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

Abstract

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 RhIII/IrIII-orthometalation in complexes 4 makes the triazolium C4-H more downfield shifted than C5-H, whereas a reverse trend, although to a lesser extent, is observed in the case of the non-chelated PdII-coordination. This difference in behavior assisted us to achieve the selective activation of triazole C4/C5 positions, not observed before, as supported by the isolation of the homo- and hetero-bimetallic complexes, 5, 6 and 7-9via C5- and C4-metalation, respectively. Furthermore, the %Vbur calculations eliminate any considerable steric influence and the DFT studies strongly support the selectivity observed during bimetalation.