Synthesis and characterization of doubly bonded and quadruply bridged trans/anti and trans/syn-(η 5-RC 5H 4) 2M 2(μ-Se) 2(μ-SePh) 2(M=Mo, W) isomers

Abstract

Reactions of a mixture of doubly bonded and double-bridged trans/anti and trans/syn-(η 5-RC 5H 4) 2M 2(CO) 2(μ-SePh) 2 isomers with elemental selenium afford a series of novel doubly bonded and quadruply bridged isomers, trans/anti- (η 5-RC 5H 4) 2M 2(μ-Se) 2(μ-SePh) 2 ( 1a, M=Mo, R=H; 2a, M=Mo, R=MeO 2C; 3a, M=Mo, R=EtO 2C; 4a, M=W, R=MeO 2C; 5a, M=W, R=EtO 2C) and trans/syn-(η 5-RC 5H 4) 2M 2(μ-Se) 2(μ-SePh) 2 ( 1b, M=Mo, R=H; 2b, M=Mo, R=MeO 2C; 3b, M=Mo, R=EtO 2C; 4b, M=W, R=MeO 2C; 5b, M=W, R=EtO 2C). Such reactions were found to involve configuration inversions of the phenyl groups bonded to selenium atoms from syn to anti or vice versa. Thus, the reaction of single isomer trans/syn-(η 5-C 5H 5) 2Mo 2(CO) 2(μ-SePh) 2 with elemental selenium in tetrahydrofuran (THF) or toluene at reflux gave single trans/anti isomer 1a, whereas trans/anti-(η 5-EtO 2CC 5H 4) 2Mo 2(CO) 2(μ-SePh) 2 reacted with selenium powder under similar conditions gave single trans/syn isomer 3b. Except for isomer 1b (previously prepared by another route), all of the above quadruply bridged isomers have been characterized by elemental analysis, MS, IR and 1H NMR spectroscopies, as well as partly by 13C NMR and 77Se NMR spectroscopies.