Formation of Ruthenium−Aminocarbene Complexes from Aldimines and Aminals

Specific pyridine‐based aldimines and aminals act as chelating ligands towards the RuCpL and RuTpL (Tp = hydrido trispyrazolylborate) fragments giving κ2N,N′‐coordinated cyclic imine complexes. Under particular conditions, as elucidated in this paper, these complexes rearrange into cyclic aminocarbene complexes. Thus, the reaction of [RuCp(L)(CH3CN)2]PF6 (L = CH3CN, PMe3, SbPh3) with 1 equiv. of py−N=CHR [R = Ph (phenyl), Fc (ferrocenyl), Np (naphthyl)] affords the cyclic aminocarbene complexes [RuCp(L)(=C(R)NH−py)]PF6, whereas when L = PPh3, PiPr3, and CO the reaction stops at the stage of the imine complex [RuCp(L)(κ2N,N′‐py−N=CHR)]PF6. Analogously, [RuTp(COD)Cl] (COD = 1,5‐cyclooctadiene) also reacts readily with the imines py−N=CHR (R = Ph, pMeOC6H4, Np) at elevated temperatures to yield the aminocarbene complexes [RuTp{=C(R)NH−py}Cl]. This process may open a new synthetic route for obtaining carbene complexes. The mechanism of the imine−aminocarbene conversion was analyzed by DFT/B3LYP calculations. Accordingly, the operation of a direct 1,2 hydrogen shift can be ruled out; the reaction seems to involve hydrido iminoacyl intermediates resulting from C−H bond activation and deprotonation/protonation steps. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)