Ruthenium carbonyls, reaction with pyrazoles

The carbonylation reaction is also applicable to other five-membered N-hetero-cycles, such as thiazoles, oxazoles, and pyrazoles [36], The reactivity of the substrates increases with increasing pfCa values of the conjugate acids of the N-heterocycles according to the series imidazole (pfCj 7.85) > thiazole (pfCa 3.37) > oxazole (pKa 2.91) > pyrazole (pKa 2.09). This indicates that the coordination of the substrates by the sp nitrogen to the ruthenium center is the key step in the carbonylation of C-H bonds in N-heterocycles. 

Pyridine itself can be reacted with olefins and carbon monoxide in the presence of a catalytic amount of Ru3(CO)i2 to give a-acylated pyridines (eq 8)T A number of olefins react with the pyridine to afford the corresponding linear p)ridyl ketones as the major products. The ruthenium-catalyzed carbonylation of 1,2-disubstituted imidazoles with olefins and carbon monoxide provides C-C bond formation at the 4-position (eq Various functional groups, e.g., ether, acetal, ester, imide, and nitrile are tolerant to the reaction conditions. The reaction of 1-methylpyrazole under similar carbonylation conditions gives 3-pyrazolyl ketones (eq 10). This result is in contrast to the Friedel-Crafts acylation of a pyrazole ring, which yields 4-pyrazolyl ketones. ... 

The formation of either mononuclear or binuclear ruthenium and osmium carbonyl complexes bearing bis(2-pyridyl)amine (Hdpa) or the deprotonated ligand (dpa) can be driven by choice of solvent and reaction temperature. For example, [Ru3(GO)i2] reacts with Hdpa in HGl solution at 200 °G to give mainly m,m-[Ru(hdpa) (GO)2Gl2], whereas in toluene solution in the absence of HGl at 200 °G, Ru(dpa)(GO)2 2 predominates. In related chemistry, [Ru(GO)2Gl2] reacts with bis(pyrazol-l-yl)methane (BPM), bis(3,5-dimethylpyrazol-l-yl)... 

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