Ruthenium(II)-Mediated Carbon−Carbon Bond Formation between Acetonitrile and Pyrrole:  Combined Experimental and Computational Study

Abstract

The reaction of TpRu(CO)(NCMe)(Me) (1) and pyrrole forms TpRu(CO){κ2-N,N-(H)NC(Me)(NC4H3)} (2). The formation of complex 2 involves the cleavage of the N−H bond and 2-position C−H bonds of pyrrole as well as a C−C bond forming step between pyrrole and the acetonitrile ligand of 1. Mechanistic studies indicate that the most likely reaction pathway involves initial metal-mediated N−H activation of pyrrole to produce TpRu(CO)(N-pyrrolyl)(NCMe) (3) followed by C−C bond formation and proton transfer. Complex 3 has been independently prepared and demonstrated to convert to 2. Computational studies support the suggested selectivity for initial N−H bond cleavage in preference to C−H bond activation.

Synthesis of heteroleptic pyrrolide/bipyridyl complexes of ruthenium(II)

“…12,13 Although pyrrolide complexes of transition metals such as rhenium 14,15 and molybdenum 16 have been reported, there are few examples reported with ruthenium(II). [17][18][19][20] For example, 18 a pyrrolide ruthenium complex has been observed through the use of a bidentate α-substituted pyrrole, producing N,O-coordinated pyrrolide-ruthenium complexes as models for catalytic intermediates in the Murai coupling reaction (A, Figure 1). These results lead us to postulate that there may be increased success with pyrrolide-metal complexation using bidentate α-substituted pyrroles.…”

“…22 Bidentate coordination of pyrrole to ruthenium has also been accomplished through the reaction of TpRu(CO)(NCMe)(Me) with pyrrole, which results in the formation of product B. 19 The product contains an N-pyrrolide ligand with a coordinating pendant imine that arose from addition to the previously coordinated acetonitrile unit, presumably via metal-mediated N-H/C-H activation of the pyrrole, accompanied by the release of methane. Interestingly, lithium pyrrolide displaced triflate from TpRu(CO)(NCMe)(OTf) to give TpRu(N-pyrrolide)(CO)(NCMe), without C-H activation, akin to reactions previously reported for rhenium.…”

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

“…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.…”

Activation of sp3 Carbon–Hydrogen Bonds by a Ruthenium(II) Complex and Subsequent Metal‐Mediated CC and CN Bond Formation

“…[6,7,9,12] [7,8] the rate-determining step for the conversion of 1 to 2 is expected to be the C À H activation event. Consistent with this hypothesis, heating 1 in a 1:1 mixture of NCCD 3 and NCCH 3 results in the formation of CH 3 D and CH 4 .…”

“…[10,11] Herein, we report initial fundamental studies of stoichiometric sp 3 Mechanistic studies suggest that aromatic C À H activations by [TpRu(L)(NCMe)Me] (L = CO or PMe 3 ) to release methane and produce [TpRu(L)(NCMe)Ar] (Ar = aryl) involve dissociation of NCMe, coordination of the aromatic substrate, and subsequent CÀH activation of the substrate. [6,7,9,12] Heating [TpRu(PMe 3 )(NCMe)Me] (1) at 608C in CH 3 CN results in C À H activation of acetonitrile to release methane and produce [TpRu(PMe 3 )(NCMe)(CH 2 CN)] [2, Eq. (1) and Figure 1 a].…”