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The syntheses of trans- [Ru(CdCHR) Cl(pp) 2 ]PF 6 (pp ) dppm, R ) 4-C 6 H 4 CtCPh, 4-C 6 H 4 -CHO, 4,4′-C 6 H 4 CtCC 6 H 4 NO 2 , (E)-4,4′-C 6 H 4 CHdCHC 6 H 4 NO 2 , 4,4′,4′′-CtCC 6 H 4 CtCC 6 H 4 -CtCC 6 H 4 NO 2 ; pp ) dppe, R ) 4-C 6 H 4 CHO, (E)-4,4′-C 6 H 4 CHdCHC 6 H 4 NO 2 ) and trans-[Ru-(CtCR)Cl(pp) 2 ] (pp ) dppm, R ) 4-C 6 H 4 CtCPh, 4-C 6 H 4 CHO, 4,4′-C 6 H 4 CtCC 6 H 4 NO 2 , (E)-4,4′-C 6 H 4 CHdCHC 6 H 4 NO 2 , 4,4′,4′′-CtCC 6 H 4 CtCC 6 H 4 CtCC 6 H 4 NO 2 ; pp ) dppe, R ) 4-C 6 H 4 -CHO, (E)-4,4′-C 6 H 4 CHdCHC 6 H 4 NO 2 ) are reported, together with X-ray structural studies of trans-[Ru(CtCR)Cl(pp) 2 ] (pp ) dppm, R ) 4-C 6 H 4 CtCPh; pp ) dppe, R ) 4-C 6 H 4 CHO, (E)-4,4′-C 6 H 4 CHdCHC 6 H 4 NO 2 ). Cyclic voltammetric, linear optical, and quadratic and cubic nonlinear optical response data for these new complexes, together with the corresponding data for the previously reported transOxidation potentials for the Ru II/III couple increase on proceeding from the neutral alkynyl complex to the analogous cationic vinylidene complex and on introduction of an acceptor group (CHO or NO 2 ); the complexes with 4-CtCC 6 H 4 NO 2 ligands are the most difficult to oxidize. In some instances, the Ru III/IV and Ru I/II processes have been identified together with, where relevant, nitro-centered reduction processes. The oxidized and reduced vinylidene complexes are shown to transform electrochemically into the corresponding alkynyl complexes. Optical absorption maxima undergo a red shift upon increase of acceptor strength, replacement of the coligand dppm with dppe, and replacement of the alkynyl ligand yne linkage with an ene linkage. Proceeding from the vinylidene complex to an analogous alkynyl complex results in a small red shift in absorption maximum and a significant increase in extinction coefficient. Quadratic molecular nonlinearities by hyper-Rayleigh scattering measurements at 1064 nm increase upon introduction of ligated metal (proceeding from precursor alkyne to alkynyl or vinylidene complex), an increase in acceptor strength (introduction of CHO or NO 2 ), alkynyl chain lengthening (in the series [4-CtCC 6 H 4 ] n -4-NO 2 , proceeding from n ) 1 and 2 to 3), and replacing the yne linkage with an ene linkage. Significant differences in β value for two vinylidene/alkynyl complex pairs suggest that they could function as precursors to protically switchable quadratic NLO materials at 1064 nm. Cubic molecular nonlinearities by Z-scan measurements at 800 nm are in many cases characterized by negative real and significant imaginary components, indicative of twophoton effects; nevertheless, a substantial increase in |γ| on proceeding to the largest molecule, trans-Ru(4,4′,4"-CtCC 6 H 4 CtCC 6 H 4 CtCC 6 H 4 NO 2 )Cl(dppm) 2 , is observed. An order of magnitude difference in γ imag values (and therefore two-photon absorption (TPA) cross sections σ 2 ) for vinylidene/alkynyl complex pairs suggest that they have potential as protically switchable TPA materials at 800 nm.

The series of complexes Ru((E)-4,4′-CtCC 6 H 4 XdCHC 6 H 4 NO 2 )(PR 3 ) 2 (η-C 5 H 5 ) (X ) CH, R ) Ph, 11a; X ) CH, R ) Me, 11b; X ) N, R ) Ph, 12a; X ) N, R ) Me, 12b) has been synthesized by reaction of RuCl(PR 3 ) 2 (η-C 5 H 5 ) with (E)-4,4′-HCtCC 6 H 4 XdCHC 6 H 4 NO 2 and deprotonation of the intermediate vinylidene complex. Complex 11a has been structurally characterized; it is the first example of a donor-acceptor organometallic "extended" chromophore bearing the prototypical acceptor -NO 2 to be crystallographically studied. Molecular quadratic hyperpolarizabilities at 1.9 µm were evaluated computationally for the complexes above and imine-and azo-linked analogues by employing ZINDO with crystallographically obtained atomic coordinates. The results are consistent with a substantial increase in quadratic nonlinearity for (i) chain lengthening of the organometallic chromophore (replacing 4-CtCC 6 H 4 NO 2 by (E)-4,4′-CtCC 6 H 4 CHdCHC 6 H 4 NO 2 ) and (ii) an azo linkage compared with an ene linkage (replacing (E)-4,4′-CtCC 6 H 4 CHdCHC 6 H 4 NO 2 by (E)-4,4′-CtCC 6 H 4 NdNC 6 H 4 NO 2 ). Little variation in computed response was found upon substituting an imine linkage for an ene linkage in the organometallic chromophore (replacing (E)-4,4′-CtCC 6 H 4 CHdCHC 6 H 4 NO 2 by (E)-4,4′-CtCC 6 H 4 NdCHC 6 H 4 NO 2 or (E)-4,4′-CtCC 6 H 4 -CHdNC 6 H 4 NO 2 ). Molecular quadratic optical nonlinearities were determined experimentally for 11a, 12a, and Ru(CtCC 6 H 4 NO 2 -4)(PR 3 ) 2 (η-C 5 H 5 ) (R ) Ph, Me) by electric-field-induced second-harmonic generation (EFISH; 11a and 12a only) and hyper-Rayleigh scattering (HRS) techniques. EFISH-derived µβ 1064 values for 11a (9700 × 10 -48 cm 5 esu -1 ) and 12a (5800 × 10 -48 cm 5 esu -1 ) are large compared to those for other organometallic complexes. Resonanceenhanced quadratic nonlinearities at 1.06 µm from HRS are large (1455 × 10 -30 cm 5 esu -1 , 11a; 840 × 10 -30 cm 5 esu -1 , 12a). Two-level-corrected values confirm a substantial increase in quadratic nonlinearity for chain lengthening but suggest a significant decrease in nonlinearity on replacing an ene linkage by an imine linkage; the latter is contrary to the ZINDO result, and the reasons for this are discussed.

The complexes Ni(C⋮CR)(PPh3)(η-C5H5) (R = 4-C6H4NO2 (3), 4,4‘-C6H4C6H4NO2 (4), (E)-4,4‘-C6H4CHCHC6H4NO2 (5), (Z)-4,4‘-C6H4CHCHC6H4NO2 (6), 4,4‘-C6H4C⋮CC6H4NO2 (7), 4,4‘-C6H4NCHC6H4NO2 (8)) have been prepared. Electrochemical data for the series of complexes NiCl(PPh3)(η-C5H5) (1), Ni(C⋮CPh)(PPh3)(η-C5H5) (2), and 3−8 have been determined. Introduction of nitro substituent (in progressing from 2 to 3) results in a substantial increase in the NiII/III oxidation potential, all of which is lost on progressing from a one-ring (3) to two-ring (4−8) chromophore. The molecular quadratic and cubic optical nonlinearities of the series of complexes have been determined by hyper-Rayleigh scattering (HRS) and Z-scan techniques, respectively. HRS measurements at 1064 nm are consistent with an increase in β upon chromophore chain-lengthening (in progressing from 3 to 7 to 5), replacing Z by E stereochemistry (in progressing from 6 to 5), and in replacing N by CH (in progressing from 8 to 5), general trends that are maintained with the two-level-corrected data. Nonlinearities for the 18-electron nickel complexes are larger than those for related 14-electron (triphenylphosphine)gold acetylides, but smaller than those for the more easily oxidizable 18-electron (cyclopentadienyl)bis(phosphine)ruthenium acetylide analogues. Z-scan data at 800 nm reveal a negative γ for the nitro-containing complexes, consistent with the dispersion effect of two-photon states contributing to the nonlinearities. An increase in γ upon chromophore chain-lengthening (in progressing from 3 to 5, 4 and 7) and replacing Z by E stereochemistry (in progressing from 6 to 5) is observed. Nonlinearities for the extended-chromophore acetylide complexes 5 and 7 are significantly less than those for the (triphenylphosphine)gold acetylide analogues.

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The series of complexes Au(C⋮CR)(PPh3) (R = Ph (2), 4-C6H4NO2 (3), 4,4‘-C6H4C6H4NO2 (4), (E)-4,4‘-C6H4CHCHC6H4NO2 (5), (Z)-4,4‘-C6H4CHCHC6H4NO2 (6), 4,4‘-C6H4C⋮CC6H4NO2 (7), 4,4‘-C6H4NCHC6H4NO2 (8)) have been synthesized by reaction of AuCl(PPh3) with the corresponding acetylene and methoxide, and complexes 3−8 have been structurally characterized. The molecular first hyperpolarizabilities for the complexes have been determined by hyper-Rayleigh scattering at 1064 nm. Introduction of the nitro substituent (in proceeding from 2 to 3) leads to a significant increase in nonlinearity. Experimental β values increase as 3 < 4 < 6 ≈ 7 < 8 < 5 consistent with nonlinearity increasing with (i) chain lengthening, (ii) replacing biphenyl (4) or yne linkage (7) by ene linkage (5), (iii) replacing (Z)-ene stereochemistry (6) with (E)-ene stereochemistry (5), and (iv) ene linkage (5) being more efficient than imino linkage (8). The same trend is observed with two-level-corrected data. A linear correlation of both experimentally-determined and two-level-corrected nonlinearities of the acetylides with precursor acetylenes is observed.

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