Aryloxide complexes of early and late transition metals: Applications in olefin metathesis

Abstract

Treatment of ruthenium chloride complexes RuCl2(PPh 3)3 1a or RuHCl(PPh3)3 1b with monodentate aryloxides in non-alcohol solvents affords pi-bound aryloxide derivatives with the general formula Ru(eta5-ArO)( o-C6H4PPh2)(PPh3) 2 9 or RuX(eta5-ArO)(PPh3) 2 (X = H (3a) or Cl (11b)). In the presence of alcohols, hydridocarbonyl complexes with the general formula RuXY(CO)(PPh 3)3 (X = H, Y = H 2a; X = H, Y = Cl 2b ) are generated by hydride abstraction and decarbonylation of formaldehyde. Treatment of 1a with one equivalent of aryloxide in the presence of isopropanol liberates the phenol and acetone, affording clean 1b in quantitative yields. Treatment of 3a with ethereal HCl gives [RuH(eta 6-ArOH)(PPh3)2]Cl 12a. Arresting sigma → pi isomerization was attempted using a P,O-chelate ligand ((+/-)-2-(diphenylphosphino)-2'-hydroxy-1,1 '-binaphthyl (binop; 29). The entropy gain was not favourable enough to prevent isomerization. The binop ligand in the product, RuCl2(binop)(PPh3) 31, is sigma-bound via the phosphorus donor, and n-bound via the 'phenoxide' ring, as indicated by detailed spectroscopic and MALDI-mass spectrometric analysis. Reaction of RuHCl(PPh3)3 1b with 3-chloro-3-methyl-1-butyne effects transformation into the alkylidene complex RuCl2(=CHCH=CMe 2)(PPh3)2 34. RuHCl(PPh3) 3 1b is commercially available or obtained via quantitative reaction of RuCl2(PPh3)3 1a with alkali aryloxides, as described above. Phosphine exchange between 34 and PCy3 is rapid at room temperature, affording RuCl 2(=CHCH=CMe2)(PCy3)2 37. Complex 34 is stable indefinitely in the solid state at room temperature under N2, but dimerizes slowly in solution to give RuCl(PPh3)2(mu-Cl)3Ru(=CHCH=CMe2)(PPh 3)2 36. A side-product arising from use of excess 3chloro-3-methyl-1-butyne in the synthesis of 34 was identified as a Ru(IV) carbyne complex RuCl3(≡CCH=CMe2)(PPh 3)2 35. t,t-Benzaldehyde azine 40 is formed as a byproduct in the synthesis of phenyldiazomethane 39. Azine 40 coordinates to ruthenium at room temperature, generating Ru 2Cl4(dppb)2(t,t-benzaldehyde azine) 52. At 50°C, a novel N-N activation reaction yields Ru2Cl4(dppb)2(NCPh) 43 and Ru 2Cl4(dppb)2(HN = CHPh) 44 in a 1:1 ratio. The structure of 43 was confirmed by X-ray analysis. A systematic investigation into ROMP of 2,3-dicarboalkoxynorbornadienes 53--55 and 2,3-diphenylamidonorbornadiene 56 via molybdenum biphenolate catalysts 49 showed that polymer tacticity was dependent on biphenolate and monomer substituents. Thermal analysis of the polymers by DSC, TGA and IR experiments showed that polymers prepared from 2,3-dicarboalkoxynorbornadiene monomers underwent C = C degradation even at 80°C. In contrast, the bulky amide polymer was stable up to 275°C. All of the polymers decompose above 300°C. Investigations of the tertiary structure of the polymers indicated no helicity in solution: though high crystallinity in the solid state could result from helicity, the extreme mechanical sensitivity of the samples precluded confirmation by wide-angle X-ray diffraction.