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Oxidatively Induced α-Hydrogen Abstraction. A Mild Protocol to Generate Terminal Titanium Alkylidenes Containing a β-Hydrogen

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posted on 31.07.2006 by Brad C. Bailey, Falguni Basuli, John C. Huffman, Daniel J. Mindiola
One-electron oxidation of the Ti(III) bis-isobutyl complexes (nacnac)Ti(CH2iPr)2 (1) (nacnac- = [ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3) and (PNP)Ti(CH2iPr)2 (4) (PNP- = N[2-P(CHMe2)2-4-methylphenyl]2) with AgOTf promotes exclusive α-hydrogen abstraction to provide the first structurally characterized examples of terminal group 4 alkylidenes bearing a β-hydrogen, namely, (nacnac)TiCHiPr(OTf) (2) and (PNP)TiCHiPr(OTf) (5). These complexes have been prepared and characterized by means of multinuclear NMR spectroscopy as well as single-crystal X-ray diffraction analysis. In the case of the nacnac framework, the reactive TiCHiPr motif can readily engage in an intramolecular Wittig-like rearrangement. However, the isobutylidene motif can be stabilized when supported by a more robust ancillary ligand such as PNP, which is demonstrated by the thermal resistance of 5 and the preparation of a rare example of a stable alkylidene methyl complex (PNP)TiCHiPr(Me) (6).