| Title
| - Probing the Effect of the Ligand X on the Properties and CatalyticActivity of the Complexes RuHX(diamine)(PPh3)2 (X = OPh,4-SC6H4OCH3, OPPh2, OP(OEt)2, CCPh, NCCHCN, CH(COOMe)2;diamine = 2,3-Diamino-2,3-dimethylbutane,(R,R)-1,2-Diaminocyclohexane)
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| Abstract
| - The title complexes with a range of X ligands have been prepared and structurally characterized and tested as precatalysts for the addition of dimethyl malonate to 2-cyclohexen-1-one and for the hydrogenation of acetophenone. The active catalyst for the first reaction is proposed to be the amido complex RuH(NHCR1R2CR1R2NH2)(PPh3)2, while that of the second is the trans-dihydride RuH2(NH2CR1R2CR1R2NH2)(PPh3)2 along with the amido complex.
- The reactivity of the ruthenium−amido bond in RuH(NH2CMe2CMe2NH)(PPh3)2 (1) toward weakacids HX and the influence of the X group on the catalytic activity of the resulting complex are exploredhere. Complex 1 reacts with the weak acids HX (X = OPh, 4-SC6H4OMe, OPPh2, OP(OEt)2, CCPh,NCCHCN, CH(COOMe)2) to form complexes of the type RuHX(tmen)(PPh3)2 (tmen = 2,3-diamino-2,3-dimethylbutane). The complexes with X = PhOH···OPh, 4-SC6H4OMe, OP(OEt)2, CCPh, CH(COOMe)2 have been characterized by X-ray crystallography. The X group is situated trans to the hydridein all cases and is bonded to ruthenium via the donor atoms O, S, P, C, and O, respectively. The phenolin the phenoxide adduct RuH(PhOH···OPh)(tmen)(PPh3)2 bridges via hydrogen bonds between the alkoxideoxygen and an amino hydrogen to form a six-membered RuO···HO···HN ring. One carbonyl oxygen ofthe malonate bonds to the Ru, while the other accepts a hydrogen bond from an amino hydrogen. Theanalogous complexes RuHX(dach)(PPh3)2 (dach = (R,R)-1,2-diaminocyclohexane) were synthesized bythe reaction of RuHCl(dach)(PPh3)2 (2) with an equimolar amount of potassium tert-butoxide and HX.For all of the complexes the Ru−H vibrational frequency and the 1H NMR chemical shift of Ru−Hcorrelate with the electronegativity of the trans atom X. The amido complex 1 and the complexes withX = CH(COOMe)2 and OPh are active catalysts for the Michael addition of dimethyl malonate to2-cyclohexen-1-one. RuH(NCCHCN)(tmen)(PPh3)2 reacts with the Michael acceptor 2-cyclohexen-1-one to give RuH(NCC(C6H9O)CN)(tmen)(PPh3)2, a trapped Michael adduct that has been characterizedby X-ray crystallography. On the basis of these observations a catalytic cycle for the Michael additionreactions is proposed that involves the addition of the C−H bond of the Michael donor to the Ru−Nbond followed by attack on the Michael acceptor and elimination of the Michael adduct, possibly by a1,3-proton migration as observed for the malononitrile adduct. Only the complexes with X = H, CCPhare catalysts or precatalysts for the hydrogenation of neat acetophenone to 1-phenylethanol in the absenceof added base under 10 atm of H2 at 20 °C. Evidence is provided that the phenylacetylide complexes areprecatalysts that are converted to the active trans-dihydride catalysts (X = H).
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