16-Electron (Arene)ruthenium Complexes with Superbasic Bis(imidazolin-2-imine) Ligands and Their Use in Catalytic Transfer Hydrogenation

The ligands N.N'-bis(1,3,4,5-tetramethyhmidazolin-2-ylidene)-1,2-ethanediamine (BLMo) and N,N'-bis(1,3-dusopropyl-4,5-dimethylmidazolin-2-ylidene)-1,2-ethanediamine (BLpr) react with [(eta(5)-C5Meo)RuCl](4) to afford cationic 16-electron half-sandwich complexes [eta(5)-C5Meo)Ru(BLR)](+) (R = Me, 3: R = iPr, 4), which resist coordination of the chloride counterion because of the strong electron-donating ability of the dumine ligands. Upon reaction with [(eta(6)-C6H6)RuCl2](2) or [(eta(6)-C10II14)RuCl2](2,) these ligands stabilize dicationic 16-electron benzene and cymene complexes of the type [(eta(6)-C6H6)Ru(BLR)](2+) (R = Me, 5, R = rPr, 6) and [(eta(6)-C10H14)Ru(BLR)](2+) (R = Me, 7; R = iPr, 8) The x-ray crystal structure of [5]Cl-2 reveals the absence of any direct Ru-Cl interaction, whereas a long Ru-Cl bond, supported by two CH center dot center dot center dot Cl hydrogen bonds, is observed for [(6)Cl]Cl in the solid state. Treatment of the dichlorids of 6 and 8 with NaBF4 affords [6](BF4)(2) and [8](BF4)(2,) which are composed of individual dications and tetrafluoroborate ions with no direct Ru-F interaction. All complexes catalyze the transfer hydrogenation of acetophenone in boiling 2-propanol ((C) Wiley-VCH Verlag GmbH & Co, KGaA, 69451 weinheim, Germany, 2009)