| Abstrakt: |
Mixed-ligand complexes, trans-Fe(CO)3LL (L = PPh3, L = PPh2Me, PPhMe2, PMe3, PPh2Et, PEt3, PPh2CH&dbd;CH2, PPh2H, AsPh3, P(OPh)3; L = PMe3, L = PEt3, PPh2Et, PCy3, PPh2Me, PPhMe; L = PEt3, L = PPh2Me; L = PPh2H, L = PPh2CH&dbd;CH2, PPh2Et; L = AsPh3, L = PPhMe2, P(OPh)3, P(OMe)3, P(OEt)3), have been obtained from the stepwise reaction of phosphines with Fe(CO)3(BDA) (BDA = benzylideneacetone) or Fe(CO)3(AsPh3)2 and from the reaction of phosphine with Fe(CO)4PPh3 in the presence of base. A strong negative correlation exists between 2JPP coupling constant values and the sum of the phosphine pKa values. By application of quantitative analysis of ligand effects, it has been shown that 2JPP for the mixed-ligand complexes correlates strongly with both χ and Ear, but not with θ. Although a near perfect fit is obtained from the three-parameter equation, a statistical analysis suggests that for this small data set there are no predictive advantages over the one-parameter pKa model. It is possible to calculate reliable 2JPP values for trans-Fe(CO)3L2 complexes with either model. An X-ray structure of solid-state trans-Fe(CO)3(PEt3)(PPh3) shows equal Fe−PEt3 and Fe−PPh3 bond distances, implying that bond strength equalization may occur when two rather different phosphines occupy trans coordination sites. |
