Preparation of Au(I), Ag(I), and Pd(II) N-Heterocyclic Carbene Complexes Utilizing a Methylpyridyl-Substituted NHC Ligand. Formation of a Luminescent Coordination Polymer

Reaction of the imidazolium N-heterocyclic carbene precursor containing a methyl-substituted pyridyl functionality
[HCH3im(CH3py)]PF6, 1, with Ag2O produces the homoleptic Ag(I) complex, [Ag(CH3im(CH3py))2]PF6, 2. In a simple
carbene transfer reaction the analogous Au(I) species, [Au(CH3im(CH3py))2]PF6, 3, is formed by treatment of 2 with
Au(tht)Cl in dichloromethane. Both 2 and 3 are structurally similar with nearly linearly coordinated NHC ligands.
The methyl group appended to the pyridyl ring inhibits rotation of the pyridyl group at room temperature. Addition
of AgBF4 to a hot propionitrile solution of 3 followed by crystallization with diethyl ether yields the one-dimensional
coordination polymer, {[AuAg(CH3im(CH3py))2(NCCH2CH3)](BF4)2}n, 4, which contains Au−Ag separations of 2.9845(5) and 2.9641(5) Å with intermetallic angles of 167.642(14)° and 162.081(9)°. This material is intensely luminescent
in the solid state and exhibits an emission band at 453 nm (λex = 350 nm). Nearly colorless [Pd(CH3im(CH3py))2Cl]PF6, 5, is produced upon treatment of 2 with PdCl2(NCC6H5)2. The Pd(II) center in 5 is coordinated to one
NHC ligand in a chelate fashion, while the second NHC is bound solely through the carbon center. The X-ray
crystal structures of 1−5 are reported.