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

Abstract

Reaction of the ruthenium half sandwich compound RuCl(η⁵-C₅H₅)(PPh₃)₂ with the uracil (Ur) substituted alkyne HCCUr in the presence of halide scavengers NH₄X (X = PF₆, BF₄, OTf) results in the formation of the vinylidene complexes [Ru(CCHUr)(η⁵-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 ¹H and ³¹P{¹H} 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(η⁷-C₇H₇)(dppe)(CCHUr)][BF₄] (dppe = 1,2-bis(diphenylphosphino)ethane) has also been prepared, but forms symmetric dimers in the solid state.