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, ν CO, and −Δ H rx for Rh(CO)(Cl)(PX 3 ) 2 and ν CO and −Δ H rx for Rh(acac)(CO)(PZ 3 ). 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 −Δ H rx point out the importance of synergistic interactions between PZ 3 and other ancillary ligands in accord with theoretical computations. Literature data for Rh(CO)(Cl)(PZ 3 ) 2 have been supplemented with new values of Δ H rx for PMe 3 (−75.6 ± 0.3 kcal/mol), P(i-Pr) 3 (−68.7 ± 0.3 kcal/mol), and PCy 3 (−66.4 ± 0.4 kcal/mol) as well as crystal structures for Rh(CO)(Cl)(P(i-Pr 3 )) 2 (Rh−P = 2.3488(3) Å) and Rh(CO)(Cl)(PCy 3 ) 2 (Rh−P = 2.3508(3)).