Preparations and characterizations of homodinuclear complexes containing flyover bridge or cyclopentadienone ligands; X-ray crystal structures of Co 2(CO) 3(PPh 3){μ-C(SiMe 3)CH–CHC(SiMe 3)–CHC(SiMe 3)}, Co 2(CO) 2(μ-CO) 2(η 4-2,5-bistrimethylsilylcyclopentadienone) 2 and 2,5-bis(trimethylsilanyl)cyclopenta-2,4-dien-1-one

Abstract

The reaction of Co 2(CO) 5(PPh 3)(μ-HCC–SiMe 3) ( 1b) with 2.5 equivalent amount of trimethylsilylacetylene in refluxed THF yielded two homodinuclear complexes containing ‘flyover bridge’ ligands, Co 2(CO) 3(PPh 3){μ-C(SiMe 3)CH–CHC(SiMe 3)–CHC(SiMe 3)} ( 2a) and a small amount of Co 2(CO) 2(μ-CO) 2(η 4-2,5-bistrimethylsilylcyclopentadienone) 2 ( 4). The yield of ( 4) was improved, while using about five equivalent amount of trimethylsilylacetylene. The crystal structures of ( 2a) and ( 4) were determined. The structure of ( 2a) can be regarded as a dimetallic frame contains three linked HCCSiMe 3 groups that are arranged in a ‘flyover-bridge’ geometry. Trimethylsilyl groups are attached to carbon atoms of the flyover bridge ligand at positions 1, 3, and 6. The ligand might be seen as the composition of two allyl groups, C1–C2–C3 and C4–C5–C6, which are joined by a single bond between C3 and C4. Each allyl group is bonded to one cobalt atom. 1,2,4-Tris-trimethysilanylbenzene was obtained from the degradation of the compound ( 2a). The crystal structure of ( 4) shows that two cyclopentadienone ligands, two terminal and two bridged carbonyls were found to be coordinated to both metal centers. The formation of the two cyclopentadienones is believed to take place via the transition metal-mediated cyclization of two alkynes with one carbon monoxide. 2,5-Bis(trimethylsilanyl)cyclopenta-2,4-dien-1-one ( 5) was obtained from the degradation of ( 4) by exposing to air in solution. The formation of ( 5) is believed to take place via the Diels–Alder type cyclization of two released cyclopentadienone ligands from ( 4).