Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 40. Transformation of terminally bound alkylidyne ligands to µ-alkylidene, µ-vinyl, µ-alkyl, and µ-aryl groups at a bimetal centre; X-ray crystal structures of [N(PPh3)2][ReW(µ-CHR)(CO)9], [ReW(µ-CH2R)(µ-Me2PCH2PMe2)(CO)7], and [ReW(µ-OCCH2R)(µ-Ph2PCH2PPh2)(CO)6{P(OMe)3}](R = C6H4Me-4)

Abstract

Treatment of the complexes [ReM(CR)(CO)₉] in tetrahydrofuran (thf) with K[BH(CHMeEt)₃], followed by addition of [N (PPh₃)₂]Cl affords the salts [N (PPh₃)₂][ReM (µ-CHR)(CO)₉](M = Cr, Mo, or W, R = C₆H₄Me-4; M = W, R = Me). The structure of one of these species (M = W, R = C₆H₄Me-4) was determined by X-ray diffraction. In the anion, the Re-W bond [3.033(1)Å] is asymmetrically spanned by the µ-CH(C₆H₄Me-4) group [µ-C-Re 2.155(8), µ-C–W 2.404(6)Å]. The rhenium atom is ligated by four CO groups and the tungsten by five of these ligands. On warming in thf solution, the bridged ethylidene complex [N(PPh₃)₂][ReW(µ-CHMe)(CO)₉] releases CO and converts to the hydrido- and vinyl-bridged salt [N(PPh₃)₂][ReW(µ-H)(µ-CHCH₂)(CO)₈]. Treatment of the compounds [N (PPh₃)₂][ReM{µ-CH (C₆H₄Me-4)}(CO)₉] with the bidentate phosphines R′₂PCH₂PR′₂(R′= Ph or Me) affords the complexes [N(PPh₃)₂][ReM{µ-CH(C₆H₄Me-4)}(µ-R′₂PCH₂PR′₂)(CO)₇](M = W, R′= Ph; M = Cr, Mo, or W, R′= Me). The rhenium–tungsten species on protonation (HBF₄·Et₂O) afford complexes [ReW(µ-CH₂C₆H₄Me-4)(µ-R′₂PCH₂PR′₂)(CO)₇] in which the p-tolylmethyl group asymmetrically bridges the metal-metal vector, being σ-bonded to the rhenium and co-ordinated to the tungsten by a three-centre, two-electron C–H⇀W bond. This result, strongly indicated by ¹H and ¹³C-{¹H} n.m.r. data, was confirmed by an X-ray diffraction study on the Me₂PCH₂PMe₂ derivative [µ-C-Re 2.302(7), µ-C-W 2.539(7)Å]. The Re–W vector [2.950(2)Å] is also spanned by the Me₂PCH₂PMe₂ ligand and a strongly semi-bridging carbonyl attached to the tungsten [W–C–O 153.6(6)°]. The Me₂PCH₂PMe₂ and CH₂C₆H₄Me-4 groups are cisoid in the bridge system. The rhenium and tungsten atoms each carry three terminally bound CO ligands. Several reactions of the bridged p-tolylmethyl rheniumtungsten compounds have been investigated, that between [ReW(µ-CH₂C₆H₄Me-4)(µ-Ph₂PCH₂PPh₂)(CO)₇] and P(OMe)₃affording the complex [ReW(µ-OCCH₂C₆H₄Me-4)(µ-Ph₂PCH₂PPh₂)(CO)₆{P(OMe)₃}], the structure of which was established by X-ray diffraction. In this compound the Re–W bond [3.155(1)Å] is bridged by the Ph₂PCH₂PPh₂ ligand and by the aryl group [Re–C 2.167(8), W–O 2.206(5)Å]. The rhenium atom carries three terminally bound CO groups and the tungsten two. A further CO ligand on tungsten semi-bridges the Re–W bond [W–C–O 157.0(6)Å], the tungsten being also ligated by the P(OMe)₃ group. The Ph₂PCH₂PPh₂ and aryl groups in the bridge system are cisoid. The n.m.r. spectra (¹H, ¹³C-{¹H}, and ³¹P-{¹H}) of the new compounds are reported and discussed.