Organometallic complexes for nonlinear optics Part 19. Syntheses and molecular quadratic hyperpolarizabilities of indoanilino-alkynyl-ruthenium complexes

The terminal alkyne 4-HC=CC6H4N=CCH=C'BuC(O)C'Bu=CH (1) and ruthenium compl ex derivatives trans-[Ru(C=C-4-C6H4N=CCH = C'BuC(O)C'Bu=CH}Cl(dppm)(2)] (2) and [Ru{C=C-4-C6H4N=CCH=C'BuC(O)C'BuC(O)C'Bu=CH}(PPh3)(2)(eta-C5H5)] (3) h ave been synthesized. An X-ray structural study of 3 reveals the expected e quivalent C-C bond lengths of the phenyl and alternating C-C and C=C bond l engths of the quinonal ring in the indoanilino-alkynyl ligand; there is a d ihedral angle of 47.59 degrees between the phenyl and quinonal rings, proba bly a result of ortho-hydrogen repulsion. Metal-centred oxidation potential s of 2 and 3 are similar to those of 'extended chain' 4-nitroaryl-alkynyl c omplex analogues. Irreversible quinonal ring-centred reductions occur at si gnificantly more negative potentials than the quasi-reversible reductions i n their nitro-containing analogues. Quadratic optical nonlinearities by hyp er-Rayleigh scattering at 1064 nm for 2 (417 x 10(-30) esu) and 3 (658 x 10 (-30) esu) are both large, but resonance enhanced. Two-level-corrected non linearities for these complexes (124 x 10(-30), 159 x 10(-30) esu, respecti vely) are also large, despite the presence of electron-donating tert-butyl groups reducing the efficiency of the (formally) electron-accepting quinona l ring in these donor-bridge-acceptor complexes. (C) 2000 Elsevier Science S.A. All rights reserved.