Experimental and computational study of pincer complexes of ruthenium with Py, CO, and N2 Ligands

Addition of pyridine to the syn and anti isomers of cis-RuHCl[(Bu2PCH2CH2)-Bu-t((E)-CH=CH)CH2PBu2t] (1) afforded a single isomer of trans,cis,anti-RuHCl(Py)[(Bu2PCH2CH2)-Bu-t((E)-CH=CH)CH2PBu2] (2), where the anti alpha-HC-RuH configuration was established by a difference NOE experiment. The carbonyl complex RuCl(CO)[CH(C2H4PBu2t)(2)] (3) was obtained from 2 under CO, and two hydride complexes, RuH(CO)[CH(C2H4PBu2)(2)] (4) and RuH(N-2)[CH(C2H4PBu2t)(2)] (5), were prepared from 3 and 1, respectively, using Li[HBEt3] as the hydride source. Decarbonylation of isoamyl alcohol with polymeric [RuCl2(COD)],, in the presence of 1,5-bis(di-tert-butylphosphino)pentane ((DBPP)-B-t) resulted in isolation of the 16-atom-ring binuclear species [RuHCl(CO)((DBPP)-B-t)](2) (6). New products 3-5 were characterized by single-crystal X-ray analysis. In the computational study, we successfully modeled complexes 1-4 using the ONIOM methodology. It was established that the bulky PBu2t groups are responsible for the electronically unfavorable cis arrangement of the CO and Cl ligands in 3. B3PW91 calculations of the transition state structures for the intramolecular olefin insertion into the Ru-H bond in anti-1, trans, cis-2, and cis, trans-2 gave barrier heights of 28.3, 27.1, and 17.7 kcal/mol, respectively.