Alkyne complexes of platinum. Part 5. Di- and tri-platinum complexes with bridging trimethylsilyl-substituted alkyne ligands; crystal structure of [Pt2(µ-PhC2SiMe3)(C8H12)2]

Abstract

Bis(trimethylsilyl) acetylene in excess reacts with [Pt(cod)₂](cod = cyclo-octa-1,5-diene) to give the diplatinum complex [Pt₂(µ-Me₃SiC₂SiMe₃)(Me₃SiC₂SiMe₃)(cod)], whereas [Pt(C₂H₄)₃] and the alkyne afford [Pt₂(µ-Me₃-SiC₂SiMe₃)(Me₃SiC₂SiMe₃)₂]. Reactions of [Pt(cod)₂] with the alkynes RCCSiMe₃(R = SiMe₃, SiMe₂Bu^t, CF₃, or Ph) in 2 : 1 mol ratio, or excess of alkyne in the case of CF₃CCSiMe₃, yields the diplatinum complexes [Pt₂(µ-RC₂SiMe₃)(cod)₂]. The nickel compounds [Ni₂(µ-RC₂SiMe₃)(cod)₂](R = SiMe₃ or Ph) have also been prepared. Reaction of PhCCSiMe₃ with [Pt(cod)₂] in 1 : 1 mol ratio gives the triplatinum complex [Pt₃(µ-PhC₂SiMe₃)₂(cod)₂], which like [Pt₂(µ-PhC₂SiMe₃)(cod)₂] undergoes dynamic behaviour in solution, as revealed by variable-temperature n.m.r. studies. An X-ray crystallographic study on the latter was carried out. Crystals are monoclinic, space group P2₁/c, Z= 4, in a unit cell of dimensions a= 14.93(1), b= 10.38(1), c= 17.463(8)Å, β= 112.79(6)°. The structure has been refined to R 0.038 (R′ 0.038) for 5 464 unique reflections to 2θ⩽ 60°(Mo-K_α, X-radiation) collected at 200 K. The PhC₂SiMe₃ ligand transversely bridges the Pt ⋯ Pt vector (2.914 Å) such that the dihedral angel between the two planes formed by the two Pt–µ–C₂ units is 97°. This, together with the long metal–metal distance and the essentially planar geometry about each platinum atom, is taken to imply little or no direct Pt–Pt bonding, with the two halves of the molecule held together by orthogonal π orbitals of the shared PhCCSiMe₃ ligand.