N-heterocyclic germylidenide and stannylidenide anions: Group 14 metal(II) cyclopentadienide analogues

Article abstract of DOI:10.1021/om100595a

The reaction of a sterically bulky β-diketiminato lithium complex [Li(^ButNacnac)] (^ButNacnac = [{N(Dip)C(Bu ^t)}₂CH]^-, Dip = C₆H ₃Prⁱ₂-2,6) with GeCl₂·dioxane has given the germanium(II) chloride complex [(^ButNacnac)GeCl] (3). Both it and its known tin analogue, [(^ButNacnac)SnCl] (4), were crystallographically characterized and found to be monomeric in the solid state. The reduction of both complexes with elemental lithium in THF led to lithium complexes of N-heterocyclic germylidenide and stannylidenide anions, viz., [(THF)Li{η⁵-EC(Bu^t)C(H)C(Bu^t)N(Dip)}] (E = Ge, 5; Sn, 6). The reduction of the germanium(II) precursor, 3, also afforded the germanium(II) amide complex [(^ButNacnac)Ge{N(H)(Dip)}] (7). The mechanisms of formation of the complexes are thought to involve a number of steps, including reductive ring contraction reactions. The crystallographic and spectroscopic data for [(THF)Li{η⁵-EC(Bu^t)C(H) C(Bu^t)N(Dip)}] indicate a significant degree of aromatic π-delocalization within their heterocycles.

Full text of DOI:10.1021/om100595a

Organometallics 2010, 29, 3655–3660 3655
DOI: 10.1021/om100595a
N-Heterocyclic Germylidenide and Stannylidenide Anions: Group 14
Metal(II) Cyclopentadienide Analogues
William D. Woodul,† Anne F. Richards,† Andreas Stasch,†
Matthias Driess,*,‡ and Cameron Jones*,†
‡
†School of Chemistry, Monash University, P.O. Box 23, Clayton, Victoria, 3800, Australia, and Institute of
€
Chemistry: Metalorganics and Inorganic Materials, Technische Universitat Berlin, Strasse des 17. Juni 135,
Sekr. C2, D-10623 Berlin, Germany
Received June 18, 2010
The reaction of a sterically bulky β-diketiminato lithium complex [Li(ButNacnac)] (ButNacnac =
[{N(Dip)C(But)}2CH]-, Dip = C6H3Pri2-2,6) with GeCl2 dioxane has given the germanium(II)
3
chloride complex [(ButNacnac)GeCl] (3). Both it and its known tin analogue, [(ButNacnac)SnCl] (4),
were crystallographically characterized and found to be monomeric in the solid state. The reduction
of both complexes with elemental lithium in THF led to lithium complexes of N-heterocyclic
germylidenide and stannylidenide anions, viz., [(THF)Li{η5-EC(But)C(H)C(But)N(Dip)}] (E = Ge,
5; Sn, 6). The reduction of the germanium(II) precursor, 3, also afforded the germanium(II) amide
complex [(ButNacnac)Ge{N(H)(Dip)}] (7). The mechanisms of formation of the complexes are
thought to involve a number of steps, including reductive ring contraction reactions. The crystallo-
graphic and spectroscopic data for [(THF)Li{η5-EC(But)C(H)C(But)N(Dip)}] indicate a significant
degree of aromatic π-delocalization within their heterocycles.
Introduction
In contrast, the monoanions, e.g., [{R3Si}EC4Me4]-, display
aromatic delocalization only when η5-coordinated to transi-
tion metal fragments.5 It was not until 2005 that considerable
aromaticity in a crystallographically authenticated dianionic
stannole complex, viz., [(μ-η5-SnC4Ph4){Li(OEt2)}2], was
demonstrated.6,7 Impressively, in 2010, a dianionic plumbole
analogue of this system, [Li(DME)3][(DME)Li(η5-PbC4Ph4)],
was reported to contain the first example of an aromatic lead
heterocycle.8
Although the intracyclic bonding in the above-mentioned
aromatic dianionic heterocycles can be represented by sig-
nificant contributions from resonance forms with tetrelene
character,2 they are best described as having tetravalent
group 14 centers. To the best of our knowledge, the only
known low-valent heavier group 14 element Cp- analogue is
found in the N-heterocyclic germylidenide complex 1(Chart1).
Cyclopentadienides (Cp-) are aromatic 6π-electron li-
gands that have been utilized in the preparation of complexes
with nearly every metal in the periodic table. The diverse
array of applications that such complexes have found in the
past 50 years (e.g., in catalysis, materials science, asymmetric
synthesis) has led to their unquestionable importance to
chemistry.1 In more recent times, considerable efforts have
been made to prepare analogues of Cp- that incorporate the
heavier group 14 elements, which could potentially be used
as ligands in the formation of transition metal complexes.
Considerable progress has been made in this direction with
the preparation of structurally characterized examples of
alkali metal salts of silole and germole anions and dianions.2
Both experimental and theoretical evidence have shown
the dianionc forms of these heterocycles, e.g., [EC4Ph4]2-
(E=Si3 or Ge4), to have considerable aromatic character.
(5) (a) Freeman, W. P.; Dysard, J. M.; Tilley, T. D.; Rheingold, A. L.
Organometallics 2002, 21, 1734. (b) Dysard, J. M.; Tilley, T. D. J. Am.
Chem. Soc. 2000, 122, 3097. (c) Dysard, J. M.; Tilley, T. D. J. Am. Chem.
Soc. 1998, 120, 8245. (d) Freeman, W. P.; Tilley, T. D.; Rheingold, A. L.
J. Am. Chem. Soc. 1994, 116, 8428. (e) Freeman, W. P.; Tilley, T. D.;
Rheingold, A. L.; Ostrander, R. L. Angew. Chem., Int. Ed. Engl. 1993, 32,
1744.
*To whom correspondence should be addressed. E-mail: cameron.
jones@monash.edu; matthias.driess@tu-berlin.de.
(1) Metallocenes. Synthesis, Reactivity, Applications; Togni, A., Hal-
terman, R., Eds.; VCH: Weinheim, Germany, 1998; Vols. 1 and 2, and
references therein.
(6) Saito, M.; Haga, R.; Yoshioka, M.; Ishimura, K.; Nagase, S.
(2) For reviews see: (a) Lee, V. Y.; Sekiguchi, A. Angew. Chem., Int.
Ed. 2007, 46, 6596. (b) Saito, M.; Yoshioka, M. Coord. Chem. Rev. 2005,
Angew. Chem., Int. Ed. 2005, 44, 6533.
(7) The solution spectroscopic characterization and reactivity of
several aromatic stannole dianions has also been reported. See for
example: (a) Saito, M.; Haga, R.; Yoshioka, M. Chem. Commun.
2002, 1002. (b) Saito, M.; Haga, R.; Yoshioka, M. Chem. Lett. 2003, 32,
912. (c) Haga, R.; Saito, M.; Yoshioka, M. J. Am. Chem. Soc. 2006, 128,
4934. (d) Saito, M.; Shomosawa, M.; Yoshioka, M.; Ishimura, K.; Nagase, S.
Organometallics 2006, 25, 2967. (e) Saito, M.; Shomosawa, M.; Yoshioka,
M.; Ishimura, K.; Nagase, S. Chem. Lett. 2006, 35, 940.
ꢀ
249, 765. (c) Dubac, J.; Guerin, C.; Meunier, P. In The Chemistry of
Organosilicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley-Inter-
science: Chichester, 1998; Vol. 2, Part 3, p 1961.
(3) (a) Hong, J.-H.; Boudjouk, P.; Castelino, S. Organometallics 1994,
13, 3387. (b) West, R.; Sohn, U.; Bankwitz, J.; Calabrase, J.; Apeloig, Y.;
Mueller, T. J. Am. Chem. Soc. 1995, 117, 11608.
(4) (a) Hong, J.-H.; Boudjouk, P. Bull. Soc. Chim. Fr. 1995, 132, 495.
(b) West, R.; Sohn, U.; Powell, D. R.; Mueller, T.; Apeloig, Y. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 1002.
(8) Saito, M.; Sakaguchi, M.; Tajima, T.; Ishimura, K.; Nagase, S.;
Hada, M. Science 2010, 328, 339.
r
2010 American Chemical Society
Published on Web 07/19/2010
pubs.acs.org/Organometallics

3656 Organometallics, Vol. 29, No. 16, 2010
Woodul et al.
Chart 1
This was reported by Driess et al. to result from the potassium
reduction of the β-diketiminato germanium(II) chloride com-
pound [(DipNacnac)GeCl] (DipNacnac = [{N(Dip)C(Me)}2-
CH]-, Dip = C6H3Pri2-2,6). The mechanism of its formation
was suggested to involve several reductive processes including a
ring contraction of the germanium heterocycle. Experimental
spectroscopic and structural data for 1 implied it to be aro-
matic, a situation that was verified by the calculated negative
nuclear independent chemical shift (NICS) values obtained for
the heterocycle (NICS(1) = -7.4 ppm, NICS(2) = -7.7 ppm).9
In contrast, the KC8 reduction of [(DipNacnac)SnCl] has been
reported to generate tin metal and small amounts of the homo-
leptic complex [Sn(DipNacnac)2] presumably via a disproportio-
nation process.10
The reductions of [(DipNacnac)ECl] (E = Ge or Sn) can be
compared to the potassium reductions of the closely related
bulky guanidinato and amidinato germanium(II) chloride
complexes [LGeCl] (L=[{N(Dip)}2CR]-, R=NPri2 (Priso),
But (Piso)). Dissimilar to the ring contraction reaction that
gave 1, these afforded the germanium(I) dimers 2 via reduc-
tive coupling processes.11,12 Compounds 2 can be considered
as intramolecularly base stabilized examples of digermynes,
RGeGeR, the remarkable further chemistry of which is
rapidly developing.13 Given that we have previously shown
the coordinating and stabilizing properties of bulky guanidi-
nates and amidinates to closely mimic those of β-diketiminates,14
we were motivated to prepare other examples of group 14
metal(I) dimers, but incorporating the latter ligands. It
was reasoned that the use of β-diketiminates bulkier than
DipNacnac might circumvent ring contraction and/or dis-
proportionation reactions from occurring during the reduc-
tion of suitable metal(II) precursors. Although this proved
not to be the case, the study has led to the first example of an
N-heterocyclic stannylidenide anion and its germanium
counterpart (cf. 1), both of which display characteristics of
aromatic systems.
Figure 1. Thermal ellipsoid plot (25% probability surface) of
the molecular structure of [(ButNacnac)GeCl] (3). Hydrogen
˚
atoms are omitted for clarity. Selected bond lengths (A) and
angles (deg) for 3: Ge(1)-N(1) 1.9394(19), Ge(1)-N(2)
2.036(2), Ge(1)-Cl(1) 2.2942(8), N(1)-C(2) 1.374(3), N(2)-
C(4) 1.328(3), C(2)-C(3) 1.368(4), C(3)-C(4) 1.432(3), N(1)-
Ge(1)-N(2) 91.99(8), N(1)-Ge(1)-Cl(1) 95.39(6), N(2)-
˚
Ge(1)-Cl(1) 93.70(6). Selected bond lengths (A) and angles
(deg) for 4: Sn(1)-N(2) 2.136(3), Sn(1)-N(1) 2.223(3), Sn(1)-
Cl(1) 2.4466(13), N(1)-C(2) 1.322(5), N(2)-C(4) 1.361(5),
C(2)-C(3) 1.419(5), C(3)-C(4) 1.389(5), N(2)-Sn(1)-N(1)
87.60(12), N(2)-Sn(1)-Cl(1) 91.82(10), N(1)-Sn(1)-Cl(1)
92.55(9).
Results and Discussion
The β-diketiminate ligand that was chosen for this study was
ButNacnac ([{N(Dip)C(But)}2CH]-), which has previously
been shown to be substantially more sterically imposing toward
N,N0-chelated metal centers than DipNacnac.15 The monomeric
germanium(II) precursor complex [(ButNacnac)GeCl] (3) was
prepared in good yield by the reaction of in situ generated
[Li(ButNacnac)] with GeCl2 dioxane in diethyl ether.16
A
3
variation of the literature procedure17 was used to synthesize
its tin(II) analogue, [(ButNacnac)SnCl] (4). Attempts to prepare
the lead counterpart of 3 and 4 by reaction of [Li(ButNacnac)]
with PbCl2 were not successful and afforded no identifiable
products.18 Similarly, the reaction of [Li(ButNacnac)] with one
equivalent of SiBr4 in the presence of tmeda did not give the
intended product, [(ButNacnac)SiBr3],19 but instead yielded
€
(9) Wang, W.; Yao, S.; von Wullen, C.; Driess, M. J. Am. Chem. Soc.
2008, 130, 9640. N.B. Two related heteroaromatic six-membered
germanium(II) heterocycles derived from [(DipNacnac)GeCl] have also
been reported. (a) Stender, M.; Phillips, A. D.; Power, P. P. Inorg. Chem.
2001, 40, 5314. (b) Yao, S.; Zhang, X.; Xiong, Y.; Schwarz, H.; Driess, M.
Organometallics, online asap article, DOI: 10.1021/om100383y.
(10) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.;
Power, P. P. Organometallics 2001, 20, 1190.
(15) (a) Bonyhady, S. J.; Jones, C.; Nembenna, S.; Stasch, A.;
Edwards, A. J.; McIntyre, G. J. Chem.;Eur. J. 2010, 16, 938. (b)
Holland, P. L. Acc. Chem. Res. 2008, 41, 905.
(16) A small amount of [(ButNacnac)Li(OEt2)] crystallized from one
reaction. Details of the X-ray crystal structure of this compound can be
found in the Supporting Information.
(17) Dove, A. P.; Gibson, V. C.; Marshall, E. L.; Rzepa, H. S.; White,
A. J. P.; Williams, D. J. J. Am. Chem. Soc. 2006, 128, 9834.
(18) The related reaction between [Li(DipNacnac)] and PbCl2 is
known to give [(DipNacnac)PbCl]. Chen, M.; Fulton, J. R.; Hitchcock,
P. B.; Johnstone, N. C.; Lappert, M. F.; Protchenko, A. V. Dalton Trans.
2007, 2770.
(11) Green, S. P.; Jones, C.; Junk, P. C.; Lippert, K.-A.; Stasch, A.
Chem. Commun. 2006, 3978.
(12) Several related 1,2-digermylene compounds bearing unsup-
ported Ge-Ge bonds have since been reported. (a) Wang, W.; Inoue,
S.; Yao, S.; Driess, M. Chem. Commun. 2009, 2661. (b) Nagendran, S.;
Sen, S. S.; Roesky, H. W.; Koley, D.; Grubmuller, H.; Pal, A.; Herbst-Irmer,
R. Organometallics 2008, 27, 5459. (c) Leung, W.-P.; Chiu, W.-K.; Chong,
K.-H.; Mak, C. W. Chem. Commun. 2009, 6822.
(19) The related reaction between [Li(DipNacnac)] and SiBr4 in the
presence of tmeda is known to give [Br2Si{N(Dip)C(Me)C(H)C-
(dCH2)N(Dip)}] via dehydrobromination of the β-diketiminate ligand.
€
(13) Power, P. P. Organometallics 2007, 26, 4362.
Driess, M.; Yao, S.; Brym, M.; von Wullen, C.; Lentz, D. J. Am. Chem.
(14) Jones, C. Coord. Chem. Rev. 2010, 254, 1273.
Soc. 2006, 128, 9628.

Article
Organometallics, Vol. 29, No. 16, 2010 3657
Scheme 1
a complex mixture of products, from which a few crystals
of the unusual lithium β-diketiminate adduct complex
[(ButNacnac)Li{BrLi(tmeda)}2] were isolated (see Support-
ing Information).
Figure 2. Thermal ellipsoid plot (25% probability surface)
of the molecular structure of [(THF)Li{η5-SnC(But)C(H)C-
(But)N(Dip)}] (6); hydrogen atoms are omitted for clarity.
˚
The spectroscopic data for 3 are comparable with those for
the known tin complex 4.17 Both complexes were crystallo-
graphically characterized, and the molecular structure of 3
can be found in Figure 1 (see Supporting Information for the
ORTEP diagram of 4). The compounds are isostructural
with each other and have similar geometries to the previously
reported systems [(DipNacnac)ECl] (E = Ge or Sn).10 How-
ever, the bond lengths within the NC3N backbones of 3 and 4
suggest a significantly reduced level of electronic delocaliza-
tion than in [(DipNacnac)ECl]. This undoubtedly results
from a considerably greater distortion of the ligand back-
bones from planarity in the more hindered compounds. An
indication of the increased steric protection afforded by the
metal centers in the bulkier systems 3 and 4 can be gauged by
comparing the CNC angles in those compounds (3, 124.3° mean;
4, 124.9° mean) with the same angles in [(DipNacnac)GeCl]
(120.5° mean) and [(DipNacnac)SnCl] (121.8° mean).10
Early attempts to reduce 3 and 4 with elemental potassium
were not encouraging, as they yielded intractable product
mixtures. As a result, attention was turned to the milder
reductant lithium, which was reacted with the two precur-
sors in THF to give moderate to high yields of yellow 5 and
deep green 6 (Scheme 1). A moderate yield of the orange
germanium(II) amide complex 7 was also isolated from the
reaction that afforded 5. The analogous tin amide, 8, could
not be crystallized from the mixture that gave 6, though an
1H NMR spectroscopic analysis of that mixture was con-
sistent with its presence. It is notable that the previously
reported reduction of [(DipNacnac)GeCl] generated signi-
ficant quantities of a complex analogous to 7, viz.,
[(DipNacnac)Ge{N(H)(Dip)}].9 Therefore, it is apparent that
the mechanisms of formation of 5, and by implication 6, are
similar to that for 1. We suggest these involve transient
lithium germylidenide or stannylidenide salts, 9, which un-
dergo ring contraction reactions to give the amide com-
plexes, 10. These then undergo salt elimination reactions
with either 3 or 4 to give 11, which are further reduced,
yielding the isolated complexes 5 and 6 and the transient
lithium amide complexes 12. The latter could participate in
solvent hydrogen abstraction reactions, yielding 7 and 8. It is
noteworthy that several closely related reductive ring con-
traction reactions have been documented as arising from the
Selected bond lengths (A) and angles (deg) for 6: Sn(1)-C(4)
2.0981(19), Sn(1)-N(1) 2.1907(16), N(1)-C(2) 1.400(2), C-
(2)-C(3) 1.394(3), C(3)-C(4) 1.415(3), Sn(1)-Li(1) 2.759(4),
N(1)-Li(1) 2.208(4), C(2)-Li(1) 2.184(4), C(3)-Li(1) 2.175(4),
C(4)-Li(1) 2.316(4), O(1)-Li(1) 1.866(4), C(4)-Sn(1)-N(1)
˚
77.12(7). Selected bond lengths (A) and angles (deg) for 5:
Ge(1)-C(4) 1.896(2), Ge(1)-N(1) 1.9660(16), N(1)-C(2)
1.404(2), C(2)-C(3) 1.387(3), C(3)-C(4) 1.421(3), Ge(1)-Li(1)
2.596(4), N(1)-Li(1) 2.215(4), C(2)-Li(1) 2.225(4), C(3)-Li(1)
2.204(4), C(4)-Li(1) 2.303(4), C(4)-Ge(1)-N(1) 83.13(8).
alkali metal reduction of, for example, [(ButNacnac)TiCl2]20
or [(ButNacnac)ZrCl3].21 Although 5 is stable in solution and
the solid state for long periods under an inert atmosphere, its
tin counterpart decomposes over several hours in solution at
ambient temperature, depositing tin metal. This process
generates, among other products, significant amounts of
the enamine (Dip)NdC(But)C(H)dC(H)(But).22 In addi-
tion, 6 also slowly decomposes in the solid state at 20 °C
and should, therefore, be stored in the freezer.
Both compounds 5 and 6 were crystallographically char-
acterized and found to be isostructural monomers (cf. di-
meric 1). As a result, only the molecular structure of 6 is
depicted in Figure 2 (see Supporting Information for the
ORTEP diagram of 5). In both 5 and 6, the Li(THF)
fragment is coordinated to an essentially planar heterocycle
in an η5-fashion with Li-Ge and Li-Sn distances that are
slightly shorter than in the aromatic dianionic tetrelole
5
4b
˚
complexes [(μ-η -GeC4Ph4){Li(dioxane)2}2] (2.70 A mean)
5
6
˚
and [(μ-η -SnC4Ph4){Li(OEt2)}2] (2.76 A mean), respec-
tively. Likewise, the Li-C distances in 5 and 6 are of the
˚
same order as those in the dianionic complexes (2.28-2.43 A
˚
and 2.19-2.41 A, respectively). The intracyclic bond lengths
˚
for 5 are close to those reported for 1 (Ge-N 1.944(2) A,
˚
˚
Ge-C 1.887(2) A, N-C 1.382(3) A, C-C 1.371(3) and
1.411(3) A) and, thus, are strongly suggestive of appreciable
9
˚
π-resonance stabilization within the heterocycle. Although
(20) Basuli, F.; Huffman, J. C.; Mindiola, D. J. Inorg. Chim. Acta
2007, 360, 246.
(21) Basuli, F.; Kilgore, U. J.; Brown, D.; Huffman, J. C.; Mindiola,
D. J. Organometallics 2004, 23, 6166.
(22) Conroy, K. D.; Piers, W. E.; Parvez, M. Organometallics 2009,
28, 6228.

3658 Organometallics, Vol. 29, No. 16, 2010
Woodul et al.
plausible that this is a result of an intermolecular exchange
and/or intramolecular migration of their Li(THF) frag-
ments, which is rapid on the NMR time scale. Cooling d8-
toluene solutions of each compound to -30 °C (i.e., close to
their solubility limits) did not result in resolution of their
spectra. Consistent with the proposed π-delocalization with-
in the heterocycles are the signals for their backbone protons,
which appear at δ 7.08 ppm (5) and δ 7.78 ppm (6), i.e.,
considerably downfield from the corresponding signals in
the precursor molecules 3 (δ 6.41 ppm) and 4 (δ 6.14 ppm).17
Furthermore, the downfield chemical shifts of the R-carbon
centers of the anions (5, δ 194.7 ppm; 6, δ 226.9 ppm) are not
dissimilar to those normally observed for germole and
stannole dianions.2,4,6,7 Perhaps, more illuminating are the
high-field resonances observed in the 7Li NMR spectra of 5
(δ -5.31 ppm) and 6 (δ -4.66 ppm). These are at comparable
chemical shifts to those reported for germole and stannole
dianionic complexes (e.g., δ -4.36 ppm for [(μ-η5-SnC4Ph4)-
{Li(OEt2)}2]).6 The high-field positions of the signals for
such complexes are thought to arise from strong shielding of
their lithium centers by diatropic ring currents above and
below the aromatic 6π-electron heterocycles.26 Delocaliza-
tion of the π-system within the stannacycle of 6 is also
indicated by the remarkable downfield chemical shift of the
signal in its 119Sn NMR spectrum (δ 524.2 ppm). This lies
more than 770 ppm to lower field than the signal for the
precursor complex, 4 (δ -252.0 ppm),17 and is markedly
downfield of resonances reported for isoelectronic stannole
dianions (e.g., [(μ-η5-SnC4Ph4){Li(OEt2)}2], δ 163.3 ppm)6
and neutral N-heterocyclic stannylenes (e.g., [:Sn{N(Mes)C-
(H)}2] (Mes=mesityl), δ 259 ppm).27 That said, such com-
parisons should be treated with some caution, as 119Sn NMR
chemical shifts for tin(II) compounds are very sensitive to
the coordination number of the metal and the nature of the
atoms bonded to it. Indeed, they can range over more than
2000 ppm.28 What is clear, however, is that there is a signifi-
cant delocalization of the negative charge on the heterocycle
in 6 away from the tin atom.
Figure 3. Thermal ellipsoid plot (25% probability surface) of
the molecular structure of [(ButNacnac)Ge{N(H)(Dip)}] (7);
hydrogen atoms (except H(3)) are omitted for clarity. Selected
˚
bond lengths (A) and angles (deg): Ge(1)-N(3) 1.9097(12),
Ge(1)-N(1) 1.9963(11), Ge(1)-N(2) 2.0377(11), N(1)-C(2)
1.3603(17), N(2)-C(4) 1.3173(17), C(2)-C(3) 1.3755(19),
C(3)-C(4) 1.4300(19), N(3)-Ge(1)-N(1) 99.31(5), N(3)-
Ge(1)-N(2) 88.60(5), N(1)-Ge(1)-N(2) 92.18(4).
there are no stannylidenide anions to compare with that in 6,
the magnitude of the bond lengths within the NC3 fragment
of the stannacycle implies a similar level of delocalization to
that in 1 and 5. Consistent with this is the Sn-C distance of
the compound, which is considerably shorter than those in
the aromatic stannole dianion [(μ-η5-SnC4Ph4){Li(OEt2)}2]
6
˚
(2.16 A mean) and the tetravalent precursor to this complex,
23
[Ph2SnC4Ph4] (2.13 A mean). Slightly at odds with the
˚
proposed delocalization over the stannacycle is its Sn-N
separation, which is comparable with those in 4, but longer
than such bonds in neutral N-heterocyclic stannylenes
Conclusions
24
˚
(known range 2.051-2.189 A). That said, the tin centers
in those heterocycles have a lower coordination number than
that in 6. Moreover, the Sn-N distance in 6 is considerably
shorter than those between localized imine fragments and
In summary, germanium(II) and tin(II) chloride complexes
incorporating a very bulky β-diketiminate ligand have been
prepared and structurally characterized. Their reduction with
elemental lithium has afforded anionic N-heterocyclic germyl-
idenide and stannylidenide complexes, the latter of which has
no precedent in the literature. The X-ray crystallographic and
spectroscopic data for these compounds indicate significant
aromatic π-delocalization over their heterocycles. Accordingly,
the systems can be viewed as group 14 metal(II) cyclopenta-
dienide analogues. Work is ongoing in our groups to explore
the possibility of using the complexes as transfer reagents in the
formation of novel d-block metal sandwich and half-sandwich
complexes.
2
˚
divalent Sn atoms, e.g., 2.278 A in [{(SiMe3)2N}Sn{κ -N,
N0-N(But)dC(H)C(H)2N(But)}].25
The molecular structure of 7 is portrayed in Figure 3 and is
essentially isostructural to [(DipNacnac)Ge{N(H)(Dip)}],9
with a puckered heterocycle that is reminiscent of the hetero-
cycle in 3. As was the case for [(DipNacnac)Ge{N(H)(Dip)}],
the exocyclic Ge-N distance in 7 is significantly shorter than
both of its endocyclic interactions. The acuteness of the angles
about the germanium(II) center (93.4° mean) of the complex
indicates a high degree of s-character to its lone pair.
1
The solution-state H and 13C NMR spectra of 7 signify
that it retains its solid-state structure in solution. Contrast-
ingly, the NMR data for 5 and 6 correspond to the com-
pounds possessing Cs symmetry in solution. It seems
(26) (a) Sekiguchi, A.; Sugai, Y.; Ebata, K.; Kabuto, C.; Sakurai, H.
J. Am. Chem. Soc. 1993, 115, 1144. (b) Paquette, L. A.; Bauer, W.; Sivik,
M. R.; B€uhl, M.; Feigel, M.; Schleyer, P.v.R. J. Am. Chem. Soc. 1990, 112,
8776.
(23) Ferman, J.; Kakareka, J. P.; Klooster, W. T.; Mullin, J. L.;
Quattrucci, J.; Ricci, J. S.; Tracy, H. J.; Vining, W. J.; Wallace, S. Inorg.
Chem. 1999, 38, 2464.
(24) As determined from a survey of the Cambridge Crystallographic
Database, June, 2010.
(25) Guzei, I. A.; Timokhin, V. I.; West, R. Acta Crystallogr., Sect. C
2006, 62, m90.
(27) Gans-Eichler, T.; Gudat, D.; Nieger, M. Angew. Chem., Int. Ed.
2002, 41, 1888.
(28) (a) Lappert, M. F.; Power, P. P.; Protchenko, A. V.; Seeber, A. L.
Metal Amide Chemistry; Wiley-VCH: Weinheim, 2009; Chapter 9.
(b) Wrackmeyer, B. In Tin Chemistry: Fundamentals, Frontiers and
Applications; Davies, A. G., Gielen, M., Pannell, K., Tiekink, E., Eds.;
Wiley: Chichester, 2008.

Article
Organometallics, Vol. 29, No. 16, 2010 3659
Table 1. Summary of Crystallographic Data for Compounds 3-7
3
4
5
6
7
empirical formula
fw
cryst syst
C
609.83
monoclinic
P21/n
12.625(3)
18.369(4)
15.562(3)
90
110.27(3)
90
3385.5(12)
4
1.196
1.008
1304
35H53ClGeN2
C35H53ClN2Sn
655.93
monoclinic
P21/n
12.5810(6)
18.6731(7)
15.7415(6)
90
111.903(5)
90
3431.2(2)
4
1.270
0.847
1376
C27H44GeLiNO
478.16
triclinic
P1
9.3348(3)
10.7638(3)
14.9412(5)
92.791(2)
107.011(3)
108.743(3)
1342.46(7)
2
C27H44LiNOSn
524.26
triclinic
P1
9.4259(2)
9.9475(3)
15.6200(4)
78.139(2)
78.782(2)
75.844(2)
1373.64(6)
2
C47H71GeN3
750.66
orthorhombic
Pbca
14.437(3)
20.288(4)
29.679(6)
90
90
90
8693(3)
8
1.147
0.738
3248
space group
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
vol (A )
Z
F(calcd) (g cm-3
)
1.183
1.158
512
1.268
0.947
548
μ (mm-1
F(000)
)
cryst size (mm)
θ range (deg)
reflns collected
Rint
unique reflns
goodness of fit
temp (K)
0.25 ꢀ 0.20 ꢀ 0.15
2.94 to 25.34
11 442
0.0449
6079
0.25 ꢀ 0.20 ꢀ 0.12
2.90 to 25.24
32 845
0.1005
6190
0.20 ꢀ 0.15 ꢀ 0.10
3.11 to 26.99
12 920
0.0276
5827
0.20 ꢀ 0.20 ꢀ 0.10
3.15 to 27.00
14 847
0.0171
5974
0.50 ꢀ 0.45 ꢀ 0.30
3.00 to 28.00
20 008
0.0215
10 470
1.014
150(2)
1.050
173(2)
0.990
173(2)
1.068
173(2)
1.023
123(2)
R1 indices [I > 2σ(I)]
wR2 indices (all data)
0.0386
0.0858
0.0580
0.0778
0.0368
0.0818
0.0271
0.0661
0.0306
0.0774
Experimental Section
123.9, 125.1, 127.3, 141.6, 144.5, 146.3 (Ar-C), 173.2 (CBut); IR
ν/cm-1 (Nujol) 1548w, 1378s, 1359m, 1312m, 1260m, 1130m,
1098m, 798m, 785m; MS (EI 70 eV), m/z (%) 610.3 (Mþ, 25),
575.3 (Mþ - Cl, 15), 244.1 (DipNCCButHþ, 100). Anal. Calcd
for C35H53ClGeN2: C 68.93, H 8.76, N 4.59. Found: C 68.94, H
8.63, N 4.61.
General Methods. All manipulations were carried out using
standard Schlenk and glovebox techniques under an atmo-
sphere of high-purity dinitrogen or argon. THF and hexane
were distilled over potassium, while diethyl ether was distilled
over Na/K alloy. 1H and 13C{1H} NMR spectra were recorded
on either Bruker DXP300 or DPX400 spectrometers and were
Preparation of [(THF)Li{η5-GeC(But)C(H)C(But)N(Dip)}]
(5) and [(ButNacnac)Ge{N(H)(Dip)}] (7). To a slurry of lithium
powder (40 mg, 5.7 mmol) in THF (40 mL) at -80 °C was added
a solution of 3 (0.15 g, 0.25 mmol) in THF (40 mL) over 5 min.
The mixture was warmed to 20 °C and stirred overnight. All
volatiles were subsequently removed in vacuo, and the residue
was extracted into hexane (15 mL). The extract was filtered and
stored at -30 °C overnight to yield yellow crystals of 5 (0.05 g,
83%). The mother liquor was concentrated to ca. 7 mL and
stored at -30 °C overnight to yield orange crystals of 7 (0.035 g,
37%). Data for 5: mp 137-139 °C; 1H NMR (300 MHz, C6D6,
298 K) δ 1.20 (d, 3JHH = 6.9 Hz, 6 H, CH(CH3)2), 1.23 (br m, 4
H, THF-CH2), 1.26 (s, 9 H, NCC(CH3)3), 1.48 (d, 3JHH = 6.9
Hz, 6 H, CH(CH3)2), 1.65 (s, 9 H, GeCC(CH3)3), 2.64 (sept,
3JHH = 6.9 Hz, 2 H, CH(CH3)2), 3.37 (br m, 4 H, THF-OCH2),
7.08 (s, 1 H, NCCH), 7.12-7.34 (m, 3 H, Ar-H); 13C{1H} NMR
(75 MHz, C6D6, 300 K) δ 22.6 (CH(CH3)2), 23.0 (CH(CH3)2),
25.3 (THF-CH2), 28.5 (CH(CH3)2), 33.2 (NCC(CH3)3), 35.1
(GeCC(CH3)3), 37.4 (NCC(CH3)3), 37.8 (GeCC(CH3)3), 68.7
(THF-OCH2), 112.5 (NCCH), 123.1, 125.8, 132.0, 146.4 (Ar-C),
147.5 (NCC), 194.7 (GeCC); 7Li{1H} NMR (155.4 MHz, C6D6,
300 K) δ -5.31; IR ν/cm-1 (Nujol) 1664w, 1546w, 1466 m,
1245s, 1190m, 1135m, 985m, 801m, 758m, 719w; MS (EI 70 eV),
m/z (%) 328.3 (DipNC(But)C(H)C(But)Hþ, 10), 270.2
(DipNC(But)C(H)CHþ, 100). Anal. Calcd for C27H44GeLiNO:
C 67.82, H 9.27, N 2.93. Found: C 67.61, H 9.01, N 2.86. Data
for 7: mp 155-160 °C (dec); 1H NMR (300 MHz, C6D6, 298 K) δ
referenced to the resonances of the solvent used. Li{1H} and
7
119Sn{1H} NMR spectra were recorded on a Bruker Avance 400
spectrometer and were referenced to external 1 M aqueous LiCl
and SnMe4, respectively. Mass spectra were obtained from the
EPSRC National Mass Spectrometric Service at Swansea Uni-
versity. IR spectra were recorded using a Nicolet 510 FT-IR
spectrometer as Nujol mulls between NaCl plates. Micro-
analyses were carried out by Campbell Microanalytical, Ottago.
A reproducible microanalyses could not be obtained for 6 due to
its thermal instability at ambient temperature in the solid state.
Melting points were determined in sealed glass capillaries under
dinitrogen and are uncorrected. The compounds ButNacnacH29
and [(ButNacnac)SnCl]17 were prepared by variations of litera-
ture procedures. All other reagents were used as received.
Preparation of [(ButNacnac)GeCl] (3). A solution of 1.6 M
BunLi in hexane (0.63 mL, 1.0 mmol) was added to a solution
of ButNacnacH (0.50 g, 1.0 mmol) in diethyl ether (15 mL) at
-80 °C over 5 min. The solution was warmed to ambient tempera-
ture and stirred for 2 h, after which time it was cooled to -80 °C
and a suspension of GeCl2 dioxane (0.23 g, 1.0 mmol) in diethyl
3
ether (15 mL) at -80 °C was added to it. The reaction mixture
was warmed to room temperature and stirred for 2 h, where-
upon volatiles were removed in vacuo. The residue was extracted
into hexane (40 mL), and the extract filtered and stored at -30 °C
overnight to yield yellow crystals of 3 (0.37 g, 61%): mp 231-
233 °C; 1H NMR (300 MHz, C6D6, 298 K) δ 1.05 (d, 3JHH
=
=
3
6.9 Hz, 6 H, CH(CH3)2), 1.11 (s, 18 H, C(CH3)3), 1.17 (d, 3JHH
1.01, 1.13, 1.20, 1.22, 1.23, 1.33 (6d, JHH = 6.9 Hz, 36 H,
CH(CH3)2), 1.13 (s, 18 H, C(CH3)3), 2.83 (sept, 3JHH = 6.9 Hz,
1 H, CH(CH3)2), 3.18 (sept, 3JHH = 6.9 Hz, 2 H, CH(CH3)2), 3.24
(sept, 3JHH = 6.9 Hz, 2 H, CH(CH3)2), 3.24 (sept, 3JHH = 6.9
Hz, 1 H, CH(CH3)2), 4.85 (s, 1 H, NH), 6.15 (s, 1 H, NCCHCN),
6.86-7.13 (m, 9 H, Ar-H); 13C{1H} NMR (75 MHz, C6D6, 300
K) δ 23.1, 23.9, 25.2, 26.6, 26.8, 27.4 (6 ꢀ CH(CH3)2), 28.6, 28.7,
28.8, 29.1 (4 ꢀ CH(CH3)2), 32.3 (C(CH3)3), 42.5 (C(CH3)3),
101.3 (NCCCN), 117.8, 121.8, 124.1, 124.7, 125.6, 126.8, 135.2,
137.5, 143.4, 144.1, 145.7, 146.0 (Ar-C), 174.1 (CBut); IR ν/cm-1
3
6.9 Hz, 6 H, CH(CH3)2), 1.30 (d, JHH = 6.9 Hz, 6 H, CH-
3
(CH3)2), 1.52 (d, JHH = 6.9 Hz, 6 H, CH(CH3)2), 2.97 (sept,
3JHH = 6.9 Hz, 2 H, CH(CH3)2), 4.05 (sept, 3JHH = 6.9 Hz, 2 H,
CH(CH3)2), 6.41 (s, 1 H, NCCHCN); 13C NMR (75 MHz,
C6D6, 298 K) δ 24.3, 24.5, 26.3, 28.3 (CH(CH3)2), 28.4, 28.5
(CH(CH3)2), 31.9 (C(CH3)3), 41.9 (C(CH3)3), 105.6 (NCCCN),
(29) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485.

3660 Organometallics, Vol. 29, No. 16, 2010
Woodul et al.
(Nujol) 1547m, 1489m, 1388m, 1362m, 1260s, 1155m, 1129m,
800m, 782m, 750m; MS (EI 70 eV), m/z (%) 751.5 (Mþ, 3), 575.3
(Mþ - DipNH, 100). Anal. Calcd for C47H71GeN3: C 75.20, H
9.53, N 5.60. Found: C 74.89, H 9.32, N 5.41.
X-ray Crystallography. Crystals of 3-7, [(ButNacnac)Li(OEt2)],
and [(ButNacnac)Li{BrLi(tmeda)}2] suitable for X-ray structural
determination were mounted in silicone oil. Crystallographic mea-
surements were made using a Nonius Kappa CCD diffractometer
using a graphite monochromator with Mo KR radiation (λ=
N.B. The quoted yields of 5 and 7 assume the mechanism
proposed for their formation (see Scheme 1) is in operation.
Preparation of [(THF)Li{η5-SnC(But)C(H)C(But)N(Dip)}]
(6). To a slurry of lithium powder (40 mg, 5.7 mmol) in THF
(30 mL) at -80 °C was added a solution of 4 (0.15 g, 0.23 mmol)
in THF (30 mL) over 5 min. The mixture was warmed to 0 °C
and stirred for 6 h, yielding a deep red solution. All volatiles were
subsequently removed in vacuo, and the deep green residue was
extracted into hexane (15 mL). The extract was filtered and
stored at -30 °C overnight to yield deep green crystals of 6 (0.04 g,
˚
0.71073 A). The structures were solved by direct methods and
refined on F2 by full matrix least-squares (SHELX9730) using all
unique data. All non-hydrogen atoms are anisotropic with hydro-
gen atoms (except the amino proton of 7) included in calculated
positions (riding model). Crystal data and details of data collections
and refinement are given in Table 1. CCDC numbers: 7811154-
7811160.
Acknowledgment. C.J. thanks the Alexander von
Humboldt (AvH) Foundation for financial support in
the form of an AvH Senior Research Award. M.D.
thanks the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for financial support.
Financial support from the Australian Research Council
(fellowships for C.J. and A.S.) and the donors of The
American Chemical Society Petroleum Research Fund
(C.J.) is also gratefully acknowledged. We also thank the
EPSRC Mass Spectrometry Service, Swansea, UK.
1
52%): mp 137-139 °C; H NMR (300 MHz, C6D6, 298 K) δ
1.25 (d, 3JHH = 6.9 Hz, 6 H, CH(CH3)2), 1.23 (br m, 4 H, THF-
CH2), 1.27 (s, 9 H, NCC(CH3)3), 1.46 (d, 3JHH = 6.9 Hz, 6 H,
CH(CH3)2), 1.58 (s, 9 H, SnCC(CH3)3), 2.77 (sept, 3JHH = 6.9
Hz, 2 H, CH(CH3)2), 3.40 (br m, 4 H, THF-OCH2), 7.16-7.33
(m, 3 H, Ar-H), 7.78 (s, 1 H, NCCH); 13C{1H} NMR (75 MHz,
C6D6, 300 K) δ 23.0 (CH(CH3)2), 23.4 (CH(CH3)2), 25.2 (THF-
CH2), 28.6 (CH(CH3)2), 33.4 (NCC(CH3)3), 35.1 (SnCC(CH3)3),
39.6 (NCC(CH3)3), 40.2 (SnCC(CH3)3), 67.9 (THF-OCH2), 116.6
(NCCH), 122.7, 124.7, 131.6, 147.7 (Ar-C), 156.6 (NCC), 226.9
(SnCC); 7Li{1H} NMR (155.4 MHz, C6D6, 300 K) δ -4.66;
119Sn{1H} NMR (149.1 MHz, C6D6, 300 K) δ 524.2 (p.w. at 1/2
height = 44 Hz); IR ν/cm-1 (Nujol) 1663w, 1546w, 1464m, 1245s,
1191m, 1136m, 985m, 804m, 757m; MS (EI 70 eV), m/z (%) 328.3
(DipNC(But)C(H)C(But)Hþ, 20), 178.1 (DipNH2þ, 100).
Supporting Information Available: Crystallographic data as
CIF files for 3-7, [(ButNacnac)Li(OEt2)], and [(ButNacnac)Li-
{BrLi(tmeda)}2]; ORTEP diagrams for 4, 5, [(ButNacnac)Li-
(OEt2)], and [(ButNacnac)Li{BrLi(tmeda)}2]; details of the crys-
tallographic experiments and selected metrical parameters for
[(ButNacnac)Li(OEt2)] and [(ButNacnac)Li{BrLi(tmeda)}2]. This
material is available free of charge via the Internet at http://
pubs.acs.org.
N.B. The quoted yield of 6 assumes the mechanism proposed
for its formation (see Scheme 1) is in operation.
€
(30) Sheldrick, G. M. SHELX-97; University of Gottingen, 1997.