Ruthenium-catalyzed hydrogenation reaction pathway

Three pathways for the ruthenium-catalyzed hydrogenations of ketones, aldehydes, and a,(3-unsaturated aldehydes with several catalyst systems were studied the direct insertion, the migratory insertion, and the concerted hydrogen transfer highlighting the catalyst/substrate configurations that lead to stereoselective differentiation. The contribution of computational chemistry were essential to differentiate these mechanisms of ruthenium-catalyzed reactions and to rationalize the experimentally observed stereochemical outcome. 

At least two reaction pathways may be postulated for the formation of INMF. The first (Scheme B, path a) involves initial reaction of CO with ammonia to give formamide, followed by methylation with Me-Ru generated via ruthenium-catalyzed CO hydrogenation. An alternative pathway would proceed via initial formation of methanol from CO/H2, to be followed by the production of methylamines and subsequent carbonylation (path b). 

Cycloaromatization of enediynes by diradical pathways in the thermal-and metal-catalyzed routes allows nonfunctionalized benzene derivatives to be prepared. The aromatization of enediynes by the action of nucleophiles produces aromatic compounds retaining the respective nucleophilic residue [333, 334]. The ruthenium-catalyzed reaction gives rise to the synthesis of various functionalized benzene derivatives. Thus, adding water, alcohols, aniline, acetylacetone, pyrroles, and dimethyl malonate to acyclic and aromatic enediynes 3.711 at 100°C for 12-24 hours in the presence of TpRuPPh3(MeCN)2PF6 (10 mol%) led to the functionalized benzenes 3.712 in satisfactory yields (Scheme 3.79) [334]. This cyclization involves regioselective nucleophilic attack of enediyne 3.711 to form a, TT-vinylruthenium intermediate 3.714 which finally converts to the benzene derivative. Experiment with labeled hydrogen atoms showed that the ruthenium n-alkyne complexes 3.713 are catalytically active. 

There are two possible pathways to homologate methanol with carbon dioxide the CO2 insertion path and CO insertion path (Scheme 2). As for the former, Fukuoka et al. reported that the cobalt-ruthenium or nickel bimetallic complex catalyzed acetic acid formation from methyl iodide, carbon dioxide and hydrogen, in which carbon dioxide inserted into the carbon-metal bond to form acetate complex [7]. However, the contribution of this path is rather small because no acetic acid or its derivatives are detected in this reaction. Besides, the time course... 

The intramolecular insertion of a hydride into a coordinated olefin is a crucial step in olefin hydrogenation catalyzed by late transition metal complexes, such as those of iridium, rhodium, and ruthenium (Chapter 15), in hydroformylation reactions catalyzed by cobalt, rhodium, and platinum complexes (Chapter 16), and in many other reactions, including the initiation of some olefin polymerizations. The microscopic reverse, 3-hydride elimination, is the most common pathway for the decomposition of metal-alkyl complexes and is a mechanism for olefin isomerizations. 

---