Enthalpies of Reaction of (.eta.5-C5H5)Ru(cyclooctadiene)Cl with Tertiary Phosphine Ligands: Ligand Substitution as a Gauge for Metal Basicity and A Linear Correlation of Bond Length and Bond Enthalpy

Abstract

The enthalpies of reaction of CpRu(COD)Cl (1) (Cp = eta(5)-C5H5; COD = cyclooctadiene) with a series of monodentate ligands, leading to the formation of CpRu(ER(3))(2)Cl (E = P, As), have been measured by anaerobic solution calorimetry in THF at 30.0 degrees C. These reactions are rapid and quantitatively lead to the formation of the corresponding CpRu(ER(3))(2)Cl complexes. The overall relative order of stability established for the preceding complexes is as follows: AsEt(3) < PPh(3) < PPh(2)Me < P(OPh)(3) < PEt(3) < P(n)Bu(3) < PPhMe(2) < PMe(3) < P(OMe)(3). Comparisons with other organometallic systems providing insights into factors influencing the Ru-L bond disruption enthalpies and metal basicity are discussed. Structural studies of two of these CpRu(ER(3))(2)Cl complexes (ER(3) = AsEt(3) (2) and PEt(3) (3)) have also been performed. Data for 2: monoclinic, C2/c; a = 30.549(5); b =. 10.523(2); c = 13.503(3) Angstrom; alpha gamma = 90 degrees; beta = 103.71(2)degrees; V = 4217.1 Angstrom(3); Z = 8; d(calcd) 2 = 1.656g cm(-1);n(obsd) 5328; R = 0.032. Data for 3: monoclinic, P2(1)/c; a 13.553(1); b = 8.283(2); c = 19.359(3) Angstrom; beta = 109.74(1)degrees; V = 2045.5 Angstrom 3; Z = 4; dcalcd = 1.422 g cm(-1); n(obsd) = 5152; R = 0.030. A relationship between bond distances and relative bond energies is made possible by the present data. This correlation is good and represents a rare example of such a relationship.