Effects of hetero atoms in the preferred structures of binuclear cyclopentadienyl manganese carbonyl analogues

Abstract

The complete series of (C4H4E)2Mn2(CO)n derivatives (E=N, P, As, Sb, Bi; n=5, 4, 3) has been examined by density functional theory in order to ascertain the effect of the basic properties of the heteroatom E on the lowest energy structures. For the pentacarbonyls (C4H4E)2Mn2(CO)5 the lowest energy structures for all but the phospholyl derivative are the same as that for the cyclopentadienyl derivative (C5H5)2Mn2(CO)5, namely structures with terminal rings, a single bridging CO group, and an MnMn single bond of lengths ranging from 2.84 to 2.88Å. The phospholyl derivative (C4H4P)2Mn2(CO)5 has a different type of structure with a bridging η5,η1-μ-C4H4P ring, all terminal CO groups, and a long Mn–Mn distance of 4.35Å indicating the lack of a bond. The lowest energy structures for the tetracarbonyls (C4H4E)2Mn2(CO)4 of all five group 15 elements (E=N, P, As, Sb, Bi) have two such bridging η5,η1-C4H4E rings, all terminal CO groups, and no MnMn bond. However, the lowest energy structures for the tricarbonyls (C4H4E)2Mn2(CO)3 are the same as that for the cyclopentadienyl derivative (C5H5)2Mn2(CO)3, namely structures with terminal rings, three bridging CO groups, and a formal MnMn triple bond of length ~2.17Å.