Ruthenium(II) complexes with (2,4,6-cycloheptatrien-1-ylidene)ethenylidene ligands: Strongly polarized allenylidene complexes

The syntheses of cationic ruthenium(II) allenylidene complexes [(1a-e)PF6] of the type [CpRu(=C=C=CR(2))(PPh(3))(2)]PF6 (1a, R(2)C: = cycloheptatrienylidene; 1b, R(2)C: = 2,7-dimethyl-4,5-benzocycloheptatrienylidene; 1c, R(2)C: = 2,7-diphenyl-4,5-benzocycloheptatrienylidene; 1d, R(2)C: = dibenzo[a,e]cycloheptatrienylidene; 1e, R(2)C: = 4,5-dihydrodibenzo[a,e]cycloheptatrienylidene) are reported. In the series la-e, the decreasing ability of R(2)C: to stabilize a positive charge results in a tuning of the electronic and optical properties by changing the relative contributions of the two canonical forms [Ru+]=C-C=CR(2) (A) and [Ru]-C=C-CR(2)(+) (B), which is studied particularly by NMR and UV/visible spectroscopy. The first molecular hyperpolarizabilitiy beta of (1b)PF6 has been determined by hyper Raleigh scattering. The X-ray crystal structures of (1b)PF5, (1d)PF5 . CH2Cl2, and the acetylide complex CpRu(C=C-C7H7-2,4,6)(PPh(3))(2) are presented.