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)( η 1 -BH 4 )(dmpe) 2, 6, (dmpe = Me 2 PCH 2 CH 2 PMe 2 ) is reported. 6 is readily prepared from trans -W(CMes)(dmpe) 2 Cl, 5, which is prepared from [W(CO) 5 C(O)Mes][N(CH 3 ) 4 ] via the isolable intermediates trans -W(CMes)(CO) 2 (Py) 2 Cl, 2, and trans -W(CMes)(CO)[P(OMe) 3 ] 3 Cl, 3 . 7 was spectroscopically fully characterized, and reactivity studies have revealed its potential in hydrogen transfer reactions. The results of studies into the reactivity of the W−H bond toward small unsaturated molecules, such as propionaldehyde, benzaldehyde, acetone, acetophenone, and benzophenone, to give the corresponding alkoxides trans -W(CMes)(dmpe) 2 (OCHR‘R‘ ‘) (R‘ = H, R‘ ‘ = Pr 9, R‘ = H, R‘ ‘ = Ph 10, R‘ = R‘ ‘ = Me 11, R‘ = Me, R‘ ‘ = Ph 12, R‘ = R‘ ‘ = Ph 13 ) are presented. Facile insertion of the C O moiety into the W−H bond was also observed with CO 2 to yield the formato-O-complex trans -W(CMes)(dmpe) 2 (OCHO), 8 . Reaction of 7 with pyridine-2-carbaldehyde yields the insertion product trans -W(CMes)(η 1 -methoxypyridine)(dmpe) 2, 14, but only at temperatures below 0 °C. 14 decomposes within minutes at room temperature. Treating 7 with 4-hydroxybenzaldehyde affords trans -W(CMes)( η 1 -4-formylphenoxy)(dmpe) 2, 15, via a simple acid−base reaction with concomitant evolution of H 2 .