Maria C. Fermin

Oxygen atom transfer with niobocene ketenes; Baeyer-Villiger chemistry with unusual Rrgioselectivities

Abstract Niobocene ketene complex 1 has been utilized as an oxygen atom transfer reagent, converting ketones and aldehydes to esters and carboxylic acids. The steric properties of compound 1 give rise to a series of relative migratory aptitudes that differs from those seen for peracids. The process may be rendered catalytic in 1 with methyltrifluoromethyldioxirane ( 4 ).

Luminescence studies on substituted niobocene ketene complexes: evidence for thermally activated excited-state processes involving arene torsion

Photophysical studies on the η2-C,O bound nibocene ketene complexes [Nb(η5-C5H4SiMe3)2(H)(OCCRR′)](R = R′= Ph 1, R = Me, R′= Ph 2) provide evidence for solution luminescence and temperature-dependent decay rates; the failure of 2 to exhibit photochemical E–Z isomerization is consistent with the operation of arene torsional modes in the thermal decay processes.

Facile synthesis of α,β-unsaturated niobium acyls via γ-hydride abstraction

Abstract The niobocene ketene complexes [C5H4(SiMe3)]2Nb(Cl)(η2-C,O-OCC(R)CH2R′(1) undergo a facile reaction with Ph3C+ BF4− to give the cationic α,β-unsaturated metal acyls of general formula [[C5H4(SiMe3)]2Nb(Cl)(η2-C(O)CRCHR′)][BF4]. The reaction is stereospecific for the production of E-alkenes, but these undergo slow isomerization to a mixture of E and Z isomers. If both ketene substituents contain accessible allylic hydrogens, the reaction shows little regioselectivity. Preliminary mechanistic studies are consistent with a direct hydride abstraction rather than an electron-transfer/H atom transfer sequence.