(EPSILON-6-(ORGANOSILYL)ARENE)CHROMIUM TRICARBONYL COMPLEXES - SYNTHESIS, CHARACTERIZATION, AND ELECTROCHEMISTRY

The synthesis of the complexes {eta(6)-C6H5Si(OEt)3}Cr(CO)3 (1), {eta(6)-C6H5SiMe(OMe)2}Cr(CO)3 (2), {eta(6)-C6H5(CH2)2Si(OMe)3}Cr(CO)3 (3), {eta(6)-1,4-C6H4[(CH2)2Si(OMe)3]2}Cr(CO)3 (4), {eta(6)-C6H5Si(Me)2H}Cr(CO)3 (5), {eta(6)-1,4-C6H4[Si(Me)2H]2}Cr(CO)3 (6), {eta(6)-C6H5Si(Me)2CH = CH2}Cr(CO)3 (7), and {eta(6)-C6H5SiMe-(NMe2)2}Cr(CO)3 (8) is described. The compounds have been prepared by direct thermal reaction of the (organosilanyl)arene either with Cr(CO)6 (in refluxing dibutyl ether-tetrahydrofuran (THF) solution) or from the acetonitrile complex (MeCN)3Cr(CO)3 in cyclohexane. Alternatively, some of these complexes can be obtained by reaction of the (eta(6)-lithiobenzene)- or (eta(6)-1,4-dilithiobenzene)Cr(CO)3 derivatives with the appropriate chlorosilane, in THF at low temperature. Photochemical reactions of these tricarbonyl complexes with tri-n-butyl phosphite, in cyclohexane at room temperature, afford the corresponding dicarbonyl-monosubstituted {eta(6)-(organosilyl)arene}Cr(CO)2(P(OBu3)) complexes 9-16. The (alkoxysilyl)arene derivatives 1-4 have been covalently linked to silica supports. New {(siloxanyl)arene}Cr(CO)3 polymers [-SiMe{eta(6)-C6H5}Cr(CO)3OSiMe2(1,4-C6H4)SiMe2O-]n (17), [-CH2CH{eta(6)-C6H5SiMe2}Cr(CO)3-]n (18), and [-SiMe2{eta(6)-1,4-C6H4}Cr(CO)3SiMe2(CH2)2SiMe2OSi(CH2)2-]n (19) as well as the dinuclear model compound {eta(6)-C6H5SiMe2(CH2)2SiMe2-}2O[Cr(CO)3]2 (20) have been prepared either by condensation or addition polymerization reactions from the monomers with the reactive Si(NMe2)2, SiCH = CH2, and SiH groups. The oxidation of the {eta(6)-(organosilyl)arene}Cr(CO)3 complexes has been studied by means of electrochemical and spectroelectrochemical (IR and EPR) techniques. The results show that the stability of the oxidation products is very dependent upon the solvent and ring substituents. An electrochemically induced process exhibiting curve crossing was observed when the oxidation was effected in the presence of P(OBu)3 in dichloromethane or propylene carbonate. Chemical modification of platinum electrodes via silanization has been studied with the alkoxysilane complexes 1-4.