Ot. Beachley et al., SYNTHESES, CHARACTERIZATION, CRYSTAL AND MOLECULAR-STRUCTURES, AND SOLUTION PROPERTIES OF ET2GA(C5H5) AND ETGA(C5H5)(2), Organometallics, 14(9), 1995, pp. 4402-4408
The compounds Et(2)Ga(C5H5) and EtGa(C5H5)(2) have been prepared by li
gand redistribution reactions in pentane solution between appropriate
quantities of GaEt(3) and Ga(C5H5)(3). Both compounds have been fully
characterized by elemental analyses, X-ray structural studies, cryosco
pic molecular weight studies in benzene solution, mass spectroscopic s
tudies, H-1 NMR studies of solutions, and 1H NMR studies of melts. Bot
h compounds exist as pure single compounds in the solid state, The com
pound [Et(2)Ga(C5H5)]infinity crystallizes in the centrosymmetric tric
linic space group P $($) over bar$$ 1 (No. 2) with a = 7.803(2) Angstr
om, b = 15.839(4) Angstrom, c = 16.318(4) Angstrom, alpha = 101.98(2)d
egrees, beta = 95.23(2)degrees, gamma = 102.72(2)degrees, V = 1904.5(8
) Angstrom(3), and Z = 8 (monomeric units). The structure consists of
polymeric chains of [Ga-C5H5]infinity, in which each gallium(III) cent
er is linked to two ethyl ligands and is in contact with one carbon at
om from each of two bridging C5H5 ligands. The other compound [EtGa(C5
H5)(2)]infinity crystallizes in the noncentrosymmetric orthorhombic sp
ace group P2(1)2(1)2(1) (NO. 19) With a = 8.213(5) Angstrom, b = 9.131
(4) Angstrom c = 14.277(10) Angstrom, V = 1070.7(11), and Z = 4 (monom
eric units). The structure was refined to R = 7.01% for those 846 refl
ections above 6 sigma, This structure is also polymeric with [Ga-C5H5]
infinity chains. Each gallium(III) center is also bonded to an ethyl l
igand and a terminal eta(1)-C5H5 ligand. When the compounds are dissol
ved in benzene, toluene, cyclohexane, CHCl3, or THF, ligand redistribu
tion reactions occur to form equilibrium mixtures of species, However,
when [Et(2)Ga(C5H5)]infinity is melted, 1H NMR spectral studies sugge
st the existence of only Et(2)Ga(C5H5), whereas when [EtGa(C5H5)(2)]in
finity is melted, a single compound does not exist and a mixture of Et
Ga(C5H5)(2), Et(2)Ga(C5H5), and Ga(C5H5)(3) is formed instead. Mass sp
ectral studies of Et(2)Ga(C5H5) are consistent with the presence of Et
(2)Ga(C5H5) in the gas phase, but when [Et(2)Ga(C5H5)]infinity is heat
ed and vaporized, uncertainty regarding the identities of the species
in the gas phase arises due to the occurrence of the ligand redistribu
tion reactions in the melt.