ORGANOMETALLIC COMPLEXES FOR NONLINEAR OPTICS .2. SYNTHESES, ELECTROCHEMICAL STUDIES, STRUCTURAL CHARACTERIZATION, AND COMPUTATIONALLY-DERIVED MOLECULAR QUADRATIC HYPERPOLARIZABILITIES OF RUTHENIUM SIGMA-ARYLACETYLIDES - X-RAY CRYSTAL-STRUCTURES OF RU(C-CPH)(PME(3))(2)(ETA-C5H5) AND RU(C-CC6H4NO2-4)(L)(2)(ETA-C5H5) (L=PPH(3), PME(3))

A series of complexes Ru(C=CC(6)H(4)R-4)(PR'(3))(2)(eta(5)-C5H5) (R = H, R' = Ph, la; R = H, R' = Me, 1b; R = NO2, R' = Ph, 2a; R = NO2, R' = Me, 2b) has been synthesized by reaction of RUCl(PR'(3))(2)(eta(5)-C5H5) with 4-HC=CC(6)H(4)R and deprotonation of the intermediate metal vinylidene complex. The complexes are of the donor-acceptor type, giving enhanced second-order nonlinear optical responses. Correlations of spectroscopic data are consistent with increased electron density at the metal upon increasing the donor strength of the phosphine and with decreased electron density at the metal upon increasing the acceptor strength of the acetylide ligand. Electrochemical data are consistent with an RU(II)/(III) couple for 1a,b, and 2a,b whose oxidation potentials vary strongly with the donor and acceptor strengths of ligands, and a NO2-ceritered LUMO for 2a,b. Enhanced solvatochromic responses are observed on replacement of 4-H by 4-NO2 on the acetylide ligand. Complexes 1b and 2a,b have been crystallographically characterized. Ru-C(1) distances for these complexes are among the shortest for ruthenium sigma-acetylide complexes. Semiempirical calculations employing ZINDO were performed; the results are consistent with increased molecular quadratic hyperpolarizabilities for (i) increasing electron density at the metal center (replacing PPh(3) by PMe(3)), (ii) increasing acceptor strength of the arylacetylide (replacing 4-H by 4-NO2), (iii) decreasing M-C(acetylide) bond length, and (iv) optimum orientation of the acetylide aryl group. Thus, the RUL(2)(eta(5)-C5H5) behaves as an efficient tunable donor group.