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)-C5H5)(PPh3)(2) with the uracil ( Ur) substituted alkyne HC CUr in the presence of halide scavengers NH4X (X = PF6, BF4, OTf) results in the formation of the vinylidene complexes [ Ru(=C=CHUr)(eta(5)-C5H5)(PPh3)(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 H-1 and P-31{H-1} 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)-C7H7)(dppe)(=C=CHUr)][BF4] (dppe = 1,2-bis-(diphenylphosphino)ethane) has also been prepared, but forms symmetric dimers in the solid state.