The reaction of bis(cyclooctadiene)nickel with Ga4[C(SiMe3)3]4 (1) yields a coordination compound analogous to [Ni(CO)4], [Ni{Ga−C(SiMe3)3}4], which shows a tetrahedral coordination of the central nickel atom, linear Ni−Ga−C groups, and very short Ni−Ga distances. Quantum-chemical DFT calculations on the model complexes [Ni(EMe)4] (E = B, Al, Ga, In, Tl) verify strong π back-donation of electron density from nickel to the empty p(π) orbitals of the group 13 elements, which is more effective than in tetracarbonylnickel itself.

Partial oxidation of the tetraalkyltetraindium(I) compound In4[C(SiMe3)3]4] 1 with halogen donors such as 1,2-dibromoethane and hexachloroethane or with mixtures of bromine and aluminum tribromide afforded novel alkylindium halides in which the indium atoms still possess unusually low oxidation states. Indium-indium single bonds between bivalent indium atoms were found in the compounds In2X2R2 (R = C(SiMe3)3, X = Cl (2) or Br (4)), which gave dimers in the solid state with all four halogen atoms in a bridging position. The tetrahedral arrangement of four indium atoms in a cluster was retained in the compound In4Br2R4 (3), in which one bromine atom occupied a mu3-bridging position above one triangular face of the In4 tetrahedron. One edge of that triangle was bridged by the second bromine atom. Mixed-valent indium atoms resulted with an average oxidation state of + 1.5.

The monomeric fragment In-C(SiMe3)3 was inserted into the Ni-Ni bond of Ni2Cp2(mu-CO)2 upon treatment of the carbonyl complex with the tetraindium(I) compound In4[C(SiMe3)3]4, 1, in a molar ratio of 4 to 1. The product (3) contains an indium atom coordinated to one alkyl substituent and two Ni(Cp)CO groups in a planar coordination sphere. Reaction of the starting compounds in a molar ratio of 2 to 1 led to the replacement of both CO ligands by two InR groups. A compound (4) was formed that is isostructural to the carbonyl nickel complex and has a Ni2 couple bridged by two InR ligands and two terminally coordinated cyclopentadienyl groups. The insertion product was not observed with the gallium derivative Ga4[C(SiMe3)3]4 (2); instead, a nickel gallium complex (5) analogous to 4 containing two bridging GaR ligands was isolated as the only product regardless of the ratio of the starting compounds. On the basis of quantum chemical calculations, we conclude that there is no evidence for an In-In or Ga-Ga bond in complexes 4 or 5, respectively. This, however, supports a butterfly geometry, which is isostructural to the starting carbonyl complex Ni2Cp2(mu-CO)2.

Treatment of the tetrahedral indium(I) cluster compound In 4 [C(SiMe 3 ) 3 ] 4 (1) with a mixture of AlI 3 and I 2 afforded the yellow diiodotriindium compound In 3 I 2 [C(SiMe 3 ) 3 ] 3 (2) in 73% yield. 1 contains a chain of three indium atoms connected by In-In single bonds. A trigonal bipyramidal structure resulted in the solid state by two iodide bridges between the terminal indium atoms.

The reaction of the tetrahedral alkylindium(I) compound In 4 [C(SiMe 3 ) 3 ] 4 (1) with bis(cyclooctadiene)platinum(0) afforded the compound Pt[InC(SiMe 3 ) 3 ] 4 (2), which is an analogue of the thermally unstable carbonyl complex Pt(CO) 4 and possesses a platinum atom tetrahedrally coordinated by four InR ligands.