Chemistry of bridging ketene from facile carbonylation of a ditungsten methylene complex with NO metal-metal bond

The reaction of Cp(CO)(3)W- (Cp = eta(5)-C5H5) with CH2I2 in CH3CN at -20 degrees C gives the dinuclear acetylide complex Cp-2(CO)(6)W-2(mu-C=C) (2). When the same reaction is carried out in methanol at -20 degrees C, a dinuclear ketene complex, Cp-2(CO)(5)W-2(mu,eta(1),eta(2)-CH2CO) (5), is isolated. The oxygen atom of the ketene unit in 5 is weakly coordinated to one of the tungsten metal centers. Upon dissolution in CH3CN at room temperature, complex 5 transforms to 2. A bridging methylene complex, Cp-2(CO)(4)[P(OMe)(3)](2)W-2(mu-CH2) (4a), has been isolated, and its facile carbonylation gives a different ketene complex, Cp-2(CO)(2)[P(OMe)(3)](2)W-2(mu,eta(1),eta(1)-CH2CO)(mu-CO) (6a), in CH3CN. Treatment of 5 with CO affords Cp-2(CO)(6)W-2(mu-CH2CO) (8), which, upon reacting-with H2O, ROH (R = Me, Et, PhCH2), and i-PrNH2, generates mononuclear complexes Cp(CO)(3)WCH2COOH (9), Cp(CO)(3)WCH2COOR (12a-c), and Cp(CO)(3)WCH2CONH(i-Pr) (14), respectively. The more-stable Cp' (Cp' = C5H4Me) analogues 2', 5', and 8' are also prepared. An experiment using a mixture of 5 and 5' to afford only 2 and 2' without the crossover product shows that intermolecular coupling is not involved in this transformation. The reaction of 5 with PR3 (R = OMe, Et, Ph) yields only the trans product Cp-2(CO)(5)(PR3)W-2(mu-CH2CO) (10a-c). But the reaction of 5 with t-BuNC gives both the trans and cis products of the ketene complex CP2(C)(5)(t-BuNC)W-2(mu-CH2CO) (11). Complexes 2', 5', 8', and 11 have been characterized by single-crystal X-ray diffraction analysis.