Crystal structure of a cobalt carbonyl complex of 2,2′-dimethylarsino-octafluoro-1,1′-bicyclobut-1-enyl. A new rearrangement product of the ligand (Me2As)C:C(Me2As)CF2·CF2

Abstract

Heating Co2(CO)6(f4fars)[f4fars = Me2As·[graphic omitted]F2] under reflux in hexane has resulted in the cleavage of a Me2As group from f4fars with subsequent dimerization of the cyclobutenyl residues to form {(Me2As)-[graphic omitted]F2}2(Me2As)2Co4(CO)9(H)2. Crystals are orthorhombic, space group C2221, with Z= 4 in a cell of dimensions: a= 16·797(3), b= 10·744(3) and c= 20·559(3)A. X-Ray diffraction data was collected by counter methods, and the structure solved by the tangent refinement technique and refined by full-matrix least-squares procedures to R0·041 for 566 observed reflections. The molecule has a crystallographic two-fold axis which bisects the bond linking the fluorocyclobutenyl groups and the Co–Co bond [2·450(9)A]. A carbonyl group bridging this bond also lies on the axis. One cobalt atom has a very distorted octahedral environment formed by the π-bond of a fluorocyclobutenyl ring [1·90(3)A], a terminal carbonyl group, a postulated hydrogen atom, and a dimethylarsine group [Co–As 2·333(6)A], which is also linked to the second type of cobalt atom [Co–As 2·391(5)A]; this latter has a trigonal bipyramidal environment with axial (bridging)dimethylarsine and carbonyl groups and equatorial terminal carbonyl groups (two) and the arsenic atom attached to the fluorocyclobutenyl ring [Co–As 2·323(6)A].