Stabilization of diborane(4) by transition metal fragments and a novel metal to π Dewar-Chatt-Duncanson model of back donation.

The feasibility of using transition metal fragments to stabilize B2H4 in planar configuration by donating 2 electrons to the boron moiety is investigated. Building upon the existing theoretical and experimental data and aided by the isolobal analogy, the model transition metal complexes Cr(CO)4B2H4 (6), Mn(CO)CpB2H4 (7), Fe(CO)3B2H4 (8) and CoCpB2H4 (9) are chosen to illustrate this unique bonding feature--bond strengthening with π-back donation. Other possible types of complexes with B2H4 and the metal fragment are also explored and the energies are compared. One of the low energy isomers wherein the planar B2H4 interacts with the metal fragment in an in-plane fashion represents a unique case study for the Dewar-Chatt-Duncanson model. In this complex the back-donation from the metal fills the π bonding orbital between the two boron atoms thus forming a B=B double bond.