[Re5(μ-H)4(CO)20]− and [Re5(μ-H)5(CO)20], Two Isolobal Analogues of Cyclopentane

The first five-membered rings of metal atoms connected by M-M or M-H-M bonds only have been obtained by a Re2 +Re3 condensation in which a polyhydride acts as a bridging bidentate ligand toward a coordinatively unsaturated fragment (see scheme below). In spite of the octahedral coordination of the Re centers, the Re5 rings display conformations (twisted and envelope) comparable with those observed for organic five-membered rings of tetrahedral carbon atoms.