π Effects Involving Rh−PZ₃ Compounds. The Quantitative Analysis of Ligand Effects (QALE)

Through the quantitative analysis of ligand effects (QALE), we have probed π effects associated with Rh−P bond lengths, νCO, and −ΔHrx for Rh(CO)(Cl)(PX3)2 and νCO and −ΔHrx for Rh(acac)(CO)(PZ3). It was found that π effects are complex and depend strongly on the nature of ancillary or other participatory groups. The results of the QALE analysis of −ΔHrx point out the importance of synergistic interactions between PZ3 and other ancillary ligands in accord with theoretical computations. Literature data for Rh(CO)(Cl)(PZ3)2 have been supplemented with new values of ΔHrx for PMe3 (−75.6 ± 0.3 kcal/mol), P(i-Pr)3 (−68.7 ± 0.3 kcal/mol), and PCy3 (−66.4 ± 0.4 kcal/mol) as well as crystal structures for Rh(CO)(Cl)(P(i-Pr3))2 (Rh−P = 2.3488(3) Å) and Rh(CO)(Cl)(PCy3)2 (Rh−P = 2.3508(3)).