Unsaturation in binuclear iron trifluorophosphine carbonyl derivatives: comparison with binary iron carbonyls

Abstract

Bridging PF3 groups are obviously very unfavorable as indicated by their absence in Fe2(CO) n (PF3)2 (n = 7, 6, 5, 4) complexes optimized by density functional theory even though many such structures have one or more bridging CO groups. Except for some Fe2(CO)7(PF3)2 structures, the two terminal PF3 groups are bonded to different irons. Structures of the saturated Fe2(CO)7(PF3)2 having one, two, and three bridging or semibridging CO groups have similar energies suggesting a fluxional system. The lowest energy structures for the unsaturated Fe2(CO) n (PF3)2 (n = 6, 5, 4) derivatives are triplet spin-state structures. However, higher energy singlet Fe2(CO) n (PF3)2 (n = 6, 5, 4) structures are found having formal iron–iron multiple bonds and various combinations of bridging and terminal CO groups leading to the favored 18-electron configurations for iron. Most singlet Fe2(CO) n (PF3)2 (n = 6, 5, 4) structures are analogous to those of the previous studied Fe2(CO) n +2 structures.