1,2-bis(dimethylphosphino) ethanehydridomesitylidynetungsten(IV). Hydride activation via the trans influence

The synthesis of the tungsten carbyne hydride complex trans-W(CMes)(dmpe)(2 )H, 7, which is obtained from the borohydride complex trans-W(CMes)(eta(1)- BH4)(dmpe)(2), 6, (dmpe = Me-2-PCH2CH2PMe2) is reported. 6 is readily prepa red from trans-W(CMes)(dmpe)(2)Cl, 5, which is prepared from [TN(CO)(5)C(O) Mes][N(CH3)(4)] via the isolable intermediates trans-W(CMes)-(CO)(2)(Py)(2) Cl, 2, and trans-W(Mes)(CO)[P(OMe)(3)](3)Cl, 3. 7 was spectroscopically ful ly characterized, and reactivity studies have revealed its potential in hyd rogen transfer reactions. The results of studies into the reactivity of the W-H bond toward small unsaturated molecules, such as propionaldehyde, benz aldehyde, acetone, acetophenone, and benzophenone, to give the correspondin g alkoxides trans-W(CMes)(dmpe)(2)(OCHR'R") (R' = H, R " = Pr 9, R' = H, R " = Ph 10, R' = R " = Me II, R' = Me, R" = Ph 12, R' R" = Ph 13) are presen ted. Facile insertion of the C=O moiety into the W-H bond was also observed with CO2 to yield the formato-O-complex trans-W(CMes)(dmpe)(2)(OCHO), 8. R eaction of 7 with pyridine-2-carbaldehyde yields the insertion product tran s-W(CMes)(eta(1)-methoxypyridine)(dmpe)(2), 14, but only at temperatures be low 0 degrees C. 14 decomposes within minutes at room temperature. Treating 7 with 4-hydroxybenzaldehyde affords trans-W(CMes)(eta(1)-4-formylphenoxy) (dmpe)(2), 15, via a simple acid-base reaction with concomitant evolution o f H-2.