Syntheses and NLO Properties of Chromium Carbonyl Arene Complexes with Conjugated Side Chains: The Amphoteric Nature of Chromium Carbonyl Complexation in Push−Pull Chromophores

Abstract

Donor- and acceptor-substituted alkynylated chromium carbonyl arene complexes Cr(CO)2L(η6-R1-C6H4)(C⋮C)nR2 (1, n = 1, L = CO, PPh3, R1 = H, o-formyl, R2 = p-C6H4-NMe2, p-C6H4-NO2, ferrocenyl; 3, n = 2, L = CO, R1 = H, R2 = p-C6H4-NMe2, p-C6H4-NO2, ferrocenyl) are easily accessible by Sonogashira alkynylations of chloroarene complexes and Cadiot−Chodkiewicz couplings of bromoalkynes with the complexed phenyl acetylene 1a (n = 1, L = CO, R1 = R2 = H), respectively. The Horner−Emmons−Wadsworth olefinations of the Cr(CO)3-complexed benzylphosphonate and (hetero)aromatic aldehydes give rise to numerous alkenylated chromium carbonyl arene complexes (E)n-Cr(CO)3(η6-C6H5)(CHCH)nR1 (6, n = 1−3, R1 = p-C6H4-NMe2, p-C6H4-NO2, 2-(4-nitrothienyl)). The linear (UV/vis spectra) and the nonlinear optical properties (hyper Rayleigh scattering measurements) of the complexes 1, 3, and 6 reveal that the chromium carbonyl arene fragment behaves electronically amphoteric, i.e., as an electron donor or electron acceptor depending on the substituent on the far end of the conjugating bridge. The first hyperpolarizability β-values ( = (8−41) × 10-30 esu) are found to be similar to those of related ferrocenyl compounds.