ENTHALPIES OF REACTION OF CPRU(COD)CL (CP=ETA(5)-C5H5 COD=CYCLOOCTADIENE) WITH CHELATING TERTIARY PHOSPHINE-LIGANDS - SOLUTION THERMOCHEMICAL INVESTIGATION OF LIGAND SUBSTITUTION AND RING STRAIN ENERGIES IN CPRU(R(2)P(CH2)(N)PR(2))CL COMPLEXES

The enthalpies of reaction of CpRu(COD)Cl (Cp = eta(5)-C5H5; COD = eta (4)-cyclooctadiene) with a series of bidentate ligands, leading to the formation of CpRu(PP)Cl complexes, have been measured by anaerobic so lution calorimetry in THF at 30.0 degrees C. The overall relative orde r of stability established for these complexes is as follows: dppm < d mpm < dppb < dppe < dppp < dppv < depe < dmpe. Comparison between enth alpies of these reactions and those of monodentate phosphine ligands a ffords a quantitative treatment of ring strain enthalpies in these org anoruthenium metallacyclic compounds. Significant ring strain energy i s displayed in the four-membered metallacycle and is on the order of 1 3 kcal/mol. A single crystal X-ray diffraction study has been performe d on one of the new complexes, CpRu(dppv)Cl [dppv = bis(diphenylphosph ino)ethylene] (C31H27ClP2Ru.CH2Cl2, P1, a 10.344(2) Angstrom, b = 11.9 07(2) Angstrom, c 13.183(1) Angstrom, alpha 67.89(1)degrees, beta 76.5 2(1)degrees, gamma = 85.96(2)degrees, V = 1462.5(5) Angstrom(3), and Z = 2). Comparisons of the thermochemical data with the C(5)Me(5)-based system and related metallacyclic complexes are also presented.