Reactions of hexamethyltungsten(VI) in the presence of trimethylphosphine. Synthesis of methyl, ethylidyne, hydrido-, alkoxo-, and other tungsten compounds. X-Ray crystal structures of trans-ethylidyne(methyl)tetrakis(trimethylphosphine)tungsten(IV) and trihydrido(phenoxo)tetrakis(trimethylphosphine)tungsten(IV)

Abstract

Hexamethyltungsten(VI) reacts with trimethylphosphine in light petroleum to give WMe₆(PMe₃), which in neat PMe₃ with u.v. irradiation gives the carbyne complex trans-WMe (CMe)(PMe₃)₄ in high yield. Under hydrogen WMe₅(PMe₃) gives quantitative yields of WH₂(PMe₃)₅ and WH₄(PMe₃)₄, with an excess and with three moles of PMe₃ respectively. WH₂(PMe₃)₅ yields cis-Wl₂(PMe₃)₄ with Mel, and with methanol in a rare example of oxidative addition as CH₃O and H, to give WH₃(OMe)(PMe₃)₄; with phenol, it yields W(OPh)₄(PMe₃)₃ which in turn, on reaction with LiNMe₂ in tetrahydrofuran, gives WH₃(OPH)(PMe₃)₄ and small amounts of W(NMe₂)₆. The protonation of WH₄(PMe₃)₄ with tetrafluoroboric acid gives [WH₃(PMe₃)₄][BF₄].

The compounds have been studied by ¹H, ³¹P, and ¹³C n.m.r. and i.r. spectroscopy and the crystal structures of trans-WMe(CMe)(PMe₃)₄(2) and WH₃(OPh)(PMe₃)₄(8) have been determined by X-ray crystallography. Crystals of (2) are tetragonal, space group I2m, with a=b= 9.699(1), c= 12.576(1)Å, and Z= 2. The structure has been refined to R= 0.014 for 337 observed diffractometer data. The unsymmetrical molecule is disordered with the Me–CW–Me unit adopting two anti-parallel orientations over the same site, thus simulating symmetry. The WC and W–C distances are found to be 1.90(3) and 2.45(3)Å, the latter somewhat longer than expected, possibly due to steric crowding. The W–P distance is 2.450(2)Å. Compound (8) is monoclinic, space group C2/m, with a= 14.547(2), b= 13.795(2), c= 13.283(2)Å, β= 101.40(2)°, and Z= 4. The structure has been refined to R= 0.0532 for 2 836 observed diffractometer data. The molecule has mirror symmetry and although the hydride atoms were not located experimentally, the molecule is presumed to have a dodecahedral geometry with the phosphines in the ‘B’ sites. Differences in W–P distances, 2.374(4) to 2.506(6)Å, are attributed to trans effects.