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

摘要

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 CoCo 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.