Synthesis and Tunability of Abnormal 1,2,3-Triazolylidene Palladium and Rhodium Complexes

Abstract

Palladation of N3-alkylated 1,2,3-triazolium salts with Pd(OAc)2 afforded a μ2−I2 bridged bimetallic complex [Pd(trz)I2]2 and monometallic bis(carbene) complexes Pd(trz)2I2 as a mixture of trans and cis isomers (trz = 1,2,3-triazol-5-ylidene). Addition of excess halide or modification of the palladation procedure from direct functionalization to a transmetalation sequence involving a silver intermediate allowed for chemoselective formation of the bis(carbene) complex, while subsequent anion metathesis with NaI produced the monometallic bis(carbene) complexes exclusively. Modification of the wingtip group had little influence on the metalation to palladium or rhodium(I) via transmetalation. According to NMR analysis using δC and 1JRh−C, subtle but noticeable tunability of the metal electronic properties was identified. In addition, phenyl wingtip groups as N-substituents in the triazolylidene ligands were susceptible to cyclopalladation in the presence of NaOAc and are thus not chemically inert.