Synthesis and Structure of [Ni{Ga−C(SiMe₃)₃}₄] and Quantum-Chemical Verification of Strong π Back-Bonding in the Model Compounds [Ni(EMe)₄] (E = B, Al, Ga, In, Tl)

The reaction of bis(cyclooctadiene)nickel with Ga 4 [C(SiMe 3 ) 3 ] 4 ( 1 ) yields a coordination compound analogous to [Ni(CO) 4 ], [Ni{Ga−C(SiMe 3 ) 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.