Reactions of TpRu(CO)(NCMe)(Me) (Tp = Hydridotris(pyrazolyl)borate) with Heteroaromatic Substrates:  Stoichiometric and Catalytic C−H Activation

Abstract

The Ru(II) complex TpRu(CO)(NCMe)(Me) (Tp ) hydridotris(pyrazolyl)borate) initiates carbon-hydrogen bond activation at the 2-position of furan and thiophene to produce methane and TpRu(CO)(NCMe)(aryl) (aryl ) 2-furyl or 2-thienyl). Solid-state structures have been determined for TpRu(CO)(NCMe)(2-thienyl) and [TpRu(CO)(µ-C,S-thienyl)] 2 . The complex TpRu(CO)(NCMe)(2-furyl) serves as a catalyst for the formation of 2-ethylfuran from ethylene and furan. DFT calculations of the C-H activation of furan by {(Tab)Ru-(CO)(Me)} (Tab ) tris(azo)borate) indicate that the C-H activation sequence does not proceed through a Ru(IV) oxidative addition intermediate.

Aromatic C−H Activation and Catalytic Hydrophenylation of Ethylene by TpRu{P(OCH2)3CEt}(NCMe)Ph

“…Extensive investigations into the hydroarylation mechanism for all three systems suggest the catalytic pathway shown in Scheme 4. 28,29,34 Initiated by NCMe dissociation from TpRu(L)(NCMe)Ph, TpRu(L)Ph coordinates and mediates ethylene insertion into the Ru-Ph moiety. Benzene coordination and C-H activation produce ethylbenzene and regenerates the unsaturated TpRu(L)Ph complex to complete the catalytic cycle.…”

“…[20][21][22][23][24][25][26][27] Our groups have been exploring the manipulation of a series of TpRu(L)(NCMe)Ar {L ) CO, PMe 3 , or P(pyr) 3 ; pyr ) N-pyrrolyl; Ar ) aryl} complexes that serve as homogeneous catalysts for the hydroarylation of olefins. 21,[28][29][30][31][32][33][34][35] * To whom correspondence should be addressed. E-mail: brent_gunnoe@ ncsu.edu.…”

Combined Experimental and Computational Study of TpRu{P(pyr)3}(NCMe)Me (pyr = N-pyrrolyl): Inter- and Intramolecular Activation of C−H Bonds and the Impact of Sterics on Catalytic Hydroarylation of Olefins

“…The lack of cyclometalation of the TpRu{P(pyr) 3 }Ph fragment suggests that 5 might be a viable catalyst for the hydroarylation of olefins as previously studied for analogous TpRu(L)(NCMe)Ph (L ) CO and PMe 3 ) complexes. [42][43][44]49 Hydrophenylation of Ethylene. TpRu{P(pyr) 3 }(NCMe)Ph (5) is an electronically similar analogue and structural variant of the previously reported olefin hydroarylation catalyst TpRu(CO)(NCMe)Ph.…”

“…40,41 Our group has been investigating the use of TpRu II {Tp ) hydridotris(pyrazolyl)borate} complexes as homogeneous catalysts for the hydroarylation of olefins. [42][43][44][45][46][47][48] For example, TpRu-(CO)(NCMe)Ph catalytically produces alkyl arenes from ethylene or simple R-olefins and arenes and is, to our knowledge, the most active homogeneous catalyst for the hydrophenylation of ethylene that proceeds through a metal-mediated C-H activation pathway. [42][43][44] In order to better understand the factors that control the catalysis and in an effort to access improved systems, we have sought to synthesize analogues of TpRu(CO)-(NCMe)Ph by formally substituting CO with alternative neutral two-electron-donating ligands.…”

Mechanisms of C–H bond activation: rich synergy between computation and experiment

“…These Ru II systems also appear more sensitive to substituent effects than the classic Cp* 2 Sc-Me system studied by Bercaw. 28 29 In general, more acidic C-H bonds appear easier to activate. Thus activation of a b-C-H bond in Et 2 O by {TpRu(PH 3 )(H)} showed a reduced barrier compared to CH 4 (relative in each case to their respective s-adduct precursors).…”