 2, the immediate
formation of a white precipitate (presumably TlCl) was
observed; analysis of the resulting filtrate confirmed the pres-
ence of [IPrH]OTf and a new carbene containing product
(Scheme 2). The latter species exhibited diagnostic coupling
between the IPr unit and Cd in the form of 111Cd and 113Cd
satellites. Fortunately the cadmium–carbene complex could be
selectively separated from [IPrH]OTf by extraction with ben-
zene, and crystals of this species could be obtained from THF/
hexanes which identified the product as the target adduct
IPrꢀCdCl2ꢀTHF (3) (Fig. 3). Notably, IPrꢀCdCl2ꢀTHF readily
Compound 3 adopts a similar coordination motif as its lighter
Group 12 element congener IPrꢀZnCl2ꢀTHF[19] with Cd–Cl
˚
bonds (2.4184(8) A average) which are longer than the reported
˚
Zn–Cl distances in IPrꢀZnCl2ꢀTHF (2.257(4) A average) due to
the larger covalent radius of Cd. A CIPr–Cd bond length of
˚
2.218(2) A was determined in 3 which is contracted in relation to
the CIPr–Cd distance within the anionic [IPr–CdCl3]ꢁ unit in 2
˚
(2.246(3) A), however, a similar CIPr–Cd bond length of
2.249(5) A was noted in [IPrꢀCdI(m-I)]2.[22] We did not extend
˚
our synthetic investigations to include the HgII adducts
IPrꢀHgX2 (X ¼ halide) as efficient routes to these species are
already known.[28]
Carbene Complexes of Group 14 Element Halides
As discussed in the Introduction, the synthesis of many novel
carbene-supported main group species (such as Si2)[4] depends
upon the availability of suitable element halide adducts as
precursors. Despite the availability of several IPr-capped spe-
cies such as IPrꢀEX2 (E ¼ Si, Ge, and Pb; X ¼ Cl or Br)[5,8,29]
and IPrꢀSiX4 (X ¼ F, Cl, or Br),[4,29b,30] the GeIV and SnIV
adducts IPrꢀGeCl4 and IPrꢀSnCl4 remained conspicuously
absent from the literature. We now report that these complexes
are readily prepared in high yield as moisture-sensitive white
solids (86 % yield each) by combining IPr with GeCl4 and
SnCl4, respectively (Scheme 3).
N(1)
C(20)
Cl(1)
Cd
N(2)
C(13)
N(4)
Cl(3)
N(3)
Cl(2)
Both IPrꢀGeCl4 (4) and IPrꢀSnCl4 (5) crystallised in nearly
isostructural arrangements (Figs 4 and 5, respectively) with the
carbene ligands occupying equatorial sites about the trigonal
bipyramidal Ge and Sn centres. Another interesting aspect of
these structures is that the central ring of each IPr donor aligns in
such a fashion as to keep its constituent atoms nearly co-planar
with the two adjacent equatorial Cl atoms (e.g. N(1)–C(1)–Ge–
Cl(1) torsion angle ¼ 6.81(14)8), thus minimising repulsive
steric interactions between the flanking Dipp groups and the
axially disposed Cl atoms. A similar geometric arrangement of
the IPr and equatorial chloro ligands exists in Robinson’s SiIV
complex IPrꢀSiCl4.[4] In line with the presence of trigonal
bipyramidal geometries in 4 and 5, nearly linear Clax–E–Clax
angles were found (Cl(3)–Ge–Cl(4) ¼ 179.66(4)8 in 4; Cl(2)–
Sn–Cl(3) ¼ 177.51(3)8 in 5) which match closely with the
corresponding Clax–Si–Clax angle of 176.94(4)8 in IPrꢀSiCl4.
Fig. 2. Thermal ellipsoid plot (30 % probability level) for [IPrH]
[IPrꢀCdCl3] (2). All hydrogen atoms and toluene solvate have been omitted
˚
for clarity. Selected bond lengths [A] and angles [deg.]: Cd–C(1) 2.246(3),
Cd–Cl(1) 2.4790(8), Cd–Cl(2) 2.4650(10), Cd–Cl(3) 2.4573(9); C(1)–Cd–
Cl(1) 114.76(7), Cl(1)–Cd–Cl(2) 103.59(3), Cl(2)–Cd–Cl(3) 112.24(4).
C(3)
˚
The CIpr–Ge bond length in 4 is 1.9921(14) A and is significantly
N(2)
C(2)
shorter than the CIPr–Ge distance in the GeII adduct IPrꢀGeCl2
C(6)
C(7)
(2.112(2) A).[8] The CIPr–Ge bond contraction in 4 relative to in
˚
C(4)
N(1)
C(1)
IPrꢀGeCl2 can be explained by both the smaller effective size of
GeIV versus GeII[31] and the greater Lewis acidity of the GeCl4
unit in comparison to GeCl2; a similar trend is found when the
C(5)
O(1)
˚
CIPr–Sn bond lengths in 5 (2.186(2) A) and IPrꢀSnCl2
Cd
(2.341(8) A)[8] are compared.
˚
The last element halide complex prepared in this study was
the PbII amide adduct, IPrꢀPbBr(NHDipp) (6). This species was
targeted as previous work in our laboratory showed that the
lighter congeners IPrꢀECl(NHDipp) (E ¼ Si, Ge, and Sn) can
undergo unusual transmetallation chemistry in the presence of
the hydride source Li[BH4].[32] The synthesis of 6 is outlined in
Scheme 4 and relies upon the use of Jones’ soluble PbII precursor
IPrꢀPbBr2 as a reagent.[5b]
Cl(2)
Cl(1)
Fig. 3. Thermal ellipsoid plot (30 % probability level) for IPrꢀCdCl2ꢀTHF (3).
All hydrogen atoms and THF solvate have been omitted for clarity.
˚
Selected bond lengths [A] and angles [deg.]: Cd–C(1) 2.218(2), Cd–Cl(1)
Compound 6 is a thermally stable (up to 2608C) yellow solid
that is soluble in organic solvents. In contrast to the known
amido-tetrelylene adducts IPrꢀECl(NHDipp) (E ¼ Si, Ge, and
2.4029(6), Cd–Cl(2) 2.4338(6), Cd–O(1) 2.3413(17); Cl(1)–Cd–Cl(2)
114.08(3), C(1)–Cd–Cl(1) 119.97(6), C(1)–Cd–Cl(2) 111.26(6), C(1)–
Cd–O(1) 112.14(8).

1238
S. M. I. Al-Rafia et al.
iPr
iPr
iPr
iPr
iPr
iPr
iPr
Cl
Ge
Cl
Cl
Sn
Cl
N
N
Cl
Cl
N
N
Cl
Cl
N
N
SnCl4
GeCl4
Et2O
Toluene
iPr
iPr
iPr
iPr
iPr
4
5
IPr
Scheme 3.
Cl(4)
Cl(1)
N(1)
N(2)
Cl(3)
Sn
C(1)
C(1)
Ge
Cl(4)
Cl(2)
N(1)
N(2)
Cl(3)
Cl(1)
Cl(2)
Fig. 5. Thermal ellipsoid plot (30 % probability level) for IPrꢀSnCl4 (5).
Fig. 4. Thermal ellipsoid plot (30 % probability level) for IPrꢀGeCl4 (4).
˚
All hydrogen atoms have been omitted for clarity. Selected bond lengths [A]
All hydrogen atoms and the minor orientation of a disordered Dipp group
˚
(40/60 ratio) have been omitted for clarity. Selected bond lengths [A] and
and angles [deg.]: C(1)–Ge 1.9921(14), Ge–Cl(1) 2.1428(5), Ge–Cl(2)
2.1455(4), Ge–Cl(3) 2.3206(5), Ge–Cl(4) 2.2516(5); C(1)–Ge–Cl(1)
118.46(4), C(1)–Ge–Cl(2) 118.93(4), C(1)–Ge–Cl(3) 88.07(4), C(1)–Ge–
Cl(4) 92.24(4), Cl(3)–Ge–Cl(4) 179.66(2); N(1)–C(1)–Ge–Cl(1) torsion
angle ¼ 6.81(14)8.
angles [deg.]: Sn–C(1) 2.186(2), Sn–Cl(1) 2.3329(7), Sn–Cl(2) 2.4229(8),
Sn–Cl(3) 2.3941(8), Sn–Cl(4) 2.3093(8); C(1)–Sn–Cl(1) 121.39(7), C(1)–
Sn–Cl(4) 118.00(3), Cl(1)–Sn–Cl(4) 120.56(7), Cl(2)–Sn–Cl(3) 177.51(3);
N(1)–C(1)–Sn–Cl(1) torsion angle ¼ ꢁ7.9(2)8.
Sn) which have up to six spectroscopically inequivalent methyl
1
iPr
iPr
iPr
iPr
iPr
environments by H NMR spectroscopy,[32] compound 6 dis-
Et2O
N
N
N
N
plays four broad peaks for the methyl environments in IPr and
one sharp doublet resonance for the methyl groups in the
NHDipp fragment. Thus it appears that the large size of the Pb
centre leads to the formation of a long CIPr–Pb bond (see below)
that enables the IPr group to rotate more freely in comparison to
its Si, Ge, and Sn analogues; moreover attempts to freeze out the
IPr motion by cooling to ꢁ908C (in d8-toluene) did not result in
any change in the above-mentioned broad spectroscopic fea-
tures from the IPr unit.
Crystals of IPrꢀPbBr(NHDipp) (6) of suitable quality for
X-ray crystallography were grown from Et2O/hexanes and the
refined structure is presented in Fig. 6. Compound 6 represents
only the third characterized example of a carbene-lead adduct
Li[NHDipp]
ꢀ
Pb
Br
Pb
Br
ꢁ LiBr
Br
NHDipp
iPr
iPr
iPr
6
Scheme 4.
with IPrꢀPbBr[25b] and Weidenbruch’s thermally unstable di-
i
i
arylplumylene adduct ImMe2 Pr2ꢀPb(Trip)2 (ImMe2 Pr2 ¼
(MeCNiPr)2C:, Trip ¼ 2,4,6-iPr3C6H2)[33] being the other known
adducts; compound 6 is, to our knowledge, the first example of a

Group 12 and 14 Element Carbene Complexes
1239
Pb
N(2)
C(1)
C(3)
Br
N(3)
N(1)
C(2)
Fig. 6. Thermal ellipsoid plot (30 % probability level) for IPrꢀPbBr(NHDipp) (6). All carbon-
bound hydrogen atoms and diethyl ether solvate molecules have been omitted for clarity. Selected
˚
bond lengths [A] and angles [deg.]: Pb–C(1) 2.437(3), Pb–Br 2.7265(4), Pb–N(3) 2.219(3); Br–Pb–
C(1) 90.29(6), Br–Pb–N(3) 96.51(7), C(1)–Pb–N(3) 90.58(9).
2 Li[HBEt3]
IPrꢂZnl2ꢂTHF
iPr
iPr
iPr
1
iPr
H
N
N
N
N
ꢀ Cd or Zn
ꢀ
BEt3
iPr
IPrꢂCdCl2
or
[IPrH][IPrꢂCdCl3]
H
metal
4 or 2 Li[HBEt3]
4 Li[HBEt3]
2
3
iPr
iPr
iPr
IPrꢂECl4
E ꢃ Ge or Sn; 4 or 5
IPrꢂBEt3
IPrH2
Scheme 5.
stable PbII amide–carbene adduct. Perhaps the most evident
structural aspect of 6 is the presence of a highly pyramidalized
Pb centre consistent with the presence of a lone pair at Pb with
high s-character (angle sum at Pb for 6 ¼ 277.38(14)8 versus
combined with lithium triethylborohydride, Li[HBEt3] (2–4
equivalents). In each case, product mixtures were obtained
which contained the known species IPrꢀBEt[335] and IPrH2[9a]
in varying amounts, as determined by 1H NMR spectroscopy,
and presumably Zn and Cd metal as insoluble products
(Scheme 5). Thus it appears that adduct formation between
the Lewis acidic BEt3 by-product and IPr was a favourable
reaction pathway in each case, with competitive hydride-
migration to the carbene carbon of either IPr (or transiently
generated IPrHþ) to form the dihydroaminal IPrH2. In the
reaction of IPrꢀZnI2ꢀTHF (1) with Li[HBEt3], no sign of the
formation of the known hydride adduct [IPrꢀZnH(m-H)]2[14e]
was observed, confirming that the choice of the hydride reagent
is important in dictating the successful formation of carbene-
supported hydride complexes. In a similar fashion as the Group
12 systems, both IPrꢀGeCl4 (4) and IPrꢀSnCl4 (5) reacted
rapidly with four equivalents of Li[HBEt3] to give mixtures
of IPrꢀBEt3 and IPrH2 (Scheme 5).
˚
285.7(5)8 in IPrꢀPbBr2). The CIPr–Pb distance in 6 is 2.437(2) A
and is the same within error as the related distance in the
thermally stable adduct IPrꢀPbBr2 (2.443(11) A);[5b] notably, the
˚
i
unstable adduct ImMe2 Pr2ꢀPb(Trip)2 has a longer C–Pb distance
[33]
˚
of 2.540(5)A.
As with the known adducts IPrꢀECl(NHDipp)
(E ¼ Si, Ge, and Sn), the Pb–Br bond is nestled in between
the flanking Dipp groups of the IPr donor, thus providing
possible future steric protection for a Pb–H bond (upon replace-
ment of the bromide group by a hydride substituent).[34]
Attempted Synthesis of New Group 12 and 14
Hydride Complexes
Following related protocols used by our group to prepare EH2
and H2EEH2 adducts,[8–11] the newly prepared compounds 1–6
were combined with the hydride sources Li[BH4] and Li[HBEt3]
in ethereal solvents.
Our group has had considerable success with Li[BH4] as a
hydride source and, accordingly, the first GeII dihydride complex
IPrꢀGeH2ꢀBH3,[8] and SnII dihydride adduct IPrꢀSnH2ꢀW(CO)[59a]
were each prepared by Cl/H exchange chemistry in the
To begin, the zinc adduct IPrꢀZnI2ꢀTHF 1, and the cadmium
complexes [IPrH][IPrꢀCdCl3] (2) and IPrꢀCdCl2 (3) each were

1240
S. M. I. Al-Rafia et al.
presence of lithium borohydride. When hydride transfer
chemistry was investigated with the higher oxidation state EIV
species IPrꢀECl4 (E ¼ Ge and Sn; 4 and 5), divergent reaction
pathways were noted. For example, when IPrꢀGeCl4 (4) was
combined with excess Li[BH4] in Et2O, the clean formation of
the known GeII dihydride IPrꢀGeH2ꢀBH[38] transpired in a 75 %
yield (according to Scheme 6). It is plausible that the formation
of a GeII species follows by the initial formation of a HGeCl3
adduct, which undergoes reductive elimination of HCl to afford
GeCl2 (likely in the form of IPrꢀGeCl2). A related transformation
has been used to generate Cl2Geꢀdioxane,[36] and Roesky and
coworkers have investigated parallel chemistry with HSiCl3 to
yield low-oxidation state silicon species.[29a,37] Despite repeated
attempts, we were unable to locate IPrꢀGeCl2 as an intermediate
in the reaction between 4 and Li[BH4]. The tin(IV) congener
IPrꢀSnCl4 (5) participated in a rapid reaction with four equiva-
lents of Li[BH4] to give IPrꢀBH3 (quantitative yield) as the only
carbene-containing product along with copious amounts of tin
metal; this result is not entirely surprising as our attempts to
generate the SnII hydride IPrꢀSnH2ꢀBH3 exclusively gave
IPrꢀBH3 and tin metal as involatile products.[8]
Compound 7 adopts a symmetrical structure in the solid state
with a two-fold rotation axis that is coincident with the Zn–CIPr
˚
bond. The carbene–zinc interaction in 7 (2.013(2) A) is short-
ened with respect to the Zn–CIPr distance in the precursor
˚
IPrꢀZnI2ꢀTHF (1) (2.0419(4) A). Furthermore, X-ray crystallo-
graphy confirmed the presence of Z2-coordination between each
BH4 unit and the Zn centre in 7. For comparison, the Raston
group observed a similar bonding arrangement in TME-
DAꢀZnCl(Z2-BH4)
(TMEDA ¼ Me2NCH2CH2NMe2),[38a]
˚
wherein the ZnꢀꢀꢀB atomic separation (2.29(2) A) was deter-
mined to be the same within experimental error as the ZnꢀꢀꢀB
˚
distance in 7 (2.252(2) A). Recently, Robinson and coworkers
reported an isostructural beryllium adduct, IPrꢀBe(Z2-BH4)2,
which was synthesized by the reaction of IPrꢀBeCl2 with two
equivalents of Li[BH4] in toluene.[38b]
The base-free zinc borohydride Zn(BH4)2 was initially
prepared by Schlesinger and coworkers in 1951[39] and was
later shown to coordinate to various Lewis bases to yield
complexes of improved thermal stability relative to Zn(BH4)2
We were successful in isolating a new borohydride-contain-
ing product from the reaction between IPrꢀZnI2ꢀTHF (1) and two
equivalents of Li[BH4] in THF (Scheme 7). Analysis of the
1
crude product by H NMR spectroscopy showed the nearly
exclusive (,95 %) presence of a new IPr-bound species along
with a minor amount of the known ZnII dihydride adduct
[IPrꢀZnH(m-H)]2.[18e] The proton-coupled 11B NMR spectrum
(in C6D6) was particularly informative as it afforded one pentet
resonance centred at ꢁ37.7 ppm (1JBH ¼ 73.3 Hz) consistent
with the retention of BHꢁ4 functionality in the product. X-Ray
crystallography was performed on colourless crystals grown
from THF/hexanes at ꢁ358C and conclusively identified the
material as the bis(borohydride)zinc complex IPrꢀZn(BH4)2 (7)
(Fig. 7 and Scheme 7).
B
N(0A)
C(2A)
Zn
C(1)
C(2)
N
iPr
iPr
iPr
iPr
iPr
iPr
iPr
Cl
Ge
Cl
H
Cl
Cl
Et2O
N
N
H
N
N
ꢀ 4 Li[BH4]
Ge
ꢁ 4 LiCl
ꢁ 3 BH3
ꢁ H2
BH3
iPr
Fig. 7. Thermal ellipsoid plot (30 % probability level) for IPrꢀZn(BH4)2
(7). All carbon-bound hydrogen atoms have been omitted for clarity, and a
two-fold rotation axis exists along the C(1)–Zn bond. Selected bond lengths
˚
4
[A] and angles [deg.]: Zn–C(1) 2.013(2), ZnꢀꢀꢀB 2.252(2), Zn–H 1.80(3) and
1.80(3), B–H 0.94(3) to 1.14(3); N–C(1)–Zn 127.56(10), N–C(1)–N0 104.9
(2), C(1)–ZnꢀꢀꢀB 126.26(7).
Scheme 6.
H
I
I
iPr
H
iPr
B
iPr
H
iPr
N
N
H
H
Zn
iPr
THF
N
2
Li[BH4]
ꢀ
Zn
O
ꢁ 2 LiI
H
N
B
iPr
H
iPr
H
iPr
7
1
Scheme 7.

Group 12 and 14 Element Carbene Complexes
1241
(which decomposes at ,658C);[40] moreover, these borohydride
complexes are useful as mild reducing agents.[40b] Thus the
synthesis of IPrꢀZn(BH4)2 (7) is a nice addition to this molecular
class and we are currently exploring this thermally stable
material (mp 104–1078C with decomposition) in the domain
of CO2 activation.[14f] Parallel chemistry was explored between
IPrꢀPbBr(NHDipp) (6) and Li[BH4] and despite NMR evidence
for the formation of a new BHꢁ4 containing product, we have
been unable to obtain crystals of suitable quality for X-ray
crystallographic analysis.
suitable for X-ray crystallography were obtained by cooling a
saturated THF solution of 1 layered with hexanes at ꢁ358C for
3 days. Mp 150–1528C (dec.). dH (500 MHz, C6D6) 7.16 (t, J 7.6,
2H, ArH), 7.05 (d, J 7.6, 4H, ArH), 6.40 (s, 2H, N–CH–), 3.59
(m, 4H, C4H8O), 2.81 (septet, J 6.8, 4H, CH(CH3)2), 1.52
(d, J 6.8, 12H, CH(CH3)2), 1.36 (m, 4H, C4H8O), 0.94
(d, J 6.8, 12H, CH(CH3)2). dH (500 MHz, CD2Cl2) 7.54
(t, J 8.0, 2H, ArH), 7.55 (d, J 8.0, 4H, ArH), 7.28 (s, 2H,
N–CH–), 3.58 (m, 4H, C4H8O), 2.67 (septet, J 7.2, 4H, CH
(CH3)2), 1.74 (m, 4H, C4H8O), 1.39 (d, J 6.5, 12H, CH(CH3)2),
1.15 (d, J 6.5, 12H, CH(CH3)2). dC (126 MHz, CD2Cl2) 173.3
(N–C–N), 146.2 (ArC), 134.2 (ArC), 131.3 (ArC), 125.7 (ArC),
124.8 (N–CH–), 69.3 (C4H8O), 29.1 (CH(CH3)2), 26.9
(CH(CH3)2), 25.6 (C4H8O), 23.7 (CH(CH3)2). Anal. Calc. for
C31H45I2N2OZn: C 47.68, H 5.81, N 3.59. Found: C 47.41,
H 5.59, N 3.59 %.
Conclusion
Various new Group 12 and 14 element halide adducts of the
hindered carbene donor IPr were prepared and structurally
authenticated by X-ray crystallography. Attempts to generate
element hydride complexes by halide/hydride metathesis
chemistry generally led to carbene–element bond cleavage and
the formation of IPr adducts with either BEt3 or BH3 by-
products (when Li[BH4] and Li[HBEt3] were used as hydride
sources); occasionally the formation of the known dihy-
droaminal IPrH2 transpired. The successful synthesis of the
soluble and thermally stable bis(borohydride) zinc complex
IPrꢀZn(BH4)2 was achieved by the reaction of IPrꢀZnI2ꢀTHF
with two equivalents of Li[BH4]; thus the nature of the hydride
source employed in halide metathesis chemistry is very impor-
tant in dictating product outcome. We are currently exploring
the reactivity of IPrꢀZn(BH4)2 in the context of carbon dioxide
reduction chemistry and as a possible soluble precursor to zinc
nanomaterials.
Synthesis of [IPrH][IPrꢀCdCl3] 2
To a solution of CdCl2 (0.14 g, 0.76 mmol) in 4 mL of
1,4-dioxane was added a solution of IPr (0.29 g, 0.76 mmol) in
4 mL of THF. The reaction vial was wrapped in aluminium foil
and the reaction mixture was stirred for 18 h to give a pale yellow
slurry. The volatiles were removed under vacuum to yield an
off-white powder. This material was dissolved in 3 mL THF, and
then 5 mL of hexanes was layered on top of the solution and the
mixture was stored at ꢁ358C overnight. This afforded 2 as a
white microcrystalline solid (0.20 g, 27 %; the yield was calcu-
lated assuming a 1 : 1 mol ratio between the reagents IPr and
CdCl2 and the final product 2). Crystals suitable for X-ray
crystallography were grown by cooling a THF/hexanes solution
of 2 to ꢁ358C for 7 days. Mp 227–2308C. dH (500 MHz, C6D6)
9.21 (s, 2H, N–CH–), 7.33 (t, J 7.5, 2H, ArH), 7.25 (d, J 7.5, 4H,
ArH), 7.06 (t, J 7.5, 2H, ArH), 6.90 (d, J 7.5, 4H, ArH), 6.57
(s, satellites: 4JH–Cd 5.6, 2H, N–CH–), 6.32 (br s, 1H, N–CH–N),
3.01 (septet, J 6.5, 4H, CH(CH3)2), 2.50 (septet, J 6.5, 4H, CH
(CH3)2), 1.71 (d, J 6.5, 12H, CH(CH3)2), 1.10 (d, J 6.5, 12H, CH
(CH3)2), 1.09 (d, J 6.5, 12H, CH(CH3)2), 0.91 (d, J 6.5, 12H, CH
(CH3)2). dC (126 MHz, C6D6) 187.9 (N–C–N), 146.2 (ArC),
145.9 (ArC), 135.6 (ArC), 133.7 (N–CH–N), 131.5 (ArC), 130.8
(ArC), 130.4(ArC), 124.28(ArC), 124.32(ArC), 124.2(N–CH–),
29.1 (CH(CH3)2), 28.8 (CH(CH3)2), 25.8 (CH(CH3)2), 24.4
(CH(CH3)2), 23.8 (CH(CH3)2). Anal. Calc. for C54H73CdCl3N4:
C 65.06, H 7.38, N 5.62. Found: C 65.00, H 7.49, N 5.49%.
Experimental
Materials and Instrumentation
All reactions were performed using standard Schlenk line
techniques under an atmosphere of nitrogen or in an inert
atmosphere glove box (Innovative Technology, Inc.). Solvents
were dried using a Grubbs-type solvent purification system[41]
manufactured by Innovative Technology, Inc., degassed
(freeze–pump–thaw method) and stored under an atmosphere of
nitrogen before use. CdCl2, ZnI2, Li[BH4], Li[HBEt3] (1.0 M
solution in THF), GeCl4, SnCl4 (1.0 M solution in heptane),
and thallium(I) trifluoromethane sulfonate (Tl[OTf]) were
purchased from Aldrich and used as received. 1,3-Bis-(2,6-
diisopropylphenyl)-imidazol-2-ylidene (IPr),[13] IPrꢀPbBr2,[5b]
and Li[NHDipp][42] were prepared according to literature
Reaction of [IPrH][IPrꢀCdCl3] 2 with Tl[OTf]: Isolation
of IPrꢀCdCl2ꢀTHF 3
1
procedures. H, 11B, 13C{1H}, 19F{1H}, and 119Sn{1H} NMR
spectra were recorded either on a Varian iNova-400 or on a
Varian iNova-500 spectrometer and referenced externally to
SiMe4 (1H and 13C{1H}), F3BꢀOEt2 (11B), CFCl3 (19F{1H}), and
SnMe4 (119Sn{1H}). Elemental analyses were performed by the
Analytical and Instrumentation Laboratory at the University
of Alberta. Melting points were measured in sealed glass
capillaries under nitrogen using a MelTemp melting point
apparatus and are uncorrected.
To
a clear, colourless solution of Tl[OTf] (39 mg,
0.11 mmol) in 3 mL of THF was added a clear, colourless
solution of [IPrH][IPrꢀCdCl3] (2) (109 mg, 0.109 mmol) in
3 mL of THF. Immediately upon the addition of 2, the formation
of a white precipitate was noted. The reaction mixture was
stirred for 18 h, and then the volatiles removed under vacuum.
The resulting off-white solid was extracted with 4 mL of
benzene, and filtered to remove insoluble by-products. The
volatiles were removed from the resulting filtrate under vacuum
to yield a white solid, which was washed with 2 ꢂ 1 mL of
hexanes and dried under vacuum to yield spectroscopically pure
IPrꢀCdCl2 as a white powder (30 mg, 48 %); note: the data
presented below is for the THF-free complex IPrꢀCdCl2. Crys-
tals suitable for X-ray crystallography were grown by cooling a
THF/hexanes solution of 3 to ꢁ358C for 5 days. Mp stable to
2608C. dH (500 MHz, C6D6) 7.21 (t, J 7.5, 2H, ArH), 7.08 (d, J
7.5, 4H, ArH), 6.41 (s, satellites: 4JH–Cd 7.2, 2H, N–CH–), 2.70
Synthetic Procedures
Synthesis of IPr ꢀ ZnI2 ꢀ THF 1
IPr (0.181 g, 0.466 mmol) and ZnI2 (0.149 g, 0.465 mmol)
were combined in 10 mL of THF at room temperature. The
reaction was allowed to proceed for 12 h, giving a pale yellow
solution. Removal of the volatiles from the reaction mixture
yielded a pale yellow powder (0.310 g, 86 %), which was
1
identified as 1 by H NMR spectroscopy. Colourless crystals

1242
S. M. I. Al-Rafia et al.
(septet, J 6.9, 4H, CH(CH3)2), 1.52 (d, J 6.5, 12H, CH(CH3)2),
0.93 (d, J 6.5, 12H, CH(CH3)2). dC (126 MHz, C6D6) 182.8 (N–
C–N), 145.8 (ArC), 134.4 (ArC), 131.1 (ArC), 129.2 (ArC),
124.6 (N–CH–), 29.1 (CH(CH3)2), 25.7 (CH(CH3)2), 23.7 (CH
(CH3)2). Anal. Calc. for C27H36CdCl2N2: C 56.70, H 6.34, N
4.90. Found: C 57.60, H 6.51, N 4.60 %.
(0.013 g; combined yield ¼ 0.289 g, 87 %). Mp 1908C (dec.).
dH (500 MHz, C6D6) 7.20 (t, J 7.5, 2H, ArH), 7.09 (d, J 7.5, 4H,
ArH), 6.41 (s, satellites: JH–119/117Sn 12.9, 2H, N–CH–), 2.97
(septet, J 6.8, 4H, CH(CH3)2), 1.46 (d, J 6.5, 12H, CH(CH3)2),
0.86 (d, J 6.5, 12H, CH(CH3)2). dC (126 MHz, C6D6) 146.7
(N–C–N), 132.7 (ArC), 131.8 (ArC), 129.3 (ArC), 125.0
(N–CH–), 124.5 (ArC), 29.3 (CH(CH3)2), 26.7 (CH(CH3)2),
22.4 (CH(CH3)2). d119Sn (185 MHz, CD2Cl2) ꢁ422.6 (s). Anal.
Calc. for C27H36Cl4SnN2: C 49.96, H 5.59, N 4.32. Found
C 49.65, H 6.06, N 4.69 %.
4
Reaction of [IPrH][IPrꢀCdCl3] 2 with Tl[OTf]: Isolation
of IPrH[OTf]
To
a clear, colourless solution of Tl[OTf] (73 mg,
0.21 mmol) in 3 mL of THF was added a clear, colourless
solution of [IPrH][IPrꢀCdCl3] (2) (0.205 g, 0.206 mmol) in
3 mL of THF. Immediately upon the addition of 2, the formation
of a white precipitate was noted. The solution was stirred for
48 h, upon which time the mother liquor was filtered. The
volatiles were removed from the filtrate under vacuum to yield
a white powder, which was washed with 2 ꢂ 2 mL of benzene
and dried under vacuum to afford a pure sample of IPrH[OTf]
(52 mg, 47 %). Mp stable to 2608C. NMR spectroscopic values
for IPrH[OTf] matched those found in the literature.[13] dH
(500 MHz, CDCl3) 9.10 (s, 1H, N–CH–N), 7.84 (s, 2H,
N–CH–), 7.59 (t, J 7.5, 2H, ArH), 7.36 (d, J 7.5, 4H, ArH),
2.42 (septet, J 6.5, 4H, CH(CH3)2), 1.28 (d, J 6.5, 12H, CH
(CH3)2), 1.22 (d, J 6.5, 12H, CH(CH3)2). dC (126 MHz, CDCl3)
144.9 (N–CH–), 138.0 (ArC), 132.3 (ArC), 129.7 (ArC), 126.4
(ArC), 29.5 (CH(CH3)2), 24.8 (CH(CH3)2), 24.2 (CH(CH3)2).
dF (470 MHz, CDCl3) ꢁ78.0 (s). Anal. Calc. for
C28H37F3N2O3S: C 62.43, H 6.92, N 5.20. Found: C 62.44,
H 6.94, N 5.26 %.
Synthesis of IPrꢀPbBr(NHDipp) 6
A solution of Li[NHDipp] (0.065 g, 0.27 mmol) in 5 mL of
cold Et2O (ꢁ358C) was added dropwise to a cold (ꢁ358C) slurry
of IPrꢀPbBr2 (0.26 g, 0.35 mmol) in 5 mL of Et2O. The resulting
mixture was warmed slowly to room temperature and stirred for
1 h to give a bright orange solution over a precipitate (LiBr). The
resulting reaction mixture was filtered through Celite and then
removal of volatiles from the filtrate yielded 6 as a yellow solid.
Crystals suitable for X-ray crystallography were grown
by cooling a Et2O/hexanes solution of 6 to ꢁ358C for 3 days
(0.170 g, 58 %). Mp stable to 2608C. nmax (Nujol)/cmꢁ1 3241w
n(N–H). dH (500 MHz, C6D6) 7.22 (br s, 2H, ArH), 7.11 (br, 4H,
ArH), 7.05 (t, J 8.0, 1H, ArH), 6.71 (d, J 8.0, 2H, ArH), 6.52
(br, 2H, N–CH–), 4.41 (s, 1H, NH), 3.17 (br, 2H, CH(CH3)2),
2.92 (br, 2H, CH(CH3)2), 2.65 (septet, J 7.0, 2H, CH(CH3)2),
1.41 (br, 6H, CH(CH3)2), 1.33 (br, 6H, CH(CH3)2), 1.14
(d, J 7.0, 12H, CH(CH3)2), 1.09 (br, 6H, CH(CH3)2), 1.01
(br, 6H, CH(CH3)2). dC (126 MHz, C6D6) 148.1 (ArC), 146.2
(ArC), 137.6 (ArC), 134.2 (ArC), 131.2 (ArC), 125.3 (ArC),
124.4 (N–CH–), 124.2 (ArC), 123.0 (ArC), 119.0 (ArC), 117.6
(ArC), 29.1 (CH(CH3)2), 28.1 (CH(CH3)2), 26.9 (CH(CH3)2),
25.8 (CH(CH3)2), 23.9 (CH(CH3)2), 23.6 (CH(CH3)2), 22.6
(CH(CH3)2). Anal. Calc. For C39H54BrN3Pb: C 54.98, H 6.39,
N 4.39. Found: C 54.85, H 6.41, N 4.89 %.
Synthesis of IPrꢀGeCl4 4
IPr (0.42 g, 1.1 mmol) and GeCl4 (0.14 mL, 1.2 mmol) were
combined in 12 mL of Et2O at room temperature. The reaction
was allowed to proceed for 3 h to give a white slurry. The white
precipitate was isolated by filtration and identified as 4 (0.57 g,
86 %). Crystals suitable for X-ray crystallography were grown
by cooling a CH2Cl2/hexanes solution of 4 to ꢁ358C for 2 days.
Mp 1858C (dec.). dH (500 MHz, CD2Cl2) 7.61 (t, J 7.9, 2H,
ArH), 7.41 (d, J 7.9, 4H, ArH), 7.31 (s, 2H, N–CH–), 2.98
(septet, J 6.5, 4H, CH(CH3)2), 1.40 (d, J 6.5, 12H, CH(CH3)2),
1.12 (d, J 6.5, 12H, CH(CH3)2). dH (400 MHz, C6D6) 7.22
(t, J 7.8, 2H, ArH), 7.12 (d, J 7.6, 4H, ArH), 6.38 (s, 2H,
N–CH–), 3.15 (septet, J 6.8, 4H, CH(CH3)2), 1.48 (d, J 6.5Hz,
12H, CH(CH3)2), 0.92 (d, J 6.5, 12H, CH(CH3)2). dC (126 MHz,
CD2Cl2) 156.5 (N–C–N), 147.3 (ArC), 132.6 (ArC), 131.5
(ArC), 124.8 (N–CH–), 124.4 (ArC), 29.6 (CH(CH3)2), 26.8
(CH(CH3)2), 22.2 (CH(CH3)2). dC (126 MHz, C6D6) 147.1
(N–C–N), 132.5 (ArC), 131.7 (ArC), 124.8 (N–CH–), 123.5
(ArC), 29.4 (CH(CH3)2), 26.7 (CH(CH3)2), 22.4 (CH(CH3)2).
Anal. Calc. for C27H36Cl4GeN2: C 53.78, H 6.02, N 4.65. Found:
C 53.75, H 6.09, N 4.47 %.
Synthesis of IPrꢀZn(BH4)2 7
To a suspension of LiBH4 (0.005 g, 0.2 mmol) in 2 mL of
THF was added a solution of 1 (0.090 g, 0.12 mmol) in 3 mL of
THF to yield a pale yellow solution. The reaction mixture was
then allowed to stir for 18 h, and then the volatiles were removed
under vacuum. The resulting pale yellow solid was washed with
2 ꢂ 2 mL of Et2O, and extracted into 3 mL of benzene before
being filtered through Celite. Removal of the solvent from
the filtrate under vacuum yielded the desired product as a white
solid (0.035 g, 63 %). Crystals suitable for X-ray diffraction
were obtained after 12 h by layering 2 mL of hexanes on top of a
solution of 7 dissolved in 1 mL of THF. Mp 104–1078C (dec.).
dH (500 MHz, C6D6) 7.17 (t, J 8.0, 2H, ArH), 7.04 (d, J 8.0, 4H,
ArH), 6.40 (s, 2H, N–CH–), 2.64 (septet, J 6.0, 4H, CH(CH3)2),
1.39 (d, J 6.0, 12H, CH(CH3)2), 0.94 (d, J 6.8, 12H, CH(CH3)2),
0.61 (br, 8H, BHꢁ4 ; assignment confirmed by broadband
11B decoupling). dC (126 MHz, C6D6) 145.6 (ArC), 133.6
(ArC), 131.6 (ArC), 124.8 (ArC), 124.6 (N–CH–), 29.0
(CH(CH3)2), 25.8 (CH(CH3)2), 23.1 (CH(CH3)2). We were
unable to locate the N–C–N resonance. dB (160 MHz, C6D6) ꢁ
37.3 (pentet, J 73.3, BHꢁ4 ). Despite repeated attempts, elemental
analyses consistently gave low values for C and N content: Anal.
Calc. for C27H44B2N2Zn: C 67.05, H 9.17, N 5.79. Found:
C 65.50, H 9.15, N 4.46 %. See the Supplementary Material
for copies of the NMR spectra for 7 (Figs S2 and S3).
Synthesis of IPrꢀSnCl4 5
To a solution of IPr (0.20 g, 0.52 mmol) in 12 mL of toluene
was added SnCl4 (0.52 mL, 0.52 mmol, 1.0 M solution in hep-
tane) at room temperature. The reaction was allowed to proceed
for 12 h to give a white slurry. The white precipitate was isolated
by filtration and identified as 5 (0.276 g). A further crop of
5 (colourless crystals of X-ray quality) was obtained by
cooling the filtrate layered with hexanes to ꢁ358C for 1 day

Group 12 and 14 Element Carbene Complexes
1243
Reaction of IPr ꢀ ZnI2 ꢀ THF 1 with Li[HBEt3]
which was characterized by 1H, 11B, and 13C{1H} NMR
spectroscopy.
To a cold (ꢁ358C) solution of 1 (100 mg, 0.128 mmol) in 8 mL
of THF was added Li[HBEt3] (0.282 mL, 1.0 M solution in
THF). The reaction mixture was allowed to warm to room
temperature and stirred for 12 h resulting in the formation of a
black slurry. The resulting slurry was then filtered through
Celite and the volatiles were removed under vacuum to yield
a pale yellow solid (58 mg), which was identified as a mix-
ture of IPrꢀBEt[335] (,90 % by 1H NMR spectroscopy),
(HCNDipp)2CH2 (IPrH2)[9a] (,2 % by 1H NMR spectroscopy),
and ,8 % of other unidentified products.
Crystallographic Details
General Details
Crystals suitable for X-ray diffraction studies were removed
from a vial in a glove box freezer and immediately coated with a
thin layer of hydrocarbon oil (Paratone-N). A suitable crystal
was then mounted on a glass fibre, and quickly placed in a low
temperature stream of nitrogen on the X-ray diffractometer.[44]
All data were collected using a Bruker APEX II CCD detector/
D8 diffractometer using MoKa or CuKa radiation, with the
crystals cooled to ꢁ1008C. The data were corrected for
absorption through Gaussian integration from the indexing of
the crystal faces or multi-scan procedures (SADABS[45] for
compounds 1 and 5; TWINABS[46] for compound 2). Crystal
structures were solved using either direct methods (SHELXS-
97[47] for compounds 1, 2, and 4–7; SIR 97[48] for
compound 3) and refined using SHELXL-97.[47] The assignment
of carbon-bound hydrogen atoms were based on the sp2 or sp3
hybridisation geometries of their attached carbon atoms, and
were give thermal parameters 20 % greater than those of their
parent atoms.
Reaction of [IPrH][IPr ꢀ CdCl3] 2 with Li[HBEt3]
Compound 2 was combined with Li[HBEt3] following a similar
procedure as above, and gave a mixture of IPrꢀBEt[335] (,68 %
by 1H NMR spectroscopy) and IPrCH[29a] (,32 % by 1H NMR
spectroscopy).
Reaction of IPr ꢀ CdCl2 with Li[HBEt3]
IPrꢀCdCl2 was combined with Li[HBEt3] following a similar
procedure as stated above with the exception that benzene was
used as the reaction solvent. A mixture of IPrꢀBEt[335] (,50 % by
1H NMR spectroscopy) and IPrH[29a] (,50 % by 1H NMR
spectroscopy) was generated.
Crystal Data for IPr ꢀ ZnI2 ꢀ THF (1)
C31H44I2N2OZn, M 779.85, colourless plate, 0.48 ꢂ 0.31 ꢂ
3
0.15 mm , monoclinic, space group C2/c, a 40.7207(14) A,
˚
3
b 9.6340(3) A, c 17.0987(6) A, b 99.7678(3)8, V 6610.6(4) A ,
Reaction of IPr ꢀ ECl4 (E 5 Ge and Sn; 4 and 5) with Four
˚
˚
˚
Z 8, Dc 1.567 g cmꢁ3, 2ymax 52.768, m(MoKa) 2.635 mmꢁ1
T 173(1) K, 25 661 reflections collected, 6749 unique reflections
,
Equivalents of Li[HBEt3]
To a solution of IPrꢀECl4 (0.15 mmol) in 12 mL of Et2O was
added Li[HBEt3] (,0.68 mmol) at room temperature. The
reaction mixture was stirred for 12 h. The mother liquor was
separated from a yellow precipitate by filtration, and removal of
the volatiles from the filtrate under vacuum gave a white solid in
each case. For E ¼ Ge, the product contained a mixture of
IPrꢀBEt3 (,90 %)[35] and IPrH2 (,10 %)[9b] as determined by
1H, 13C{1H), and 11B NMR spectroscopy; whereas for E ¼ Sn,
the product contained a mixture of IPrꢀBEt3 (,81 %)[35] and
IPrH2 (,19 %)[9b] as determined by 1H, 13C{1H), and 11B NMR
spectroscopy.
[R(int) 0.0118], Final GoF 1.047, R1 (on F2) 0.0213; wR2 (on F2)
ꢁ3
˚
0.0544[I . 2s(I)], max/minelectron density 1.072/–0.786e A
CCDC No. 934973.
,
Crystal Data for [IPrH][IPr ꢀ CdCl3] (2 ꢀ 2.5 Toluene)
C
71.5H93CdCl3N4, M 1227.25, colourless plate, 0.49 ꢂ 0.18 ꢂ
3
0.08mm , triclinic, spacegroupP1, a 14.985(2) A, b16.849(2)A,
˚ ˚
˚
c 18.063(2) A, a 61.6908(15)8, b 73.7219(16)8, g 58.9672(15)8,
3
V 3436.7(8) A , Z 2, Dc 1.186 g cmꢁ3, 2ymax 55.208, m(MoKa
)
˚
0.476 mmꢁ1, T 173(1) K, 67 722 reflections collected,
27 625 unique reflections [R(int) 0.0702], Final GoF 1.061, R1
(on F2) 0.0602; wR2 (on F2) 0.1702 [I . 2s(I)], max/min elec-
Reaction of IPr ꢀ GeCl4 4 with Li[BH4]: Alternate Preparation
of IPr ꢀ GeH2 ꢀ BH3
tron density 1.890/–1.275 e Aꢁ3, CCDC No. 934974. Special
˚
refinement conditions: Both components of the twin were
indexed with the program CELL_NOW.[49] The second twin
component can be related to the first component by 1808 rotation
about the [0 1 0] axis in real space and about the [1/2 1 1/2] axis
in reciprocal space. Integrated intensities for the reflections
from the two components were written into a SHELX-97 HKLF
5 reflection file with the data integration program SAINT (ver-
sion 7.68A)[50] using all reflection data (exactly overlapped,
partially overlapped, and non-overlapped). The refined value of
the twin fraction (SHELXL-97 BASF parameter) was 0.5057(7).
To a mixture of 4 (0.197 g, 0.33 mmol) and Li[BH4] (0.032 g,
1.5 mmol) was added 12 mL of Et2O at room temperature. The
reaction mixture was allowed to proceed for 12 h to give a yel-
low slurry. The volatiles were removed under vacuum and the
product was extracted with 10 mL of benzene. Filtration of the
mixture followed by removal of the solvent from the filtrate
yielded a white solid (0.120 g, 75 %), which was identified as
IPrꢀGeH2ꢀBH3 by 1H and 11B NMR spectroscopy.[8]
Reaction of IPr ꢀ SnCl4 5 with Four Equivalents of Li[BH4]:
Generation of IPr ꢀ BH3
Crystal Data for IPr ꢀ CdCl2 ꢀ THF (3 ꢀ THF)
C35H52CdCl2N2O2, M 716.09, colourless block, 0.38 ꢂ 0.32 ꢂ
IPrꢀSnCl4
5 (0.10 g, 0.15 mmol) and Li[BH4] (14 mg,
3
0.24 mm , orthorhombic, space group P212121, a 13.9468(8) A,
˚
0.64 mmol) were combined in 12 mL of diethyl ether. The
reaction mixture was stirred for 12 h and the mother liquor was
separated from the black precipitate by filtration. The solvent
was removed from the filtrate under vacuum to give the known
species IPrꢀBH[343] as a white powder (62 mg, quantitative yield)
3
˚
˚
˚
b 15.8702(9) A, c 16.5113(9) A, V 3654.6(4) A , Z 4, Dc
1.301 g cmꢁ3, 2ymax 54.888, m(MoKa) 0.774 mmꢁ1, T 173(1) K,
32 290 reflections collected, 8318 unique reflections [R(int)
0.0288], Final GoF 1.027, R1 (on F2) 0.0249; wR2 (on F2) 0.0671

1244
S. M. I. Al-Rafia et al.
[I . 2s(I)], max/min electron density 0.762/–0.332 e Aꢁ3, Flack
parameter ꢁ0.021(16), CCDC No. 934975.
[2] (a) S. D´ıez-Gonza´lez, N. Marion, S. P. Nolan, Chem. Rev. 2009, 109,
3612. doi:10.1021/CR900074M
(b) C. M. Crudden, D. P. Allen, Coord. Chem. Rev. 2004, 248, 2247.
doi:10.1016/J.CCR.2004.05.013
[3] (a) N. Kuhn, A. Al-Sheikh, Coord. Chem. Rev. 2005, 249, 829.
doi:10.1016/J.CCR.2004.10.003
˚
Crystal Data for IPr ꢀ GeCl4 (4)
C27H36Cl4N2Ge, M 602.97, colourless plate, 0.50 ꢂ 0.43 ꢂ
3
0.25 mm , monoclinic, space group P21/n, a 10.9535(6) A,
˚
(b) R. Wolf, W. Uhl, Angew. Chem. Int. Ed. 2009, 48, 6774.
doi:10.1002/ANIE.200902287
(c) Y. Wang, G. H. Robinson, Chem. Commun. 2009, 5201.
(d) Y. Wang, G. H. Robinson, Inorg. Chem. 2011, 50, 12326.
doi:10.1021/IC200675U
˚
˚
b 13.9137(8) A, c 19.7796(10) A, b 104.6640(10)8, V 2961.3
˚
3
(3) A ,
Z
4, Dc 1.373 g cmꢁ3
,
2ymax 54.848, m(MoKa
)
1.435 mmꢁ1, T 173(1) K, 25 317 reflections collected, 5880
unique reflections [R(int) 0.0203], Final GoF 1.044, R1 (on F2)
0.0267; wR2 (on F2) 0.0700 [I . 2s(I)], max/min electron den-
(e) D. Martin, M. Melaimi, M. Soleilhavoup, G. Bertrand,
Organometallics 2011, 30, 5304. doi:10.1021/OM200650X
[4] Y. Wang, Y. Xie, P. Wei, R. B. King, H. F. Schaefer III, P. v. R.
Schleyer, G. H. Robinson, Science 2008, 321, 1069. doi:10.1126/
SCIENCE.1160768
[5] (a) A. Sidiropoulos, C. Jones, A. Stasch, S. Klein, G. Frenking, Angew.
Chem. Int. Ed. 2009, 48, 9701. doi:10.1002/ANIE.200905495
(b) C. Jones, A. Sidiropoulos, N. Holzmann, G. Frenking, A. Stasch,
Chem. Commun. 2012, 48, 9855. doi:10.1039/C2CC35228A
[6] For the recent formation of tetrelylones bis adducts (LBꢀEꢀLB; E ¼ Si
and Ge; LB ¼ Lewis base), see: (a) K. C. Mondal, H. W. Roesky, M. C.
Schwarzer, G. Frenking, B. Niepo¨tter, H. Wolf, R. Herbst-Irmer,
D. Stalke, Angew. Chem. Int. Ed. 2013, 52, 2963. doi:10.1002/ANIE.
201208307
sity 0.595/–0.448 e Aꢁ3, CCDC No. 934976.
˚
Crystal Data for IPr ꢀ SnCl4 (5)
C27H36Cl4N2Sn, M 649.07, colourless plate, 0.40 ꢂ 0.15 ꢂ
3
0.11 mm , monoclinic, space group P21/c, a 20.016(2) A,
˚
˚
˚
b 10.1625(12) A, c 16.1110(19) A, b 109.0380(10)8, V 3097.9
˚
3
(6) A ,
Z , 2ymax 55.128, m(MoKa)
4, Dc 1.392 g cmꢁ3
1.187 mmꢁ1, T 173(1) K, 26 165 reflections collected, 7114
unique reflections [R(int) 0.0320], Final GoF 1.063, R1 (on F2)
0.0320; wR2 (on F2) 0.0733 [I . 2s(I)], max/min electron den-
sity 0.929/–0.310 e Aꢁ3, CCDC No. 934977.
˚
(b) Y. Xiong, S. Yao, G. Tan, S. Inoue, M. Driess, J. Am. Chem. Soc.
2013, 135, 5004. doi:10.1021/JA402477W
[7] H. Braunschweig, R. D. Dewhurst, K. Hammond, J. Mies, K. Radacki,
A. Vargas, Science 2012, 336, 1420. doi:10.1126/SCIENCE.1221138
[8] K. C. Thimer, S. M. I. Al-Rafia, M. J. Ferguson, R. McDonald,
E. Rivard, Chem. Commun. 2009, 7119.
[9] (a) S. M. I. Al-Rafia, A. C. Malcolm, S. K. Liew, M. J. Ferguson,
E. Rivard, J. Am. Chem. Soc. 2011, 133, 777. doi:10.1021/JA1106223
(b) S. M. I. Al-Rafia, O. Shynkaruk, S. M. McDonald, S. K. Liew,
M. J. Ferguson, R. McDonald, R. H. Herber, E. Rivard, Inorg. Chem.
2013, 52, 5581. doi:10.1021/IC4005455
Crystal Data for IPr ꢀ PbBr(NHDipp) (6 ꢀ Et2O)
C43H64BrN3OPb, M 926.07, pale yellow block, 0.34 ꢂ 0.31 ꢂ
3
0.21 mm , monoclinic, space group P21/c, a 12.1775(8) A,
˚
˚
˚
b 18.1343(12) A, c 20.6224(14) A, b 105.4880(10)8, V 4388.7
˚
3
(5) A ,
Z , 2ymax 55.248, m(MoKa)
4, Dc 1.402 g cmꢁ3
4.787 mmꢁ1, T 173(1) K, 38 522 reflections collected, 10 146
unique reflections [R(int) 0.0331], Final GoF 1.015, R1 (on F2)
0.0264; wR2 (on F2) 0.0639 [I . 2s(I)], max/min electron
density 1.984/–0.648 e Aꢁ3, CCDC No. 934978.
˚
[10] (a) M. Y. Abraham, Y. Wang, Y. Xie, P. Wei, H. F. Schaefer III,
P. v. R. Schleyer, G. H. Robinson, J. Am. Chem. Soc. 2011, 133, 8874.
doi:10.1021/JA203208T
(b) S. M. I. Al-Rafia, A. C. Malcolm, R. McDonald, M. J. Ferguson, E.
Rivard, Chem. Commun. 2012, 48, 1308. doi:10.1039/C2CC17101E
[11] S. M. I. Al-Rafia, A. C. Malcolm, R. McDonald, M. J. Ferguson,
E. Rivard, Angew. Chem. Int. Ed. 2011, 50, 8354. doi:10.1002/ANIE.
201103576
Crystal Data for IPr ꢀ Zn(BH4)2 (7)
C27H44B2N2Zn, M 483.63, colourless plate, 0.21 ꢂ 0.12 ꢂ
3
0.07 mm , monoclinic, space group C2/c, a 16.6074(5) A, b
˚
3
9.4081(3) A, c 17.7919(5) A, b 90.3920(10)8, V 2779.81(14) A ,
˚
˚
˚
Z 4, Dc 1.156 g cmꢁ3, 2ymax 140.348, m(CuKa) 1.320 mmꢁ1
T 173(1) K, 9055 reflections collected, 2600 unique reflections
,
[R(int) 0.0196], Final GoF 1.043, R1 (on F2) 0.0338; wR2 (on F2)
[12] (a) For selected recent advances in this area, see: R. Kinjo,
B. Donnadieu, M. Ali Celik, G. Frenking, G. Bertrand, Science 2011,
333, 610. doi:10.1126/SCIENCE.1207573
ꢁ3
˚
0.0994 [I . 2s(I)], max/min electron density 1.412/–0.320 e A
CCDC No. 935984.
,
(b) B. Ine´s, M. Patil, J. Carreras, R. Goddard, W. Thiel, M. Alcarazo,
Angew. Chem. Int. Ed. 2011, 50, 8400. doi:10.1002/ANIE.201103197
(c) S. J. Bonyhady, D. Collis, G. Frenking, N. Holzmann, C. Jones,
A. Stasch, Nat. Chem. 2010, 2, 865. doi:10.1038/NCHEM.762
(d) J. J. Weigand, K.-O. Feldmann, F. D. Henne, J. Am. Chem. Soc.
2010, 132, 16321. doi:10.1021/JA106172D
Supplementary Material
Crystallographicdata for IPrꢀZnI2 and NMR data for IPrꢀZn(BH4)2
are available on the Journal’s website.
(e) C. L. Dorsey, B. M. Squires, T. W. Hudnall, Angew. Chem. Int. Ed.
2013, 52, 4462. doi:10.1002/ANIE.201301137
[13] L. Jafarpour, E. D. Stevens, S. P. Nolan, J. Organomet. Chem. 2000,
Acknowledgement
The authors thank Alberta Innovates-Technology Futures (New Faculty
Award to E. R.; Graduate Award to S. M. I. A.), the Canada Foundation for
Innovation, and the Natural Sciences and Engineering Council (Discovery
Grant to E. R.; Undergraduate Research Student Award to K. C. D.) for
support of this work.
606, 49. doi:10.1016/S0022-328X(00)00260-6
[14] (a) T. R. Jensen, C. P. Schaller, M. A. Hillmyer, W. B. Tolman,
J. Organomet. Chem. 2005, 690, 5881. doi:10.1016/J.JORGAN
CHEM.2005.07.070
(b) B. Bantu, G. Manohar Pawar, U. Decker, K. Wurst, A. M. Schmidt,
M. R. Buchmeiser, Chemistry 2009, 15, 3103. doi:10.1002/CHEM.
200802670
(c) P. L. Arnold, I. J. Casely, Z. R. Turner, R. Bellabarba, R. B. Tooze,
Dalton Trans. 2009, 7236,
References
[1] (a) A. J. Arduengo III, R. L. Harlow, M. Kline, J. Am. Chem. Soc.
1991, 113, 361. doi:10.1021/JA00001A054
(b) A. J. Arduengo III, H. V. Rasika Dias, R. L. Harlow, M. Kline,
J. Am. Chem. Soc. 1992, 114, 5530. doi:10.1021/JA00040A007
(c) For an early report of a stable acyclic carbene, see: A. Igau,
H. Grutzmacher, A. Baceiredo, G. Bertrand, J. Am. Chem. Soc. 1988,
110, 6463. doi:10.1021/JA00227A028
(d) Y. Lee, B. Li, A. H. Hoveyda, J. Am. Chem. Soc. 2009, 131, 11625.
doi:10.1021/JA904654J
(e) X. Liu, C. Cao, Y. Li, P. Guan, L. Yang, Y. Shi, Synlett 2012, 23,
1343. doi:10.1055/S-0031-1290957

Group 12 and 14 Element Carbene Complexes
1245
(f) For a report of a carbene-zinc catalyst which activates CO2, see:
O. Jacquet, X. Frogneux, C. Das Neves Gomes, T. Cantat, Chem. Sci.
2013, 4, 2127. doi:10.1039/C3SC22240C
(b) A. C. Filippou, O. Chernov, G. Schnakenburg, Angew. Chem. Int.
Ed. 2009, 48, 5687. doi:10.1002/ANIE.200902431
[30] R. S. Ghadwal, S. S. Sen, H. W. Roesky, G. Tavcar, S. Merkel,
D. Stalke, Organometallics 2009, 28, 6374. doi:10.1021/OM9007696
[31] R. D. Shannon, Acta Crystallogr. 1976, 32A, 751.
[32] S. M. I. Al-Rafia, R. McDonald, M. J. Ferguson, E. Rivard, Chemistry
2012, 18, 13810. doi:10.1002/CHEM.201202195
[33] F. Stabenow, W. Saak, M. Weidenbruch, Chem. Commun. 1999, 1131.
[34] Currently there are no examples of stable Pb–H bonds involving lead in
the þ2 state: L. Pu, B. Twamley, P. P. Power, J. Am. Chem. Soc. 2000,
122, 3524. doi:10.1021/JA993346M
[15] C. Xu, R. T. Beeler, G. J. Grzybowski, A. V. G. Chizmeshya,
D. J. Smith, J. Mene´ndez, J. Kouvetakis, J. Am. Chem. Soc. 2012, 134,
20756. doi:10.1021/JA309894C
[16] H.-J. Scho¨nherr, H.-W. Wanzlick, Chem. Ber. 1970, 103, 1037.
doi:10.1002/CBER.19701030407
[17] For a recent review of Group 12 element carbene complexes, see:
S. Budagumpi, S. Endud, Organometallics 2013, 32, 1537.
doi:10.1021/OM301091P
[18] (a) N. P. Mankad, D. S. Laitar, J. P. Sadighi, Organometallics 2004, 23,
[35] J. Monot, M. Makhlouf Brahmi, S. -H Ueng, C. Robert, M. Desage-El
Murr, D. P. Curran, M. Malarcia, L. Fensterrbank, E. Lacoˆte, Org. Lett.
2009, 11, 4914. Note: The 1H and 11B NMR data for IPrꢀBEt3 are listed
as being in CDCl3, but in fact all NMR data for this species were
acquired in C6D6. doi:10.1021/OL902012C
3369. doi:10.1021/OM0496380
(b) E. Y. Tsui, P. Mu¨ller, J. P. Sadighi, Angew. Chem. Int. Ed. 2008, 47,
8937. doi:10.1002/ANIE.200803842
(c) C. H. Lee, T. R. Cook, D. G. Nocera, Inorg. Chem. 2011, 50, 714.
doi:10.1021/IC102017T
[36] (a) S. P. Kolesnikov, I. S. Rogozhin, O. M. Nefedov, Izv. Akad. Nauk
(d) C. D. Abernethy, R. J. Baker, M. L. Cole, A. J. Davies, C. Jones,
Transition Met. Chem. 2003, 28, 296. doi:10.1023/A:1022979412307
(e) A. Rit, T. P. Spaniol, L. Maron, J. Okuda, Angew. Chem. Int. Ed.
2013, 52, 4664. doi:10.1002/ANIE.201300749
SSSR [Khim] 1974, 10, 2379.
(b) T. Fjeldberg, A. Halland, B. E. R. Schilling, M. F. Lappert,
A. J. Thorne, J. Chem. Soc., Dalton Trans. 1986, 1551.
[37] A. P. Singh, R. S. Ghadwal, H. W. Roesky, J. J. Holstein, B. Dittrich,
J.-P. Demers, V. Chevelkov, A. Lange, Chem. Commun. 2012, 48,
7574. doi:10.1039/C2CC33835A
[19] A. Doddi, C. Gemel, R. W. Siedel, M. Winter, R. A. Fischer, Poly-
hedron 2013, 52, 1103. doi:10.1016/J.POLY.2012.06.067
[20] For the synthesis of IMesꢀZnCl2ꢀTHF (IMes ¼ [(HCNMes)2C: Mes ¼
2,4,6-Me3C6H2), see: D. Wang, K. Wurst, M. Buchmeiser,
J. Organomet. Chem. 2004, 689, 2123. doi:10.1016/J.JORGAN
CHEM.2004.03.039
[21] In one case, crystals of the THF-free adduct IPrꢀZnI2 were isolated
from a reaction mixture containing 1 and unreacted IPr. See the
Supplementary Material for full crystallographic details of IPrꢀZnI2
(CCDC 934972).
[38] (a) G. A. Koutsantonis, F. C. Iee, C. L. Raston, J. Chem. Soc. Chem.
Commun. 1975, 1994.
(b) R. J. Gilliard, Jr, M. Y. Abraham, Y. Wang, P. Wei, X. Xie,
B. Quillian, H. F. Schaefer III, P. v. R. Schleyer, G. H. Robinson, J. Am.
Chem. Soc. 2012, 134, 9953. doi:10.1021/JA304514F
[39] G. D. Barbaras, C. Dillard, A. E. Finholt, T. Wartik, K. E. Wilzbach,
H. I. Schlesinger, J. Am. Chem. Soc. 1951, 73, 4585. doi:10.1021/
JA01154A025
[22] M. Ma, A. Sidiropoulos, L. Ralte, A. Stasch, C. Jones, Chem. Commun.
[40] (a) H. No¨th, E. Wiberg, L. P. Winter, Z. Anorg. Allg. Chem. 1969, 370,
2013, 49, 48. doi:10.1039/C2CC37442K
209. doi:10.1002/ZAAC.19693700502
[23] A. J. Arduengo III, J. R. Goerlich, F. Davidson, W. J. Marshall,
Z. Naturforsch 1999, 54b, 1350.
[24] Z. Zhu, R. C. Fischer, J. C. Fettinger, E. Rivard, M. Brynda,
P. P. Power, J. Am. Chem. Soc. 2006, 128, 15068. doi:10.1021/
JA066108H
(b) M. Tajbakhsh, M. M. Lakouraj, F. Mohanazadeh, A. Ahmadi-
Nejhad, Synth. Commun. 2003, 33, 229. doi:10.1081/SCC-120015705
[41] A. B. Pangborn, M. A. Giardello, R. H. Grubbs, R. K. Rosen,
F. J. Timmers, Organometallics 1996, 15, 1518. doi:10.1021/
OM9503712
[25] For related examples of backbone C- activation in NHC, see:
(a) J. I. Bates, P. Kennepohl, D. P. Gates, Angew. Chem. Int. Ed.
2009, 48, 9844. doi:10.1002/ANIE.200905401
[42] J. T. Patton, S. C. Feng, K. A. Abboud, Organometallics 2001, 20,
3399. doi:10.1021/OM010101L
[43] Y. Wang, B. Quillian, P. Wei, C. S. Wannere, Y. Xie, R. B. King,
H. F. Schaefer III, P. v. R. Schleyer, G. H. Robinson, J. Am. Chem. Soc.
2007, 129, 12412. doi:10.1021/JA075932I
[44] H. Hope, Prog. Inorg. Chem. 1994, 41, 1. doi:10.1002/
9780470166420.CH1
[45] G. M. Sheldrick, SADABS, version 2008/1; Universita¨t Go¨ttingen:
(b) Y. Wang, Y. Xie, M. Y. Abraham, R. J. Gillard Jr., P. Wei,
H. F. Schaefer III, P. v. R. Schleyer, G. H. Robinson, Organometallics
2010, 29, 4778. doi:10.1021/OM100335J
[26] We have noted that IPr and Cl2Geꢀdioxane do react in THF to give
spectroscopically pure IPrꢀGeCl2 (by 1H NMR) when the reaction
times are limited to 30 min.
Go¨ttingen, Germany, 2008.
[27] (a) R. J. Baker, A. J. Davies, C. Jones, M. Kloth, J. Organomet. Chem.
2002, 656, 203. doi:10.1016/S0022-328X(02)01592-9
(b) E. D. Blue, T. B. Gunnoe, J. F. Peterson, P. D. Boyle, J. Organomet.
Chem. 2006, 691, 5988. doi:10.1016/J.JORGANCHEM.2006.09.051
(c) R. S. Ghadwal, R. Azhakar, H. W. Roesky, K. Pro¨pper, B. Dittrich,
C. Goedecke, G. Frenking, Chem. Commun. 2012, 48, 8186.
doi:10.1039/C2CC32887A
[46] G. M. Sheldrick, TWINABS, version 2008/2; Universita¨t Go¨ttingen:
Go¨ttingen, Germany, 2008.
[47] G. M. Sheldrick, Acta Crystallogr. 2008, A64, 112.
[48] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano,
C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori,
R. Spagna, J. Appl. Cryst. 1999, 32, 115. doi:10.1107/
S0021889898007717
[28] S. Pelz, F. Mohr, Organometallics 2011, 30, 383. doi:10.1021/
OM101154Z
[29] (a) R. S. Ghadwal, H. W. Roesky, S. Merkel, J. Henn, D. Stalke,
[49] G. M. Sheldrick, CELL_NOW, version 2008/2; Universita¨t Go¨ttingen:
Go¨ttingen, Germany, 2008.
[50] G. M. Sheldrick, SAINT, version 7.68A; Bruker AXS Inc.: Madison
WI, 2008.
Angew. Chem. Int. Ed. 2009, 48, 5683. doi:10.1002/ANIE.200901766