Oxidative Alkenylation of Arenes Using Supported Rh Materials: Evidence that Active Catalysts are Formed by Rh Leaching

Electron-Deficient Ru(II) Complexes as Catalyst Precursors for Ethylene Hydrophenylation

Ruthenium(II) complexes with the general formula TpRu(L)(NCMe)Ph (Tp = hydrido(trispyrazolyl)borate, L = CO, PMe3, P(OCH2)3CEt, P(pyr)3, P(OCH2)2(O)CCH3) have previously been shown to catalyze arene alkylation via Ru-mediated arene C–H activation including the conversion of benzene and ethylene to ethylbenzene. Previous studies have suggested that the catalytic performance of these TpRu(II) catalysts increases with reduced electron-density at the Ru center. Herein, three new structurally related Ru(II) complexes are synthesized, characterized, and studied for possible catalytic benzene ethylation. TpRu(NO)Ph2 exhibited low stability due to the facile elimination of biphenyl. The Ru(II) complex (TpBr3)Ru(NCMe)(P(OCH2)3CEt)Ph (TpBr3 = hydridotris(3,4,5-tribromopyrazol-1-yl)borate) showed no catalytic activity for the conversion of benzene and ethylene to ethylbenzene, likely due to the steric bulk introduced by the bromine substituents. (Ttz)Ru(NCMe)(P(OCH2)3CEt)Ph (Ttz = hydridotris(1,2,4-triazol-1-yl)borate) catalyzed approximately 150 turnover numbers (TONs) of ethylbenzene at 120 °C in the presence of Lewis acid additives. Here, we compare the activity and features of catalysis using (Ttz)Ru(NCMe)(P(OCH2)3CEt)Ph to previously reported catalysis based on TpRu(L)(NCMe)Ph catalyst precursors.

Advances in Group 10 Transition-Metal-Catalyzed Arene Alkylation and Alkenylation

On a large scale, the dominant method to produce alkyl arenes has been arene alkylation from arenes and olefins using acid-based catalysis. The addition of arene C-H bonds across olefin C═C bonds catalyzed by transition-metal complexes through C-H activation and olefin insertion into metal-aryl bonds provides an alternative approach with potential advantages. This Perspective presents recent developments of olefin hydroarylation and oxidative olefin hydroarylation catalyzed by molecular complexes based on group 10 transition metals (Ni, Pd, Pt). Emphasis is placed on comparisons between Pt catalysts and other group 10 metal catalysts as well as Ru, Ir, and Rh catalysts.

Rhodium-Catalyzed Redox-Neutral Olefination of Aryldiazenes with Acrylate Esters via C-H Activation and Transfer Hydrogenation

Rh(III)-catalyzed redox-neutral C-H olefination of aryldiazenecarboxylates has been realized using arylate esters as the olefinating reagents. This reaction proceeds under mild and redox-neutral conditions, resulting in integration of C-H activation and transfer hydrogenation. The chemoselectivity complements that of previously reported rhodium-catalyzed coupling of the same substrates.