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

Abstract

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 BB double bond.