N-Heterocyclic carbene stabilized adducts of alkyl magnesium amide, bisalkyl magnesium and Grignard reagents: Trapping oligomeric organo s-block fragments with NHCs

Article abstract of DOI:10.1039/c0dt00693a

Developing N-heterocyclic carbene (NHC) chemistry of simple organomagnesium compounds, this study reports the synthesis, X-ray crystallographic, and NMR spectroscopic characterization of three such new carbene complexes. The 1:1 alkyl magnesium amide:carb

Full text of DOI:10.1039/c0dt00693a

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www.rsc.org/dalton | Dalton Transactions
N-Heterocyclic carbene stabilized adducts of alkyl magnesium amide, bisalkyl
magnesium and Grignard reagents: trapping oligomeric organo s-block
fragments with NHCs†
Alan R. Kennedy, Robert E. Mulvey* and Stuart D. Robertson*
Received 21st June 2010, Accepted 4th August 2010
DOI: 10.1039/c0dt00693a
Developing N-heterocyclic carbene (NHC) chemistry of simple organomagnesium compounds, this
study reports the synthesis, X-ray crystallographic, and NMR spectroscopic characterization of three
such new carbene complexes. The 1 : 1 alkyl magnesium amide : carbene complexes nBuMg(TMP)·IPr 1
and nBuMg(HMDS)·IPr 2 both exist as mononuclear complexes in the crystal but differ in solution as 2
remains intact whereas 1 undergoes a dynamic exchange involving partial decoordination of IPr [TMP
is 2,2,6,6-tetramethylpiperidide; IPr is 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene); HMDS is
1,1,1,3,3,3-hexamethyldisilazide]. Reaction of commercial nBu2Mg with IPr surprisingly produced the
organoaluminium carbene complex nBu3Al·IPr, 3, which also forms a simple mononuclear structure in
the crystal. The presence of the Al could be traced to the deliberate addition of a small quantity of
Et3Al as a stabilizing agent in the commercial nBu2Mg reagent. Repeating this reaction with Al-free
nBu2Mg afforded the hemisolvated carbene complex nBu8Mg4·2IPr, 4, the stoichiometry of which is
dictated by its structure rather than by that used in the initial reaction mixture. The molecular structure
of 4 is tetranuclear with a linear chain of 4 Mg centres bridged by nBu ligands and capped at each end
by terminal nBu and IPr ligands. Synthesized by treating the Grignard reagent nBuMgCl with IPr,
nBuMgCl·IPr, 5, forms a cyclodimer structure with chloro bridges and terminal nBu and IPr ligands.
to the stabilizing heterocycle, while Alexakis has utilized such a
Introduction
functionalized NHC as a catalyst for asymmetric allylic alkylation
Originally thought to be only transient intermediates which could
with Grignard reagents although no structural intermediates were
not be isolated,1 carbenes have advanced to the forefront of
chemistry research in the past twenty years. Interest escalated
after the groundbreaking discovery that they could be prepared
as air-stable crystalline solids by incorporating the carbene centre
into a heteroatomic ring and providing a large amount of steric
protection.2 These neutral N-heterocyclic carbene (NHC) species
act as potent two electron s-donors, one of their principal areas of
utility being in catalysis3 where they can replace phosphines due
to their greater nucleophilicity and consequently their stronger
interactions with metal centres. One of their major attractions
in catalysis is that carbenes can be subtly tuned by modifying
the steric and electronic contributions of the N-bound organic
groups. NHCs have consequently been studied in conjunction with
virtually every metallic element of the periodic table.4 However,
NHC chemistry of the s-block metals, particularly the alkaline
earth metals, has seen much less attention than the transition
metals. The group of Arnold,5 amongst others,6 has made progress
in this territory by utilizing functionalized NHCs,7 which act as
polydentate donors to magnesium via both neutral s-donating
divalent carbon centre(s) and also anionic arm(s) lying pendant
reported.8 Smith et al. have also exploited a tris(carbene)borate
magnesium complex as a ligand transfer reagent.9 Pertinent to
this study, only a handful of simpler monodentate neutral Mg-
NHC complexes are known, which have generally been studied
from the point of view of developing the chemistry of carbenes
as opposed to using carbenes to advance alkaline earth metal
chemistry. Arduengo10 prepared a pair of carbene adducts of the
bis-alkyl Et2Mg; showing via single-crystal X-ray diffraction that
one of these adducts exists as a dimer in the solid-state (I, Fig. 1);
while a series of NHC stabilized dicyclopentadienyl group 2 metal
complexes have also been synthesised (II).11 A THF solvated
structure of MgCl2·NHC was also elucidated and recently reported
(III),12 while Roesky and Stalke recently divulged a bisalkynyl
magnesium carbene adduct as a dimer (IV).13 Hill has prepared
carbene adducts of M[N(SiMe3)2]2 (M = Mg, Ca, Sr, Ba)14 as
monomers (V) and subsequently has elegantly converted the Mg
derivative to a Mg4 hydride cluster (VI) which displays the highest
H : Mg ratio of any such hydride to date and is dependent on the
coordination of the NHC ligand for stability.14b
Given the scarcity of Mg carbene adducts in the literature, par-
ticularly heteroleptic Mg species containing two distinct anions,
coupled with our longstanding interest in s-block chemistry,15 we
decided to pursue a series of such adducts with mixed alkyl-amido
magnesium species. Thus we report herein the successful synthesis
and solid-state structures of two new alkyl-amido magnesium
carbene adducts. Further to this we shed some light on the
potential structure of nBu2Mg, an important utility bis-alkyl
magnesium reagent which has never before been characterized
WestCHEM, Department of Pure and Applied Chemistry, University
of Strathclyde, Glasgow, UK, G1 1XL. E-mail: r.e.mulvey@strath.ac.uk;
Fax: (+44)141-5520876
† Electronic supplementary information (ESI) available: Synthetic pro-
tocol, molecular structure and CIF file for [nBuMg(HMDS)]2 and
CIF files for 1–5. CCDC reference numbers 775962–775967. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c0dt00693a
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Fig. 1 Crystallography characterized carbene adducts of simple magnesium compounds.
crystallographically either in the absence or presence of a donor,
via identification of a novel carbene-stabilized modification
whereby a linear [nBu2Mg]4 fragment has been trapped by two
terminating carbene molecules. Finally, we also present the first
crystallographically characterized carbene adduct of a Grignard
(RMgCl) reagent as a dimer species containing a central planar
Mg2Cl2 ring.
to be recrystallized IPr. This apparent failure of the carbene
to coordinate to the electropositive metal was attributed to the
combined steric bulk of the tBu and TMP ligands preventing the
bulky carbene from gaining sufficient proximity. Consequently, we
next examined the slightly less bulky iPrMg(TMP). Unfortunately,
the crystalline product was again shown to be only IPr.
Results and discussion
(1)
Synthesis and solution studies of alkylamido magnesium carbene
adducts 1 and 2
We commenced our study by pursuing a carbene stabilized
alkyl magnesium amide adduct with the much studied utility
base 2,2,6,6-tetramethylpiperidide (TMP) as the amide. Specifi-
n
On moving to the linear Bu derivative of the alkyl Mg amide
(eqn (1)), a crop of crystals developed whose H and 13C NMR
1
t
cally, a sample of BuMg(TMP) was dissolved in a mixture of
spectra in C6D6 suggested that coordination of the carbene to the
alkaline earth metal had occurred to give complex 1. Specifically, in
the 1H NMR spectrum, the olefinic unit and the iPr methine group
resonated moderatelyupfieldcomparedtothoseinthe freecarbene
(6.49 and 2.82 ppm respectively; cf. 6.62 and 2.96 ppm in IPr)16
hexane and toluene and an equimolar amount of 1,3-bis-(2,6-
diisopropylphenyl)imidazol-2-ylidene [IPr: chosen due to its ease
of preparation and robustness of handling]16 was introduced. After
stirring, the clear, pale yellow solution was cooled to -30 ◦C. How-
ever, the crystals deposited were found by 1H NMR spectroscopy
n
as did the Mg-bound CH2 group of the Bu chain (-0.42 ppm,
9092 | Dalton Trans., 2010, 39, 9091–9099
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cf. 0.05 in [nBuMg(m-TMP)]2),17 while in the 13C NMR spectrum
the carbene carbon resonated at a frequency (189.7 ppm; cf .
220.6 ppm in IPr)16 typical for a coordinated carbene. This upfield
shift of the Mg-CH2 resonance has previously been attributed
to the placement of these methylene protons in the shielding
cone of the aromatic ring of the carbenes pendant arm, since
the adamantyl substituted derivative of I did not cause such a
starting material, suggesting that, unlike 1, 2 is not undergoing a
dynamic process in solution. As in the case of 1, the most indicative
resonances of a carbene adduct being formed were those of the
olefin, methine and Mg-CH2 functionalities (1H NMR spectrum)
and the carbene carbon (13C NMR spectrum) which resonated
at -0.33, 2.75, 6.40 and 187.0 ppm, respectively, all considerably
shielded with respect to those of the starting materials [Mg-CH2 of
[nBuMg(HMDS)]2 resonates at 0.05 ppm – ESI†] and are typical
of carbene coordination.
n
i
shift.10 While the combination of TMP, Bu and Pr resonances
1
made the aliphatic region of the H spectrum complicated, all
the hydrogen atoms in 1 could be assigned (see experimental
section for complete details). However, of particular interest in
these spectra were the presence of resonances attributable to both
free IPr and also free [nBuMg(TMP)]2, suggesting an equilibrium
between the two starting materials and the adduct 1 was taking
place (eqn (2)).
Solid state structures of 1 and 2
The molecular structures of the alkyl-amido magnesium carbene
adducts 1 and 2 were elucidated via single-crystal X-ray diffraction
and the results are displayed in Fig. 2 and 3, respectively while
pertinent bond parameters are supplied in Table 1. Table 2 contains
relevant crystallographic data.
(2)
As mentioned earlier, the overlap caused by the multiple
aliphatic resonances in the approximate range 0.95–2.00 ppm of
the 1H NMR spectrum meant that integration of these resonances
was futile. However, the resonances representing the olefinic,
iPr CH and Mg-CH2 fragments are sufficiently well separated
for integration to be effective. Consequently, these regions were
used to determine the relative amounts of each species in the
equilibrium. The sample was subsequently subjected to a variable
1
temperature H NMR study (in C7D8), the results of which are
displayed in Fig. S1 (ESI†). It initially appeared that as the
temperature was reduced, the equilibrium shifted to the right,
favouring the carbene adduct over the two starting materials
while at 260 K this equilibrium reversed and began to favour
the starting materials. However, when the variable temperature
study was repeated with a sealed insert containing ferrocene as an
integration standard, a depreciation in the relative amount of all
three components of the equilibrium was witnessed, particularly
of [nBuMg(TMP)]2, suggesting that the results of this study are
considerably altered by the precipitation of the alkyl magnesium
amide species.
n
Fig. 2 Molecular structure of BuMg(TMP)·IPr (1) with selected atom
labels. Hydrogen atoms are omitted for clarity and thermal ellipsoids are
displayed at the 50% probability level.
Next, we turned our attention to the carbene adduct of the
related alkyl magnesium amide BuMg(HMDS). For consistency
we utilized the nBu derivative, which to the best of our knowledge
has never been properly characterized. Its sBu isomer was reported
by Raston et al. in 1986 as a dimer in the solid state.18 This product
was formed in kinetic preference to the nBu isomer when the parent
amine HMDS(H) was reacted with an equimolar amount of the
s
mixed alkyl magnesium reagent BuMgnBu. Formed from a salt
metathesis reaction of tBuMgCl and NaHMDS, the tBu isomer is
also known to exist as a dimer.19 Our X-ray crystal study shows
n
that the Bu isomer, like the branched alkyl derivatives, is also a
dimer in the solid state with terminal alkyl chains and bridging
amido groups (see ESI Fig. S2 for full details†).
Stirring a solution of [nBuMg(HMDS)]2 in the presence of
◦
Fig. 3 Molecular structure of nBuMg(HMDS)·IPr (2) with selected atom
labels. Hydrogen atoms are omitted for clarity and thermal ellipsoids are
displayed at the 50% probability level.
IPr (eqn (1)) followed by cooling to -30 C, resulted in crystals
of 2. Upon dissolution in C6D6, this product displayed NMR
spectra consistent with a 1 : 1 adduct, with no evidence of either
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 1 and 2
1
2
1
2
C(1)–N(1)
C(1)–N(2)
Mg(1)–C(1)
Mg(1)–N(3)
Mg(1)–C(40)
1.360(2)
1.362(2)
2.254(2)
1.980(1)
2.126(2)
1.363(3)
1.366(3)
2.268(2)
1.995(2)
2.140(2)
N(1)–C(1)–N(2)
103.1(1)
125.4(1)
130.0(1)
125.35(6)
108.77(7)
125.87(4)
102.9(2)
127.3(2)
126.1(2)
125.6(1)
108.8(1)
125.6(1)
N(1)–C(1)–Mg(1)
N(2)–C(1)–Mg(1)
C(1)–Mg(1)–N(3)
C(1)–Mg(1)–C(40)
N(3)–Mg(1)–C(40)
Table 2 Crystallographic data and refinement details for compounds 1, 2, 3, 4, 5 and [nBuMg(HMDS)]2
1a
2
3
4
5
[nBuMg(HMDS)]2
Empirical formula
Mol. Mass
Crystal system
C40H63MgN3
610.24
Orthorhombic
Pna21
18.7980(8)
11.7552(5)
17.4673(7)
90
90
90
3859.8(3)
4
0.71073
16 084
C37H63MgN3Si2
630.39
Monoclinic
C39H63AlN2
586.89
C86H144Mg4N4
1331.29
Monoclinic
P21/n
17.5342(11)
13.7504(8)
17.7758(12)
90
91.904(6)
90
4283.4(5)
2
C62H90Cl2Mg2N4
1010.90
Monoclinic
P21/n
12.5268(3)
14.3634(5)
35.1522(11)
90
97.089(2)
90
6276.5(3)
4
0.71073
36 444
12 334
0.0522
7550
C20H54Mg2N2Si4
483.63
Monoclinic
Triclinic
¯
Space group
P21/c
P1
C2/c
˚
a [A]
18.5673(8)
11.0931(4)
19.6693(9)
90
9.5150(5)
10.4747(4)
19.0528(8)
97.775(3)
97.597(4)
93.331(4)
1859.37(14)
2
16.3833(5)
11.1092(3)
17.1805(5)
90
˚
b [A]
˚
c [A]
a [◦]
b [◦]
g [◦]
99.065(4)
90
4000.7(3)
4
0.71073
41 501
9642
0.0857
4962
0.949
92.001(3)
90
3125.04(16)
4
0.71073
11 966
4261
0.0264
3413
1.075
3
˚
V [A ]
Z
˚
l [A]
0.71073
16 290
8474
0.0519
4024
1.5418
Measured reflections
Unique reflections
Rint
Observed rflns [I>2s(I)]
GooF
21 729b
7556
0.0333
5867
21 729b
11576
0.882
0.928
0.832
1.096
R [on F, obs rflns only]
wR [on F2,all data]
0.0396
0.0837
0.259/-0.204
0.0652
0.1255
0.496/-0.290
0.0545
0.0907
0.253/-0.274
0.0638
0.1760
0.401/-0.294
0.0700
0.2065
0.649/-0.699
0.0466
0.1224
0.694/-0.268
-3
˚
Largest diff. peak/hole [e A ]
a Flack parameter refined to 0.35(12). b Total number of entries in HKLF 5 format dataset for a two component twin (rotation by 180◦ about 1 0 0).
As can be seen from these figures, the coordination of the
carbene molecule to the Mg centre has broken up the dimeric
alkyl magnesium amide species to generate a monomeric 1 : 1
adduct, consistent with the NMR data (vide supra). This results in
a three-coordinate distorted trigonal planar metal centre (R∠Mg =
359.99◦ 1; 360.00◦ 2). To alleviate steric strain, the amides and the
carbene rings lie perpendicular to the plane defined by the trigonal
planar MgL3 unit. The plane of the carbene C3N2 ring lies at
89.10(7)◦ and 86.99(9)◦ to the C(1)–Mg(1)–C(40)–N(3) plane in
1 and 2, respectively, while the plane generated by the NR2 unit
of the amide lies at 83.38(8)◦ and 86.32(7)◦ to the C(1)–Mg(1)–
C(40)–N(3) plane in each case. The perpendicular relationships are
facilitated by the lack of bulk associated with the linear alkyl ligand
since these angles are considerably larger than the corresponding
angles in the bulkier symmetric complex (HMDS)2Mg·IPr (V)
which are 50.64(5)◦ and 79.06(4)◦, respectively.14b
alkylmagnesium amides [average Mg–N distances in the starting
17
˚
˚
materials are 2.119 A and 2.110 A, respectively]. Unsurprisingly
the terminal nature of the Mg–C bonds in both dimer and carbene
adduct species means the Mg–C distances are almost identical.
Complexes 1 and 2 represent rare examples of a three-coordinate
Mg monomer of type Mg(L-)2·donor and are indeed the first such
alkylamido derivatives.20
Synthesis and solid state structure of bisalkyl magnesium carbene
adduct 4
Having successfully characterized a pair of alkyl-amido magne-
sium carbene adducts, we moved our attention to the carbene
adduct of the related utility bis-alkyl magnesium species nBu2Mg.
The synthesis of a similar 1 : 1 adduct appeared straight forward.
Specifically, equimolar amounts of the two reagents were gently
heated in hexane with stirring. The resulting crystalline product
(3), which was formed in poor yield even after cooling to -70 ◦C,
was subjected to analysis both in solution and in the solid state. Its
1H and 13C NMR spectra both displayed all the peaks expected for
a coordinated IPr molecule (olefin and iPr methine peaks at 6.41
˚
The Ccarbene–Mg distances in each case [1, 2.254(2) A; 2,
˚
2.268(2) A] are consistent with those witnessed in other such
magnesium carbene adducts and are marginally shorter than
˚
in the bisamidomagnesium derivative V [2.276(2) A], the closer
proximity of the bulky carbene to the metal may again reflect the
lower steric bulk of the linear nBu ligand. The monomeric nature
of the alkyl magnesium amide fragment in 1 and 2 results in a
n
and 2.74 ppm) and a Bu group (M–CH2: -0.35 ppm), however,
the integration of these peaks suggested that three nBu groups were
present per molecule of IPr. To our surprise, rather than being a
trimeric [nBu2Mg]3 fragment with a capping carbene molecule at
either end the solid state structure showed this to be a monomeric
˚
significant shortening of the Mg–N bond length [1.980(2) A and
˚
1.995(2) A, respectively] since this nitrogen centre is no longer
bridging two electropositive metals as is the case in the parent
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112.65(8)◦ and the Calkyl–Al–Calkyl angles in the slightly narrower
range 107.57(8)–113.37(9)◦. The Ccarbene–Al distance [2.118(2)
˚
A] is noticeably longer than the Calkyl–Al distances [average
˚
1.993 A]. The Ccarbene–Al distance is consistent with that of the
only other crystallographically characterized trialkyl aluminium
adduct, that of Me3Al·carbene (carbene = 1,3-diisopropyl-4,5-
dimethylimidazol-2-ylidene) reported by Robinson et al. in 1996
23
˚
[2.124(6) A]. However, while the average Calkyl–Al bond length
˚
of 3 is similar to that in Robinson’s structure [2.001 A], the
methyl derivative shows a much wider range in such bond lengths
˚
[1.940(5)–2.062(7) A]. In both cases, these bonds are longer
than those of the only other carbene stabilized AlC3 monomer,
namely the trisalkynyl (tBuCC)3Al·carbene (carbene = 1,3,4,5-
24
˚
tetramethylimidazol-2-ylidine) [average = 1.941 A].
As a consequence of this unexpected complication, we decided
n
to prepare our own Bu2Mg in situ and react it with IPr. For
n
this preparation, a solution of BuMgCl was slowly added to a
stirring suspension of BuNa in hexane at 0 ◦C. After stirring
n
Fig. 4 Molecular structure of adventitious nBu3Al·IPr (3) with se-
lected atom labels. Hydrogen atoms are omitted for clarity and
thermal ellipsoids are displayed at◦ the 50% probability level. Se-
overnight, this solution was filtered through Celite to remove
precipitated NaCl and then an equimolar amount of IPr was
introduced. The crude product obtained gave a 1H NMR spectrum
which displayed both coordinated and uncoordinated IPr in a 1 : 1
ratio. Broad resonances were witnessed for hydrogen atoms of
the Bu groups, with two resonances in the negative region of
the spectrum at -0.1 and -0.6 ppm, with a relative integration
of 1 : 3, suggesting that two different Mg–CH2 environments (and
thus at least two distinct Bu groups) are present. Interestingly,
complete integration suggested a total of four Bu groups per
carbene molecule. Matching this stoichiometry, this reaction was
therefore repeated but with only half as much IPr added (eqn
(3)). The recrystallised product (4) gave a H NMR spectrum
˚
lected bond lengths (A) and angles ( ): C(1)–N(1) 1.364(2), C(1)–N(2)
1.373(2), Al(1)–C(1) 2.118(2), Al(1)–C(30) 1.993(2), Al(1)–C(40) 1.990(2),
Al(1)–C(50) 1.996(2); N(1)–C(1)–N(2) 102.4(1), N(1)–C(1)–Al(1) 127.5(1),
N(2)–C(1)–Al(1) 129.6(1), C(1)–Al(1)–C(30) 109.42(7), C(1)–Al(1)–C(40)
101.59(8), C(1)–Al(1)–C(50) 112.65(8), C(30)–Al(1)–C(40) 113.37(9),
C(30)–Al(1)–C(50) 107.57(8), C(40)–Al(1)–C(50) 112.24(9).
n
n
n
adduct with three nBu groups bound to the metal centre (Fig. 4).
We initially postulated that this species was in fact a contacted ion
pair imidazolium salt of formula [IPr(H)]+[nBu3Mg]-. However,
we could not find a satisfactory location for the extra proton
on the carbene. The two most likely locations would be on the
‘carbene’ carbon or on the olefinic backbone; however, the solid
state structure clearly shows that the ‘carbene’ carbon is trigonal
planar (sp2) and the NMR spectra suggested the carbene moiety
is symmetric which would not be the case if the olefinic fragment
was carrying an extra proton. The most reasonable explanation
for this was that we had not actually formed a magnesium
compound at all, but an aluminium nBu3Al carbene adduct. Such a
hypothesis was supported by the metal–carbene bond, which was
1
consistent with that previously seen, with the olefin and methine
functionalities of the coordinated IPr molecule resonating at 6.37
and 2.81 ppm respectively. The molecular structure of 4 (Fig. 5)
was elucidated by X-ray crystallography which showed it to be
a centrosymmetric linear tetranuclear arrangement of nBu2Mg
n
molecules with bridging Bu groups, capped at either end with
a combination of IPr and terminal nBu groups.
˚
noticeably shorter [2.118(2) A] than any previously determined
Mg–carbene interaction. We subsequently confirmed this was the
n
case by preparing an authentic sample of Bu3Al·IPr from the
(3)
analogous reaction of the tris-alkyl aluminium reagent with the
parent carbene. A comparison of NMR spectra and unit cell
parameters from X-ray crystallographic data confirmed that 3 was
indeed nBu3Al·IPr. On inspection of the commercially purchased
“nBu2Mg”, we found that it contains ~5–10% Et3Al as a stabilising
agent. It would therefore appear that alkyl exchange has occurred
between the Al and Mg species, with the Al species being ‘trapped’
by the carbene, presumably due to the larger charge-density on the
formally Al3+ trication. The Al species is then simply obtained by
preferential crystallization. The poor yield mentioned earlier is
attributable to the small amount of tris-alkyl aluminium present
with respect to the bis-alkyl magnesium in solution.
This unexpected structure provides a rationale for the broad
nBu resonances in the H NMR spectrum since three chemically
1
and magnetically inequivalent nBu groups are present as shown in
Fig. 6. As mentioned earlier, the Mg-CH2 resonances appear at
-0.1 and -0.6 ppm in a 1 : 3 ratio. While it would be tempting to
assign the major Mg-CH2 resonance (-0.6 ppm) to the bridging
butyl groups (that is Bub + Buc) and the minor resonance
(-0.1 ppm) to the terminal butyl group (Bua), we surmise that
the major resonance belongs to Bua and Bub (i.e. those which
lie only two bonds from the carbene) while the minor resonance
The solid state structure of 3 represents a rare example of an
aluminium carbene adduct (the majority of which are tri-hydride21
or tri-halide12,22 derivatives) and shows a distorted tetrahedral AlC4
centre with the Ccarbene–Al–Calkyl angles lying in the range 101.59(8)–
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those of other10 alkyl magnesium carbene adducts (vide supra).
Of the Mg-alkyl bond distances, the Mg(1)–C(40) bond (i.e. the
˚
terminal alkyl group) is unsurprisingly the shortest [2.143(3) A].
Of the bridging alkyl-Mg bonds, there is a slight disparity in the
bond distances. The longest are those attached to the carbene-
˚
bound magnesium centre [Mg(1)–C(30) 2.303(3) A; Mg(1)–C(50)
˚
2.342(2) A], the elongation being a consequence of both electronic
(electron donation from the carbene results in a marginally less
electropositive Mg centre) and steric (the bulk of the carbene)
reasons. The cumulative effect of this is seen in the Mg(2)–C(30)
˚
˚
[2.229(3) A] and Mg(2)–C(50) [2.207(3) A] bonds, which are
˚
noticeably shorter. Finally, the internal Mg(2)–C(60) [2.250(3) A]
and Mg(2)–C(60A) [2.290(3) A] bonds are intermediate between
˚
these two extremes and are closer to a typical Mg–Cbridging bond
length such as those witnessed in dimeric [tBu2Mg]2 whose Mg–
29
Fig.
5
Molecular structure of [nBu2Mg]4·2IPr (4) with selected
˚
atom labels. Hydrogen atoms are omitted for clarity and ther-
mal ellipsoids are displayed at the 50% probability level. Sym-
metry transformations used to generate equivalent atoms: 2 - x,
Cbridging bond lengths display an average of 2.3016 A.
Having ‘trapped’ a tetranuclear fragment of presumably poly-
meric nBu2Mg, the ratio of starting materials was altered to 1 : 4 in
anattempttoobtainalonger bis-alkylmagnesium chain. However,
y, -z. Selected bond lengths (A) and angles (◦): C(1)–N(1)
˚
2
-
1.372(3), C(1)–N(2) 1.367(3), Mg(1)–C(1) 2.285(2), Mg(1)–C(30) 2.303(3),
Mg(1)–C(40) 2.143(3), Mg(1)–C(50) 2.342(2), Mg(2)–C(30) 2.229(3),
Mg(2)–C(50) 2.207(3), Mg(2)–C(60) 2.250(3), Mg(2)–C(60A) 2.290(3);
N(1)–C(1)–N(2) 103.1(2), N(1)–C(1)–Mg(1) 128.5(2), N(2)–C(1)–Mg(1)
128.3(2), C(1)–Mg(1)–C(30) 103.1(1), C(1)–Mg(1)–C(40) 117.0(1),
C(1)–Mg(1)–C(50) 107.0(1), C(30)–Mg(1)–C(40) 115.3(1), C(30)–
Mg(1)–C(50) 107.0(1), C(40)–Mg(1)–C(50) 111.6(1), Mg(1)–C(30)–Mg(2)
74.3(1), Mg(1)–C(50)–Mg(2) 73.9(1), C(30)–Mg(2)–C(50) 108.1(1),
C(30)–Mg(2)–C(60) 113.7(1), C(30)–Mg(2)–C(60A) 103.7(1), C(50)–
Mg(2)–C(60) 108.7(1), C(50)–Mg(2)–C(60A) 116.9(1), C(60)–Mg(2)–
C(60A) 105.9(1), Mg(2)–C(60)–Mg(2A) 74.1(1).
1
the resulting product was shown by H NMR spectroscopy and
comparison of its unit cell parameters to indeed be 4, suggesting
that this tetranuclear structure is produced regardless of the ratio
of the starting materials.
Since there appears to be no steric reason why a 1 : 1 carbene
n
adduct of Bu2Mg cannot exist; either as a monomer such as 1
or 2, or a dimer such as the ethyl derivative I; we propose that
the oligomeric form of 4 occurs predominantly as a consequence
of electronic factors. An attempt was therefore made to prepare
a 1 : 1 adduct via an alternative pathway, namely by preparing a
1 : 1 carbene adduct of the related Grignard reagent nBuMgCl (5)
and then replacing the chloride anion with another nBu group via
a simple salt metathesis using nBuLi according to eqn (3).
The intermediate Grignard adduct 5 was isolated as large
crystals upon slowly cooling to room temperature of a warmed
hexane solution containing an equimolar amount of nBuMgCl and
IPr. As in the case of the previously discussed Mg carbene adducts,
Fig. 6 Structure of 4 showing its distinct types of Bu ligand.
represents Buc which lies four bonds away from the carbene since
an upfield shift is typical for a Mg-alkyl group upon coordination
of a donor such as a carbene to the adjacent metal centre (vide
supra).
the principal resonances of interest in the H NMR spectrum
1
were those of the olefin (6.42 ppm) and methine (2.83 ppm)
functionalities of the carbene and the metal bound CH2 fragment
(-0.62 ppm), while the carbene carbon resonated at 188.1 ppm in
the 13C spectrum. There was no evidence of uncoordinated IPr.
Integration of the butyl resonances with respect to those of the
carbene indicated that one nBu group was present per carbene. One
of the resonances representing another CH2 of the nBu group could
not be resolved in the 1H spectrum, however a HSQC experiment
confirmed that it was present and was in fact hidden under one
This structure represents the first crystallographically charac-
terized example of this important utility bis-alkyl magnesium
species, the closest structure obtained thus far being TMEDA
solvated sBu2Mg, which crystallized preferentially from a solution
of ‘Bu2Mg’ containing both nBu and sBu ligands.25 Other similar
examples include a dioxane bridged polymer of neoPe2Mg,26 a pair
of nBu2Mg structures co-complexed with MOtBu/TMEDA (M =
Na, K)27 and dianionic [MgnBu4]2- with DABCO bridged sodium
cations [DABCO = diazabicyclo(2,2,2)octane].28 The tetranuclear
spirocyclic structure (4) shows two distinct Mg environments,
both of which are distorted tetrahedral. The first [Mg(1)] has two
i
of the doublets representing a methyl group of the carbene Pr
arm.
The 1 : 1 nature of this product was confirmed via its molecular
structure (Fig. 7) which showed that in this case the Grignard
reagent dimerizes with its chloride anions in the bridging position,
resulting in a pair of four-coordinate distorted tetrahedral mag-
nesium centres and a central four-membered Mg2Cl2 ring. Due
to disorder in the organic periphery of this non-centrosymmetric
structure a detailed description of its bond parameters is unwar-
ranted. The structure does however show that the Mg2Cl2 ring is
planar, with the Mg centres displaying distorted tetrahedral geom-
etry. The C3N2 ring of the heterocyclic carbene lies approximately
coplanar with the plane of the two chlorine anions, resulting in
n
bridging and one terminal Bu group with one carbene carbon
completing the coordination sphere [range 103.1(1)–117.0(1)◦]
n
while the second [Mg(2)] simply has four bridging Bu groups
attached [range 103.7(1)–116.9(1)◦]. The central Mg2C2 ring is
planar (R = 360.0◦) while the outer rings are slightly distorted
from planarity (R = 363.4◦), probably as a consequence of the
coordination of the bulky carbene to one of the Mg centres. The
˚
carbene–magnesium bond distance [2.285(2) A] is consistent with
9096 | Dalton Trans., 2010, 39, 9091–9099
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Experimental section
General
All reactions and manipulations were carried out under a protec-
tive argon atmosphere using either standard Schlenk techniques
or a glove box. All solvents were dried over Na/benzophenone
and freshly distilled prior to use. IPr16 and [nBuMg(TMP)]217 were
prepared according to literature methods. nBu2Mg and nBuMgCl
n
were purchased from Aldrich and used as received while Bu3Al
1
was purchased from Alfa-Aesar and used as received. H and
13C NMR spectra were recorded on a Bruker AV400 MHz
1
spectrometer (operating at 400.03 MHz for H and 100.58 MHz
for 13C). All 13C NMR spectra were proton decoupled. Satisfactory
elemental analyses could not be obtained due to the sensitive
1
nature of the compounds, evidence of purity is provided via H
NMR spectra (see Fig. S3–S7 in the ESI† and below for full
assignments).
Fig. 7 Molecular structure of [nBuMgCl·IPr]2 (5) with selected atom
labels. Hydrogen atoms are omitted for clarity and thermal ellipsoids are
displayed at the 50% probability level. This structure is disordered over
one of the nBu groups and the carbene ligands, but only one component is
shown.
Synthesis of nBuMg(TMP)·IPr (1)
Hexane (5 mL) was added via syringe to a mixture of nBuMg(TMP)
(0.111 g, 0.5 mmol) and IPr (0.194 g, 0.5 mmol). Toluene was then
added dropwise, with sonication, until a homogeneous solution
was obtained. This was cooled to -30 ◦C where colourless
crystals (0.171 g, 56%) developed. 1H NMR (400.13 MHz, C6D6,
the bulky 2,6-diisopropylphenyl groups protecting these otherwise
exposed anions by provide steric shielding above and below
them.
2
n
300 K): -0.42 (t, 2H, JH,H = 8 Hz, Mg–CH2), 0.97 (s, 12H,
The metathetical reaction of 5 with BuLi (eqn (3)) was then
2
TMP Me), 0.98 (d, 12H, JH,H = 7 Hz, CHMe2) 1.21 (t, 9H,
carried out in hexane at room temperature. A white precipitate,
presumably LiCl, was noticed as soon as the alkyl lithium reagent
was added. This was filtered and the resulting solution was
cooled to -30 ◦C to precipitate crystals which were shown by
NMR spectroscopy and X-ray diffraction to be the previously
discussed 4 suggesting that the metathesis reaction to form putative
monomeric “nBu2Mg·IPr” has taken place with oligomerization
and loss of some IPr ligand to generate the tetranuclear magnesium
chain species 4.
2JH,H = 7 Hz, CH2CH2CH3), 1.44 (d, 12H, 2JH,H = 7 Hz, CHMe2)
[b CH2 (TMP) hidden under this (shown by HSQC) – integral
2
actually adds up to 16 (12 + 4)], 1.73 (sex, 2H, JH,H = 7 Hz,
CH2CH2CH3), 1.89 (m, 4H, CH2CH2CH3 and TMP g CH2), 2.82
2
(sept, 4H, JH,H = 7 Hz, CHMe2), 6.49 (s, 2H, olefin), 7.11 (d,
4H, 2JH,H = 8 Hz, meta CH), 7.21 (t, 2H, 2JH,H = 8 Hz, para CH).
1
13C{ H} NMR (100.58 MHz, C6D6, 300 K): 11.8 (Mg–CH2), 14.5
(CH2CH2CH3), 20.8 (g CH2 TMP), 23.4 (CHMe2), 25.8 (CHMe2),
28.8 (CHMe2), 32.3 (CH2CH2CH3), 33.6 (CH2CH2CH3), 34.2
(TMP Me), 40.7 (b CH2 TMP), 51.6 (a C TMP), 123.7 (olefin),
124.4 (meta CH), 130.7 (para CH), 135.7 (ipso), 146.1 (ortho), 189.7
(carbene).
Conclusion
This study has considerably expanded upon the limited previous
reports of magnesium carbene adducts, principally through the
preparation of a pair of monomeric alkylmagnesium amide
complexes with a carbene donor. We have also, to the best of
our knowledge, established a new application for N-heterocyclic
carbenes, namely as trapping agents for oligomeric fragments of
organometallic polymers30 that, by extrapolation, could provide
valuable insight into the numerous unknown structures of solvent-
free organo-s-block (especially important lithium and magnesium)
compounds, many of which are suspected of being polymeric
but which remain to be structurally elucidated. Further to this
we have characterized for the first time a carbene stabilized
Grignard reagent and also revealed a potential problem in
organomagnesium chemistry; that is the potential of aluminium
containing compounds, used as stabilizing agents in commer-
cial organomagnesium samples, to preferentially react and give
unusual or unexpected results which cannot be conventionally
explained.
Synthesis of nBuMg(HMDS)·IPr (2)
This complex was prepared using the same method as described
n
above for 1 using BuMg(HMDS) (0.121 g, 0.5 mmol) in place
of BuMg(TMP). This was cooled to -70 ◦C to give a crop of
n
colourless crystals (0.236 g, 75%). 1H NMR (400.13 MHz, C6D6,
300 K): -0.33 (t, 2H, 2JH,H = 8 Hz, Mg–CH2), 0.01 (s, 18H, SiMe3),
2
2
0.97 (d, 12H, JH,H = 7 Hz, CHMe2), 1.20 (t, 3H, JH,H = 7 Hz,
2
CH2CH2CH3), 1.41 (d, 12H, JH,H = 7 Hz, CHMe2), 1.70 (sex,
2
2
2H, JH,H = 7 Hz, CH2CH2CH3), 1.89 (quin, 2H, JH,H = 8 Hz,
2
CH2CH2CH3), 2.75 (sept, 4H, JH,H = 7 Hz, CHMe2), 6.40 (s,
2
2H, olefin), 7.10 (d, 4H, JH,H = 8 Hz, meta CH), 7.21 (t, 2H,
1
2JH,H = 8 Hz, para CH). 13C{ H} NMR (100.58 MHz, C6D6,
300 K): 4.8 (SiMe3), 10.7 (Mg–CH2), 14.3 (CH2CH2CH3), 23.4
(CHMe2), 25.3 (CHMe2), 28.6 (CHMe2), 31.8 (CH2CH2CH3), 32.8
(CH2CH2CH3), 124.0 (olefin), 124.5 (meta CH), 130.8 (para CH),
135.3 (ipso), 145.8 (ortho), 187.0 (carbene).
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Synthesis of nBu3Al·IPr (3)
against F2 and all independent reflections by the full-matrix
least-squares method using the SHELXL-97 program.31 Selected
crystallographic and refinement parameters are given in Table
2. CCDC 775962–775967 contain the supplementary crystallo-
graphic data for this paper.†
nBu3Al (0.5 mL, 0.7M in heptane, 0.35 mmol) was added via
syringe to a suspension of IPr (0.136 g, 0.35 mmol) to yield a
white suspension. Toluene was added dropwise with stirring until
homogeneous. Upon cooling to -30 ◦C a crop of colourless crystals
developed (0.144 g, 70%). 1H NMR (400.13 MHz, C6D6, 300 K):
2
2
Acknowledgements
-0.35 (t, 6H, JH,H = 8 Hz, Al–CH2), 0.96 (d, 12H, JH,H = 7 Hz,
2
CHMe2), 1.03 (t, 9H, JH,H = 7 Hz CH2CH2CH3), 1.43 (d, 12H,
We would like to thank the UK EPSRC (through grant awards
EP/F063733/1 and EP/D076889/1) and the Royal Society
(through a Wolfson merit award to R.E.M.).
2JH,H = 7 Hz, CHMe2), 1.49 (m, 12H, CH2CH2CH3) 2.74 (sept,
2
4H, JH,H = 7 Hz, CHMe2), 6.41 (s, 2H, olefin), 7.13 (d, 4H,
2JH,H = 8 Hz, meta CH), 7.26 (t, 2H, JH,H = 8 Hz, para CH).
2
1
13C{ H} NMR (100.58 MHz, C6D6, 300 K): 10.5 (Al–CH2), 14.4
(CH2CH2CH3), 22.7 (CHMe2), 26.0 (CHMe2), 28.9 (CHMe2),
30.4 (CH2CH2CH3), 124.1 (meta CH), 124.5 (olefin), 130.7 (para
CH), 135.7 (ipso), 145.9 (ortho), 191.0 (carbene).
References
1 For a excellent review of the pursuit of the first stable NHC see: F. E.
Hahn and M. C. Jahnke, Angew. Chem., Int. Ed., 2008, 47, 3122–3172.
2 A. J. Arduengo III, R. L. Harlow and M. Kline, J. Am. Chem. Soc.,
1991, 113, 361–363.
3 (a) S. Diez-Gonza´lez, N. Marion and S. P. Nolan, Chem. Rev., 2009,
109, 3612–3676; (b) X. Bantreil, J. Broggi and S. P. Nolan, Annu. Rep.
Prog. Chem., Sect. B: Org. Chem., 2009, 105, 232–263.
Synthesis of nBu8Mg4·2IPr (4)
nBuMgCl (0.5 mL, 2M in Et2O, 1 mmol) was added via syringe
to a suspension of nBuNa (0.080 g, 1 mmol) in hexane (5 mL) at
4 D. Bourissou, O. Guerret, F. P. Gabba¨ı and G. Bertrand, Chem. Rev.,
2000, 100, 39–91.
0
◦C. After stirring overnight, this mixture was filtered through
5 (a) S. A. Mungur, S. T. Liddle, C. Wilson, M. J. Sarsfield and P.
L. Arnold, Chem. Commun., 2004, 2738–2739; (b) P. L. Arnold, I.
S. Edworthy, C. D. Carmichael, A. J. Blake and C. Wilson, Dalton
Trans., 2008, 3739–3746; (c) P. L. Arnold, I. J. Casely, Z. R. Turner, R.
Bellabarba and R. B. Tooze, Dalton Trans., 2009, 7236–7247.
6 D. Zhang and H. Kawaguchi, Organometallics, 2006, 25, 5506–5509.
7 O. Ku¨hl, Chem. Soc. Rev., 2007, 36, 592–607.
Celite to remove NaCl and washed with more hexane (2 ¥ 5 mL).
IPr (0.194 g, 0.5 mmol) was added from a solid addition tube and
stirred. Toluene was added dropwise until a homogeneous solution
was obtained and this was cooled to -30 ◦C to precipitate a crop of
colourless crystals. (0.283 g, 85%). 1H NMR (400.13 MHz, C6D6,
300 K): -0.6 (br, 24H, Mg–CH2 ¥ 6), -0.1 (br, 4H, Mg–CH2 ¥ 2),
0.98 (d, 12H, 2JH,H = 7 Hz, CHMe2), 1.1 (br, 24H, CH2CH2CH3 ¥
8 O. Jackowski and A. Alexakis, Angew. Chem., Int. Ed., 2010, 49, 3346–
3350.
2
9 I. Nieto, F. Cervantes-Lee and J. M. Smith, Chem. Commun., 2005,
3811–3813.
8), 1.44 (d, 24H, JH,H = 7 Hz, CHMe2), 1.7 (br, 32H,
CH2CH2CH3 ¥ 8), 2.81 (sept, 8H, 2JH,H = 7 Hz, CHMe2), 6.37 (s,
10 A. J. Arduengo III, H. V. R. Dias, F. Davidson and R. L. Harlow, J.
4H, olefin), 7.13 (d, 8H, 2JH,H = 8 Hz, meta CH), 7.26 (t, 4H, 2JH,H
=
Organomet. Chem., 1993, 462, 13–18.
1
8 Hz, para CH). 13C{ H} NMR (100.58 MHz, C6D6, 300 K): 10.2
(Mg–CH2), 14.5 (CH2CH2CH3), 23.5 (CHMe2), 25.7 (CHMe2),
28.8 (CHMe2), 32.0 (CH2CH2CH3), 124.1 (olefin), 124.4 (meta
CH), 130.7 (para CH), 136.1 (ipso), 145.8 (ortho), 197.3 (carbene).
11 (a) A. J. Arduengo III, F. Davidson, R. Krafczyk, W. J. Marshall and
M. Tamm, Organometallics, 1998, 17, 3375–3382; (b) H. Schumann, J.
Gottfriedsen, M. Glanz, S. Dechert and J. Demtschuk, J. Organomet.
Chem., 2001, 617–618, 588–600.
12 B. Bantu, G. M. Pawar, K. Wurst, U. Decker, A. M. Schmidt and M.
R. Buchmeiser, Eur. J. Inorg. Chem., 2009, 1970–1976.
13 A. Stasch, S. P. Sarish, H. W. Roesky, K. Meindl, F. Dall’Antonia, T.
Schulz and D. Stalke, Chem.–Asian J., 2009, 4, 1451–1457.
14 (a) A. G. M. Barrett, M. R. Crimmin, M. S. Hill, G. Kociok-Ko¨hn, D.
J. MacDougall, M. F. Mahon and P. A. Procopiou, Organometallics,
2008, 27, 3939–3946; (b) M. Arrowsmith, M. S. Hill, D. J. MacDougall
and M. F. Mahon, Angew. Chem., Int. Ed., 2009, 48, 4013–4016.
15 (a) R. Forret, A. R. Kennedy, J. Klett, R. E. Mulvey and S. D.
Robertson, Organometallics, 2010, 29, 1436–1442; (b) W. Clegg, B.
Synthesis of nBuMgCl·IPr (5)
nBuMgCl (0.25 mL, 2M in Et2O, 0.5 mmol) was added via syringe
to a suspension of IPr (0.194 g, 0.5 mmol) in hexane (5 mL). This
initially gave a clear solution until a white precipitate formed after
2 min of stirring. The suspension was heated until homogeneous
and slowly cooled to room temperature overnight in a Dewar flask
of hot water to yield a crop of colourless crystals (0.187 g, 74%).
1H NMR (400.13 MHz, C6D6, 300 K): -0.62 (t, 2H, 2JH,H = 9 Hz,
´
Conway, P. Garc´ıa-Alvarez, A. R. Kennedy, R. E. Mulvey, L. Russo, J.
Saßmannshausen and T. Tuttle, Chem.–Eur. J., 2009, 15, 10702–10706;
´
(c) J. Garc´ıa-Alvarez, D. V. Graham, E. Hevia, A. R. Kennedy and R.
E. Mulvey, Dalton Trans., 2008, 1481–1486.
Mg–CH2), 0.98 (d, 12H, 2JH,H = 7 Hz, CHMe2), 1.24 (t, 3H, 2JH,H
=
16 A. J. Arduengo III, R. Krafczyk, R. Schmutzler, H. A. Craig, J. R.
Goerlich, W. J. Marshall and M. Unverzagt, Tetrahedron, 1999, 55,
14523–14534.
7 Hz CH2CH2CH3), 1.46 (d, 12H, 2JH,H = 7 Hz, CHMe2), 1.46 (m,
2H, CH2CH2CH3) 1.59 (sex, 2H, CH2CH2CH3), 2.83 (sept, 4H,
2JH,H = 7 Hz, CHMe2), 6.42 (s, 2H, olefin), 7.13 (d, 4H, 2JH,H = 7 Hz,
17 E. Hevia, A. R. Kennedy, R. E. Mulvey and S. Weatherstone, Angew.
Chem., Int. Ed., 2004, 43, 1709–1712.
2
1
meta CH), 7.26 (t, 2H, JH,H = 7 Hz, para CH). 13C{ H} NMR
(100.58 MHz, C6D6, 300 K): 10.3 (Mg–CH2), 14.8 (CH2CH2CH3),
23.2 (CHMe2), 25.8 (CHMe2), 28.8 (CHMe2), 32.7
(CH2CH2CH3), 33.1 (CH2CH2CH3), 123.9 (olefin), 124.1 (meta
CH), 130.3 (para CH), 135.8 (ipso), 145.8 (ortho), 188.1 (carbene).
18 L. M. Englehart, B. S. Jolly, P. C. Junk, C. L. Raston, B. W. Skelton
and A. H. White, Aust. J. Chem., 1986, 39, 1337–1345.
19 B. Conway, E. Hevia, A. R. Kennedy, R. E. Mulvey and S. Weather-
stone, Dalton Trans., 2005, 1532–1544.
20 (a) A. R. Kennedy, R. E. Mulvey and J. H. Schulte, Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun., 2001, 57, 1288–1289; (b) A. C. Avent,
C. F. Caro, P. B. Hitchcock, M. F. Lappert, Z. Li and X.-H. Wei, Dalton
Trans., 2004, 1567–1577; (c) X. He, J. J. Morris, B. C. Noll, S. N. Brown
and K. W. Henderson, J. Am. Chem. Soc., 2006, 128, 13599–13610.
21 (a) A. J. Arduengo III, H. V. R. Dias, J. C. Calabrese and F. Davidson, J.
Am. Chem. Soc., 1992, 114, 9724–9725; (b) R. J. Baker, A. J. Davies, C.
Jones and M. Kloth, J. Organomet. Chem., 2002, 656, 203–210; (c) R.
X-Ray diffraction data
Crystallographic data was collected at 123(2) K on Oxford
Diffraction instruments. Structures were refined to convergence
9098 | Dalton Trans., 2010, 39, 9091–9099
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The Royal Society of Chemistry 2010
©

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J. Baker, M. L. Cole, C. Jones and M. F. Mahon, J. Chem. Soc., Dalton
Trans., 2002, 1992–1996.
22 (a) A. Stasch, S. Singh, H. W. Roesky, M. Noltemeyer and H.-G.
Schmidt, Eur. J. Inorg. Chem., 2004, 4052–4055; (b) R. S. Ghadwal,
H. W. Roesky, R. Herbst-Irmer and P. G. Jones, Z. Anorg. Allg. Chem.,
2009, 635, 431–433.
23 X.-W. Li, J. Su and G. H. Robinson, Chem. Commun., 1996, 2683–2684.
24 M. Schiefer, N. D. Reddy, H.-J. Ahn, A. Stasch, H. W. Roesky, A.
C. Schlicker, H.-G. Schmidt, M. Noltemeyer and D. Vidovic, Inorg.
Chem., 2003, 42, 4970–4976.
26 M. Parvez, A. D. Pajerski and H. G. Richey Jr., Acta Crystallogr., Sect.
C: Cryst. Struct. Commun., 1988, 44, 1212–1215.
27 N. D. R. Barnett, W. Clegg, A. R. Kennedy, R. E. Mulvey and S.
Weatherstone, Chem. Commun., 2005, 375–377.
28 P. C. Andrikopoulos, D. R. Armstrong, E. Hevia, A. R. Kennedy, R.
E. Mulvey and C. T. O’Hara, Chem. Commun., 2005, 1131–1133.
29 K. B. Starowieyski, J. Lewinski, R. Wozniak, J. Lipkowski and A.
Chrost, Organometallics, 2003, 22, 2458–2463.
30 W. Clegg, S. T. Liddle, R. E. Mulvey and A. Robertson, Chem.
Commun., 2000, 223–224.
25 N. D. R. Barnett, W. Clegg, R. E. Mulvey, P. A. O’Neil and D. Reed, J.
Organomet. Chem., 1996, 510, 297–300.
31 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112–122.
This journal is
The Royal Society of Chemistry 2010
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