Organometallic Complexes for Nonlinear Optics. 22.¹ Quadratic and Cubic Hyperpolarizabilities of trans-Bis(bidentate phosphine)ruthenium σ-Arylvinylidene and σ-Arylalkynyl Complexes

Abstract

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.

Multistate Redox‐Active Metalated Triarylamines

“…The organic alkynes each show a single irreversible oxidation process at around 1.4 V, which is assigned to the triphenylamine center. Coordination of 4-ethynyl-N,N-diphenylaniline to the electron-donating ruthenium metal center to afford 3 results in a decrease in the potential required for oxidation of the triphenylamine unit to 0.90 V, with a ruthenium-localized oxidation that occurs at 0.37 V, significantly lower than that of the related trans-[Ru(CϵCR)Cl(dppe) 2 ] (R = H, Ph) complexes, for which Ru II/III processes are typically observed at around 0.55 V. [22] Both the NPh 2 and ruthenium oxidation processes in 3 are fully reversible. The CV of the linear Fe-Ru alkynyl complex 4 is consistent with the sequential loss of three electrons in distinct, fully reversible oxidation steps with E°c entered at 0.19, 0.56, and 0.93 V (Figure 4a).…”

Electron-donor/acceptor properties of carbynes, carbenes, vinylidenes, allenylidenes and alkynyls as measured by electrochemical ligand parameters

“…Although a number of the estimated ligand parameters for vinylidenes should be taken cautiously (namely those based on the potentials quoted [87][88][89][90] for irreversible oxidation waves of vinylidene complexes with the trans{RuCl(LL) 2 } + centers), they generally are consistent with the others based on the potentials of reversible oxidation processes and therefore the set allows some conclusions to be drawn, such as the following ones.…”

“…The electrochemical ligand parameters for vinylidenes (Table 6) have been estimated in two ways: (i) when ligating the trans-{ReCl(dppe) 2 } center [29], a Rh I T-shaped center [35][36][37] or the half-sandwich {Mo(g 7 -C 7 H 7 ) (dppe)} + site [56] (all with known E s and b parameters), P L was directly obtained by using PickettÕs equation (5), and E L was derived thereof from relation (8); (ii) when ligating trans-{RuCl(LL) 2 } + (LL = dppe [86,87], dppm [88][89][90] or {RuCl(Me 2 bipy)(PPh 3 ) 2 } + [85]) with unknown E s and b values, E L was directly estimated by using LeverÕs equation (6), and P L was then obtained from expression (8). Method (ii) requires the knowledge of E L for all the ligands of the metal center and that used, along this work, for dppm (E L = 0.35 V vs. NHE) is now proposed on the basis of various arguments (see Appendix A).…”

Luminescent and Electronic Properties of Stilbenoid NCN‐Pincer PtII Compounds

“…[52][53][54][55] In practice, torsion angles around 0-5°are commonly found in the solid-state structures, [56][57][58] although a small part of the reported stilbenoid molecules show larger torsion angles ranging from 20 to 27°. [59][60][61] Such deviations from coplanarity can be explained by a combination of alkenyl-H-ortho-H repulsion and by crystal packing forces.…”