Synthesis and crystal structures of [(iPr₃P)₂Cu(μ- ESiMe₃)(InMe₃)] (E = S, Se): Lewis acid-base adducts with chalcogen atoms in planar coordination

The structures of [(iPr₃P)₂Cu(μ-SSiMe ₃)(InMe₃)] and [(iPr₃P)₂Cu(μ- SeSiMe₃)(InMe₃)] were determined by single-crystal X-ray diffraction. Both complexes are Lewis acid-base adducts of the InMe₃ acceptor and the chalcogen donor atom linking a Me₃Si group and a (iPr₃P)₂Cu moiety. They are very unstable under atmospheric conditions and decompose at ambient temperatures. Results of DFT calculations for these complexes and the related hypothetical [(Me ₃P)₂Cu(μ-SSiMe₃)(InMe₃)] compound show that the unusual planar coordination of the chalcogen atoms is due to steric crowding. Lewis acid-base adducts of trimethylindium and phosphane-stabilized copper(I) (trimethylsilyl)chalcogenolates were synthesized and characterized by X-ray crystal structure determination. They are very unstable under atmospheric conditions and decompose at ambient temperatures. DFT calculations reveal that the unusual planar coordination of the chalcogen atoms is due to steric crowding.