Metal carbonyl clusters: thermodynamics of their formation and stability. Some novel results on cobalt, rhodium, ruthenium, and mixed clusters

Abstract

A series of reversible cluster formation and degradation reactions with neutral metal carbonyls and carbonyl hydrides was studied by high-pressure IR-spectroscopy, under CO and/or H2 pressure, in alkane solutions. Fundamental reversible reactions were analyzed for cobalt, rhodium, ruthenium, and mixed Co-Fe, Co-Ru and Co-Rh carbonyl systems. Log K vs l/T equations, their graphical illustrations and thermodynamic parameters are given for the homometallic Co, Rh and Ru systems.In the combined system of Co and Ru carbonyls and hydridocarbonyls proper conditions were found where mixed hydridocarbonyl clusters are obtained in stable equilibria with the homonuclear compounds. Of the COx(HRu)4_x(CO)12 species the one with x=3 is strongly favored thermodynamically. -In the mixed Co-Fe system no thermodynamically stable compound could be found: HCo3Fe(CO)1 decomposes irreversibly, under CO as well as H2 or N, to homometallic species.Of particular interest is the coordinatively unsaturated mixed species CoRh(CO)7, which represents a key link between the homo-and hetero-metallic equilibria of these metals.The connection of our data with thermochemical results from other laboratories, and their application to bond enthapy calculations is presented.

Away from phosgene: reductive carbonylation of nitroarenes and oxidative carbonylation of amines, understanding the mechanism to improve performance

“…However, [Ru 3 (CO) 12 ] is known to be in equilibrium with [Ru(CO) 5 ] under high CO pressure (eqn ( 14)). 118,119 Ru 3 (CO) 12 + 3CO 3Ru(CO) 5 (14) By use of a high-pressure IR cell and spectral subtraction techniques we have evidenced that, under our conditions, the reaction is almost completely shifted towards [Ru(CO) 5 ], only about 5% of the starting [Ru 3 (CO) 12 ] remaining at equilibrium. A typical test to identify the real cluster nature of the active catalyst in systems of this kind is to examine the turnover frequency as a function of the total metal concentration.…”

Exploration of Fluorine Chemistry at the Multidisciplinary Interface of Chemistry and Biology

“…This leveling phenomenon was best interpreted by taking into account the formation of and the catalysis by a Co–Rh mixed-metal complex. When we reached this conclusion, Horváth, Bor, and Pino at ETH reported synthesis, characterization, and some reactions of an interesting coordinatively unsaturated Co–Rh mixed metal complex, CoRh(CO) 7 (eq ), − which was eventually identified as the catalyst species in our HF-ADS reaction. Rh 4 false( CO false) 12 + 2 Co 2 false( CO false) 8 ⇌ K 1 4 CoRh false( CO false) 7 …”

Regiodivergent Access to Five- and Six-Membered Benzo-Fused Lactams: Ru-Catalyzed Olefin Hydrocarbamoylation

“…In the case of iodide, direct formation of a bridged complex 5c was observed, which is then transformed to [Ru 3 (CO) 9 (μ 3 -I)] − ( 7 ) with a triply bridged iodide ligand. Because the equilibrium between Ru 3 (CO) 12 and its monomeric Ru(CO) 5 species needs high CO pressure, it is reasonable to rule out a possibility that the added halide ions dissociate the trinuclear precursor into a monomeric species under the present reaction conditions. On the basis of these results, we postulate that complexes 5 might be a common catalytically active species responsible for the 5- exo -cyclization process under catalytic system A…”