Synthesis and Structures of Gallium Alkylthiolate Compounds

Gallium alkylthiolate complexes have been prepared from gallium amide complexes and thiols. The amide complex [Ga(NMe2)3]2 reacts with excess t-BuSH to give the amine adduct Ga(S-t-Bu)3(HNMe2). In contrast, the bulky amide complex Ga(N-i-Pr2)3 reacts with t-BuSH to give the homoleptic thiolate dimer [Ga(S-t-Bu)3]2. The analogous reaction between Ga(N-i-Pr2)3 and i-PrSH produces the salt [i-Pr2NH2][Ga(S-i-Pr)4], which on heating under vacuum loses amine and thiol to give the dimer [Ga(S-i-Pr)3]2. Reactions of [i-Pr2NH2][Ga(S-i-Pr)4] and [Ga(S-t-Bu)3]2 with excess pyridine give the adducts Ga(SR)3(py) (R = i-Pr or t-Bu). X-ray crystallographic studies show that the dimers have two bridging thiolate ligands. The Ga(μ-SR)2Ga four-membered ring in [Ga(S-i-Pr)3]2 has a planar anti geometry while the ring in [Ga(S-t-Bu)3]2 has a butterfly syn configuration. In the solid state, Ga(S-t-Bu)3(HNMe2) and [i-Pr2NH2][Ga(S-i-Pr)4] have trigonal-pyramidal and distorted tetrahedral geometries, respectively. The [Ga(SR)3]2 compounds exhibit solution fluxional behavior consistent with two separate processes, bridge-terminal thiolate exchange and effective inversion at the bridging sulfur atoms. Ab initio molecular orbital calculations on [Ga(SH)2(μ-SH)]2 at the MP4(SDQ) level predict activation energies for the two processes of 17.6 and 11.9 kcal/mol, respectively. Crystal data are as follows. Ga(S-t-Bu)3(HNMe2), C14H34GaNS3 at 223 K: P21/n (monoclinic), a = 9.6373(5) Å, b = 12.7183(7) Å, c = 16.9708(9) Å, β = 91.9810(10)°, and Z = 4. [i-Pr2NH2][Ga(S-i-Pr)4], C18H44GaNS4 at 223 K: P21/n (monoclinic), a = 12.0179(6) Å, b = 15.4813(8) Å, c = 14.3875(8) Å, β = 93.801(1)°, and Z = 4. [Ga(S-i-Pr)3]2, C18H42Ga2S6 at 223 K: P-1(triclinic), a = 8.6813(8) Å, b = 9.2969(8) Å, c = 11.1804(10) Å, α = 107.385(2)°, β = 95.987(1)°, γ = 117.285(1)°, and Z = 1. [Ga(S-t-Bu)3]2, C24H54Ga2S6 at 223 K: C2/c (monoclinic), a = 10.0630(10) Å, b = 17.698(2) Å, c = 19.836(2) Å, β = 98.500(10)°, and Z = 4.