Homogeneous Hydrogenation of Alkenes Catalyzed by the Ruthenium−Hydride Complex (PCy₃)₂(CO)(Cl)RuH:  Spectroscopic Observation of the Ruthenium−Ethyl and Ruthenium−Ethylene−Hydride Intermediate Species

Abstract

The ruthenium−hydride complex (PCy3)2(CO)(Cl)RuH (1a) was found to catalyze the hydrogenation of terminal and cyclic alkenes. For example, the reaction of 1-hexene with 4 atm of H2 in the presence of 1a (1-hexene:1a = 8300:1) produced the hydrogenation product 2 (TON = 12 000 h-1). The treatment of 1a with excess ethylene led to the observation of both the ruthenium−ethyl and ruthenium−ethylene−hydride species 4a and 5a, respectively. The thermodynamic parameters for the equilibria among 1a, 4a, and 5a were estimated from the VT NMR data. These results are consistent with a monohydride mechanistic pathway.

Ruthenium Complexes Featuring Unsymmetrical N‐Heterocyclic Carbene Ligands–Useful Olefin Metathesis Catalysts for Special Tasks

“…[21] Selectivity issues related to CÀ C bond migration remain a major obstacle to numerous potential industrial applications of olefin metathesis. 3a This problem is typically connected with relatively easy decomposition of general-purpose symmetrical NHC-based catalysts during the reaction leading to the production of Ru-hydride complexes and other species [22] responsible for this unwanted process. [23] Therefore, the observed high fidelity exhibited by uNHC systems is of particular interest.…”

Searching for the Hidden Hydrides: The Competition between Alkene Isomerization and Metathesis with Grubbs Catalysts

“…More recently, chemists have sought to exploit isomerization processes, and some significant methodological gains have been achieved;7 Donohoe et al8 recently highlighted the effectiveness of isomerization as a synthetic tactic. Hong et al characterized diruthenium hydride species 2 ,9 Arisawa and co‐workers10 and, more recently, Fogg et al11 prepared 3 ;12 complex 4 is also known,13 and all three species are known to act as isomerization catalysts. For example, 1.5 mol‐% 2 catalyzed the isomerization of allyl benzene to E / Z 2‐methylstyrene in 76 % yield over 24 h at 40 °C 9a.…”

Regioselective Hydrogenation of α,β-Unsaturated Ketones over Wilkinson’s Catalyst

“…This result corresponds to the sluggish (Cy 3 P) 2 Ru(CO)(Cl)H catalyzed hydrogenation of internal alkenes. 6 No hydrogenation was observed upon the addition of another substituent to either the a-or b-carbon (Table 1, entries 3 and 4). Aromatic substitution as in the case of trans-chalcone (4e) had an even larger negative effect on hydrogenation as is corroborated by TOF, TON and yield values considerably lower than those of pent-3-en-2-one (4b) ( …”