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 provides 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 benzaldehyde complexes (4-RC6H4CHO)Cr(CO)3. These react with the Wittig reagent Bu3P = CHC6H4NO2 to provide nitrostilbene complexes (4-RC6H4CH = CH-4'-C6H4NO2)Cr(CO)3, a new class of organometallic complexes with potential nonlinear optics applications. The E isomers of the nitrostilbene compounds may be separated from the Z isomers; the former were characterized by spectroscopic and crystallographic means. For (4-Me2NC6H4CH = CH-4'-C6H4NO2)Cr(CO)3, 13E, monoclinic, P2(1)/c, a = 7.710(3) angstrom, 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, monoclinic, 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) angstrom, 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 = 18.305(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 stilbene 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 studies of models.