Phosphinoalkylidene and -alkylidyne Complexes of Titanium: Intermolecular C-H Bond Activation and Dehydrogenation Reactions

Masahiro Kamitani; Balazs Pinter; Keith Searles; Marco G Crestani; Anne Hickey; Brian C Manor; Patrick J Carroll; Daniel J Mindiola

doi:10.1021/jacs.5b06973

Phosphinoalkylidene and -alkylidyne Complexes of Titanium: Intermolecular C-H Bond Activation and Dehydrogenation Reactions

J Am Chem Soc. 2015 Sep 23;137(37):11872-5. doi: 10.1021/jacs.5b06973. Epub 2015 Sep 11.

Authors

Masahiro Kamitani¹, Balazs Pinter¹, Keith Searles¹, Marco G Crestani², Anne Hickey², Brian C Manor¹, Patrick J Carroll¹, Daniel J Mindiola¹

Affiliations

¹ Department of Chemistry, University of Pennsylvania , 231 South 34th Street, Philadelphia, Pennsylvania 19104, United States.
² Department of Chemistry and Molecular Structure Center, Indiana University , Bloomington, Indiana 47405, United States.

PMID: 26302157
DOI: 10.1021/jacs.5b06973

Abstract

The ethylene complex (PNP)Ti(η(2)-H2C═CH2)(CH2(t)Bu) or (PNP)Ti═CH(t)Bu(CH2(t)Bu) (PNP(-) = N[2-P(CHMe2)2-4-methylphenyl]2) reacts with H2CPPh3 to form the κ(2)-phosphinoalkylidene (PNP)Ti═CHPPh2(Ph) (1). Compound 1 activates benzene via the transient intermediate [(PNP)Ti≡CPPh2] (C). By treatment of (PNP)Ti═CH(t)Bu(OTf) with LiCH2PPh2, 1 or its isotopologue (PNP)Ti═CDPPh2(C6D5) (1-d6) can be produced by an independent route involving intermediate C, which activates benzene or benzene-d6 and dehydrogenates cyclohexane-d12. Addition of MeOTf to 1 results in elimination of benzene concomitant with the formation of the phosphonioalkylidyne complex, [(PNP)Ti≡CPPh2Me(OTf) (2). Theoretical studies of 2 suggest a resonance structure having dominant Ti-C triple-bond character with some contribution also from a C-P multiple bond.