Mercury complexes of N-heterocyclic carbenes derived from imidazolium-linked cyclophanes: synthesis, structure, and reactivity

Abstract

A range of mercury-imidazolylidene complexes have been prepared by reaction of imidazolium-linked cyclophanes with mercury(II) acetate. For cyclophanes based on meta-xylyl groups the mercury complexes are mononuclear and exhibit unprecedented structures in which the mercury atom is bound within the cyclophane ring, the two NHC donors being mutually trans. For cyclophanes based on ortho-xylyl or 2,6-lutidinediyl groups the mercury complexes are dinuclearwith a [Hg(mu-L)2Hg] core, in which each mercury atom is coordinated by one NHC from each cyclophane unit. The mononuclear and dinuclear complexes have been structurally characterized. Studies of the NHC-pyridinophane mercury complex indicated that the NHC-Hg bonding is labile,suggesting that the dinuclear complex based on the [Hg(mu-L)2Hg] core existed in equilibrium with amononuclear complex [HgL]. The labile nature of the NHC-Hg bonding was further established by a redox transmetalation reaction of a dinuclear NHC-Hg(II) complex with a Pd(0) source, which afforded an NHC-Pd(II) complex.