RELATIVE FINDING ENERGIES OF TERTIARY PHOSPHINE-LIGANDS TO THE CP(ASTERISK)RUOCH(2)CF(3) (CP(ASTERISK)=ETA(5)-C(5)ME(5)) MOIETY

The enthalpies of reaction of (CpRuOR(f))(2) (1; Cp* = eta(5)-C(5)Me( 5), OR(f) = OCH2CF3) with PR(3) = PCy(3) (2) and (PPr3)-Pr-i (3) have been measured by solution calorimetry in THF at 30 degrees C. In order to test the internal consistency of the approach, a thermochemical cy cle was constructed involving reactions of CpRu(PR(3))OR(f) with tert iary phosphine and phosphite ligands (L) leading to the formation of C pRu(L)(2)OR(f) complexes. The range of these reaction enthalpies span s some 11 kcal/mol. Furthermore, complex 1 reacts directly with smalle r cone angle phosphine to quantitatively yield CpRu(L)(2)OR(f) comple xes. To allow for full comparison of the present thermochemical inform ation with that of the parent CpRu(L)(2)Cl (L = PR(3)) system, synthe tic efforts were directed toward the isolation of a CpRu(COD)OR(f) (C OD = cyclooctadiene) complex. Surprisingly, the straightforward reacti on of 1 with COD leads to the isolation of a tetramethylfulvene comple x, C(5)Me(4)CH(2)Ru(COD) (4), resulting from an alcohol elimination re action. A single-crystal X-ray diffraction study of 4 has been perform ed. Thermochemical comparisons with the CpRu(L)(2)Cl system are also presented.