Structures, bonding, and reaction chemistry of the neutral organogallium(I) compounds (GaAr)n (n = 1 or 2) (Ar = terphenyl or related ligand): An experimental investigation of Ga-Ga multiple bonding

Article abstract of DOI:10.1021/ja028579j

The synthesis, structure, and properties of several new organogallium(I) compounds are reported. The monovalent compounds GaAr* (Ar* = C₆H₃-2,6-Trip₂, Trip = C₆H₂-2,4,6-Pr₃ⁱ 1), GaAr^# (Ar# = C₆H₃-2,6(Bu^tDipp)₂, Bu^tDipp = C₆H₂-2,6- Prⁱ₂-4-Bu^t, 4), and the dimeric (GaAr′)₂ (Ar′ = C₆H₃-2,6-Dipp₂, Dipp = C₆H₃-2,6-Prⁱ2, 6) were synthesized by the reaction of "Gal" with (Et₂O)LiAr*, (Et₂O)LiAr# (3), or (LiAr′)₂. Compounds 1 and 4 were isolated as green crystals, whereas 6 was obtained as a brown-red crystalline solid. All three compounds dissolved in hydrocarbon solvents to give green solutions and almost identical UV/visible spectra. Cryoscopy of 1 and 6 showed that they were monomeric in cyclohexane. Crystals of 1 and 4 were unsuitable for X-ray crystal structure determinations, but an X-ray data set for 6 showed that it was weakly dimerized in the solid with a long Ga - Ga bond of 2.6268(7) A and a trans-bent CGaGaC core array. The 1,2-diiodo-1,2-diaryldigallane compounds {Ga(Ar*)I}₂ (2), {Ga(Ar^#)I}₂ (5), and {Ga(Ar′)I}₂ (7) were isolated as byproducts of the synthesis of 1, 4, and 6. The crystal structures of 2 and 7 showed that they had planar ICGaGaCl core arrays with Ga - Ga distances near 2.49 A, consistent with Ga - Ga single bonding. Treatment of 1, 4, and 6 with B(C₆F₅)3 immediately afforded the 1:1 donor-acceptor complexes ArGa{B(C₆F₅)₃} (Ar = Ar*, 8; Ar#, 9; Ar′, 10) that featured almost linear gallium coordination, Ga - B distances near the sum of the covalent radii of gallium and boron, as well as some close Ga...F contacts. Compound 1 also reacted with Fe(CO)₅ under ambient conditions to give Ar*GaFe(CO)₄ (11), which had been previously synthesized by the reaction of GaAr*Cl2 with Na₂Fe(CO)₄. Reaction of 1 with 2,3-dimethyl-1,3-butadiene afforded the compound {Ar*GaCH₂C(Me)C(Me)CH₂}₂ (12) that had a 10-membered 1,5-Ga₂C₈ ring with no Ga - Ga interaction. Stirring 1 or 6 with sodium readily gave Na₂{Ar*GaGaAr*} (13) and Na₂(Ar′GaGaAr′) (14). The former species 13 had been synthesized previously by reduction of GaAr*Cl2 with sodium and was described as having a Ga - Ga triple bond because of the short Ga - Ga distance and the electronic relationship between [Ar*GaGaAr*]^2- and the corresponding neutral group 14 alkyne analogues. Compound 14 has a similar structure featuring a trans-bent CGaGaC core, bridged by sodiums which were also coordinated to the flanking aryl rings of the Ar′ ligands. The Ga - Ga bond length was found to be 2.347(1) A, which is slightly (ca. 0.02 A) longer than that reported for 13. Reaction of Ga{N(Dipp)C(Me)}₂CH, 15 (i.e., GaN/NDipp₂), which is sterically related to 1, 4, and 6, with Fe(CO)₅ yielded Dipp₂N/NGaFe(CO)₄ (16), whose Ga - Fe bond is slightly longer than that observed in 11. Reaction of the less bulky LiAr″ (Ar″ = C₆H₃-2,6-Mes₂) with "Gal" afforded the new paramagnetic cluster Ga₁₁Ar₄″ (17). The ready dissociation of 1, 4, and 6 in solution, the long Ga - Ga distance in 6, and the chemistry of these compounds showed that the Ga - Ga bonds are significantly weaker than single bonds. The reduction of 1 and 6 with sodium to give 13 and 14 supplies two electrons to the di-gallium unit to generate a single bond (in addition to the weak interaction in the neutral precursor) with retention of the trans-bent geometry. It was concluded that the stability of 13 and 14 depends on the matching size of the sodium ion, and the presence of Na - Ga and Na - Ar interactions that stabilize their Na₂Ga₂ core structures.

Full text of DOI:10.1021/ja028579j

Published on Web 02/11/2003
Structures, Bonding, and Reaction Chemistry of the Neutral
Organogallium(I) Compounds (GaAr)n (n ) 1 or 2) (Ar )
Terphenyl or Related Ligand): An Experimental Investigation
of Ga-Ga Multiple Bonding
Ned J. Hardman, Robert J. Wright, Andrew D. Phillips, and Philip P. Power*
Contribution from the Department of Chemistry, UniVersity of California, DaVis,
One Shields AVenue, DaVis, California 95616
Received September 17, 2002 ; E-mail: pppower@ucdavis.edu
Abstract: The synthesis, structure, and properties of several new organogallium(I) compounds are reported.
The monovalent compounds GaAr* (Ar* ) C6H3-2,6-Trip2, Trip ) C6H2-2,4,6-Pri3, 1), GaAr# (Ar# ) C6H3-
2,6(ButDipp)2, ButDipp ) C6H2-2,6-Pri2-4-But, 4), and the dimeric (GaAr′)2 (Ar′ ) C6H3-2,6-Dipp2, Dipp )
C6H3-2,6-Pri2, 6) were synthesized by the reaction of “GaI” with (Et2O)LiAr*, (Et2O)LiAr# (3), or (LiAr′)2.
Compounds 1 and 4 were isolated as green crystals, whereas 6 was obtained as a brown-red crystalline
solid. All three compounds dissolved in hydrocarbon solvents to give green solutions and almost identical
UV/visible spectra. Cryoscopy of 1 and 6 showed that they were monomeric in cyclohexane. Crystals of 1
and 4 were unsuitable for X-ray crystal structure determinations, but an X-ray data set for 6 showed that
it was weakly dimerized in the solid with a long Ga-Ga bond of 2.6268(7) Å and a trans-bent CGaGaC
core array. The 1,2-diiodo-1,2-diaryldigallane compounds {Ga(Ar*)I}2 (2), {Ga(Ar#)I}2 (5), and {Ga(Ar′)I}2
(7) were isolated as byproducts of the synthesis of 1, 4, and 6. The crystal structures of 2 and 7 showed
that they had planar ICGaGaCI core arrays with Ga-Ga distances near 2.49 Å, consistent with Ga-Ga
single bonding. Treatment of 1, 4, and 6 with B(C6F5)3 immediately afforded the 1:1 donor-acceptor
complexes ArGa{B(C6F5)3} (Ar ) Ar*, 8; Ar#, 9; Ar′, 10) that featured almost linear gallium coordination,
Ga-B distances near the sum of the covalent radii of gallium and boron, as well as some close Ga‚‚‚F
contacts. Compound 1 also reacted with Fe(CO)5 under ambient conditions to give Ar*GaFe(CO)4 (11),
which had been previously synthesized by the reaction of GaAr*Cl2 with Na2Fe(CO)4. Reaction of 1 with
2,3-dimethyl-1,3-butadiene afforded the compound {Ar*GaCH2C(Me)C(Me)CH2}2 (12) that had a 10-
membered 1,5-Ga2C8 ring with no Ga-Ga interaction. Stirring 1 or 6 with sodium readily gave
Na2{Ar*GaGaAr*} (13) and Na2(Ar′GaGaAr′) (14). The former species 13 had been synthesized previously
by reduction of GaAr*Cl2 with sodium and was described as having a Ga-Ga triple bond because of the
short Ga-Ga distance and the electronic relationship between [Ar*GaGaAr*]2- and the corresponding neutral
group 14 alkyne analogues. Compound 14 has a similar structure featuring a trans-bent CGaGaC core,
bridged by sodiums which were also coordinated to the flanking aryl rings of the Ar′ ligands. The Ga-Ga
bond length was found to be 2.347(1) Å, which is slightly (ca. 0.02 Å) longer than that reported for 13.
Reaction of Ga{N(Dipp)C(Me)}2CH, 15 (i.e., GaN∧NDipp2), which is sterically related to 1, 4, and 6, with
Fe(CO)5 yielded Dipp2N∧NGaFe(CO)4 (16), whose Ga-Fe bond is slightly longer than that observed in 11.
Reaction of the less bulky LiAr′′ (Ar′′ ) C6H3-2,6-Mes2) with “GaI” afforded the new paramagnetic cluster
Ga11Ar4′′ (17). The ready dissociation of 1, 4, and 6 in solution, the long Ga-Ga distance in 6, and the
chemistry of these compounds showed that the Ga-Ga bonds are significantly weaker than single bonds.
The reduction of 1 and 6 with sodium to give 13 and 14 supplies two electrons to the di-gallium unit to
generate a single bond (in addition to the weak interaction in the neutral precursor) with retention of the
trans-bent geometry. It was concluded that the stability of 13 and 14 depends on the matching size of the
sodium ion, and the presence of Na-Ga and Na-Ar interactions that stabilize their Na2Ga2 core structures.
octahedral metal arrays (e.g., {M(η5-C5Me5)}6 (M ) Ga2 or
Introduction
In3)), more strongly bonded tetramers featuring M4 tetrahedra
Metal-metal bonded clusters of the heavier group 13
elements of formula (MR)n (M ) Al-Tl; R ) organo or related
group) are an extremely interesting compound class, whose
chemistry has undergone rapid development over the past
decade.1-9 They can be isolated in various degrees of aggrega-
tion that include weakly bonded hexamers, which have distorted
(1) (a) Uhl, W. Coord. Chem. ReV. 1997, 163, 1. (b) Janiak, C. Coord. Chem.
ReV. 1997, 163, 107. (c) Uhl, W. ReV. Inorg. Chem. 1998, 18, 239. (d)
Linti, G.; Schno¨ckel, H. Coord. Chem. ReV. 2000, 206-207, 285. (e)
Schno¨ckel, H.; Schnepf, A. AdV. Organomet. Chem. 2001, 47, 235.
(2) Loos, D.; Baum, E.; Ecker, H.; Schno¨ckel, H.; Downs, A. J. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 860.
9
10.1021/ja028579j CCC: $25.00 © 2003 American Chemical Society
J. AM. CHEM. SOC. 2003, 125, 2667-2679
2667

A R T I C L E S
Hardman et al.
(e.g., {Al(η5-C5Me5)}4,4 [M{C(SiMe3)3}]4 (M ) Al-Tl5)), and
feebly bonded dimers (e.g., [M{η5-C5(CH2Ph)5}]2 (M ) In6 or
Tl7), which have M-M distances that are ca. 0.7-0.8 Å longer
than single bonds. Rare examples of higher aggregates include
(GaCH2CMe2Ph)n,8 of unknown structure, or the tricapped
trigonal prismatic (GaBut)9.9 A notable feature of the clusters
in which n g 4 is that they are electron deficient with M-M
bond orders <1. When n ) 3, it is in principle possible to form
a trigonal planar M-M bonded (MR)3 cluster in which the
metals are connected by two-center two-electron donor-
acceptor bonds, although unfilled metal valence orbitals are still
present. In a neutral, dimeric RMMR species, multiple M-M
bonding becomes a possibility, but apart from the weakly
interacting [M{η5-C5(CH2Ph)5}]2 (M ) In or Tl)6,7 compounds
mentioned above, no dimeric group 13 element (MR)2 species
with M-M distances approaching the sum of their covalent radii
have been isolated as stable compounds.
of the nature of the Ga-Ga bonding in the Na2(RGaGaR)
compound class have been seen in the five years since the
original publication, apart from an isolated report that described
the effects of changing the alkali metal to potassium. That
work27 (which also confirmed the original Na2(Ar*GaGaAr*)
structure) suggested that the alkali metal exerted a large effect,
because a product of formula K2(Ar*Ga4Ar*) was isolated. It
contained a square Ga4 array incorporated in a K2Ga4 cluster
with no possibility for Ga-Ga triple bonding. In 1998, it was
suggested that the synthesis of a neutral “digallene” compound
of formula Ar*GaGaAr* corresponding to the removal of 2
sodiums from the reduced complex Na2(Ar*GaGaAr*), or 2
electrons from the putative dianion [Ar*GaGaAr*]2-, as shown
in eqs 1 and 2
Na2Ar*GaGaAr* -2Na8 Ar*GaGaAr* or 2:GaAr* (1)
-8 Ar*GaGaAr* or 2:GaAr* (2)
Our interest in such compounds derives from investigations
of the reaction of the bulky terphenyllithium reagent LiAr* (Ar*
) C6H3-2,6-Trip2; Trip ) C6H2-2,4,6-Pri3) with the monohalides
of indium and thallium where it was hoped that the neutral
dimers Ar*MMAr* (M ) In10 or Tl11) would be produced.
However, the monomers MAr* were isolated instead. These
compounds, which have unique one-coordinate metals, represent
the lowest members (i.e., n ) 1) of the (MR)n series. Their
synthesis prompted speculation on the bonding in their boron,
aluminum, and gallium congeners. The gallium derivative was
of particular interest due to the information it might provide on
the nature of the gallium-gallium bond in the landmark
compound Na2(Ar*GaGaAr*), which was described as triply
bonded.12 This description resulted in a vigorous discussion on
multiple bonding of the heavier main group elements. The most
notable feature of the debate was that it was based almost
exclusively on the results of calculations on various model
species.13-26 Surprisingly, no new experimental investigations
-2e
[Ar*GaGaAr*]2-
would provide useful information on the Ga-Ga bonding.28 If
an Ar*GaGaAr* product could be shown to have a short Ga-
Ga distance that corresponded to a double bond, then triple
bonding in Na2(Ar*GaGaAr*) would be supported. On the other
hand, if the product was monomeric, that is, :GaAr*, multiple
bonding would be unlikely in Na2(Ar*GaGaAr*). Prior to the
work reported here, no stable :GaR or RGaGaR species had
been described. In fact, no stable group 13 compounds corre-
sponding to the formula REER (E ) B-Tl, R ) alkyl, aryl,
silyl, amide groups, etc.), in which the separation of the group
13 elements approached the sum of their covalent radii, were
known, although the compounds HMMH (M ) Ga or In) have
been detected recently by IR spectroscopy in a low temperature
(12 K) matrix29-31 (see below). In this paper, the synthesis,
characterization, and reaction chemistry of several gallium aryls
corresponding to the formula (GaAr)1 or 2 (Ar ) terphenyl and
related ligands) are now described. The types of ligand used to
stabilize the compounds discussed in this paper are given by
the following illustrations.
(3) Beachley, O. T.; Churchill, M. R.; Fettinger, J. L.; Pazik, J. C.; Victoriano,
L. J. Am. Chem. Soc. 1986, 108, 4666.
(4) Dohmeier, C.; Robl, C.; Tacke, M.; Schno¨ckel, H. Angew. Chem., Int. Ed.
Engl. 1991, 30, 564.
(5) (a) Uhl, W.; Hiller, M.; Layh, M.; Schwarz, W. Angew. Chem., Int. Ed.
1992, 31, 1364. (b) Schluter, R. O.; Cowley, A. H.; Atwood, D. A.; Jones,
R. A.; Atwood, J. L. J. Coord. Chem. 1993, 30, 25. (c) Uhl, W.; Graupner,
R.; Layh, M.; Schu¨tz, U. J. Organomet. Chem. 1995, 493, C1. (d) Schitter,
C.; Roesky, H. W.; Ro¨pken, C.; Herbst-Irmer, R.; Schmidt, H.-G.;
Noltemeyer, M. Angew. Chem., Int. Ed. Engl. 1993, 32, 1729. (e) Uhl,
W.; Keimling, S. U.; Klinkhammer, K. W.; Schwarz, W. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 64.
(6) Schumann, H.; Janiak, C.; Go¨rlitz, F.; Loebel, J.; Dietrich, A. J. Organomet.
Chem. 1989, 363, 243.
(7) Schumann, H.; Pickhardt, J.; Bo¨rner, U. Angew. Chem., Int. Ed. 1987, 26,
790.
(8) Beachley, O. T.; Noble, M. J.; Allendoerfer, R. D. J. Organomet. Chem.
1999, 582, 32.
(9) Uhl, W.; Cuypers, L.; Harms, K.; Kaim, W.; Wanner, M.; Winter, R.; Koch,
R.; Saak, W. Angew. Chem., Int. Ed. 2001, 40, 566.
(10) Haubrich, S. T.; Power, P. P. J. Am. Chem. Soc. 1998, 120, 2202.
(11) Niemeyer, M.; Power, P. P. Angew. Chem., Int. Ed. 1998, 37, 1277.
(12) Su, J.; Li, X.-W.; Crittendon, C.; Robinson, G. H. J. Am. Chem. Soc. 1997,
119, 5471.
(23) Grunenberg, J.; Goldberg, N. J. Am. Chem. Soc. 2000, 122, 6045.
(24) Ko¨ppe, R.; Schno¨ckel, H. Z. Anorg. Allg. Chem. 2000, 626, 1095.
(25) Himmel, H.-G.; Schno¨ckel, H. Chem.-Eur. J. 2002, 8, 10.
(26) The debate on the Ga-Ga bonding in Na2(Ar*GaGaAr*), which is difficult
to resolve solely by theoretical argument, need not be revisited here. It is
enough to say that the various bonding models proposed and theoretically
calculated have led to descriptions of the Ga-Ga bond that varied from
between single and double to triple, as well as calculated bond orders that
range from slightly below two to less than three. For example, bond indices
of 2.019 and 2.794 have been calculated for Na2ArGaGaAr model species
by two different methods in ref 16. For a very useful discussion of various
theoretical approaches as well as ELF calculations, see: Molina, J. M.;
Dobado, J. A.; Heard, G. L.; Bader, R. F. W.; Sundberg, M. R. Theor.
Chem. Acc. 2001, 105, 365.
(13) Klinkhammer, K. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 2320; Angew.
Chem. 1997, 109, 2414.
(14) Xie, Y.; Grev, R. S.; Su, J.; Schaefer, H. F.; Schleyer, P. v. R.; Su, J.; Li,
X.-W.; Robinson, G. H. J. Am. Chem. Soc. 1998, 120, 3773.
(15) Bytheway, I.; Lin, Z. J. Am. Chem. Soc. 1998, 120, 12133.
(16) Xie, Y.; Schaefer, H. F.; Robinson, G. H. Chem. Phys. Lett. 2000, 317,
174.
(17) Gru¨tzmacher, H.; Fa¨ssler, T. F. Chem.-Eur. J. 2000, 6, 2317.
(18) Simons, R. S.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1997,
119, 11705.
(19) Cotton, F. A.; Cowley, A. H.; Feng, X. J. Am. Chem. Soc. 1998, 120, 1795.
(20) Allen, T. L.; Fink, W. H.; Power, P. P. Dalton Trans. 2000, 407.
(21) Bridgeman, A. J.; Ireland, L. R. Polyhedron 2001, 20, 2841.
(22) Takagi, N.; Schmidt, M. W.; Nagase, S. Organometallics 2001, 20, 1646.
(27) Twamley, B.; Power, P. P. Angew. Chem., Int. Ed. 2000, 39, 3500.
(28) Power, P. P. Dalton Trans. 1998, 2939.
9
2668 J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003

Chemistry of Neutral Organogallium(I) Compounds
A R T I C L E S
crystals of 1. Combined yield of 1 ) 1.4 g, 34%, yield of 2 ) 1.0 g,
20%. The overall yield of 1 and 2 based on (Et2O)LiC6H3-2,6-Trip2 is
54%. 1: mp 210-216 °C. 1H NMR (400 MHz, C6D6, 25 °C): δ 1.11
The physical and chemical behavior of the neutral (GaAr)1 or 2
species show that any Ga-Ga bonding in such compounds is
weak and the compounds exist as monomers in dilute hydro-
carbon solution. In effect, the pair of electrons at each gallium
behaves more as a lone pair than a bond pair. This conclusion
is in agreement with calculations22 and also with their chemistry
as explored in this paper. The weak Ga-Ga interactions appear
to be marginally stronger than closed shell interactions in main
group and transition metal compounds.32 Reduction of the
(GaAr)1 or 2 species to give Na2(ArGaGaAr) supplies two
electrons to the di-gallium unit to generate a single Ga-Ga
bond. This supplements the weak Ga-Ga bond in the neutral
precursor while preserving the trans-bent C-Ga-Ga-C ge-
ometry. The stability of the Na2(ArGaGaAr) species depends
on the matching size of the Na+ ions and the presence of Na-
Ga and Na-Ar interactions that stabilize the Na2Ga2 cluster at
the core of these molecules.
3
(d, 12H, p-CH(CH3)2) JHH ) 6.8 Hz, 1.20 (d, 24H, o-CH(CH3)2)
3JHH ) 6.8 Hz, 2.79 (sept, 2H, p-CH(CH3)2) 3JHH ) 6.4 Hz, 3.03 (sept,
4H, o-CH(CH3)2) 3JHH ) 6.8 Hz, 7.03 (d, 2H, m-C6H3) 3JHH ) 7.2 Hz,
7.08 (s, 4H, m-Trip). 13C {1H} NMR (100.6 MHz, C6D6, 25 °C): δ
24.49 (CH(CH3)2), 24.94 (CH(CH3)2), 25.21 (CH(CH3)2), 30.94 (o-
CH(CH3)2), 34.84 (p-CH(CH3)2), 121.15 (m-Trip), 122.15 (p-C6H3),
136.32 (m-C6H3) 144.13 (i-Trip), 147.52 (o-C6H3), 148.52 (p-Trip),
150.24 (o-Trip), 176.26 (i-C6H3). UV/vis λmax nm (ꢀ mol L-1 cm-1):
350 (1900), 436 (700). 2: mp 230-232 °C, dec. 1H NMR (300 MHz,
3
C6D6, 25 °C): δ 1.04 (d, 12H, CH(CH3)2) JHH ) 6.9 Hz, 1.25 (d,
3
3
12H, CH(CH3)2) JHH ) 6.9 Hz, 1.35 (d, 12H, CH(CH3)2) JHH ) 6.9
3
Hz, 2.90 (sept, 2H, p-CH(CH3)2) JHH ) 6.9 Hz, 3.00 (sept, 4H,
o-CH(CH3)2) JHH ) 6.9 Hz, 7.03, 7.04, 7.19 (m, Ar-H). 13C {1H}
3
NMR (75 MHz, C6D6, 25 °C): δ 24.50, 24.59 (CH(CH3)2), 24.75, 24.84
(CH(CH3)2), 26.41 (CH(CH3)2), 31.08, 32.10 (o-CH(CH3)2), 34.84
(p-CH(CH3)2), 120.73 (m-Trip), 122.14 (p-C6H3), 128.53 (m-C6H3),
138.21 (i-Trip), 144.66 (o-C6H3), 147.47 (p-Trip), 149.51 (o-Trip),
153.75 (i-C6H3). UV/vis λmax 218 nm, shoulder.
Experimental Section
(Et2O)LiAr# (3). The compound Ar#I was synthesized in a manner
General Procedures. All manipulations were carried out by using
modified Schlenk techniques under an atmosphere of N2 or in a Vacuum
Atmospheres HE-43 drybox. All solvents were distilled from molten
Na/K alloy and degassed three times prior to use. The compounds
(Et2O)LiC6H3-2,6-Trip2,33 LiC6H3-2,6-Dipp2,34 (LiC6H3-2,6-Mes2)2,35
Ga{(NDippCMe)2CH}36 (Dipp ) C6H3-2,6-Pri2), and “GaI”37 were
prepared according to literature procedures. 2,3-Dimethyl-1,3-butadiene
and Fe(CO)5 were trap-to-trap vacuum distilled and dried with 4 Å
molecular sieves. Tris(pentafluorophenyl)borane was used as received
1
similar to that described previously for Ar*I.34 mp 218-220 °C. H
NMR (300 MHz, CDCl3, 25 °C): δ ) 1.08 (d, 12H, o-CH(CH3)2)
3
3JHH ) 6.9 Hz, 1.21 (d, 12H, o-CH(CH3)2) JHH ) 6.9 Hz, 1.37 (s,
3
18H, p-C(CH3)3), 2.53 (sept, 4H, CH(CH3)2)) JHH ) 6.9 Hz, 7.14 (d,
2H, m-C6H3) 3JHH ) 7.5, 7.20 (s, 4H, m-ButDipp), 7.39 (t, 1H, p-C6H3)
3JHH ) 7.5 Hz. 13C {1H} NMR (C6D6, 75 MHz, 25 °C): δ ) 23.84
(CH(CH3)2), 25.39 (CH(CH3)2), 31.35 (CH(CH3)2), 31.97 (C(CH3)3),
35.27 (C(CH3)2), 111.20 (i-C6H3), 119.77 (m-ButDipp), 127.47 (p-C6H3),
128.40 (m-C6H3), 140.15 (i-ButDipp), 145.286 (o-ButDipp), 146.93 (o-
C6H3), 150.77 (p-ButDipp). The lithium salt 3 was synthesized in a
manner similar to that for (Et2O)LiC6H3-2,6-Trip2.33 mp 171-172 °C.
1H NMR (300 MHz, C6D6, 25 °C): δ ) 0.50 (t, 6H, (CH3CH2)2O)
3JHH ) 6.9 Hz, 1.23 (d, 12H, CH(CH3)2) 3JHH ) 6.9 Hz, 1.31 (d, 12H,
1
from Albemarle Corp. H, 11B, 13C, and 19F NMR were recorded on
Varian 300 and 400 spectrometers and referenced to known standards.
UV/vis data were recorded on a Hitachi-1200, while infrared data were
recorded as Nujol mulls using a Perkin-Elmer 1430 instrument. The
EPR spectrum of 17 was obtained with use of a Bruker CWX band
spectrometer operating near 9.6 GHz. Melting points were recorded
using a Meltemp apparatus and are uncorrected.
3
CH(CH3)2) JHH ) 6.9 Hz, 1.39 (s, 18H, C(CH3)3), 2.69 (q, 4H,
3
3
(CH3CH2)2O) JHH ) 6.9 Hz, 3.55 (sept, 4H, CH(CH3)2) JHH ) 6.9
Hz, 7.29 (d, 2H, m-C6H3) JHH ) 7.5 Hz, 7.35 (s, 4H, m-ButDipp),
3
GaAr* (1) and I(Ar*)GaGa(Ar*)I (2). A rapidly stirred toluene
(20 mL) slurry of “GaI” (1.49 g, 7.60 mmol), cooled to ca. -78 °C in
a dry ice-acetone bath, was treated dropwise with a toluene (30 mL)
solution of (Et2O)LiC6H3-2,6-Trip2 (4.20 g, 7.60 mmol) over a period
of 1 h. The solution was then allowed to come to room temperature
over a period of ca. 12 h, whereupon the solvents were removed under
reduced pressure. The residue was heated for 1 h at 60 °C under reduced
pressure to remove any remaining traces of solvent. It was then
suspended in hexane (100 mL), heated to 60 °C, and allowed to settle
for 2 h while maintaining this temperature. Filtration of the supernatant
green solution through Celite afforded a green filtrate which was
allowed to cool to room temperature. Storage in an ca. -20 °C freezer
for 15 h gave green crystals of product 1. The remaining orange solid
residue in the original Schlenk tube was then extracted with benzene
(ca. 50 °C, 80 mL) and filtered. The filtrate was allowed to cool to
room temperature to yield yellow crystals of 2. The dark green
supernatant solution was then decanted and pumped to dryness to afford
a green residue which was redissolved in hot hexane (60 °C, 100 mL).
Cooling in a freezer at ca. -20 °C afforded a further crop of green
7.41 (t, 1H, p-C6H3) JHH ) 7.5 Hz. 13C {1H} NMR (C6D6, 75 MHz,
3
25 °C): δ ) 13.76 ((CH3CH2)2O), 24.67 (CH(CH3)2), 24.87 (CH-
(CH3)2), 30.23 (CH(CH3)2), 31.91 (C(CH3)3), 34.85 (C(CH3)2), 66.33
((CH3CH2)2O), 119.20 (m-ButDipp), 122.88 (m-C6H3), 123.33 (p-C6H3),
146.34 (o-ButDipp), 146.95 (i-ButDipp), 147.90 (o-C6H3), 150.55 (p-
ButDipp), 189.89 (i-C6H3).
GaAr# (4). This compound was synthesized in a manner similar to
that for 1 and isolated as green crystals. Yield: 1.1 g, 25%. mp 201-
1
203 °C. H NMR (300 MHz, C6D6, 25 °C): δ ) 1.19 (d, 12H, CH-
3
3
(CH3)2) JHH ) 6.9 Hz, 1.26 (d, 12H, CH(CH3)2) JHH ) 6.9 Hz, 1.36
(s, 18H, C(CH3)3), 3.10 (sept, 4H, CH(CH3)2) 3JHH ) 6.9 Hz, 7.08 (d,
2H, m-C6H3) 3JHH ) 7.5 Hz, 7.16 (t, 1H, p-C6H3) 3JHH ) 7.5 Hz, 7.40
(s, 4H, m-ButDipp). 13C NMR (75 MHz, C6D6, 25 °C): δ ) 24.30
(CH(CH3)2), 25.12 (CH(CH3)2), 30.94 (CH(CH3)2), 31.70 (C(CH3)3),
35.04 (C(CH3)2), 119.99 (m-ButDipp), 128.20 (m-C6H3), 129.15 (p-
C6H3), 136.71 (i-ButDipp), 144.23 (o-C6H3), 147.18 (o-ButDipp), 150.75
(p-C6H3), 176.45 (i-C6H3). UV/vis nm (ꢀ mol L-1 cm-1): 350 (1800),
434 (510).
I(Ar#)GaGa(Ar#)I (5). This compound was synthesized as yellow
crystals in a manner similar to that for 2. Yield: 0.81 g, 15%. mp
210-213 °C. 1H NMR (300 MHz, C6D6, 25 °C): δ ) 1.074 (d, 12H,
CH(CH3)2), 1.30 (d, 12H, CH(CH3)2), 1.42 (s, 18H, C(CH3)3), 3.04
(sept, 4H, CH(CH3)2), 7.020 (t, 1H, p-C6H3), 7.151 (m, 2H, m-C6H3),
7.368 (s, 4H, 2m-ButDipp). 13C {1H} NMR (75 MHz, C6D6, 25 °C):
δ ) 24.76 CH(CH3)2, 26.30 CH(CH3)2, 31.05 CH(CH3)2, 31.82
C(CH3)3, 35.13 C(CH3)3, 120.88 (m-ButDipp), 129.85 (m-C6H3), 130.25
(p-C6H3), 144.42 (i-ButDipp), 146.94 (o-ButDipp), 148.56 (o-C6H3),
151.57 (p-ButDipp), 156.10 (i-C6H3).
(29) Himmel, H.-J.; Manceron, L.; Downs, A. J.; Pullumbi, P. J. Am. Chem.
Soc. 2002, 124, 4448.
(30) Himmel, H.-J.; Manceron, L.; Downs, A. J.; Pullumbi, P. Angew. Chem.,
Int. Ed. 2002, 41, 796; Angew. Chem. 2002, 114, 829.
(31) Downs, A. J.; Himmel, H.-J.; Manceron, L. Polyhedron 2002, 21, 473.
(32) Pyykko¨, P. Chem. ReV. 1997, 97, 597.
(33) Schiemenz, B.; Power, P. P. Organometallics 1996, 15, 958.
(34) Schiemenz, B.; Power, P. P. Angew. Chem., Int. Ed. Engl. 1996, 35, 2150.
(35) Ruhlandt-Senge, K.; Ellison, J. J.; Wehmschulte, R. J.; Pauer, F.; Power,
P. P. J. Am. Chem. Soc. 1993, 115, 11353.
(36) Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000, 1491.
(37) Green, M. L. H.; Mountford, P.; Smout, G. J.; Speel, S. R. Polyhedron
1990, 9, 2763.
9
J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003 2669

A R T I C L E S
Hardman et al.
Ar′GaGaAr′ (6) and (I)Ar′GaGaAr′(I) (7). A rapidly stirred
toluene (20 mL) slurry of “GaI” (1.49 g, 7.60 mmol), cooled to ca.
-78 °C, was treated dropwise with a toluene (40 mL) solution of
(LiAr′)2 (3.07 g, 3.80 mmol) over ca. 1 h, after which time the mixture
was allowed to come to room temperature over a period of 6 h. Stirring
was discontinued, and the suspension was allowed to settle. The dark
green supernatant solution was filtered through Celite and concentrated
to ca. 15 mL, whereupon a yellow-orange precipitate formed. This was
allowed to settle, and the solution was separated by decantation. The
yield of the orange-yellow solid, which is almost pure 7, is 1.10 g
(0.93 mmol, 24.4%). The green supernatant liquid was stored at ca.
-20 °C in a freezer for 12 h to afford a brown-red crystalline solid.
This was recrystallized from a minimum volume of warm hexane to
afford the product 6 as red-brown crystals. Yield: 0.90 g, 0.96 mmol,
Ar′Ga{B(C6F5)3} (10). This compound was synthesized as colorless
crystals in a manner similar to that for 8. Yield: 0.66 g, 68%. mp
1
218-220 °C. H NMR (300 MHz, C6D6, 25 °C): δ ) 0.89 (d, 12H,
3
3
o-CH(CH3)2) JHH ) 6.9 Hz, 1.08 (d, 12H, o-CH(CH3)2) JHH ) 6.9
3
Hz, 2.75 (sept, 4H, CH(CH3)2) JHH ) 6.9 Hz, 6.93 (d, 4H, m-Dipp)
3JHH ) 7.5 Hz, 7.03 (d, 2H, m-C6H3) JHH ) 7.5 Hz, 7.16 (m, 3H,
3
p-C6H3 and p-Dipp). 13C {1H} NMR (C6D6, 75 MHz, 25 °C): δ )
23.27 (CH(CH3)2), 25.87 (CH(CH3)2), 31.16 (CH(CH3)2), 123.82 (m-
Dipp), 129.15 (m-C6H3), 130.68 (p-Dipp), 131.32 (p-C6H3), 135.85 (br,
C6F5), 137.47 (i-Dipp), 138.83 (br, C6F5), 141.76 (br, C6F5), 146.25
(br, C6F5), 146.72 (o-C6H3), 147.79 (o-Dipp), 149.37 (br, C6F5), 152.61
(i-C6H3). 11B NMR (128 MHz, C6D6, 25 °C): δ ) -17.73. 19F NMR
(376 MHz, C6D6, 25 °C): δ ) -127.03 (o-C6F5), -154.24 (p-C6F5),
-159.06 (m-C6F5).
1
25.3%. mp 206-210 °C. H NMR (C6D6, 400 MHz, 25 °C): δ 1.07
Ar*GaFe(CO)4 (11). A toluene (30 mL) solution of 1 (0.30 g, 0.54
mmol) was treated via syringe with Fe(CO)5 (0.3 mL, 2.3 mmol) with
rapid stirring at room temperature. The solution remained green at first,
but upon stirring for 24 h at room temperature, the color was discharged,
and a colorless solid was precipitated. The solution was then heated to
ca. 100 °C to redissolve the precipitate. Upon cooling to room
temperature over ca. 3 h, large pale yellow crystals of 11‚toluene were
formed. Yield: 0.28 g, 72%. All spectroscopic data were consistent
with those previously reported. The crystal structure of 11‚toluene
showed geometric parameters similar to those reported for 11‚Et2O.
(d, 3JHH ) 6.6 Hz, 24H, CH(CH3)2), 1.09 (d, 3JHH ) 6.6 Hz, 24H, CH-
(CH3)), 2.98 (sept, 3JHH ) 6.7 Hz, 8H, CH(CH3)2), 7.02 (d, 3JHH ) 7.6
Hz, 8H, m-Dipp), 7.14, 7.19, 7.21 (m, Ar-H). 13C {1H} NMR (100.6
MHz, C6D6, 25 °C): δ 25.01 (CH(CH3)2), 25.37 (CH(CH3)2), 30.92
(CH(CH3)2), 123.03 (p-C6H3), 123.40 (m-Dipp), 128.20 (m-C6H3),
128.80 (i-Dipp), 138.87 (o-C6H3), 144.72 (p-Dipp), 147.16 (o-Dipp),
173.80 (i-C6H3). UV/vis (hexanes) λmax nm (ꢀ mol L-1 cm-1): 350
(1600), 437 (520). 7, Yield: 1.10 g, 0.93 mmol. mp > 260 °C decomp.
3
1H NMR (400 MHz, C6D6, 25 °C): δ 0.99 (d, JHH ) 6.4 Hz, 24H,
3
o-CH(CH3)2), 1.18 (d, JHH ) 6.4 Hz, 24H, o-CH(CH3)2), 2.96 (sept,
3JHH ) 6.4 Hz, 8H, o-CH(CH3)2), 7.11-7.15 (m, m-C6H3, m-, p-Dipp),
7.29 (t, 3JHH ) 7.6 Hz, 2H, p-C6H3). 13C {1H} NMR (100.6 MHz, C6D6,
25 °C): δ ) 25.43 (o-CH(CH3)2), 26.83 (o-CH(CH3)2), 31.23 (o-CH-
(CH3)2), 123.39 (p-C6H3), 124.58 (m-Dipp), 129.83 (i-Dipp), 130.60
(m-C6H3), 140.40 (o-C6H3), 145.36 (p-C6H3), 148.07 (o-Dipp), 152.12
(i-C6H3).
{Ar*GaCH2C(Me)C(Me)CH2}2 (12). To a stirred solution of GaAr*
(0.56 g, 1 mmol) in 25 mL of toluene at ca. 0 °C was added 2,3-
dimethyl-1,3-butadiene (0.11 mL, 1 mmol) dropwise. Upon addition,
the solution immediately turned light brown, and after the solution was
warmed to room temperature, stirring was continued for ca. 1 h.
Subsequently, the solvent was removed under reduced pressure, and
the residue was treated with hexanes (30 mL). Upon filtering, the
solution was reduced to a volume of ca. 5 mL. Overnight storage at
-20 °C afforded the product as colorless crystals. Yield: 0.15 g, 23%.
mp 71-78 °C. 1H NMR (400 MHz, C6D6, 25 °C): δ ) 1.16 (d,
3JHH ) 6.9 Hz, 24H, o-CH(CH3)2), 1.22 (d, 3JHH ) 6.9 Hz, 24H, o-CH-
Ar*Ga{B(C6F5)3} (8). At room temperature, GaAr*, 1 (0.551 g, 1
mmol), was dissolved in toluene (20 mL) with rapid stirring. B(C6F5)3
(0.512 g, 1 mmol) in toluene (20 mL) was added dropwise, whereupon
the dark green color of the solution began to fade until the solution
had become colorless upon completion of the addition. All volatile
materials were removed under reduced pressure, and the remaining solid
was redissolved in hexane (10 mL). Slow cooling in an ca. -20 °C
freezer overnight yielded 8 as X-ray quality, colorless crystals. Yield:
0.81 g, 76.4%. mp 187-189°, 201 °C dec. 1H NMR (300 MHz, C6D6,
25 °C): δ 0.97 (d, 12H, CH(CH3)2) 3JHH ) 6.6 Hz, 1.17 (d, 12H, CH-
3
(CH3)2), 1.26 (d, JHH ) 6.6 Hz, 24H, p-CH(CH3)2), 1.30 (s, 12H,
3
GaCH2C(CH3)), 1.74 (s, 8H, GaCH2C(CH3)), 2.81 (d, JHH ) 6.6 Hz,
3
2H, p-CH(CH3)2), 3.09 (d, JHH ) 6.9 Hz, 4H, o-CH(CH3)2), 7.17 (s,
8H, m-Trip), 7.30-7.32 (m, 6H, p-, m-C6H3). 13C NMR (100.6 MHz,
C6D6, 25 °C): δ ) 21.5 (GaCH2C(CH3)), 121.9 (m-Trip), 127.7
(p-C6H3), 132.5 (m-C6H3), 139.91 (ipso-Trip), 147.5 (o-Trip), 147.9
(o-C6H3), 149.7 (p-Trip), 153.4 (i-C6H3).
3
3
(CH3)2) JHH ) 6.9 Hz, 1.24 (d, 12H, CH(CH3)2) JHH ) 6.6 Hz, 2.86
3
(sept, 6H, p-CH(CH3)2) JHH ) 6.9 Hz, 6.96-7.03 (m, Ar-H), 7.09
(s, 4H, o-Trip-H). 13C {1H} NMR (75 MHz, C6D6, 25 °C): δ 23.54
(CH(CH3)2), 23.79 (CH(CH3)2), 25.90 (CH(CH3)2), 31.28 (o-CH(CH3)2),
33.89 (p-CH(CH3)2), 121.80 (m-Trip), 129.61 (p-C6H3), 131.28 (p-Trip),
135.02 (m-C6H3), 135.66 (br, C6F5), 138.29 (br, C6F5), 138.91 (br, C6F5),
146.32 (br, C6F5), 146.83 (i-Trip), 147.81 (o-Trip), 149.38 (br, o-C6F5),
150.86 (o-C6H3), 152.17 (i-C6H3). 11B NMR (128 MHz, C6D6, 25 °C):
δ -18.93. 19F NMR (376 MHz, C6D6, 25 °C): δ -126.85 (o-C6F5),
-153.63 (p-C6F5), -158.90 (m-C6F5).
Na2(Ar*GaGaAr*) (13). Diethyl ether (30 mL) was added to a
Schlenk tube containing GaAr* (1.10 g, 1.9 mmol) and sodium metal
(0.30 g, 13 mmol). The solution was stirred for 4 h, during which time
the color changed from green to dark red. Crystallization from the ether
solution over 12 h at ca. -20 °C afforded X-ray quality crystals of 13
as red blocks. Yield: 0.42 g, 38%. A single-crystal cell check and
melting point were consistent with the reported data.12
Na2(Ar′GaGaAr′) (14). A solution of 6 (1.02 g, 1.9 mmol) in diethyl
ether (30 mL) was added to sodium metal (0.30 g, 13 mmol) and stirred
for 4 h at 25 °C, during which time the color changed from green to
dark red. The solution was separated from the excess sodium,
concentrated, and cooled in a -20 °C freezer for 30 h to afford 14 as
dark red parallelepipeds. Yield: 0.37 g, 38%. mp 121-123 °C dec >
270 °C. 1H NMR (400 MHz, C6D6, 25 °C): δ 1.12 (d, 3JHH ) 6.8 Hz,
Ar#Ga{B(C6F5)3} (9). This compound was synthesized as colorless
crystals in a manner similar to that for 8. Yield: 0.71 g, 65%. mp
184-186 °C. 1H NMR (400 MHz, C6D6, 25 °C): δ ) 0.980 (d, 12H,
3
3
o-CH(CH3)2) JHH ) 6.9 Hz, 1.19 (d, 12H, o-CH(CH3)2) JHH ) 6.9
Hz, 1.292 (s, 18H, p-C(CH3)3), 2.84 (sept, 4H, CH(CH3)2)) 3JHH ) 6.9
Hz, 6.95 (d, 2H, m-C6H3) 3JHH ) 7.5 Hz, 7.00 (t, 1H, p-C6H3) 3JHH
)
3
7.5 Hz, 7.253 (s, 4H, m-ButDipp), 7.39 (t, 1H, p-C6H3) 3JHH ) 7.5 Hz.
13C {1H} NMR (100.6 MHz, C6D6, 25 °C): δ ) 23.57 CH(CH3)2, 25.97
CH(CH3)2, 31.37 C(CH3)3, 31.54 CH(CH3)2, 35.29 C(CH3)2, 120.84
(m-ButDipp), 129.85 (m-C6H3), 131.24 (p-C6H3), 135.62 (br, C6F5),
139.15 (br, C6F5), 141.64 (br, C6F5), 146.25 (br, C6F5), 147.08 (o-C6H3),
147.54 (o-ButDipp), 149.35 (br, C6F5), 151.02 (i-C6H3), 153.30 (p-
ButDipp). 11B NMR (128 MHz, C6D6, 25 °C): δ ) 18.03. 19F NMR
(376 MHz, C6D6, 25 °C): δ -127.05 (o-C6F5), -153.56 (p-C6F5),
-158.80 (m-C6F5).
24H, CH(CH3)3), 1.14 (d, JHH ) 6.8 Hz, 24H, CH(CH3)2, 2.90 (sept,
3JHH ) 6.8 Hz, 8H, CH(CH3)2), 7.10 (d, 3JHH ) 8.0 Hz, 4H, m-C6H3),
3
3
7.18 (d, JHH ) 8.0 Hz, 8H, m-Dipp), 7.21 (t, JHH ) 8.0 Hz, 2H,
p-C6H3), 7.31 (t, JHH ) 7.6 Hz, 4H, p-Dipp). 13C {1H} NMR (100.6
3
MHz, C6D6, 25 °C): δ 24.31 (CH(CH3)2), 24.43 (CH(CH3)2), 30.72
(CH(CH3)2), 122.82 (p-C6H3), 128.19 (m-Dipp), 128.37 (m-C6H3),
131.39 (p-Dipp), 139.65 (o-C6H3), 141.04 (i-Dipp), 146.82 (o-Dipp),
149.25 (i-C6H3). UV/vis (hexanes) λmax nm (ꢀ mol L-1 cm-1): 342
(2700), 439 (1500), 528 (1200).
9
2670 J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003

Chemistry of Neutral Organogallium(I) Compounds
A R T I C L E S
Table 1. Selected Crystallographic Data for Compounds 2, 3, 8-10, 12, 16, and 17
(2)
(3)
Ar#Li‚Et2O
(8)
(9)
(Ar*GaI)2‚2C H
Ar*GaB(C F )
Ar#GaB(C F )
6
6
6
5 3
6
5 3
formula
fw
color, habit
cryst syst
space group
a, Å
C84H110Ga2I2
1512.96
yellow, block
triclinic
P1h
13.969(9)
15.832(11)
17.957(9)
89.50(3)
71.97(2)
89.94(3)
3776(4)
2
C47H63LiO
590.86
colorless, block
monoclinic
P21/n
9.2139(7)
16.7871(13)
24.6129(19)
90.9000(10)
92.268(2)
107.3310(10)
3804.0(5)
4
C54H49BF15Ga
1063.46
colorless, parallelepiped
monoclinic
P21/n
12.446(2)
18.815(4)
20.580(4)
C56H53BF15Ga
1091.51
colorless, block
triclinic
P1h
11.9331(9)
12.5786(9)
17.8282(13)
b, Å
c, Å
R, °
â, °
92.692(6)
97.6470(10)
γ, °
V, Å3
4813.7(16)
4
2527.5(3)
2
Z
cryst dim, nm
0.37 × 0.28 × 0.21
0.65 × 0.45 × 0.43
0.15 × 0.08 × 0.08
0.25 × 0.28 × 0.25
d
calc, g cm-3
1.331
1.032
1.467
1.434
µ, mm-1
1.573
13 493
11 564
0.0694
0.059
12 072
9847
0.0579
0.667
9815
6913
0.0527
0.637
15 131
12 607
0.0378
no. of reflns
no. of obsd reflns
R1 obsd reflns
wR2, all
0.1577
0.1774
0.1508
0.1228
(10)
Ar′GaB(C F )
(12)
(16)
(17)
(Ar*Ga(CH C(CH ))2)2
Dipp2N∧NGaFe(CO)4‚C H
Ar4Ga11‚3C H
7 8
6
5 3
2
3
6
7
formula
fw
C96H74F30Ga2
1958.61
C84H118Ga2
1267.22
C40H49FeGaN2O4
747.38
C213H200Ga22
4293.57
color, habit
cryst syst
space group
a, Å
b, Å
c, Å
colorless, block
monoclinic
P21/c
17.216(2)
22.819(5)
22.301(3)
colorless, block
monoclinic
P21/n
9.0470(4)
26.8579(11)
15.3625(6)
colorless, block
orthorhombic
Pnma
22.0914(8)
16.5373(6)
10.5410(4)
red, block
orthorhombic
P212121
18.4464(9)
20.6011(10)
25.3976(12)
R, °
â, °
102.876(5)
94.2690(10)
γ, °
V, Å3
8541(2)
4
3722.5(3)
2
3851.0(2)
4
9651.5(8)
4
Z
cryst dim, mm
0.36 × 0.24 × 0.23
0.18 × 0.14 × 0.12
0.44 × 0.30 × 0.34
0.25 × 0.22 × 0.21
d
calc, g cm-3
1.523
1.131
1.289
1.826
µ, mm-1
0.745
0.765
8553
4963
0.0509
1.117
6505
5607
0.0330
3.062
17 717
13 248
0.0493
no. of reflns
no. of obsd reflns
R1 obsd reflns
wR2, all
19 434
13 461
0.0555
0.1381
0.1262
0.0948
0.1258
Dipp2N∧NGaFe(CO)4 (16). A solution of GaN∧NDipp2, 15 (0.80
g, 1.64 mmol), in toluene (30 mL) at ca. 0 °C was treated via syringe
with Fe(CO)5 (0.30 mL, 2.30 mmol) with rapid stirring. The reaction
mixture was allowed to warm to room temperature and was stirred for
a further 12 h, after which time a colorless precipitate had formed.
The suspension was then heated until the precipitate had completely
dissolved. Cooling to room temperature over a period of 4 h afforded
colorless, X-ray quality crystals of Dipp2N∧NGaFe(CO)4. Yield: 0.28
g, 26%. mp 279-280 °C. IR: 1900, 1915, 1940, 2010 cm-1. 1H NMR
(300 MHz, C6D6, 25 °C): δ 1.04 (d, 3JHH ) 6.6 Hz, 12H, CH(CH3)2),
1.41 (d, 3JHH ) 6.6 Hz, 12H, CH(CH3)2), 1.52 (s, 6H, CMe), 2.99 (sept,
3JHH ) 6.6 Hz, 4H, CH(CH3)2), 5.08 (s, 1H, methine CH), 7.10, 7.12,
7.21, 7.24 (m, Ar-H). 13C {1H} NMR (75 MHz, C6D6, 25 °C): δ
24.34 CH(CH3)2), 24.62 C(CH3)), 24.89 CH(CH3)2), 29.34 CH(CH3)2),
101.18 (γ-C), 125.02 (m-Dipp), 128.97 (p-Dipp), 139.54 (o-Dipp;
CCHC(CH3)2), 143.25 (C(CH3)), 169.80 (CN), 214.85 (CO).
Ga11(C6H3-2,6-Mes2)4 (17). LiC6H3-2,6-Mes2 (1.10 g, 3.43 mmol)
and GaN∧NDipp2 (1.67 g, 3.43 mmol) were combined in a Schlenk
tube equipped with a stir bar, and toluene (40 mL) was added. The
solution was allowed to stir for 12 h with heating to 75 °C. After 12
h, the deep red solution was reduced in volume to incipient crystal-
lization (5-10 mL) and placed in a freezer at ca. -20 °C. After three
weeks, dark red crystals along with some pale yellow crystals were
obtained and separated by hand. The pale yellow crystals were found
to be Ga{(NDippCMe)2CH} (checked by melting point and unit cell
dimensions). The red crystals were found to be Ga11(C6H3-2,6-Mes2)4
(6)‚1.5 toluene. Yield: 0.20 g, 12% (based on GaN∧NDipp2).
X-ray Crystallographic Studies. Sample preparation consisted of
removing the crystal from the Schlenk tube under a rapid flow of argon
and immediately submerging it in hydrocarbon oil. A suitable crystal
was selected, mounted on a glass fiber, attached to a copper pin, and
rapidly placed in a cold stream of N2 (-183 °C) of the diffractometer
for data collection.38 Data were collected on a Bruker SMART 1000
diffractometer with use of Mo KR (λ ) 0.71073 Å) radiation and a
CCD area detector. Data collection and processing were performed
using the programs SMART39a and SAINT39b provided by Bruker AXS.
Empirical absorption corrections were applied for samples 8-10, 12,
16, and 17 using SADABS.39c The crystal structures were solved using
either direct methods or the Patterson option in SHELXS40a and refined
by the full-matrix least-squares procedure in the SHELXL40a program.
During the initial refinements of structures 2 and 17, both displayed
(38) Hope, H. Prog. Inorg. Chem. 1995, 41, 1.
(39) (a) SMART: Area-Detector Software Package; Bruker AXS, Inc.: Madison,
WI, 1993. (b) SAINT: Area-Detector Integration Software; Bruker AXS,
Inc.: Madison, WI, 1995. (c) SADABS: Area-Detector Absorption
Correction; Bruker AXS, Inc.: Madison, WI, 1996.
(40) (a) SHELXL PC, version 5.03; Bruker AXS, Inc.: Madison, WI, 1994.
(b) Cooper, R. I.; Gould, R. O.; Parsons, S.; Watkin, D. J. J. Appl.
Crystallogr. 2002, 35, 168.
9
J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003 2671

A R T I C L E S
Hardman et al.
evidence of twinning. Using the program ROTAX,40b we determined
the appropriate twinning laws and refined the structures normally. All
non-hydrogen atoms were refined anisotropically, while hydrogen atoms
were placed at calculated positions and included in refinement using a
riding model. Structure 12 contained disordered alkene and methyl
groups (C(38), C(39), and C(40)), which occupied two positions with
50% probability. The central Ga3 unit in compound 17 (i.e., Ga(3),
Ga(4), Ga(5)) was rotationally disordered between two positions. The
gallium atoms were refined satisfactorily with 50% occupancy. Some
details of the data collection and refinement are given in Table 1. Further
details are provided in the Supporting Information. Compound 16
contains a rotationally disordered toluene molecule which was modeled
with variable occupancy. Compound 17 crystallized with three disor-
dered toluene molecules, two of which were disordered around a two-
fold rotation axis, whereas the third was translationally disordered. The
carbons were modeled successfully with variable occupancies. Hydro-
gens were not added to the disordered toluenes.
Table 2. Selected Interatomic Distances (Å) and Angles (deg) for
2, 3, 6, 7
I(Ar*)GaGa(Ar*)I (2)
I(Ar′)GaGa(Ar′)I (7)
Ga(1)-Ga(1A)
2.482(2)
2.502(2)
2.514(2)
2.5373(14)
1.973(7)
1.983(6)
Ga(1)-Ga(2)
2.493(2)
2.525(2)
2.541(2)
1.976(10)
1.979(9)
Ga(2)-Ga(2A)
Ga(1)-I(1)
Ga(1)-I(1)
Ga(2)-I(2)
Ga(1)-C(1)
Ga(2)-C(31)
Ga(2)-I(2)
Ga(1)-C(1)
Ga(2)-C(37)
C(1)-Ga(1)-Ga(2) 127.1(3)
C(1)-Ga(1)-Ga(1A) 130.5(2)
I(1)-Ga(1)-Ga(1A) 110.80(5)
C(1)-Ga(1)-I(1)
Ga(2)-Ga(1)-I(1)
119.8(3)
112.73(5)
C(1)-Ga(1)-I(1)
118.8(2)
Ga(31)-Ga(2)-Ga(1) 130.1(2)
C(37)-Ga(2)-Ga(2A) 129.6(2)
I(2)-Ga(2)-Ga(2A) 110.22(5)
C(31)-Ga(2)-I(2)
Ga(1)-Ga(2)-I(2)
120.4(2)
109.38(5)
C(37)-Ga(2)-I(2)
119.2(2)
(Et2O)LiAr# (3)
Ar′GaGaAr′ (6)
Li(1)-C(1)
Li(1)-O(1)
C(1)-C(6)
C(1)-C(2)
O(1)-C(39)
O(1)-C(41)
2.036(2)
1.881(2)
1.418(1)
1.422(1)
1.442(2)
1.432(2)
Ga(1)-Ga(1A)
Ga(1)-C(1)
C(1)-C(2)
2.6268(7)
2.025(3)
1.402(4)
1.412(4)
Results and Discussion
C(1)-C(6)
C(1)-Ga(1)-Ga(1A) 123.16(7)
The following compounds are the main concern of the
discussion: 1, GaAr* (Ar* ) C6H3-2,6-Trip2); 2, I(Ar*)GaGa-
(Ar*)I; 3, (Et2O)LiAr# (Ar# ) C6H3-2,6-(ButDipp)2); 4, GaAr#;
5, I(Ar#)GaGa(Ar#)I); 6, Ar′GaGaAr′ (Ar′ ) C6H3-2,6-Dipp2);
7, I(Ar′)GaGa(Ar′)I; 8, Ar*Ga{B(C6F5)3}; 9, Ar#Ga{B(C6F5)3};
C(2)-C(1)-C(6)
Ga(1)-C(1)-C(2)
Ga(1)-C(1)-C(6)
C(1) ring to
118.0(2)
122.6(2)
119.2(2)
89.2
O(1)-Li(1)-C(1) 164.4(2)
C(2)-C(1)-C(6) 114.97(9)
C(39)-O(1)-Li(1) 120.46(13)
C(41)-O(1)-Li(1) 120.08(12)
C(39)-O(1)-C(41) 113.46(11)
CGaGaC core
C(7) and C(19) ring 89.8, 85.7
to C(1) ring
C(1)‚‚‚C(4) vector to 2.8
CGaGaC
10, Ar′Ga{B(C6F3)3}; 11, Ar*GaFe(CO)4; 12, {Ar*GaCH2C-
(Me)C(Me)CH2}2; 13, Na2(Ar*GaGaAr*); 14, Na2(Ar′GaGaAr′);
15, GaN∧NDipp2; 16, (Dipp2N∧NGa)Fe(CO)4; and 17, Ga11-
Ar′′4 (Ar′′ ) C6H3-2,6-Mes2).
overcome the crystallization problems seen with 1. Unfortu-
nately, 4, which was also obtained as green crystals, had the
same X-ray diffraction characteristics as 1. In contrast, the
reaction of the less crowded (LiAr′)2 reagent with “GaI” afforded
X-ray quality, brown-red crystals of the dimer (GaAr′)2 (6).41
This compound has a long Ga-Ga bond of 2.6268(7) Å with a
trans-bent CGaGaC (Ga-Ga-C ) 123.16(7)°) core (vide infra).
Despite the poor diffraction characteristics of 1 and 4, yellow
crystals of the related 1,2-diiododigallane coproducts 2 and 7,
obtained via eqs 3 and 5, could be characterized by X-ray
crystallography. Important structural data for 2, 3, 5-7 are given
in Table 2.
Synthesis, Characterization, and Reactions. The reaction
of “GaI”37 with (Et2O)LiAr*,33 (LiAr′)2,34 or (Et2O)LiAr# (3)
yielded the organogallium(I) compounds GaAr* (1), GaAr# (4),
or Ar′GaGaAr′ (6)41 along with the aryliododigallanes {Ga-
(Ar*)I}2 (2), {Ga(Ar#)I}2 (5), or {Ga(Ar′)I}2 (7)41 as shown in
eqs 3-5. The lithium aryl 3 was synthesized in a manner similar
to that described for (Et2O)LiAr*.33 The products of eqs 3-5
can be separated readily through recrystallization from either
hexane or benzene because of the lower solubility of the iodo
“GaI” + LiAr* ) GaAr* + I(Ar*)GaGa(Ar*)I (3)
1
2
The green color of 1 and 4 observed in the crystal phase was
retained in hydrocarbon (hexane, cyclohexane, benzene, ether)
solution. Furthermore, the brown-red crystals of 6 also dissolved
in various hydrocarbons to afford green solutions that were very
similar to those of 1 and 4. Consistent with the visual appearance
of these solutions, the UV/vis spectra of compounds 1, 4, and
6 (Table 5) in hexane were almost identical to each other and
featured two absorptions near 350 and 435 nm. Cryoscopic
studies of 1 and 6 in cyclohexane were undertaken to determine
the aggregation number in solution. Data for 1 were recorded
at two different molalities of 1.83 × 10-2 and 3.03 × 10-2
mol/kg, that is, 18.3 and 30.3 mmolal. The freezing point
depression corresponded to a MW of 540 ( 40 g/mol. Because
the MW of GaAr* is 551.51 g/mol, the data show that 1 exists
primarily as a monomer in cyclohexane at these concentrations.
Similar studies of 6 afforded molecular weights consistent with
a monomeric structure. Thus, 6, although it is weakly associated
in the crystal phase, resembles 1 in that it dissociates to
monomers in cyclohexane. Clearly, both the UV/visible and the
cryoscopic data are in harmony with regard to the existence of
1, 4, and 6 as monomers in hydrocarbon solvents. The 1H NMR
spectra displayed absorptions corresponding to the presence of
“GaI” + LiAr# ) GaAr# + I(Ar#)GaGa(Ar#)I
(4)
4
5
2”GaI” + 2(LiAr′)2 ) Ar′GaGaAr′ + I(Ar′)GaGa(Ar′)I (5)
6
7
compounds 2, 5, and 7 in these solvents. Unfortunately, 1 or 4,
which were obtained as green crystals, were unsuitable for X-ray
crystallography. Attempts to grow X-ray quality crystals of 1
from ether, tetrahydrofuran, toluene, benzene, hexane, and
pentane, or by slow sublimation at 190 °C and 0.05 Torr, were
unsuccessful. The crystals obtained by the above methods
appeared to be well-formed, but they did not extinguish in
polarized light, and rotation images on the diffractometer
displayed only a small number of diffraction spots at low θ
angles. In addition, an X-ray powder diffraction analysis was
attempted, but the results were inconclusive. The synthesis of
GaAr#, 4, in which the para-Pri groups of the flanking aryl rings
were replaced by But groups, was undertaken primarily to
(41) Hardman, N. J.; Wright, R. J.; Phillips, A. D.; Power, P. P. Angew. Chem.,
Int. Ed. 2002, 41, 2842.
9
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Chemistry of Neutral Organogallium(I) Compounds
A R T I C L E S
Table 3. Selected Interatomic Distances (Å) and Angles (deg) for 8-10
Ar*Ga{B(C F ) } (8)
Ar#Ga{B(C F ) } (9)
Ar′Ga{B(C F ) } (10)
6 5 3
6
5 3
6
5 3
Ga(1)-B(1)
2.110(3)
1.943(3)
1.636(5)
1.639(5)
1.616(5)
2.394(2)
173.28(14)
106.3(3)
115.5(3)
115.3(3)
Ga(1)-B(1)
Ga(1)-C(1)
B(1)-C(39)
B(1)-C(45)
B(1)-C(51)
Ga(1)‚‚‚F(1)
B(1)-Ga(1)-C(1)
C(39)-B(1)-C(45)
C(39)-B(1)-C(51)
C(45)-B(1)-C(51)
2.108(2)
1.939(1)
1.632(2)
1.638(2)
1.628(2)
2.435(2)
172.97(6)
108.3(1)
115.9(1)
115.9(1)
Ga-Ba
Ga-C
2.129(3), 2.118(3)
1.949(3), 1.948(3)
1.633(5), 1.628(4)
1.617(5), 1.632(5)
1.633(5), 1.624(4)
2.344(2)
176.44(13), 175.51(13)
106.2(3), 105.8(2)
115.5(3), 114.7(3)
115.7(3), 117.1(2)
Ga(1)-C(1)
B(1)-C(37)
B-C
B(1)-C(43)
B-C
B-C
Ga‚‚‚F
B-Ga-C
C-B-C
C-B-C
C-B-C
B(1)-C(49)
Ga(1)‚‚‚F(1)
B(1)-Ga(1)-C(1)
C(37)-B(1)-C(43)
C(37)-B(1)-C(49)
C(43)-B(1)-C(49)
a Two crystallographically independent molecules.
Scheme 1. Reactions of the Monomer GaAr*
found to have structural parameters very similar to those of 13
(cf. Table 4). Compound 1 also reacted rapidly with B(C6F5)3
or Fe(CO)5 in hydrocarbon solvent at room temperature to afford
Ar*Ga{B(C6F5)3}, 8, or Ar*GaFe(CO)4, 11. It is notable that
no forcing conditions, for example, refluxing or photolysis, were
required to induce these reactions to occur. The related GaAr#
and Ar′GaGaAr′ compounds 4 and 6 also reacted readily with
B(C6F5)3 to yield the products 9 and 10. The three B(C6F5)3
adduct species 8-10 were characterized by X-ray crystal-
lography. The 11B NMR spectra of 8-10 display relatively sharp
singlets at δ -18.93, -18.03, and -17.73 ppm, respectively.
Three 19F NMR signals that correspond to the ortho, meta, and
para fluorines were also observed in each case. The sterically
related GaN∧NDipp2, 15,36 reacted with Fe(CO)5 to give the
product Dipp2N∧NGaFe(CO)4, 16, which is related to 11.
Treatment of 1 with 2,3-dimethyl-1,3-butadiene resulted in
the addition product 12, which featured a 10-membered Ga2C8
ring in which the Ga- -Ga separation is 5.736 Å. The synthesis
of (GaAr′′)n was attempted through the reaction of (LiAr′′)2 with
“GaI”, but this yielded colorless crystals of IGaAr′′2. To avoid
this result, GaN∧NDipp2 (15) was used as the gallium source.
However, treatment of this compound with (LiAr′′)2 did not
yield (GaAr′′)n. Instead, it afforded the unique paramagnetic
cluster Ga11Ar′′4 (17).
Ar*, Ar#, and Ar′ groups only, and the 13C NMR spectra
indicated low field ipso C absorptions at δ 176.26 (1), 176.45
(4), and 173.80 (6), which show that this atom is substituted
by an electropositive metal.
In the absence of X-ray structural data for compounds 1 and
4, they were further characterized by their chemical behavior.
Several reactions were examined as shown in Scheme 1.
Reaction of 1 with B(C6F5)3, Fe(CO)5, 2,3-dimethyl-1,3-
butadiene, or sodium afforded the products Ar*GaB(C6F5)3 (8),
Properties of the Gallium Aryls 1, 4, and 6 and Their
Halogen Derivatives 2, 5, and 7. Compounds 1, 4, and 6 are
relatively rare examples of neutral organogallium(I) com-
pounds.1 Only a handful of such molecules are known, and they
display either tetrameric (with Ga4 tetrahedra),1c,4 quasi hex-
americ,2 or nonameric9 structures in the solid state. In the
tetramers, the Ga-Ga bond lengths in the Ga4 tetrahedra are in
the range 2.57-2.71 Å,1c which is longer than the ca. 2.50 Å
expected for a single bond from the sum of covalent radii. This
is in keeping with the electron-deficient nature of the Ga4 array,
where the formal Ga-Ga bond order is 2/3. Although all
previously reported neutral organogallium(I) compounds are
associated in the solid state, they may dissociate to monomers
in solution or the vapor phase. Electron diffraction studies of
Ar*GaFe(CO)4 (11),42 (Ar*Ga-CH2C(Me)C(Me)CH2)2 (12),
and Na2(Ar*GaGaAr*) (13).12 The products 11 and 13 have
been reported previously by Robinson and co-workers, but they
were synthesized by different synthetic routes that involved the
reaction of GaAr*Cl2 with Na2Fe(CO)4 to give 1142 or the
reduction of GaAr*Cl2 by excess sodium to give 13.12 The
structure of 11, which crystallized with one molecule of toluene
per asymmetric unit, was essentially identical to that previously
reported42 where it cocrystallized with a molecule of ether. The
compound Na2(Ar*GaGaAr*), 13, was identified via a unit cell
check, 13C NMR, and UV/vis spectroscopic data. In the original
synthetic report, it was noted that during the reduction of
GaAr*Cl2 the solution initially turned green.12 In our hands,
the same phenomenon was observed upon treatment of GaAr*Cl2
with sodium. If the reaction mixture was separated from the
sodium after ca. 3 h, the green color persisted, and it was
possible to crystallize 1 in ca. 10% yield from this solution.
The related compound Na2(Ar′GaGaAr′) 14 could be synthe-
sized by stirring solutions of 6 or 7 with excess sodium. It was
characterized spectroscopically and crystallographically and was
Ga(η5-C5Me5)43 and GaC(SiMe3)3 vapors have revealed a
44
monomeric nido GaC5 structure in the case of the former and
a monomeric structure with a one-coordinate metal for the latter
species. Stabilization of unassociated Ga(I) compounds in the
solid state can be effected by polydentate ligands as in GaTpBut2
(Tp ) tris(pyrazolyl)borato)45 and GaN∧NDipp2 15,36 which
(43) Haaland, A.; Martinsen, K.-G.; Volden, H. V.; Loos, D.; Schno¨ckel, H.
Acta Chem. Scand. 1994, 48, 172.
(44) Haaland, A.; Martinsen, K.-G.; Volden, H. V.; Kaim, W.; Waldho¨r, E.;
Uhl, W. Organometallics 1996, 15, 1146.
(42) Su, J.; Li, X.-W.; Crittendon, R. C.; Campana, C. F.; Robinson, G. H.
Organometallics 1997, 16, 4511.
9
J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003 2673

A R T I C L E S
Hardman et al.
Table 4. Selected Interatomic Distances (Å) and Angles (deg) for 12-14, 16, 17
Na2(Ar*GaGaAr*) (13)
Na2(Ar′GaGaAr′) (14)
Ga(1)-Ga(2)
Ga-C
Ga-Na
Ga-Na
Na-C
2.3243(10)
Ga(1)-Ga(1A)
Ga(1)-C(1)
2.3469(12)
2.045(6), 2.036(6)
3.065(3), 3.103(3)
3.085(3), 3.102(3)
2.847(6), 3.045(7)
2.850(6), 3.048(7)
2.876(6), 3.051(6)
2.934(6), 3.062(6)
2.992(6), 3.070(7)
3.105(6), 3.100(7)
3.102(6)
3.127(6)
125.93(17), 134.03(10)
122.4(4)
121.3(4)
120.6(4)
2.059(5)
3.058(2)
3.101(2)
3.034(5)
2.984(5)
2.933(5)
2.940(6)
3.051(5)
3.021(5)
2.937(5)
2.879(6)
2.886(6)
3.004(5)
130.69(13)
121.9(3)
121.5(3)
88.6
Ga(1)-Na(1)
Ga(1)-Na(1A)
Na(1)-C(7)
Na(1)-C(9)
Na(1)-C(10)
Na(1)-C(11)
Na(1)-C(19)
Na(1)-C(20)
Na(1)-C(21)
Na(1)-C(22)
Na(1)-C(23)
Na(1)-C(24)
C(1)-Ga(1)-Ga(1A)
Ga(1)-C(1)-C(2)
Ga(1)-C(1)-C(6)
Ga(2)-C(37)-C(38)
Ga(2)-C(37)-C(42)
C(1),C(37) (ring) to
C(1)Ga(1)Ga(2)C(37)
C(1)-Ga(1)-Ga(1A)
Ga(1)-C(1)-C(2A)
Ga(1)-C(1)-C(6A)
C(1) (ring) to
123.1(4)
84.5, 87.6
C(1)Ga(1)Ga(1A)C(11)
{Ar*GaCH C(Me)C(Me)CH }2 (12)
Dipp2N∧NGaFe(CO)4 (16)
2
2
Ga(1)-C(1)
1.992(3)
1.985(5)
1.978(3)
av. 1.554(10)
1.330(10)
113.52(12)
121.39(12)
125.09(12)
Ga(1)-N(1)
Ga(1)-Fe(1)
Fe(1)-C(16)
Fe(1)-C(17)
Fe(1)-C(18)
O(1)-C(16)
O(2)-C(17)
O(2)-C(18)
1.9273(11)
Ga(1)-C(37)
2.2851(3)
1.795(2)
1.777(2)
1.772(2)
1.149(2)
1.162(3)
1.142(2)
Ga(1)-C(41)
C(41)-C(40)
C(38)-C(40)
C(1)-Ga(1)-C(37)
C(1)-Ga(1)-C(41)
C(37)-Ga(1)-C(41)
Ga14Ar4′′ (17)
Ga(2)-Ga(1)-Ga(2A)
Ga(1)-Ga(2)
Ga(1)-Ga(2A)
Ga(1)-Ga(4)
Ga(1)-Ga(5A)
Ga(2)-Ga(3)
Ga(2)-Ga(5A)
Ga(3)-Ga(7A)
Ga(3)-Ga(6)
Ga(3)-Ga(5)
Ga(4)-Ga(5)
Ga(4)-Ga(7)
Ga(4)-Ga(4A)
Ga(5)-Ga(1A)
Ga(5)-Ga(2A)
Ga(6)-Ga(7)
Ga(6)-Ga(7A)
Ga(1)-C(1)
2.529(1)
2.563(1)
2.603(1)
2.664(2)
2.547(2)
2.648(2)
2.610(2)
2.652(2)
2.667(3)
2.661(2)
2.564(2)
2.638(2)
2.664(2)
2.648(2)
2.558(2)
2.557(2)
1.991(6)
1.996(6)
77.36(3)
102.42(3)
102.62(3)
76.41(3)
132.55(2)
138.4(2)
81.18(4)
67.65(4)
77.02(5)
104.51(5)
92.32(7)
92.00(7)
98.67(6)
58.01(6)
65.06(6)
96.39(6)
58.21(6)
54.83(3)
91.96(6)
54.81(5)
63.78(6)
57.68(4)
65.12(5)
60.14(4)
55.02(3)
70.15(4)
Ga(1)-Ga(2)-Ga(1A)
Ga(7)-Ga(6)-Ga(7A)
Ga(6)-Ga(7)-Ga(6A)
C(1)-Ga(1)-Ga(2)
C(1)-Ga(1)-Ga(2A)
Ga(2)-Ga(1)-Ga(4)
Ga(4)-Ga(1)-Ga(2A)
Ga(1A)-Ga(2)-Ga(3)
Ga(1)-Ga(2)-Ga(3)
Ga(2)-Ga(3)-Ga(5)
Ga(2)-Ga(3)-Ga(5)
Ga(6)-Ga(3)-Ga(5)
Ga(5)-Ga(3)-Ga(4)
Ga(6)-Ga(3)-Ga(4)
Ga(1)-Ga(4)-Ga(3)
Ga(3)-Ga(4)-Ga(5)
Ga(6)-Ga(4)-Ga(7)
Ga(5)-Ga(4)-Ga(6)
Ga(3)-Ga(4)-Ga(6)
Ga(30)-Ga(5)-Ga(4)
Ga(1A)-Ga(5)-Ga(2A)
Ga(2)-Ga(5)-Ga(4)
Ga(3)-Ga(6)-Ga(4)
Ga(4)-Ga(6)-Ga(7)
Ga(6)-Ga(7)-Ga(4)
Ga(7)-C(25)
Table 5. UV/Vis Spectroscopic Data (nm, mol L-1 cm-1) for 1, 4,
and 6 in Hexane Solution
it is bidentate, it is slightly more crowded due to its bonding
mode. A monomeric structure is observed for this compound
in the solid state.36
GaAr*, 1
GaAr#, 4
GaAr′, 6
350 (1900)
350 (1800)
350 (1600)
436 (700)
434 (510)
437 (520)
Compounds 1, 4, and 6 are closely related to their indium
and thallium congeners MAr* (M ) In,10 Tl11) and Ar′InInAr′.46
Uniquely, the indium and thallium MAr* species are unasso-
ciated in the solid state and have one-coordinate metals, whereas
Ar′InInAr′,46 the indium analogue of Ar′GaGaAr′, 6, is also
weakly associated in the crystalline phase. At present, it is not
feature three- and two-coordinate gallium in the solid state,
respectively. The latter has v-shaped coordination at gallium
and displays carbene-like behavior. The N∧NDipp2 group
sterically resembles the ligands Ar*, Ar#, and Ar′, but, because
(45) Kuchta, M. C.; Bonanno, J. B.; Parkin, G. J. Am. Chem. Soc. 1996, 118,
(46) Wright, R. J.; Phillips, A. D.; Hardman, N. J.; Power, P. P. J. Am. Chem.
Soc. 2002, 124, 8538.
10914.
9
2674 J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003

Chemistry of Neutral Organogallium(I) Compounds
A R T I C L E S
Figure 1. Thermal ellipsoid (30%) drawings of 2, 3, 6, 9, 12, 14, 16, and 17. Hydrogen atoms are not shown. Selected bond distances and angles for these
compounds and 7, 8, 10, and 13 are given in Tables 2-4. The disorder in the alkene units of 12 is not shown. Only one of the crystallographically independent
molecules of 17 is illustrated.
possible to say with certainty that the gallium analogues 1 and
4 are monomeric in the solid state like their indium and thallium
congeners because of the poor diffraction characteristics of their
crystals. Nonetheless, the structures of InAr*10 and Ar′InInAr′46
suggest that an analogous structural relationship between GaAr*,
1, and Ar′GaGaAr′, 6, is a possibility. Cryoscopy of 1 in
cyclohexane solution showed that it was monomeric at con-
centrations of ca. 18 and 30 mmolal. Cryoscopic studies1c of
[GaC(SiMe3)3]447 and [GaC(SiMe2Et)3]448 at concentrations of
10 mmolar afforded trimeric formulas masses, which were
interpreted as equilibria between monomeric and tetrameric
structures. Only at more dilute concentrations of ca. 1 mmolar
were monomeric formulas obtained for these Ga(I) alkyls. The
results suggest that 1 is even more weakly associated than these
compounds because a monomeric structure is maintained to
higher concentrations. The analogous compound 4 was synthe-
sized in a manner similar to that for 1 by the reaction of Et2-
OLiAr# (3) with GaI. The altered para substituents on the
flanking aryl rings did not solve the crystallographic problems
encountered for 1. Nonetheless, the lithium derivative 3 crystal-
lized readily (Figure 1). It has a two-coordinate lithium with a
(47) Uhl, W.; Hiller, W.; Layh, M.; Schwartz, W. Angew. Chem., Int. Ed. Engl.
1991, 30, 173.
(48) Uhl, W.; Jantschak, A. J. Organomet. Chem. 1998, 555, 263.
9
J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003 2675

A R T I C L E S
Hardman et al.
short Li-C distance of 2.036(2) Å and a wide interligand angle
of 164.4(2)°.
(2) Å), in contrast to the short In-C bonds (ca. 2.14(1) Å) in
the donor-acceptor complexes ArIn{B(C6F5)3} (Ar ) Ar′ or
Ar*).46
The crystal structure of red-brown 6 (Figure 1) shows that it
is associated as a dimer in the solid state. It has a trans-bent,
CGaGaC core structure with a bending angle of 123.16(7)° and
a Ga-Ga distance of 2.6268(7) Å.41 It is the first dimeric
gallium structure of this type to be isolated and could be
described as a “digallene”. This name is misleading, however,
because the Ga-Ga bond is ca. 0.1 Å longer than single Ga-
Ga bonds in tetraorganodigallanes and the single Ga-Ga bonds
of ca. 2.49 Å observed in 2 and 7 (vide infra).1,5 Furthermore,
upon dissolving the red-brown 6 in hydrocarbon solution, its
color changes to green, and its UV/vis spectrum is essentially
identical to those of 1 and 4. Cryoscopic studies confirm that 6
is essentially monomeric in cyclohexane, which underlines the
weakness of the Ga-Ga bond. This is in agreement with recent
low-temperature matrix isolation studies of HMMH (M ) Ga
or In) species, which indicate very low couplings between the
symmetric and asymmetric HMMH stretching modes. The
antisymmetric stretching mode for HGaGaH is located at a
wavenumber close to that of monomeric :GaH, which indicates
a very weak interaction between the MH fragments.29-31 These
experimental findings are consistent with calculations20,22,49,50
for a range of RGaGaR model species which displayed trans-
bent structures and long GaGa distances in the range 2.608-
2.768 Å. An AIM analysis of the SCF function of MeGaGaMe
has yielded a Ga-Ga bond order of 0.821.20,51 Earlier calcula-
tions have also indicated low bond strengths in a variety of
hypothetical group 13, RMMR, dimers, and a Ga-Ga bond
strength of ca. 3 kcal mol-1 was calculated.49
Supporting evidence for the weakness of the Ga-Ga bond
in 6 comes from a comparison of the Ga-C distance, 2.025(3)
Å, with the Ga-C bond lengths in complexes formed by the
:GaAr ligands. In these compounds, for example, 8-11 (see
below), the Ga-C bond lengths are near 1.94 Å. The shorter
Ga-C bonds may be accounted for in terms of an increased
ionic contribution to the Ga-C bond strength upon removal of
electron density from gallium through donation of the lone pair
to an acceptor in compounds such as 8-11.52 If strong donor-
acceptor bonding were also present in 6, a shorter Ga-C bond
should have been observed because the gallium electron pair
density would be more concentrated in the bonding region
midway between the galliums in a strongly bonded dimer. In
other words, there would be less electron density and conse-
quently a greater δ+ charge present at gallium, and a shorter
Ga-C bond should have resulted. In 6, this shortening is not
observed, and the Ga-C bond length is closer to the 2.06(2) Å
reported for the vapor phase structure of the monomer GaC-
(SiMe3)3.44 A similar argument has been used recently to
rationalize the long In-C bonds in the monomer InAr*
(In-C ) 2.260(7) Å) and the dimer Ar′InInAr′ (In-C ) 2.256-
In summary, all currently available experimental data point
to a weak interaction between the gallium centers in 1, 4, and
6. It is notable that, unlike 6, the color of both 1 and 4 are
green in the solid. This indicates that 1 and 4 are either
monomeric in the solid or so weakly interacting that the n-p
chromophore is essentially unaffected.
Compounds 2 and 7 are very rare examples of a digallane
bearing one halogen substituent at each gallium. The structure
of 2 (Figure 1) features two crystallographically independent
centrosymmetric molecules that have Ga(Ar*)I units linked by
Ga-Ga bonds 2.482(2) and 2.502(2) Å in length. The structure
of 7 features a Ga-Ga distance of 2.493(2) Å with an essentially
coplanar I(ipso-C)Ga-Ga(ipso-C)I array. These distances are
slightly shorter than the sum of the covalent radii for gallium
(2.50 Å) and the 2.515(3) Å Ga-Ga bond observed in the aryl
Trip2GaGaTrip2.53 The very large Ar* and Ar′ substituents are
oriented trans to each other, and the Ga-Ga-C angles are 14-
21° wider than the Ga-Ga-I angle. The Ga-C distances, av.
1.98(1) Å, are similar to the 2.008(7) Å observed in the structure
of Trip2GaGaTrip2. The Ga-I bonds 2.514(2)-2.541(2) Å are
similar to the 2.53(1) Å average seen in the structure of I2-
GaN∧NDipp2.54 The compound most comparable to 2 and 7 is
the Ga-Ga bonded dimer [Ga(Cl)Mes*]2 (Mes* ) C6H2-2,4,6-
But3).55 Although full details of the structure were not given, a
Ga-Ga bond length of 2.438(6) Å was reported. The signifi-
cantly shorter bond in this compound is consistent with the
decreased effective radius of gallium because of the more
electronegative chlorine substituent. The fact that the Ga-Ga
distances in 2 and 7 are close to that expected for a normal
single bond shows that the long Ga-Ga distance in 6 is not
due to steric effects but arises from its electronic structure.
Reaction Chemistry of 1, 4, and 6. The donor-acceptor
compounds 8-10 are readily formed upon mixing of 1, 4, or 6
with B(C6F5)3 in toluene (eq 6). The rapidity of the reaction is
a reflection of the dissociated nature of 1, 4, and 6 and the
GaAr + B(C6F5)3 PhMe8 ArGa{B(C6F5)3}
(6)
25 °C
Ar ) Ar*, 8; Ar#, 9; Ar′, 10
availability of the gallium lone pair for complex formation.
Important bond distances and angles are given in Table 3. The
compounds have almost linearly coordinated galliums, and the
Ga-B bond distances in 8 (2.110(3) Å), 9 (2.108(2) Å) (Figure
1), and 10 (av. 2.124(6) Å) are similar to the 2.10 Å predicted
for a single bond from the sum of the covalent radii of Ga (1.25
Å) and B (0.85 Å). The distances are shorter than the average
Ga-B bond lengths reported for a variety of gallium substituted
carboranes (2.14-2.33 Å),56,57 which, however, contain three-
and four-coordinate gallium. The Ga-B bonds in 8-10 are ca.
(49) Treboux, G.; Barthelat, J.-C. J. Am. Chem. Soc. 1993, 115, 4870.
(50) Palagyi, Z.; Schaefer, H. F.; Kapuy, E. Chem. Phys. Lett. 1993, 203, 195.
(51) There are several methods of calculating bond orders (AIM, WBI, NBO,
etc.) which can give answers that vary by almost one unit (cf. refs 16 and
26). However, AIM, NBO, NAO, WBI bond order calculations for trans-
HGaGaH all provide bond orders less than one in agreement with the
published result for MeGaGaMe.20 Allen, T. L.; Fink, W. H.; Power, P.
P., unpublished work.
(52) Alternatively, the GaAr monomer could feature a lone pair orbital that is
mostly 4s in character and a Ga-C bond that involves a Ga 4p orbital.
When the GaAr species becomes strongly bound through gallium, the
character of the gallium bonding orbitals changes to some degree toward
sp hybridization so that shorter bonds to gallium are observed.
(53) He, X.; Bartlett, R. A.; Olmstead, M. M.; Ruhlandt-Senge, K.; Sturgeon,
B. E.; Power, P. P. Angew. Chem., Int. Ed. Engl. 1993, 32, 717.
(54) Stender, M.; Eichler, B. E.; Hardman, N. J.; Power, P. P.; Prust, J.;
Noltemeyer, M.; Roesky, H. W. Inorg. Chem. 2001, 40, 2794.
(55) Cowley, A. H.; Decken, A.; Olazabal, C. A. J. Organomet. Chem. 1996,
524, 27.
(56) Hosmane, N. S.; Lu, K.-J.; Zhang, H.; Maguire, J. A. Organometallics
1997, 16, 5163.
(57) Schubert, D. M.; Bandman, M. A.; Rees, W. S.; Knobler, C. B.; Lu, P.;
Nam, W.; Hawthorne, M. F. Organometallics 1990, 9, 2046.
9
2676 J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003

Chemistry of Neutral Organogallium(I) Compounds
A R T I C L E S
Table 6. Selected Structural Parameters and IR Stretching Frequencies for Some LGaFe(CO)4 Complexesa
-1
compound
Ga coord. no.
Fe−Ga (Å)
Ga−Nor Ga−C (av.)
CO stretch (cm
)
ref
Ar*GaFe(CO)4, 11b
2
3
4
4
2.248(7)
2.2851(4)
2.2731(4)
2.315(3)
1.9435(19)
1.9273(11)
2.221(2)
2032, 1959, 1941, 1929
2010, 1940, 1915, 1900
2037, 1966, 1942
42
this work
67
66
Dipp2N∧NGaFe(CO)4, 16b
c
Cp*GaFe(CO)4
b
TpMe2GaFe(CO)4
1.991(15)
2011, 1919, 1890
a The stretching frequencies for Ph3PFe(CO)4 are 2052, 1979, and 1947 cm-1 68 b Abbreviations are defined in the text. c Cp* ) (η5-C5Me5).
.
0.04 Å shorter than the average Ga-B bond distance in the
recently reported complexes Dipp2N∧NGa{B(C6F5)3}58 and η5-
C5Me5Ga{B(C6F5)2},58,59 where the gallium has a higher
coordination number.58,59 The Ga-C bonds in 8 (1.943(3) Å),
9 (1.939(1) Å), and 10 (1.949(3) Å) are shorter than those
generally observed in organogallium(I) compounds,1 and even
shorter than those observed in 2 and 7 despite the higher formal
oxidation state of gallium in these species. More significantly,
the Ga-C distances are ca. 0.08 Å shorter than those observed
in Ar′GaGaAr′, 6. As argued above for 6, it is probable that
the removal of electron density from gallium, due to its donor
action in complex formation, results in a larger δ+ charge on
gallium, which gives rise to a stronger ionic factor in the Ga-C
bond. Also of note is the relatively close (within van der Waals
radii ca. 3.4 Å) Ga‚‚‚F distances in 8 (2.394(2) Å), 9 (2.435(2)
Å), and 10 (2.384(2) Å). However, these distances are at least
0.45 Å longer than Ga-F single bonds that span the range from
1.83 to 1.95 Å for four-coordinate gallium(III) fluoro com-
pounds.60 The closest Ga‚‚‚F interaction involves F(1), and the
C- -F(1) distance is lengthened from the average of 1.346(6) Å
observed for the remaining 14 C-F bonds to 1.378(4) Å (C-
F(1) av.). In addition, the C(37)-B(1)-Ga(1) angle is slightly
narrower (104.6(2)°) than the other two C(ipso)-B-Ga angles
(106.9(2)° and 107.5(2)°) for the perfluorophenyl rings in 8 (a
similar discrepancy is not observed in 9). These data suggest
that the lengthening of the C-F bond and the slight narrowing
of the Ga-B-C angle are caused by Ga‚‚‚F interactions. The
weak interactions appear to exist only in the solid state as the
19F NMR spectra of 8-10 are consistent with three signals
detected for the ortho, meta, and para fluorines in the three C6F5
rings. The donor action of the gallium causes the geometry at
boron in B(C6F5)3 to change from trigonal planar to distorted
tetrahedral. The extent of the geometrical change from trigonal
planar to tetrahedral of the B(C6F5)3 moiety has been taken to
be an indication of the strength of the donor-acceptor interac-
tions.61 The sums of the C-B-C angles in and 8, 9, and 10
are 337.1(1)°, 340.0(3)°, and 337.5(3)°, respectively. These can
be compared with the previously reported values for η5-C5Me5-
Al{B(C6F5)3} (339.8(2)°),62 η5-C5Me5Ga{B(C6F5)3}64 (342.2(2)°),
and Dipp2N∧NGa{B(C6F5)3} (333.6(2)°).58 By this criterion, the
order of increasing Lewis basicity is Ga(η5-C5Me5) < 4 <
Al(η5-C5Me5) < 6 ≈ 1 < GaN∧NDipp2. It is possible that
GaN∧NDipp2, 15, behaves as a stronger Lewis base than 1 or
6 due to the increased electron density at gallium provided by
the η2-â-diketiminate ligand and the increased metal coordina-
tion number in GaN∧NDipp2. Also of note in the structures of
8-10 is the pattern of C-B-C angles in which one angle
(105.8-108.3°) is narrower than the other two (114.7-117.1°),
which are probably due to steric interactions between the
terphenyl and C6F5 ligands.
The facile reactions of GaAr* (1) or GaN∧NDipp2 (15) with
Fe(CO)5 at room temperature, which afforded the complexes
Ar*GaFe(CO)4, 11, or Dipp2N∧NGaFe(CO)4, 16 (eq 7), under-
line their monomeric character. Compound 11 was previously
-CO
GaAr* or GaN∧NDipp2 + Fe(CO)5
8
25 °C
1
15
Ar*GaFe(CO)4 or Dipp2GaN∧NFe(CO)4 (7)
11 16
synthesized via the reaction of Ar*GaCl2 with Na2Fe(CO)4,
structurally characterized and described as a ferrogallyne, that
is, having an iron gallium triple bond.42 This view has not been
sustained by calculations, and the gallium-iron bonding is best
described by strong σ donation from gallium to iron with weak
iron to gallium π-bonding.63-65 The fact that 1 or 15 displace
CO from Fe(CO)5 at room temperature without heating or
photolysis is consistent with the strong σ-donor and monomeric
characteristics of 1 and 15 rather than any multiple bond
character in the complexes. The structures of compounds 1142
and 16 provide an opportunity to study the dependence of
gallium-metal bond lengths on the coordination number in a
series of donor complexes.42,66,67 All four compounds in Table
6 feature gallium(I) centers behaving as Lewis bases toward an
iron tetracarbonyl fragment. The structure of 16 (Figure 1)
incorporates a mirror plane containing C(2), Ga(1), Fe(1), C(17),
O(2), C(18), and O(3). The Ga(1)-N(1) distance undergoes a
shortening in excess of 0.11 Å in comparison with the free
ligand GaN∧NDipp2 (Ga-N ) 2.054(2) Å), and this is
consistent with the results discussed for 8-10. It can be seen
in Table 6 that the shortest Fe-Ga bond corresponds to the
two-coordinate gallium complex 11.42 An increase in the gallium
coordination to three in the complex 16 results in an ca. 0.05 Å
increase in the Fe-Ga bond length. A further increase in the
gallium coordination number to four in the complex TpMe2-
65
GaFe(CO)4 results in a lengthening of the Fe-Ga bond by
ca. 0.03 Å. The (η5-C5Me5)GaFe(CO)466 complex, in which the
gallium coordination number may be approximated to four,
occupies a seemingly anomalous position. However, it can be
seen that the Ga-ligand interactions in this complex are the
(58) Hardman, N. J.; Power, P. P.; Gorden, J. D.; Macdonald, C. L. B.; Cowley,
A. H. Chem. Commun. 2001, 1866.
(59) Jutzi, P.; Neumann, B.; Reumann, G.; Schebaum, L. O.; Stammler, H.-G.
Organometallics 2001, 20, 2854.
(60) For example: Neumuller, B.; Gahlmann, F. Angew. Chem., Int. Ed. Engl.
1993, 32, 1710. Kraiter, T.; Neumuller, B. Z. Anorg. Allg. 1995, 621, 597.
Kopp, M. R.; Neumuller, B. Z. Anorg. Allg. Chem. 1999, 625, 1413.
(61) Jacobsen, H.; Berke, H.; Do¨ring, S.; Kehr, G.; Erker, G.; Fro¨lich, R.; Meyer,
O. Organometallics 1999, 18, 1724.
(62) Gorden, J. D.; Voigt, A.; Macdonald, C. L. B.; Silverman, J. S.; Cowley,
A. H. J. Am. Chem. Soc. 2000, 122, 950.
(63) Feng, X.; Cotton, F. A. Organometallics 1998, 17, 128.
(64) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113.
(65) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683.
(66) Reger, D. L.; Garza, D. G.; Rheingold, A. L.; Yap, G. P. A. Organometallics
1998, 17, 3624.
(67) Jutzi, P.; Neumann, B.; Reumann, G.; Stammler, H.-G. Organometallics
1998, 17, 1305.
9
J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003 2677

A R T I C L E S
Hardman et al.
longest in the series, which may permit a stronger than expected
Fe-Ga interaction.
preliminary form.41 The latter crystallizes as centrosymmetric
molecules that feature a planar, trans-bent C(1)Ga(1)Ga(1A)C-
(1A) core with sodiums that are complexed by Dipp rings and
which almost symmetrically bridge the galliums on each side
of the core (Figure 1). Inspection of the data in Table 4 shows
that there are only minor differences in the structural parameters
of 13 and 14. The strengths of the sodium interactions with the
galliums and the aryl rings are very similar as are the average
Ga-Ga-C angles. The gallium-gallium distance is ca. 0.02
Å longer in 14. This is somewhat surprising in view of the lower
steric crowding in 14, which might be expected to afford a
shorter Ga-Ga bond. However, the difference in the Ga-Ga
bond length is relatively small, and it is possible that the para
substituents can affect the Ga-Ga bond length in ways that
are not completely understood at present.22 As already men-
tioned, it was the description of the Ga-Ga bond in 13 as a
triple one which sparked the current general debate on multiple
bonding between heavier main group elements. Without revisit-
ing the theoretical arguments on either side of that debate (which
can be found in refs 12-25 and in a number of reviews28,31,70),
the results obtained for 1, 4, and 6 clearly show that they have
weak Ga-Ga bonds consistent with a bond order below one.20,51
Two-electron reduction of 1 and 6 to give 13 or 14 generates a
single bond between the galliums. The weak interaction of the
neutral precursor is also preserved as indicated by the mainte-
nance of the trans-bent CGaGaC geometry with only a slight
decrease in the amount of bending. The structures of 13 and 14
also display Na-Aryl, Ga-Na-Ga bridging, and, possibly,
terphenyl-terphenyl interactions that can shorten the Ga-Ga
bond. The stability of the Na2Ga2 core structures is critically
dependent on the size of the alkali metal reductant employed,
because reductions with potassium afford a different product
with a Ga4 ring core structure.27
The CO stretching frequencies of the complexes (Table 6)
may be compared with those of Ph3PFe(CO)4 (2052, 1979, and
1947 cm-1).68 It can be seen that the frequencies of all of the
gallium-iron complexes are lower than the corresponding ones
in the phosphine complex, implying that the σ/π donor-acceptor
ratio for the gallium ligands is greater than that of PPh3. In
other words, the amount of Fe-Ga π-back-bonding in the
complexes is likely to be small and inconsistent with the
existence of a Ga-Fe triple bond. These experimental findings
are in agreement with several calculations,63-65 and the low
degree of Fe-Ga π-back-bonding in the complexes can be
accounted for, at least in part, by differences in energy levels
between the two bonding fragments. In :GaH, the triplet state
has been calculated to be 46.6 kcal/mol-1 higher in energy than
the singlet state.49 Apparently, the p-orbitals in :GaR are much
higher in energy than the lone pair. They are also probably
significantly higher in energy than the valence orbitals of Fe-
(CO)4. This energy difference reduces the back-bonding interac-
tion between iron and gallium. Nonetheless, the Fe-Ga bonds
in the complexes in Table 6 are up to ca. 0.2 Å shorter than
those observed for Fe-Ga single bonds. This difference can
be rationalized by considering the types of orbitals that
participate in bonding. For example, in the singly bonded Fe-
Ga complex (η5-C5H5)(CO)2FeGaBut2,69 the gallium employs
a p-orbital or a hybrid orbital with some s character to bond to
iron. In complex 11, GaAr* may use a 4p orbital (or an orbital
with 4p and some s character) to bond to the aryl group with
the lone pair located primarily in a 4s orbital (or 4s orbital with
some p character), leaving two empty, 4p orbitals at gallium.
The gallium 4s2 electron pair is used to bond to iron. The 4s
orbital has a smaller radius than the 4p orbital, and a shorter
Fe-Ga bond results. The low coordination number of gallium
in 11 may also be a factor in shortening the bond.
The attempted use of the less crowded ligand -C6H3-2,6-
Mes2 (Ar′′) to obtain a neutral, higher aggregate cluster of
formula (GaAr′′)n (n > 2) afforded the product Ga11Ar4′′, 17,
in which 7 of 11 galliums do not carry substituents. The apparent
ligand stripping is analogous to that seen in the preparation of
In8Ar4′′ under similar conditions.71 The isolation of higher
aggregate complexes for gallium and indium with use of the
smaller Ar′′ substituent underlines the vital importance of steric
effects for the stabilization of 1, 4, or 6. Furthermore, the higher
degree of aggregation for 17 in comparison to that for In8Ar4′′
is not unexpected because of the smaller size of gallium. The
cluster crystallizes with two crystallographically independent
Ga11Ar4′′ molecules. There is an odd number of electrons, and
the EPR spectrum of the compound displays a broad (ca. 60
G) signal at g ) 2.0237. The cluster skeleton, which contains
a two-fold symmetry axis, is composed of two outer Ga4 rhombs
in which two of the four galliums are substituted by an Ar′′
group and a central unit of three unsubstituted gallium atoms,
Ga(3), Ga(4), and Ga(5), which are disordered over two
positions of 50% occupancy. Intermetallic distances within the
Ga4 rhombs and the central Ga3 triangle average 2.552(3) and
2.662(4) Å, respectively. Other distances are provided in Tables
2-4. Interestingly, there are some examples of molecules that
The rapid reaction of 1 with 2,3-dimethyl-1,3-butadiene to
give the cyclic product 12 (Figure 1) is also in agreement with
the monomeric character of 1. No “monomeric” cycloaddition
product containing a five-membered ring as illustrated by
was obtained, however. It seems possible that a strained
geometry would be imposed on such a ring by the presence of
the double bond and planar gallium coordination. This could
lead to Ga-C bond cleavage and subsequent dimerization to
give 12. Some details of the structure of 12 are provided in
Table 4, where it can be seen that the structural parameters are
consistent with those previously observed in organogallium
compounds.
The structures of the reduced species Na2Ar*GaGaAr*, 13,
and Na2Ar′GaGaAr′, 14, which were synthesized by stirring 1
and 6 with sodium, are very similar. The structure of 13 has
been determined twice,12,27 and the most recent data are given
in Table 4.27 The structure of 14 was recently presented in a
(70) Robinson, G. H. Acc. Chem. Res. 1999, 32, 773. Downs, A. J. Coord. Chem.
ReV. 1999, 59, 189. Robinson, G. H. Chem. Commun. 2000, 2175. Power,
P. P. Struct. Bonding 2002, 103, 57.
(71) Eichler, B. E.; Hardman, N. J.; Power, P. P. Angew. Chem., Int. Ed. 2000,
39, 383.
(68) Martin, L. R.; Einstein, F. W. B.; Pomeroy, R. K. Inorg. Chem. 1985, 24,
2777.
(69) He.; X.; Bartlett, R. A.; Power, P. P. Organometallics 1994, 13, 548.
9
2678 J. AM. CHEM. SOC. VOL. 125, NO. 9, 2003

Chemistry of Neutral Organogallium(I) Compounds
A R T I C L E S
contain Ga4 and Ga3 moieties in the literature. For instance,
the clusters M2[Ga3(C6H3-2,6-Mes2)3] (M ) Na,72 K73) and K2-
[Ga4(C6H3-2,6-Trip2)2]27 possess the triangular and square planar
arrays of gallium similar to those seen in 7. The Ga11 cluster
forms part of a rapidly expanding series of group 13 metal
clusters where aggregation numbers currently range from 2
to 84.74
the related species Na2(Ar′GaGaAr′), which have Ga-Ga bond
lengths (ca. 2.32-2.34 Å) that are ca. 0.3 Å shorter than that
in the neutral dimer Ar′GaGaAr′. It was the very short Ga-Ga
bond originally observed in Na2(Ar*GaGaAr*),12 as well as the
analogy between an uncomplexed dianion [ArGaGaAr]2- and
an alkyne, that led to the conclusion that a Ga-Ga triple bond
was present.12 This conclusion was supported by some theo-
retical calculations,13-17 but other theoretical papers ques-
tioned19,20,23-26 this bonding description and demonstrated the
importance of factors such as Na-Aryl and Na-Ga interactions
in shortening the Ga-Ga bond. The reduction of GaAr* with
potassium instead of sodium to afford the ring compound
K2Ar*Ga4Ar* demonstrated the critical importance of the size
of the alkali metal to the stability of Na2Ar*GaGaAr*.27
Furthermore, the experimental results described here have
permitted a separation of the Ga-Ga bonding in the reduced
species 13 and 14 into its component parts and show that it
consists of a weak Ga-Ga interaction, similar to that in the
neutral precursors 1 and 6, plus a single bond generated by the
two-electron reduction of the di-gallium unit.
Conclusions
The experiments described in this paper show that the
compounds GaAr*, GaAr#, and GaAr′ exist as green monomers
in solution. Both GaAr* and GaAr# maintain their green color
as crystalline solids, whereas GaAr′ weakly dimerizes to form
red-brown crystals. Accordingly, it is probable that in the solid
state GaAr* and GaAr# are more weakly associated than the
Ar′GaGaAr′ dimer. The chemical behavior of the gallium
monoaryls in solution is consistent with their formulation as
monomers rather than dimers. The weakness of the Ga-Ga
bonding can be attributed primarily to the large energy difference
between the frontier lone pair and p-orbitals of the GaAr
monomers.49 Thus, in the neutral gallium aryls, the gallium
valence electrons behave essentially as lone pairs rather than
bond pairs. The reductions of GaAr* or GaAr′ with sodium
readily afford the landmark compound Na2(Ar*GaGaAr*)12 or
Acknowledgment. We are grateful to the National Science
Foundation (CHE-0096913) for financial support and the
Albemarle Corp. for a gift of B(C6F5)3.
Supporting Information Available: X-ray data (CIF) for 2,
3, 8, 9, 10, 12, 15, and 17. This material is available free of
charge via the Internet at http://pubs.acs.org.
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