Inorganic Chemistry, Vol.44, No.25, 9506-9517, 2005
Coupling of an aldehyde or ketone to pyridine mediated by a tungsten imido complex
The reactivity of W(NPh)(o-(Me3SiN)(2)C6H4)(py)(2) and W(NPh)(o-(Me3SiN)(2)C6H4)(PiC)(2) (py = pyridine; pic = 4-picoline) with unsaturated substrates has been investigated. Treatment of W(NPh)(o-(Me3SiN)(2)C6H4)(py)(2) with diphenylacetylene or 2,3-dimethyl-1,3-butadiene generates W(NPh)(o-(Me3SiN)(2)C6H4)(n(2)-PhC&3bond; CPh) (1) and W(NPh)(o-(Me3SiN)2C6H4)(n(4-)CH(2)=C(Me)C(Me)=CH2) (3), respectively, while the addition of ethylene to W(NPh)(o-(Me3SiN)2C6H4)(py)2 generates the known metallacycle W(NPh)(o-(Me3SiN)(2)C6H4)(CH2CH2CH2CH2). The addition of 2 equiv of acetone to W(NPh)(o-(Me3SiN)2C6H4)(PiC)2 provides the azaoxymetallacycle W(NPh)(o-(Me3SiN)(2)C6H4)(OCH(Me)(2))(OC(Me)(2)-o-C5H3N-p-Me) (4), the result of acetone insertion into the ortho C-H bond of picoline. Similarily, the addition of 2 equiv of RC(O)H [R = Ph, Bu-t] to W(NPh)(o-(Me3SiN)(2)C6H4)(PY)(2) generates W(NPh)(o-(Me3SiN)(2)C6H4)(OCH2R)(OCH(R)-o-C5H4N) [R = Ph, 5; Bu-t, 6]. In contrast, reaction between W(NPh)(o-(Me3SiN)2C6H4)(PY)2 and 2-pyridine carboxaldehyde yields the diolate W(NPh)(o-(Me3SiN)2C6H4)(CCH(C5H4N)CH(C5H4N)O) (7). The synthesis of W(NPh)(o-(Me3SiN)(2)C6H4)(PMe3) (py)(n(2)-OC(H)C6H4-p-Me) (9), formed by the addition of p-tolualdehyde to a mixture of W(NPh)(o-(Me3SiN)2C6H4)(PY)2 and PMe3, Suggests that an n(2)-aldehyde intermediate is involved in the formation of the azaoxymetallacycle, while the isolation of W(NPh)(o-(Me3SiN)(2)C6H4)(Cl)(OC(Me)(CMe3)-o-C5H4N) (10), formed by the reaction of pinacolone with W(NPh)(o-(Me3SiN)2C6H4)(PY)2, in the presence of adventitious CH2CI2, suggests that the reaction proceeds via the hydride W(NPh)(o-(Me3SiN)(2)C6H4)(H)(OC(Me)(CMe3)-O-C5H4N).