Reactions of palladium(ii) and platinum(ii) bis(azido) complexes with isocyanides: synthesis and structural characterization of palladium(ii) and platinum(ii) complexes containing carbodiimido (or bis(carbodiimido)) and bis(tetrazolato) ligands

Abstract

Bis(azido)palladium(II) complexes Pd(N₃)₂L₂ (L = PMe₃, PMe₂Ph, PEt₃, PMePh₂) reacted with two equivalents of 2,6-dimethylphenyl isocyanide to give the Pd(II) complexes, trans-Pd[CN₄(R)](NCN–R)L₂ (R = 2,6-Me₂C₆H₃, L = PMe₃, 1; PMe₂Ph, 2; PEt₃, 3; PMePh₂, 4) containing a carbodiimido ligand and a C-coordinated 5-membered tetrazolato ligand. X-Ray structures of 1 and 2 identified the formation of palladium(II) complexes with a carbodiimido group, in which a nitrogen of the linear NCN moiety is bonded to the metal center, and with a tetrazolato ring formed via 1,3-dipolar cycloaddition of the isocyanide to the coordinated azido bond. Heating the isolated complexes 1 and 3 at 60 °C for 5 h converted them into the bis(carbodiimido)palladium(II) complexes, trans-Pd[NCN–R]₂L₂ (R = 2,6-Me₂C₆H₃, L = PMe₃, 5; PEt₃, 6). The reactions of 2,6-dimethylphenyl isocyanide with Pd(N₃)₂L₂ (L = PMe₃, PEt₃) also gave the same complexes directly. Reaction of Pd(N₃)₂(dppe) with 2,6-dimethylphenyl isocyanide also caused the formation of the bis(carbodiimido) complex Pd[NCN–2,6-Me₂C₆H₃]₂(dppe), 7 in 75% yield. However, reactions of M(N₃)₂(PMe₃)₂ (M = Pd or Pt) with tert-butyl isocyanide resulted in the formation of bis(tetrazolato) compounds, M[CN₄(R)]₂(PMe₃)₂ (R = tert-butyl, M = Pd, 8; Pt, 9) by the cycloaddition of isocyanide to the coordinated azido bond. The same reactions with other isocyanides such as cyclohexyl and n-butyl isocyanides afforded bis(tetrazolato) complexes, trans-M[CN₄(R)]₂L₂ (M = Pd, R = C₆H₁₁, L = PMe₃: 10_anti,syn; M = Pd, R = n-Bu, L = PMe₃: 11_anti,syn; M = Pt, R = n-Bu, L = PMe₃: 12_anti,syn; M = Pt, R = n-Bu, L = PEt₃: 13_anti,syn), which show a mixture of syn and anti isomers in solution. Molecular structures of 11_anti, 12_anti, and 13_syn have been determined by X-ray crystallography.