The electronic structure and bonding in W2(μ-H)2(OiPr)4(DMPE)2 and a comparison with Mo2(OiPr)4(DMPE)2

The bonding in the recently reported [1] W2(μ-H)2(OiPr)4(DMPE)2 (OiPr=isopropoxide; DMPE=bis(dimethylphosphino)ethane) molecule is investigated via the computational method of Fenske and Hall and the results are compared with those of a previous study of the electronic structure of Mo2(OiPr)4(DMPE)2 by Bursten and coworkers [2]. In the dimolybdenum system, a Mo–Mo triple bond of configuration σ2π4δ2nb (nb=nonbonding) unites the two molybdenum atoms of oxidation states 0 and 4+. The introduction of the two bridging hydrides reduces the metal–metal bond order to two in W2(μ-H)2(OiPr)4(DMPE)2 and by analogy the bonding between the tungsten atoms can be described as σ2π2δ2nb. Although there is extensive mixing of the W–W and W–H σ bonds, an orbital can still be ascribed as a W–W σ bond. An analogy is made to the bonding in B2H42−, an ethane-type molecule, and to B2H6.