An Alternate Route to the Active Chiral Hydrogenation Catalysts [Ru(bisphosphine)(H)(solvent)3]+: Synthesis, Characterization, and Catalytic Evaluation

Synthesis and Reactivity of Ruthenium(BINAP)(PPh3)

Ru(BINAP)(PPh3)HCl cleanly reacts with LiCH2TMS to give Ru(BINAP)(PPh3) (1) that has been fully characterized, including by X-ray diffraction (BINAP and TMS stand for (2,2'-bis(diphenylphosphino)-1,1'-binaphthyl and trimethylsilyl respectively). In sharp contrast with other carbonyl-free phosphine complexes of Ru(0), 1 demonstrates a strikingly high thermal stability and no propensity for intramolecular C-H activation (cyclometalation). Yet 1 coordinates acetonitrile and readily exchanges its PPh3 ligand with alkenes and dienes, thus behaving like a "masked" 16-e Ru(0) species. Electron-poor alkenes coordinate more readily than electron-rich ones, which testifies for the nucleophilic character of the Ru(0)-BINAP fragment. While being thermally stable, 1 is highly reactive and is capable of activating C-H and N-H bonds, and even of cleaving an inert N-Et bond. The combination of high reactivity and stability originates from the P,arene-chelation by the BINAP ligand, i.e., the coordinated π-arene stabilizes Ru(0) to prevent cyclometalation, yet it can slide upon substrate coordination, thereby enabling a variety of inert bond activation reactions to occur under mild conditions.

A Fortuitous, Mild Catalytic Carbon–Carbon Bond Hydrogenolysis by a Phosphine-Free Catalyst

The putative catalyst trans-[Ru((S,S)-skewphos)(H)2((R,R)-dpen)] (skewphos = 2,4-bis(diphenylphosphino)pentane; dpen = 1,2-diphenylethylenediamine) transforms the trifluoroacetyl amide 2,2,2-trifluoro-1-(piperidin-1-yl)ethanone under mild conditions (4 atm H2, room temperature, 4–24 h, 1 mol-% Ru, 15 mol-% KOtBu in tetrahydrofuran) to generate the formylated amine 1-formylpiperidine and fluoroform via C–C bond hydrogenolysis. Catalysts are also prepared by reacting cis-[Ru(η3-C3H5)(MeCN)2(COD)]BF4 (COD = 1,5-cyclooctadiene) with diamine ligands in situ. Low-temperature NMR studies provided insight into this reaction.

Bis(2-diphenylphosphinoxynaphthalen-1-yl)methane: transition metal chemistry, Suzuki cross-coupling reactions and homogeneous hydrogenation of olefins

Transition metal complexes of bis(2-diphenylphosphinoxynaphthalen-1-yl)methane (1) are described. Bis(phosphinite) 1 reacts with Group 6 metal carbonyls, [Rh(CO)2Cl]2, anhydrous NiCl2, [Pd(C3H5)Cl]2/AgBF4 and Pt(COD)I2 to give the corresponding 10-membered chelate complexes 2, 3 and 5-8. Reaction of 1 with [Rh(COD)Cl]2 in the presence of AgBF4 affords a cationic complex, [Rh(COD){Ph2P(-OC10H6)(mu-CH2)(C10H6O-)PPh2-kappaP,kappaP}]BF4 (4). Treatment of 1 with AuCl(SMe2) gives mononuclear chelate complex, [(AuCl){Ph2P(-OC10H6)(mu-CH2)(C10H6O-)PPh2-kappaP,kappaP}] (9) as well as a binuclear complex, [Au(Cl){mu-Ph2P(-OC10H6)(mu-CH2)(C10H6O-)PPh2-kappaP,kappaP}AuCl] (10) with ligand 1 exhibiting both chelating and bridged bidentate modes of coordination respectively. The molecular structures of 2, 6, 7, 9 and 10 are determined by X-ray studies. The mixture of Pd(OAc)2 and effectively catalyzes Suzuki cross-coupling reactions of a range of aryl halides with aryl boronic acid in MeOH at room temperature or at 60 degrees C, giving generally high yields even under low catalytic loads. The cationic rhodium(I) complex, [Rh(COD){Ph2P(-OC10H6)(mu-CH2)(C10H6O-)PPh2-kappaP,kappaP}]BF4 (4) catalyzes the hydrogenation of styrenes to afford the corresponding alkyl benzenes in THF at room temperature or at 70 degrees C with excellent turnover frequencies.

A Ruthenium−Dihydrogen Putative Intermediate in Ketone Hydrogenation

The compound fac-[Ru((R)-BINAP)(H)(2-PrOH)3]+ (6) (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) reacts with (R,R)-dpen (dpen = 1,2-diphenylethylenediamine) under H2 at -60 degrees C in 2-PrOH-d8/CD2Cl2 to generate the cationic dihydrogen putative intermediate trans-[Ru((R)-BINAP)(H)(eta2-H2)((R,R)-dpen)]+ (2') without H-D exchange between the hydrogen ligands and the solvent. A 1H NMR study concludes that the dihydrogen ligand in 2' does not protonate 2-PrOH to a catalytically significant extent, and that 2' requires an added base or hydride source to be an active catalyst.