Towards new coordination modes of 1,2,3-triazolylidene: controlled by the nature of the 1(st) metalation in a heteroditopic bis-NHC ligand

An unusual effect of the nature of the first metal coordination of a heteroditopic N-heterocyclic carbene ligand (L2) towards the coordination behavior of 1,2,3-tzNHC is explored. The first metal coordination at the ImNHC site (complexes 3 and 4) was noted to substantially influence the electronics of the 1,2,3-triazolium moiety leading to an unprecedented chemistry of this MIC donor. Along this line, the Rh(III)/Ir(III)-orthometalation in complexes 4 makes the triazolium C(4)–H more downfield shifted than C(5)–H, whereas a reverse trend, although to a lesser extent, is observed in the case of the non-chelated Pd(II)-coordination. This difference in behavior assisted us to achieve the selective activation of triazole C(4)/C(5) positions, not observed before, as supported by the isolation of the homo- and hetero-bimetallic complexes, 5, 6 and 7–9via C(5)- and C(4)-metalation, respectively. Furthermore, the %V(bur) calculations eliminate any considerable steric influence and the DFT studies strongly support the selectivity observed during bimetalation.