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Catalytic Hydroarylation of Ethylene Using TpRu(L)(NCMe)Ph (L = 2,6,7-Trioxa-1-phosphabicyclo[2,2,1]heptane): Comparison to TpRu(L′)(NCMe)Ph Systems (L′ = CO, PMe3, P(pyr)3, or P(OCH2)3CEt)

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posted on 20.02.2016, 09:40 by Evan E. Joslin, Claire L. McMullin, T. Brent Gunnoe, Thomas R. Cundari, Michal Sabat, William H. Myers
The Ru­(II) complex TpRu­[P­(OCH2)2(OCCH3)]­(NCMe)­Ph (4; Tp = hydridotris­(pyrazolyl)­borate) has been synthesized and isolated. At 90 °C, TpRu­[P­(OCH2)2OCCH3]­(NCMe)­Ph in C6D6 produces TpRu­[P­(OCH2)2(OCCH3)]­(NCMe)­Ph-d5 and C6H5D. TpRu­[P­(OCH2)2(OCCH3)]­(NCMe)­Ph catalyzes the hydrophenylation of ethylene at 90 °C to produce ethylbenzene with 90 turnovers (TOs) after 50 h. Catalyst deactivation occurs by the formation of the η3-allyl complex TpRu­[P­(OCH2)2(OCCH3)]­(η3-C3H4Me). Kinetic studies of stoichiometric C6D6 activation by TpRu­(L)­(NCMe)­Ph (L = CO, P­(OCH2)3CEt, PMe3 P­(OCH2)2(OCCH3)) to give TpRu­(L)­(NCMe)­Ph-d5 and C6H5D reveal that the reactions occur with the following relative rates: PMe3 (kobs = [1.36(4)] × 10–5 s–1) > P­(OCH2)3CEt (kobs = 1.20(2) × 10–5 s–1) > P­(OCH2)2(OCCH3)­(kobs = 7.2(5) × 10–6 s–1) > CO (kobs = [4.62(3)] × 10–6 s–1). These rates correlate linearly with Ru­(III/II) potentials of the four TpRu­(L)­(NCMe)­Ph complexes. DFT calculations have been used to model catalytic olefin hydroarylation by TpRu­[P­(OCH2)2(OCCH3)]­(NCMe)­Ph (4) and to rationalize the observed differences in the various TpRu­(L)­(NCMe)­Ph catalysts.