The [Ga2(C5Me5)]+ ion: Bipyramidal double-cone structure and weakly coordinated, monovalent Ga +

Article abstract of DOI:10.1002/anie.200503028

(Figure Presented) Partial protolysis of GaCp* with [H-(OEt ₂)₂]⁺[BAr^F]^- afforded the Ga^I compound [Ga₂Cp*]⁺[BAr ^F]^- (see structure). Experimental and computational studies confirm the mainly ionic structure of the cation, in which the Ga ⁺ ions are only weakly covalently stabilized by a bridging Cp* ligand. Initial experiments point to the interesting synthetic potential of this compound as a source for Ga⁺ in solution.

Full text of DOI:10.1002/anie.200503028

Communications
ing to Scheme 1, 1 can be prepared quantitatively by
controlled protolysis of [GaCp*].
Scheme 1. Reaction of [GaCp*] with [H(OEt2)2][BArF].
Treatment of a solution of [GaCp*] in fluorobenzene with
one half molar equivalent of [H(OEt2)2][BArF] in fluoroben-
zene at 258C leads to an immediate color loss of the initial
yellowish reaction mixture. Product 1 is precipitated by slow
addition of n-hexane as small, colorless needles in reprodu-
cible good yields of around 85%. The formation of 1 is similar
to the synthesis of [Cp*Si][B(C6F5)4] by protolysis of [Cp*2Si]
with [Cp*H2][B(C6F5)4] in dichloromethane recently reported
by Jutzi and co-workers.[12] Compound 1 is very well soluble in
fluorobenzene but almost insoluble in nonpolar solvents such
as n-hexane or toluene. In the presence of strongly coordi-
nating solvents such as THF, compound 1 decomposes
immediately under formation of [GaCp*] and other uniden-
Organogallium Complexes
DOI: 10.1002/anie.200503028
The [Ga2(C5Me5)]+ Ion: Bipyramidal Double-
Cone Structure and Weakly Coordinated,
Monovalent Ga+**
Beatrice Buchin, Christian Gemel, Thomas Cadenbach,
Rochus Schmid, and Roland A. Fischer*
1
tified side products. The H NMR spectrum of 1 in fluoro-
benzene shows signals for the protons of the BArF group at
d = 7.64 (4H) and 8.32 ppm (8H) as well as a singlet at d =
1.69 ppm (15H) for the chemically equivalent methyl groups
of the Cp* ring. The 71Ga NMR signal for 1 at d = À519 ppm is
distinctly downfield shifted compared to the respective signal
for [GaCp*] (d = À653 ppm)[13] and those of the arene
complexes [Ga(arene)2][GaX4] (d = À609 to À675 ppm).[20]
The 1H NMR spectrum of a 1:1 mixture of 1 and [GaCp*] in
fluorobenzene reveals a coalesced signal at d = 1.80 ppm.
Obviously, a fast exchange of Ga+ ions between [GaCp*]
Who understands how to play with weak interactions and
metastable states can break new synthetic ground in organo-
element chemistry. In this context, AlI and GaI compounds
and metalloid clusters of Group 13 investigated by Schnöckel
and co-workers are considered as milestones.[1,2] The good
accessibility of low-coordinate GaI organyls such as
[GaCp*],[3,4] [Ga(ddp)] (Cp* = C5Me5; ddp = 2-{(2,6-diiso-
propylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}-2-
pentene)[5] and GaR (R = C(SiMe3)3,[6] Si(SiMe3)[7]) allows
inter alia their use as exceptionally electron-rich carbenoid
ligands in organometallic chemistry,[8,9] a field which we have
been focusing on for quite some time.[10] Aiming at complex
cations of the type [M(ECp*)n]m+, we recently investigated
the reaction of [GaCp*] with [M(NCCH3)6][BArF]2 (M = V,
Cr, Fe, Co, Ni; BArF = [B{C6H3(CF3)2}4].[11] Surprisingly, a
redox-neutral Cp* transfer to the transition metal is observed
in certain cases, which is accompanied by the formation of the
title compound [Ga2Cp*][BArF] (1) as a by-product. Accord-
À
units is taking place, which points to a comparably weak Ga
Cp* interaction as well as a complete dissociation of 1 into
ions in solution.
[14]
¯
Compound 1 crystallizes in the triclinic space group P1.
The cation shows an unusual, highly symmetric bipyramidal
double-cone structure, in which both gallium atoms are
almost exactly above and below the center of the C5 ring,
respectively (Figure 1). The ionic bonding situation is
[*] B. Buchin, Dr. C. Gemel, T. Cadenbach, Dr. R. Schmid,
Prof. Dr. R. A. Fischer
Lehrstuhl für Anorganische Chemie II
Organometallics & Materials
Ruhr-Universität Bochum
44780 Bochum (Germany)
Fax: (+49)234-321-4174
E-mail: roland.fischer@ruhr-uni-bochum.de
Figure 1. Structure of the [Ga2(C5Me5)]+ ion of 1 (ORTEP plot: 50%
ellipsoids; hydrogen atoms have been omitted for clarity). Selected
[**] Organometal Complexes of d-Block Elements, Part 41. Part 40:
Ref. [10b]
.
À
À
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
bond lengths [Š] and angles [8]: Ga1 Cp*centr. 2.228, Ga2 Cp*centr.
2.237; Ga1-Cp*centr.-Ga2 178.2.
1074
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1074 –1076

Angewandte
Chemie
À
reflected by the Ga Cp*centr. distances of 2.228 Š and 2.237 Š,
which are significantly longer than that in [GaCp*] (2.081 Š)
in the solid state as well as in the gas phase. The individual
À
Ga C distances of 2.505 to 2.562 Š hardly deviate from each
other (cf. the solid-state structure of [GaCp*]: 2.380–
2.421 Š).[15,16] The Ga1-Cp*centr.-Ga2 arrangement is almost
linear (178.28).[17] Similar structures with Cp* as a symmetri-
cally coordinated bridging ligand are very rare. One example
is
[Cs2Cp*([18]crown-6)2]+[Cs4Cp3Cp*2([18]crown-6)2]À,
whose cation reveals the structural motif [Cs2Cp*]+ analogous
to 1.[18,19]
The crystal packing (Figure 2) of the ions places each Ga
atom between two of the four [C6H3(CF3)2] groups of the
Figure 3. Frontier orbitals of [Ga2Cp]+ and [Al2Cp]+ (left) and the
monomers [GaCp] and [AlCp] (right).
1, 6.1 eV in [GaCp]), which leads to a significant weakening of
the p bond to each individual E.
Thus, the [Ga2(C5Me5)]+ ion can be regarded as a
stabilized, almost “naked” Ga+ ion, which is not known in
solution under ordinary conditions. Accordingly, 1 should
serve as a selective source for highly reactive Ga+. Co-
ꢀ
crystallization of 1 with soft p donors such as HC C(SiMe3),
ꢀ
PhC CPh, divinyldisiloxane, t,t,t-1,5,9-cyclododecatriene,
and ferrocene led to neither new isolable products nor a
shift of the 1H NMR signals. However, treatment with
electron-rich decamethylferrocene resulted in a clean redox
reaction under deposition of gallium metal and formation of
[GaCp*] and the ferrocenium cation [Cp*2Fe]+. Treatment of
1 with strong Lewis acids (B(C6F5)3) or hard nucleophiles
(LiCl) led to decomposition or disproportionation and Ga
deposition. However, the salt 1 reacts cleanly as a source for
Ga+ with K[ddp] to give [GaCp*] and [Ga(ddp)] (Scheme 2).
Figure 2. Mercury plot of the crystal packing of 1 (ball-and-stick model
for the cation, wireframe-plot for the anion); hydrogen atoms and
C6H5F are omitted for clarity.
anion. The distances of the Ga atoms to the individual C
atoms of the [BArF] ion differ only slightly from each other
(3.4–4.0 Š), but are too long to be considered as a directed
À
bonding interaction. Similarly, the Ga F contacts in 1
(> 3.7 Š) are very long, and thus not comparable to the
crown-ether cesium interaction in the above example.
The stabilization of GaI ions in solution by arene
complexes is known, but only in halogeno-bridged complexes.
A typical example for this is [Ga(mesitylene)2][GaX4], which
Scheme 2. Reaction of 1 with K[ddp].
À
reveals distinctly shorter Ga Caryl distances than 1 (ca.
3.0 Š).[20] Figure 3 shows the frontier orbital schemes of the
model compounds [Ga2Cp]+ and [Al2Cp]+ (B3LYP/cc-
pVDZ).[21] Cp adopts the role of a typical bridging ligand in
an electron-deficient compound with multicenter bonds. The
two free electron pairs of the EI centers result from the
interaction of the doubly occupied s(pz) orbitals with the
occupied a1-symmetric y1 orbital of the Cp ligand and are
found in the nonbonding and the antibonding s orbital,
As shown by 1H NMR spectroscopy, 1 also reacts cleanly
with Li[N(SiMe3)2] in fluorobenzene under selective cleavage
of [GaCp*] and formation of a new sepecies, which could be
the so far unknown GaI amide [Ga{N(SiMe3)2}]n. The
isolation and characterization of this new species is still in
progress. The high reactivity of 1, in particular the reactions
with soft anionic nucleophiles, point to the potential of the
title compound as a source of Ga+ for the synthesis of new GaI
compounds. This applies similarly to the protonation of
[(Cp*Al)4] in fluorobenzene, which leads to a dark red
solution, the characterization of which we are currently
working on. In general it can be expected that analogous
protonation of clusters of the type [Ma(ECp*)b] with [H-
À
respectively. The elongated Ga Cpcentr. distances of 1 (ca.
0.2 Š longer than those in [GaCp*]) are very well reproduced
in the optimized structures and are explained by a decrease of
the covalent contribution. The p–p* splitting for the ionic
compounds [E2Cp]+ is slightly larger than for [ECp] (7 eV in
Angew. Chem. Int. Ed. 2006, 45, 1074 –1076
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
1075

Communications
(OEt2)2][BArF] leads to cleavage of Cp*H and formation of
interesting new and reactive products.
[14] Crystal structure analysis of 1·C6H5F: crystal size: 0.25 ” 0.20 ”
¯
0.15 mm, triclinic, P1, a = 10.272(3), b = 13.231(3), c =
18.852(2) Š, a = 92.643(18), b = 92.006(15), g = 112.327(19)8,
V= 2363.8(10) Š3, Z = 2, 1calcd = 1.636 mgmÀ3, 2Vmax = 50.108,
l(MoKa) = 0.71073 Š, T= 105(2) K. A total of 28404 reflections
Experimental Section
(8322 unique) were measured on
a Oxford Excalibur 2
1: A solution of [H(EtO2)2][BArF] (200 mg, 0.197 mmol) in fluoro-
benzene (3 mL) was added slowly to a solution of [GaCp*] (85 mg,
0.415 mmol) in fluorobenzene (3 mL), whereupon the color changed
immediately from yellow to colorless. The reaction mixture was
stirred for a few minutes at room temperature, then the solvent was
reduced in vacuo to about 2 mL, and the product was precipitated by
addition of n-hexane to give a white crystalline solid. The solvent was
removed by filtration, the residue washed with hexane (2 ” 2 mL), and
dried in vacuo. Yield: 188 mg (84%). Recrystallization of the crude
diffractometer [R(int) = 0.0527]. The structural solution and
refinement was done using the programs SHELXS-97 and
SHELXL-97. The final values for R1 and wR2(F2) were 0.0518
and 0.0944 (all data). CCDC-281940 contains the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[15] D. Loos, E. Baum, A. Ecker, H. Schnöckel, Angew. Chem. 1997,
109, 894 – 896; Angew. Chem. Int. Ed. Engl. 1997, 36, 860 – 862.
[16] A. Haaland, K.-G. Martinsen, H. V. Volden, D. Loos, H.
Schnöckel, Acta Chem. Scand. 1994, 48, 172 – 174.
[17] The structural motif Ga-X-Ga is reminiscent of the monomeric
unit of the neutral gallium suboxide Ga2O, see: a) T. R.
Burkholder, J. T. Justein, L. Andrews, J. Phys. Chem. 1992, 96,
10189 – 10195; b) S. Gowtham, A. Costales, R. Pandey, J. Phys.
Chem. B 2004, 108, 17295 – 17300.
[18] P. Jutzi, G. Reumann, J. Chem. Soc. Dalton Trans. 2000, 2237 –
2244.
[19] F. Olbrich, unpublished results.
[20] H. Schmidbaur, Angew. Chem. 1985, 97, 893 – 904; Angew.
Chem. Int. Ed. Engl. 1985, 24, 893 – 904.
product by slow diffusion of hexane into a solution of
1 in
fluorobenzene at 258C gave well-formed needle-shaped single
crystals.
1H NMR (fluorobenzene/C6D6, 208C): d = 8.30 (8H, [BArF]),
7.63 (4H, [BArF]), 1.69 ppm (15H, C5Me5); 1H NMR (CD2Cl2, 208C):
d = 7.73 (8H, [BArF]), 7.57 (4H, [BArF]), 2.24 ppm (15H, C5Me5);
13C NMR (CD2Cl2, 208C): d = 162.2 (q, J = 50 Hz, [BArF]), 135.2
([BArF]), 129.2 (q, J = 31.5 Hz, [BArF]), 125.0 (q, J = 272.4 Hz,
[BArF]), 123.5 (C5Me5), 117.9 ([BArF]), 10.1 ppm (C5Me5); 71Ga
NMR (CD2Cl2, 208C): d = À519 ppm; elemental analysis calcd (%)
for C48H32BF25Ga2 (1·C6H5F): C 46.72, H 2.61; found: C 46.27, H 2.85.
Quantum-chemical calculations: All calculations were performed
by using the Gaussian 03 program package[22] with the hybrid
exchange-correlation functional B3LYP[23, 24] and the all-electron
basis set cc-pVDZ.[25, 26] All structures were fully optimized and
characterized as stationary minima by inspection of the vibrational
frequencies.
À
[21] For information on M ECp bonds, see: J. Uddin, G. Frenking, J.
Am. Chem. Soc. 2001, 123, 1683 – 1693.
[22] Gaussian03 (RevisionB.04), M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A.
Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M.
Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M.
Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,
T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E.
Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S.
Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q.
Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G.
Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J.
Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong,
C. Gonzalez, J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 2003.
[23] A. D. Becke, J. Chem. Phys. 1993, 98, 5648 – 5652.
Received: August 25, 2005
Revised: September 28, 2005
Published online: December 15, 2005
Keywords: carbenoids · cyclopentadienyl compounds · gallium ·
.
Group 13 elements
[1] C. Dohmeier, D. Loos, H. Schnöckel, Angew. Chem. 1996, 108,
141 – 161; Angew. Chem. Int. Ed. Engl. 1996, 35, 129 – 149.
[2] A. Schnepf, H. Schnöckel, Angew. Chem. 2002, 114, 3682 – 3704;
Angew. Chem. Int. Ed. 2002, 41, 3533 – 3552.
[3] P. Jutzi, B. Neumann, G. Reumann, H. G. Stammler, Organo-
metallics 1998, 17, 1305 – 1314.
[4] P. Jutzi, L. O. Schebaum, J. Organomet. Chem. 2002, 654, 176 –
179.
[5] N. J. Hardman, B. E. Eichler, P. P. Power, Chem. Commun. 2000,
1991 – 1992.
[24] R. G. Parr, W. Yang, C. Lee, Phys. Rev. B 1988, 37, 785 – 789.
[25] J. T. H. Dunning, J. Chem. Phys. 1989, 90, 1007 – 1023.
[26] A. K. Wilson, D. E. Woon, K. A. Peterson, J. T. H. Dunning, J.
Chem. Phys. 1999, 110, 7667 – 7676.
[6] W. Uhl, W. Hiller, M. Layh, W. Schwarz, Angew. Chem. 1992,
104, 1378 – 1380; Angew. Chem. Int. Ed. Engl. 1992, 31, 1364 –
1366.
[7] G. Linti, J. Organomet. Chem. 1996, 520, 107 – 113.
[8] R. A. Fischer, J. Weiss, Angew. Chem. 1999, 111, 3002 – 3022;
Angew. Chem. Int. Ed. 1999, 38, 2830 – 2850.
[9] R. Murugavel, V. Chandrasekhar, Angew. Chem. 1999, 111,
1289 – 1293; Angew. Chem. Int. Ed. 1999, 38, 1211 – 1215.
[10] a) C. Gemel, T. Steinke, M. Cokoja, A. Kempter, R. A. Fischer,
Eur. J. Inorg. Chem. 2004, 4161 – 4176; b) B. Buchin, C. Gemel,
T. Cadenbach, R. A. Fischer, Inorg. Chem. 2005, submitted .
[11] B. Buchin, Diploma Thesis, Ruhr Universität Bochum
(Bochum), 2005.
[12] P. Jutzi, A. Mix, B. Rummel, W. W. Schoeller, B. Neumann, H.-G.
Stammler, Science 2004, 305, 849 – 851.
[13] D. Loos, H. Schnöckel, J. Organomet. Chem. 1993, 463, 37 – 40.
1076
www.angewandte.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1074 –1076