ORGANOTRANSITION-METAL COMPOUNDS FOR PHOTONICS - SYNTHESES AND STRUCTURES OF A SERIES OF (NITROSTILBENE)CHROMIUM TRICARBONYL COMPLEXES

Treatment of Cr(CO)6 with 4-substituted benzaldehyde dialkyl acetals p rovides the new arene complexes [4-RC6H4CH(OR')2]Cr(CO)3 (R = Me2N, H, Me3Si, F3C; R' = Me, Et), which are readily hydrolyzed to the benzald ehyde complexes (4-RC6H4CHO)Cr(CO)3. These react with the Wittig reage nt Bu3P = CHC6H4NO2 to provide nitrostilbene complexes (4-RC6H4CH = CH -4'-C6H4NO2)Cr(CO)3, a new class of organometallic complexes with pote ntial nonlinear optics applications. The E isomers of the nitrostilben e compounds may be separated from the Z isomers; the former were chara cterized by spectroscopic and crystallographic means. For (4-Me2NC6H4C H = CH-4'-C6H4NO2)Cr(CO)3, 13E, monoclinic, P2(1)/c, a = 7.710(3) angs trom, b = 13.953(3) angstrom, c = 17.016(4) angstrom, beta = 99.80(3)- degrees, and Z = 4. For (C6H5CH = CH-4'-C6H4NO2)Cr(CO)3,14E, monoclini c, P2(1)/c, a = 10.141(4) angstrom, b = 13.767(3) angstrom, c = 11.768 (3) angstrom, beta = 108.82(3)-degrees, and Z = 4. For (4-Me3SiC6H4CH = CH-4'-C6H4NO2)Cr(CO)3, 15E, orthorhombic, Pbca, a = 11.745(8) angstr om, b = 15.644(4) angstrom, c = 22.255(6) angstrom, and Z = 8. For (4- F3CC6H4CH = CH-4'-C6H4NO2)Cr(CO)3, 16E, monoclinic, P2(1)/c, a = 18.30 5(6) angstrom, b = 12.641(4) angstrom, c = 15.208(5) angstrom, beta = 92.59 (3)-degrees, and Z = 8. The structural data show that the stilbe ne fragments maintain planarity with only slight deviations attributed to crystal packing forces and thermal motion. The absorption spectra of these deep red compounds are interpreted in light of theoretical st udies of models.