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)-C 5H5) with 4-HC=CC(6)H(4)R and deprotonation of the intermediate metal vinylidene complex. The complexes are of the donor-acceptor type, givi ng enhanced second-order nonlinear optical responses. Correlations of spectroscopic data are consistent with increased electron density at t he metal upon increasing the donor strength of the phosphine and with decreased electron density at the metal upon increasing the acceptor s trength of the acetylide ligand. Electrochemical data are consistent w ith an RU(II)/(III) couple for 1a,b, and 2a,b whose oxidation potentia ls 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. Compl exes 1b and 2a,b have been crystallographically characterized. Ru-C(1) distances for these complexes are among the shortest for ruthenium si gma-acetylide complexes. Semiempirical calculations employing ZINDO we re performed; the results are consistent with increased molecular quad ratic hyperpolarizabilities for (i) increasing electron density at the metal center (replacing PPh(3) by PMe(3)), (ii) increasing acceptor s trength of the arylacetylide (replacing 4-H by 4-NO2), (iii) decreasin g M-C(acetylide) bond length, and (iv) optimum orientation of the acet ylide aryl group. Thus, the RUL(2)(eta(5)-C5H5) behaves as an efficien t tunable donor group.