M.C. White/Q. Chen Chem 153 Hydrogenation -155 Week of october 15. 2002 Monohydride catalysts: RuClH(PPh3) 3 Vilkinson's original report In contrast to the rhodium system, ethanol plays an intimate part in the hydrogenation mechanism; in the absence of such a co-solvent, hydrogenation is exceedingly slow. Wilkinson Nature 1965(208)1203 RuCl2(PPh3)2 cat. H2(1 atm), benzene: ethanol, rt The active species was identified as the monohydnide, thought to form via heterolytic cleavage of H2, with ethanol acting as a base. The monohydride can also be prepared in 100% benzene if quivalent of NEt3 is added. One mole of H2 is absorbed with respect to Ru and amine hydrochloride is quantitatively formed. Wilkinson J. Chem. Soc.(A)19683143 RuCh(PPh3)3 H2(1 eq Phap---Ru(l +“ CI THNE NEt,(I eq), benzene PPh trigonal bipyramidal. Skapski Chem Effect of base RuCh(PPh3h cat H2(126 atm), base(I eq) fully satuturated benzene,40°C,6h EtNA aniline 952 Naco Tsuneda Bull Chem. Soc. pn. 1973 (46)279M.C. White/Q. Chen Chem 153 Hydrogenation -155- Week of October 15, 2002 Monohydride catalysts: RuClH(PPh3)3 O O cat. H2 (126 atm), base (1 eq) benzene, 40oC, 6h RuCl2(PPh3)2 O O Base % Conversion NEt3 Et2NH BuNH2 aniline Ca2CO3 Na2CO3 none 95.4 95.4 86.5 88.1 95.2 73.0 76.0 Effect of base on conversion fully satuturated products + Tsuneda Bull. Chem. Soc. Jpn. 1973 (46) 279. RuCl(H)(PPh3)3, highly distorted trigonal bipyramidal. Skapski Chem. Comm. 1968 1230. Wilkinson's original report: cat. H2 (1 atm), benzene:ethanol, rt quantitative The active species was identified as the monohydride, thought to form via heterolytic cleavage of H2, with ethanol acting as a base. The monohydride can also be prepared in 100% benzene if an equivalent of NEt3 is added. One mole of H2 is absorbed with respect to Ru and amine hydrochloride is quantitatively formed. Wilkinson J. Chem. Soc. (A) 1968 3143. Ph3P Ru(II) PPh3 PPh3 H Cl RuCl2(PPh3)2 "In contrast to the rhodium system, ethanol plays an intimate part in the hydrogenation mechanism; in the absence of such a co-solvent, hydrogenation is exceedingly slow." Wilkinson Nature 1965 (208) 1203. RuCl2(PPh3)3 H2 (1 eq) NEt3 (1 eq), benzene + -Cl +HNEt3