Application of tethered ruthenium catalysts to asymmetric hydrogenation of ketones, and the selective Hydrogenation of aldehydes

An improved method for the synthesis of tethered ruthenium(II) complexes of monosulfonylated diamines is described, together with their application to the hydrogenation of ketones and aldehydes. The complexes were applied directly, in their chloride form, to asymmetric ketone hydrogenation, to give products in excess of 99% ee in the best cases, using 30 bar of hydrogen at 60 °C, and to the selective reduction of aldehydes over other functional groups

Synthesis and Characterization of New Dicationic Dihydrogen Complexes of Ruthenium

A series of new dicationic dihydrogen complexes of the type trans-$[Ru(\eta^2-H_2)(L)(dppm)_2][X]_2 (L=CH_3CN, CH_2=CHCN, C_6H_5CN, C_6H-5NC, CO; X 5 BF_4, OTf; dppm = Ph_2PCH_2PPh_2)$ have been prepared by protonating the precursor hydrides using either $HBF_4 . Et_2O or HOTf$. The variable temperature spinlattice relaxation times $(T_1, ms)$ and the H, D coupling constants of the $\eta^2-HD$ isotopomers indicate the intact nature of the H-H bond in these derivatives. The H-H distances of the dihydrogen complexes bearing trans-nitrile ligands are not significantly affected by the sterics and the electronics of the nitrile. On the other hand, the H-H distances of the dihydrogen complexes bearing either isonitrile or CO ligand are comparable to those possessing chelating diphosphine ligands of greater bite angle. Also, the thermal stabilities of these complexes are significantly less than those bearing diphosphines of greater bite angle. The trans- $[Ru(H)(CH_3CN)(dppm)_2][BF_4]$ complex has been characterized by X-ray crystallography

Iridium-Catalyzed C–H Borylation of Heterocycles Using an Overlooked 1,10-Phenanthroline Ligand: Reinventing the Catalytic Activity by Understanding the Solvent-Assisted Neutral to Cationic Switch

The preformed catalyst [Ir­(Cl)­(COD)­(1,10-phenanthroline)] (<b>2</b>; COD = cyclooctadiene) was found to be highly effective in a model reaction for the borylation of N-Boc-indole at the 3-position with B₂pin₂ (pin = pinacolato) as the borylating agent to give consistently 99% yield with 0.5 mol % catalyst loading. The corresponding in situ formed catalyst from [Ir­(Cl)­(COD)]₂ and 1,10-phenanthroline provided very inconsistent results for the same reaction (0–94% conversion). We propose this to be due to the competing formation of a catalytically inactive cationic complex, [Ir­(COD)­(1,10-phenanthroline)]⁺Cl^– (<b>1</b>), in a noncoordinating solvent such as octane. Complexes <b>1</b> and <b>2</b> were characterized using solid-state NMR (¹³C and ³⁵Cl) in conjunction with XPS to be cationic and neutral, respectively. The X-ray crystal structure of a pentavalent neutral Ir complex, [Ir­(Cl)­(COD)­(2,2′-bipyridine)] (<b>3</b>), was also obtained for comparison purposes. Using catalyst <b>2</b>, the total synthesis of <i>Meridianin G</i> was accomplished in 87% overall isolated yield in a one-pot, three-step process