Phosphorus/metal interconversion complex

As described in Chapter 2, phosphines have sufficiently large barriers to inversion that phosphines with three different substituents can be resolved. In contrast, the inversion of configuration at phosphorus in metal-phosphido complexes tends to occur near room temperature. In imsaturated transition metal complexes, a vacant acceptor orbital stabilizes the planar transition state. This effect is shown by the interconversion between pyramidal structures through a planar transition state, like the one shown in Equation 4.101 and formed during inversion of related compounds. - In saturated middle and late transition metal complexes, inductive effects explained below destabilize the groimd state and lead to lower barriers to inversion. The presence of an ancillary planar phosphide or amide ligand can contribute to a low barrier by accepting the lone pair from a p)Tamidal phosphide, as in Equation 4.101. 

Phosphorus-31 2D-EXSY NMR spectra have afforded evidence of sym-cis/sym-trans interconversions in a series of cyclopalladated tertiary phosphite complexes of type [Pd(/i-Cl)(P(OR )2(OC6H3R ))]2. The platinum analog behaved in a similar manner/ P NMR 2D-EXSY spectroscopy was also employed to probe the dynamics of interconversion between covalent and dative metal-bonded isomers of the mixed metal dinuclear complex [NiPd(CNMe)3(dppm)2](PF6)2. Isomer populations were strongly solvent-dependent with free energies of activation for interconversion of ca 67 kJ mol at 298 Dinuclear complexes of trimethylplatinum(IV) halides have been synthesized (26). The dominant solution structures were... 

The trimetallic complex [Fe3(CO)8(p-PPh)2(PF3)] has been obtained from the corresponding [Fe3(CO)8(p-PPh)2(MeCN)J compound by displacement of MeCN (method G). The structure, which is based on a square-pyramidal array of three iron and two phosphorus atoms, consists of isomers whose interconversion has been studied by variable-temperature 19F and 31P NMR spectroscopy. A trimetallic PF3 complex containing mercury bonded to two metals results from the reactions... 

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