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: 10anti,syn; M = Pd, R = n-Bu, L = PMe3: 11anti,syn; M = Pt, R = n-Bu, L = PMe3: 12anti,syn; M = Pt, R = n-Bu, L = PEt3: 13anti,syn), which show a mixture of syn and anti isomers in solution. Molecular structures of 11anti, 12anti, and 13syn have been determined by X-ray crystallography.