Syntheses and NLO properties of chromium carbonyl arene complexes with conjugated side chains: The amphoteric nature of chromium carbonyl complexation in push-pull chromophores

Donor- and acceptor-substituted alkynylated chromium carbonyl arene complex es Cr(CO)(2)L(eta(6)-R-1-C6H4)(C=C)(n)R-2 (1, n = 1, L = CO, PPh3, R-1 = H, o-formyl, R-2 = p-C6H4-NMe2, p-C6H4NO2, ferrocenyl; 3, n = 2, L = CO, R-1 = H, R-2 = p-C6H4-NMe2, p-C6H4-NO2, ferrocenyl) are easily accessible by So nogashira alkynylations of chloroarene complexes and Cadiot-Chodkiewicz cou plings of bromoalkynes with the complexed phenyl acetylene 1a (n =, L = CO, R-1 = R-2 = H), respectively. The Horner-Emmons-Wadsworth olefinations of the Cr(CO)(3)-complexed benzylphosphonate and (hetero)aromatic aldehydes gi ve rise to numerous alkenylated chromium carbonyl arene complexes (E)(n)-Cr (CO)(3)(eta(6)-C6H5)(CH=CH)(n)R-1 (6, n = 1-3, R-1 = p-C6H4-NMe2, p-C6H4-NO 2, 2-(4-nitrothienyl)). The linear (UV/vis spectral and the nonlinear optic al properties (hyper Rayleigh scattering measurements) of the complexes 1, 3, and 6 reveal that the chromium carbonyl arene fragment behaves electroni cally amphoteric, i.e., as an electron donor or electron acceptor depending on the substituent on the far end of the conjugating bridge. The first hyp erpolarizability beta-values (beta(333)(0) = (8-41) x 10(-30) esu) are foun d to be similar to those of related ferrocenyl compounds.