Transition metal vinylidene complexes as supramolecular building blocks: nucleobase-mediated self-assembly of crystals with hexagonal symmetry

Reaction of the ruthenium half sandwich compound RuCl(eta(5)-C(5)H(5))(PPh(3))(2) with the uracil (Ur) substituted alkyne HCtriple bond, length as m-dash]CUr in the presence of halide scavengers NH(4)X (X = PF(6), BF(4), OTf) results in the formation of the vinylidene complexes Ru(double bond, length as m-dash]Cdouble bond, length as m-dash]CHUr)(eta(5)-C(5)H(5))(PPh(3))(2)]X] which crystallize in the hexagonal space group P6(3)/m. The hexagonal symmetry inherent to the system is due to the formation of a hydrogen bonded array mediated by the two sets of donor-acceptor units on the uracil, resulting in the formation of a cyclic "rosette" containing six ruthenium cations. In solution the (1)H and (31)P{(1)H} NMR spectra of the vinylidene complexes are both concentration and temperature dependent, in accord with the presence of monomer-dimer equilibria in which the rate of rotation of the vinylidene group is fast on the NMR timescale in the monomeric species, but slow in the dimers. The isoelectronic molybdenum-containing vinylidene complex Mo(eta(7)-C(7)H(7))(dppe)(double bond, length as m-dash]Cdouble bond, length as m-dash]CHUr)]BF(4)] (dppe = 1,2-bis(diphenylphosphino)ethane) has also been prepared, but forms symmetric dimers in the solid state.