No abstract

On exposure to NaOMe (≥3 equiv) in CH2Cl2–MeOH at 23 °C, the first-generation Grubbs catalyst RuCl2(PCy3)2(CHPh) (1a) is immediately transformed into the six-coordinate methoxyhydride complexes RuH(OMe)(CO)2(PCy3)2 (4a) and RuH(OMe)(CO)(H2)(PCy3)2 (5a). Complex 5a can be recycled into 4a under conditions conducive to removal of H2. The second-generation catalyst RuCl2(IMes)(PCy3)(CHPh) (1b; IMes = N,N′-bis(mesityl)imidazol-2-ylidene) reacts more slowly, requiring several hours even at 20 equiv of NaOMe, and terminates at five-coordinate RuH(OMe)(CO)(IMes)(PCy3) (3b). Experiments in the presence of added PCy3 reveal that consumption of 1a, but not 1b, proceeds via the four-coordinate intermediate formed by equilibrium loss of phosphine, a function of the lability of the PCy3 ligand at ambient temperatures. The poor accessibility of such an intermediate for 1b at 23 °C retards salt metathesis and inhibits further reaction of 3b. For the bis(PCy3) analogue 3a, fast transformation into 4a is proposed to involve reversible loss of PCy3, coordination of methanol, σ-metathesis of methanol at the hydride site to liberate H2, and β-elimination/decarbonylation of bound methoxide. Competitive uptake of H2 by 3a yields six-coordinate 5a (the dihydrogen adduct of 3a). Independent routes to RuH(OMe)(CO)2(L)(PCy3) (4a/b; a, L = PCy3; b, L = IMes) were developed: these involved sequential transformation of RuHCl(CO)(L)(PCy3) (2a/b) into the bis-carbonyl adducts RuHCl(CO)2(L)(PCy3) (7a/b) under CO, conversion of 7a/b into the more reactive triflates RuH(OTf)(CO)2(L)(PCy3) (8a/b), and reaction of 8a/b with equimolar NaOMe. Dihydride 6b was also prepared, by reaction of 8b with NaH.

The design of a reactor for operando nuclear magnetic resonance (NMR) monitoring of high-pressure gas-liquid reactions is described. The Wisconsin High Pressure NMR Reactor (WiHP-NMRR) design comprises four modules: a sapphire NMR tube with titanium tube holder rated for pressures as high as 1000 psig (68 atm) and temperatures ranging from -90 to 90 °C, a gas circulation system that maintains equilibrium concentrations of dissolved gases during gas-consuming or gas-releasing reactions, a liquid injection apparatus that is capable of adding measured amounts of solutions to the reactor under high pressure conditions, and a rapid wash system that enables the reactor to be cleaned without removal from the NMR instrument. The WiHP-NMRR is compatible with commercial 10 mm NMR probes. Reactions performed in the WiHP-NMRR yield high quality, information-rich, and multinuclear NMR data over the entire reaction time course with rapid experimental turnaround.

An unexpected "generation gap" is uncovered between the Grubbs catalysts RuCl 2 (L)(PCy 3 )-(dCHPh) (1a, L = PCy 3 ; 1b, L = IMes, N,N 0 -bis(mesityl)imidazol-2-ylidene) in their reactions with hydrogen versus methanol, in the presence of base. Treatment of the first-generation catalyst 1a with H 2 and NEt 3 (CH 2 Cl 2 , 60 °C, 1000 psi H 2 ) affords RuHCl(H 2 )(PCy 3 ) 2 (2a) in 75% yield within 30 min, as determined by in situ NMR analysis. Complex 2a is in turn efficiently converted (96%; 2 h) into the important hydrogenation catalyst RuHCl(CO)(PCy 3 ) 2 (3a) by mild thermolysis with methanol and NEt 3 (4:1 CH 2 Cl 2 -MeOH, 60 °C), 72% net yield for the 1a-3a transformation. In comparison, subjecting the second-generation catalyst 1b to this two-step process effects <40% net conversion to RuHCl(CO)(IMes)(PCy 3 ) (3b) (hydrogenolysis of 1b: ca. 60% RuHCl(H 2 )(IMes)-(PCy 3 ) (2b) (1 h); carbonylation of isolated 2b: 65% 3b (2.5 h)), owing to the susceptibility of the dihydrogen derivative 2b to disproportionation and decomposition. The opposite trend in efficiency for 1a versus 1b is found for methanolysis under argon in the presence of base: 1b undergoes 83% conversion to 3b, versus <60% for the 1a-3a transformation (4:1 CH 2 Cl 2 -MeOH, 60 °C). This difference reflects the longer duration of the methanolysis reaction (8 h for 1a vs 4 h for 1b; cf. 30 min and 1 h, respectively, for hydrogenolysis) and the lower thermal robustness of 1a. These findings highlight the importance of tailored, catalyst-specific approaches in devising efficient tandem catalysis methodologies based on the first-and second-generation Grubbs complexes. They are directly relevant to the improved synthesis of advanced polymer materials via tandem ROMPhydrogenation and potentially relevant to RCM-and CM-functionalization processes. † Part of the Dietmar Seyferth Festschrift. Dedicated to Prof. Dietmar Seyferth, in honor of his many years of leadership and commitment to the highest standards of excellence in organometallic chemistry.

Clean, high-yield routes are established to the important catalyst chlorobis(tricyclohexyl- , or with the appropriate NHC ligand, then PCy 3 . Advantages over prior routes to these complexes lie in the high yields from a conveniently accessible precursor, the absence of by-products that otherwise prove difficult to remove, and the short reaction times under experimentally convenient conditions.