Low-valent isocyanide complexes and clusters of palladium and platinum. Crystal structure of [Pt{C(NR)N(R)C(NR}(RNC)2](R = 2,6-Me2C6H3)

Abstract

Reduction of [PtCl₂(RNC)₂](R = 2,6-Me₂C₆H₃) with sodium amalgam in the presence of isocyanide gave two clusters, [Pt₃(RNC)₆](1a) and [HgPt₆(RNC)₁₂](2a), and two metallocycles, [P[graphic omitted]R}(RNC)₂](3a) and [P[graphic omitted] (NR)}(RNC)₂](4a). In (2a) the six Pt atoms define a trigonal prism whose edges are associated with bridging and terminal isocyanide groups and the mercury atom is sandwiched by the two triangular Pt₃ cores. The structure of (4a) was determined by X-ray analysis: space group Pbcn, a= 18.542(11), b= 22.702(5), c= 22.197(5)Å, and Z= 8. In a similar reaction of [PdCl₂(2,6-Me₂C₆H₃NC)₂], palladium analogues of (1a) and (4a) were isolated. Reduction of [MCl₂(RNC)₂](M = Pt or Pd) having bulky R groups 2,4-Bu^t₂-6-MeC₆H₂ or 2,4,6-Bu^t3C₆H₂ gave the corresponding triangular trimetallic complexes [M₃(RNC)₆]. Six isocyanide molecules are bound to the metals as terminal and bridging ligands in the 2,4-di-t-butyl-6-methylphenyl isocyanide complex, and as only terminal isocyanide ligand in the 2,4,6-tri-t-butylphenyl isocyanide. Emission spectra of (2a) and the triangular palladium complexes were measured at 77 K; the former showed a fluorescence band at ca. 720 nm and the latter a phosphorescence band at ca. 640 nm.