Gas-Phase Structure of the Monomeric Alkylgallium(I) Compound Ga[C(SiMe₃)₃] and the Electrochemical Behavior of Ga₄[C(SiMe₃)₃]₄ and In₄[C(SiMe₃)₃]₄ with EPR Evidence for a Ga₄R₄ Radical Anion

Abstract

The gallium(I) compound Ga4[C(SiMe3)3]4 (1) with a tetrahedral Ga4 core in the solid state gives on evaporation the monomeric Ga(I) alkyl Ga[C(SiMe3)3] with the unique structural situation of a Ga atom solely coordinated by one singly bonded carbon ligand. Its molecular structure was determined now by gas-phase electron diffraction yielding a Ga−C bond length of 206.4(17) pm, similar to that found in the solid state for the tetramer and much longer than in compounds with gallium in the normal oxidation state of +3. As shown by cyclic voltammetry, 1 and the analogous cluster In4[C(SiMe3)3]4 (2) could both be reversibly reduced at about −2 V vs Fc+/0. Whereas the reduced organoindium tetramer did not exhibit any detectable EPR signals between 4 and 300 K, the gallium analogue showed an EPR spectrum compatible with the formulation [(RGa0.75) 4]•-; i.e. the unpaired electron was found to be delocalized over all four metal centers (a(69Ga) = 1.93 mT, a(71Ga) = 2.45 mT, 4 Ga).

Ni[In{C(SiMe3)3}4]: An Organometallic Nickel-Indium Compound Analogous to [Ni(CO)4]

“…[8] In contrast to CO, the ER fragments almost exclusively occupy bridging positions between two metal atoms in the known derivatives. A single case of terminal coordination was recently reported by Fischer et al in [(CO) 4 Fe(AlCp*)], [9] for which significant p backbonding from the metal atom to the ligand was calculated. Up to now, analogues of mononuclear, binary carbonyl complexes with exclusively terminal ER groups were unknown.…”

“…The monomeric alkyl ± element(i) compounds E ± R containing the bulky alkyl substituent C(SiMe 3 ) 3 and the monovalent, coordinatively and electronically unsaturated elements Ga, In, and Tl have recently been identified unambiguously as degradation products of the tetrahedral clusters E 4 [C(SiMe 3 ) 3 ] 4 .…”

“…[4] The tetrathallium compound is only weakly associated in the solid state and dissociates completely to the monomer on dissolution in benzene, [3] while the tetragallium cluster shows complete dissociation into the monomers only at high dilution in benzene. [1] The most stable of the clusters is In 4 [C(SiMe 3 ) 3 ] 4 (1). [2] Owing to its low thermal stability the monomeric fragment could not be characterized by electron diffraction, [4] and dissociation was not observed even in highly diluted solutions in benzene.…”

“…[1] The most stable of the clusters is In 4 [C(SiMe 3 ) 3 ] 4 (1). [2] Owing to its low thermal stability the monomeric fragment could not be characterized by electron diffraction, [4] and dissociation was not observed even in highly diluted solutions in benzene. [2] However, InR was detected as a reactive intermediate by trapping reactions with benzil derivatives in boiling n-hexane.…”

“…Hence, 2 is isostructural with [Ni(CO) 4 4 ]. [13] The complex Ni[SnR 2 ] 4 is also similar, [14] although the frontier orbitals of the SnR 2 groups do not correspond exactly to those of InR.…”