Palladium(ii) pincer complexes of a C,C,C-NHC, diphosphonium bis(ylide) ligand

A new family of pincer palladium(II) complexes bearing an electron-rich C,C,C-NHC, diphosphonium bis(ylide) ligand of LX2-type was prepared through the dual N-functionalization of 1H-imidazole by (3-bromopropyl) triphenylphosphonium bromide. Selected basic conditions allowed the sequential coordination of the NHC and phosphonium ylide moieties to Pd(II). This strategy led to an original ortho-metallated complex where the Pd center is bonded to four carbon atoms of three different natures: carbenic (sp(2)), arylic (sp(2)), and chiral ylidic (sp(3)). Protonation of the latter afforded NHC, diphosphonium bis(ylide) pincer Pd(II) complexes as a mixture of meso-and dl-diastereomers (de = 50%). The selectivity of C-coordination was rationalized on the basis of DFT calculations, evidencing the quasi-degeneracy of the two diastereomeric forms.