Chemistry of Unsaturated Group 6 Metal Complexes with Bridging Hydroxy and Methoxycarbyne Ligands. 4. Carbonyl, Isocyanide, and Diphosphine Derivatives of the Complexes [M2(η5-C5H5)2(μ-COMe)(μ-PR2)2]BF4 (M = W, R = Ph; M = Mo, R = Et)

The unsaturated complexes [M2Cp2(μ-COMe)(μ-PR2)2]BF4 [M = W, R = Ph (1a); M = Mo, R = Et (1b); Cp = η5-C5H5] react with CO under pressure [ca. 4 atm (1a) or ca. 60 atm (1b)] to give the corresponding electron-precise dicarbonyl derivatives [M2Cp2(μ-COMe)(μ-PR2)2(CO)2]BF4, which display a parallel arrangement of the carbonyl ligands (W−W = 2.9020(5) A for the ditungsten complex). The reactions with CNtBu take place rapidly at room temperature to give analogously the corresponding derivatives with parallel isocyanide ligands, cis-[M2Cp2(μ-COMe)(μ-PR2)2(CNtBu)2]BF4. At low temperature, however, a less stable isomer can be detected, which in the ditungsten system is identified as the isomer having a transoid arrangement of isocyanide groups, trans-[M2Cp2(μ-COMe)(μ-PR2)2(CNtBu)2]BF4, while for the dimolydenum system that isomer is identified as the ketenylimine complex [Mo2Cp2{μ-η1:η1-C(OMe)C(NtBu)}(μ-PEt2)2(CNtBu)]BF4, a product resulting from the C−C coupling between carbyne and isocyanide ligands; these pro...