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 )PF 6 ] of the type [CpRu( C C CR 2 )(PPh 3 ) 2 ]PF 6 ( 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 1a − 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 β of ( 1b )PF 6 has been determined by hyper Raleigh scattering. The X-ray crystal structures of ( 1b )PF 6, ( 1d )PF 6 ·CH 2 Cl 2, and the acetylide complex CpRu(C⋮C−C 7 H 7 -2,4,6)(PPh 3 ) 2 are presented.