Synthesis, X-ray crystal structure, and reactions of dihydridopentakis(trimethylphosphine)molybdenum(II): crystal structure of the carbon dioxide insertion product, (formato-O,O′)hydridotetrakis(trimethylphosphine)molybdenum(II)

Abstract

The reduction of MoCl₄(thf)₂(thf = tetrahydrofuran) by magnesium, in the presence of trimethylphosphine, in thf produces the dihydride MoH₂(PMe₃)₅. This compound reacts with CO₂ to give the formate MoH(O₂CH)(PMe₃)₄, with acetic and trifluoroacetic acids to give MoH(O₂CR)(PMe₃)₄(R = Me or CF₃), respectively, and with phenyl isocyanate to give MoH[PhNC(H)O](PMe₃)₄. The structures of the dihydride and the formate have been determined by X-ray crystallography. Crystals of the dihydride contain two independent molecules, the structures of which are identical within the limits of experimental error and have a pentagonal bipyramidal co-ordination geometry with the hydrides in the equatorial girdle along with three phosphines. In this equatorial group two phosphines are almost ‘trans’ to the hydrides and show the longest Mo–P distances 2.460(3)–2.478(3)Å. The unique equatorial Mo–P bond length is 2.403(3), 2.407(3)Å, whilst the axial Mo–P lengths are in the range 2.424(3)–2.428(3)Å. The Mo–H distances lie in the range 1.67(3)–1.76(4)Å. Molecules of the formate are also pentagonal bipyramidal with mm(C_2v) molecular symmetry. The hydride and symmetrically bidentate formate groups are mutually trans. The Mo–P bond lengths show similar differences to those found in the hydride [Mo–P_ax 2.426(3), Mo–P_eq 2.369(3)Å]. The Mo–H and Mo–O distances are 1.68(3) and 2.318(4)Å, respectively.