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 reactions between arylethynes (either BuLi activated or Et3N assisted) and Ru2(RDMBA)4X2, where RDMBA is either N,N ‘-dimethylbenzamidinate (R = H) or N,N ‘-dimethyl-m-methoxybenzamidinate (R = m-MeO) and X is either Cl- or NO3 -, resulted in the compounds Ru2(RDMBA)4(C⋮CC6H4Y)2 (Y = H (1a,b), 4-NO2 (2a,b), 4-CN (3a,b), 3-CN (4a,b), 4-NMe2 (5a,b); R = H (a), m-MeO (b)). The single-crystal X-ray diffraction study of 1b and 2a revealed the linear alignment of the arylethynyl ligands along the Ru−Ru vector. All of the compounds display two Ru-based one-electron processes, an oxidation and a reduction, and their electrode potentials correlate linearly with the Hammett constants of substituent Y. Compounds 5a,b display an additional pair of one-electron processes attributed to the oxidation of 4-NMe2 groups, on the basis of which an extensive electron delocalization along the metallayne backbone was inferred.

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