Silylmethyl and related complexes. Part 4. Preparation, properties, and crystal and molecular structure of tetrakis[(trimethylsilylmethyl)-copper(I)], an alkyl-bridged, square-planar, tetranuclear copper(I) cluster

Abstract

Interaction of Li(CH₂SiMe₃) with Cul gives [{Cu(CH₂SiMe₃)}₄] a thermally stable, light-petroleum-soluble, colourless copper(I) alkyl, which by cryoscopy is a tetramer in benzene and a hexamer in cyclohexane. An X-ray crystal-structure determination at –40 °C shows that the complex consists of discrete centrosymmetric units containing a square plane of copper atoms with the methylene carbons lying in the same plane and bridging the edges. Crystals are monoclinic with a= 6.355(4), b= 12.636(7), c= 17.938(11)Å, β= 90.84(5)°, space group P2₁/c. Relevant distances and angles are: Cu–Cu 2.417 and Cu–C (mean) 2.02 Å; Cu–Cu–Cu 89.8, 90.2, Cu–C–Cu (mean) 73.5, and C–Cu–C (mean) 163.5°. Decomposition (thermal or photochemical) occurs via a homolytic path. Reactions with some organic halides (C₃H₅Br, Phl, SiMe₃Cl, or PhCH₂Br) are outlined, showing for the most part simple metathetical X–CH₂SiMe₃ exchanae, but less readily than with alkyls of Li or Mg. Addition of Li(CH₂SiMe₃) appears to yield Li[Cu(CH₂SiMe₃)₂].