Five-electron donor versus seven-electron donor bridging phospholyl rings in binuclear cobalt carbonyl derivatives

Abstract

The lowest energy (C 4H 4P) 2Co 2(CO) n ( n = 3, 2, 1) structures have exclusively terminal phospholyl ligands and correspond closely to those of the analogous cyclopentadienyl derivatives (C 5H 5) 2Co 2(CO) n . Thus the lowest energy (C 4H 4P) 2Co 2(CO) n structures are the singly bridged trans-(η 5-C 4H 4P) 2Co 2(CO) 2(μ-CO) with a formal Co–Co single bond, the doubly bridged (η 5-C 4H 4P) 2Co 2(μ-CO) 2 with a formal Co Co double bond, and either singlet or triplet singly bridged (η 5-C 4H 4P) 2Co 2(μ-CO). Higher energy triplet (C 4H 4P) 2Co 2(CO) n structures are found with a five-electron donor η 5,η 1-C 4H 4P ligand bridging a cobalt–cobalt bond. None of the (C 4H 4P) 2Co 2(CO) n ( n = 3, 2, 1) structures has a seven-electron donor η 5,η 1-C 4H 4P ligand without a metal–metal bond in contrast to the lowest energy (C 4H 4P) 2Mn 2(CO) n ( n = 5, 4) structures.