The electronic structure and bonding in W-2(mu-H)(2)((OPr)-Pr-i)(4)(DMPE)(2) and a comparison with Mo-2((OPr)-Pr-i)(4)(DMPE)(2)

The bonding in the recently reported [1] W-2(mu -H)(2)((OPr)-Pr-i)(4)(DMPE) (2) ((OPr)-Pr-i= isopropoxide; DMPE =bis(dimethylphosphino)ethane) molecule is investigated via the computational method of Fenske and Hall and the re sults are compared with those of a previous study of the electronic structu re of Mo-2((OPr)-Pr-i)(4)(DMPE)(2) by Bursten and coworkers [2]. In the dim olybdenum system, a Mo-Mo triple bond of configuration sigma (2)pi (4)delta (2)(nb) (nb = nonbonding) unites the two molybdenum atoms of oxidation sta tes 0 and 4 +. The introduction of the two bridging hydrides reduces the me tal-metal bond order to two in W-2(mu -H)(2)((OPr)-Pr-i)(4)(DMPE)(2) and by analogy the bonding between the tungsten atoms can be described as sigma ( 2)pi (2)delta (2)(nb). Although there is extensive mixing of the W-W and W- H sigma bonds. an orbital can still be ascribed as a W-W sigma bond. An ana logy is made to the bonding in B2H42-, an ethane-type molecule, and to B2H6 . (C) 2001 Elsevier Science B.V. All rights reserved.