HEATS OF PROTONATION OF TRANSITION-METAL COMPLEXES - THE EFFECT OF PHOSPHINE BASICITY ON METAL BASICITY IN CPIR(CO)(PR3) AND FE(CO)3(PR3)2

Titration calorimetry has been used to determine the effects of phosphine ligand basicity on the heats of protonation (DELTA-H(HM)) of the metal in the CpIr(CO)(PR3) and Fe(CO)3(PR3)2 complexes (PR3 = P(p-ClC6H4)3, PPh3, P(p-MeOC6H4)3, PMePh2, PMe2Ph, PMe3) With CF3SO3H at 25.0-degrees C in 1,2-dichloroethane solvent. The DELTA-H(HM) values of the CpIr(CO)(PR3) compounds range from -29.2 (PR3 = P(p-ClC6H4)3) to -33.2 kcal mol-1 (PR3 = PMe3), and those of the Fe(CO)3(PR3)2 compounds range from -14.1 (PR3 = PPh3) to -23.3 kcal mol-1 (PR3 = PMe3). Linear correlations of metal basicity (DELTA-H(HM)) with phosphine basicity (DELTA-H(HP) or pK(a)) show that increasing the phosphine basicity by 1.0 kcal mor, increases the CpIr(CO)(PR3) basicity by 0.298 kcal mol-1 and the Fe(CO)3(PR3)2 basicity by 0.458 kcal mol-1 per PR3 ligand. For both the Ir and Fe complexes, the DELTA-H(HM) values correlate linearly with the respective nu(CO) values. The effect of the indenyl, CS, and CO ligands on the basicities (AH(HM)) of (indenyl)Ir(CO)(PPh3), CpIr(CS)(PPh3), and Cp*Ir(CO)2 are also discussed.