Synthesis and isomerisation of two metallated N,O-complexes of ruthenium: Models for the Murai reaction

Two isomers of the N,O-coordinated acetylpyrrolyl complex [Ru(PPh3)2(CO)(NC4H3C(O)CH3)H] {cis-N,H (1) and trans-N,H (2)} have been prepared as models for catalytic intermediates in the Murai reaction. Complex 2 isomerises to 1 upon heating via a dissociative pathway (ΔH‡ = 195 ± 41 kJ mol−1; ΔS‡ = 232 ± 62 J mol−1 K−1); the mechanism of this process has been modeled using density functional calculations. Complex 2 displays moderate catalytic activity for the Murai coupling of 2′-methylacetophenone with trimethylvinylsilane, but 1 proved to be catalytically inactive under the same conditions.

Thermolysis of the N-keto pyrrolyl phosphine PPh2(NC4H3C(O)CH3-2) with [Ru(PPh3)3(CO)H2] affords the acetyl pyrrolyl complex cis-N,H-[Ru(PPh3)2(CO)(NC4H3C(O)CH3)H] (1), which is also the product of heating the stereoisomer, trans-N,H-[Ru(PPh3)2(CO)(NC4H3C(O)CH3)H] (2). The activity of these complexes for ketone–alkene coupling (Murai reaction) is described.Figure optionsDownload as PowerPoint slide