No abstract

An aniline coordinated to tungsten undergoes alkylation at C4 or protonation at C2. In the latter case, a second electrophilic addition is possible at C3, followed by nucleophilic addition at C4.

Upon coordination to {TpW(PMe3)(NO)}, phenol tautomerizes to a cyclohexadienone (a 2H-phenol). The uncoordinated, nonaromatic double bond of this ligand undergoes stepwise addition of electrophiles followed by nucleophiles to produce 4,5-disubstituted cyclohexenone complexes. The metal stabilizes the intermediate cationic ligand and sterically blocks one face of the ligand, resulting in a high degree of stereo- and regiocontrol. These substituted cyclohexenones are readily liberated from the metal by oxidative decomplexation.

A series of complexes of the form TpM(NO)(L′)(η 2 -L) are prepared (where L is a nitrile, ketone, or alkene, M ) W or Mo, L′ ) PMe 3 , MeIm, Tp ) hydridotris(pyrazolyl)borate). These complexes are subjected to various electrophiles (e.g., alkyl halides, Brønsted acids) to systematically probe the ability of the π-basic transition metal to affect the reactivity of the dihapto-coordinated ligand. Alkylation is observed at the heteroatom of the ketone and the nitrile, but depending on the reagent, alkylation of the nitrosyl ligand or addition to the complexed π-bond also occurs. The structures of several nitrilium complexes and a rare example of an η 2 -acetonium complex are also reported.

No abstract

The complex TpW(NO)(PMe 3 )(η 2 -benzene) was treated with an excess of phenol to generate TpW-(NO)(PMe 3 )(η 2 -2H-phenol) as a mixture of two stereoisomers. This complex in the presence of base undergoes reactions with several common classes of electrophiles, including benzaldehyde, alkyl iodides, and Michael acceptors, to form new C-C bonds. Methyl and ethyl iodide react at C2 to form 2-alkyl-2H-phenol complexes, whereas the Michael acceptors react at C4 to give 4-alkyl-4H-phenol complexes. In both cases, the electrophile adds to the complexed phenol stereoselectively, anti to the metal. In the case of benzaldehyde, an aldol condensation reaction occurs at C2 to form a rare example of a thermally stable o-quinone methide complex. Crystal structures of the 2-ethyl-2H-phenol and the phenyl o-quinone methide complexes are included.

No abstract

No abstract