Four- and Five-co-ordinate Complexes

—Four- and Five-co-ordinate Complexes.— Epimerization and phosphine exchange in (Fe( -C sH 6)I(CO)(PPh2X)] (X=NRCHMePh, R=Me or Et) take place at the same rate and probably occur by phosphine dissociation and the formation of a three-co-ordinate intermediate as in analogous manganese complexes mentioned in Section 3.  

Intramolecular rearrangements of four-co-ordinate molecules of C2V symmetry can occur by Berry pseudorotation mode) as in SF4 or, in principle, by a non- 

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The topics of four- and five-co-ordinate complexes are conveniently linked by a study of the kinetics of ligand dissociation and intramolecular rearrangement for a series of cations [MLs]+(M = Co, Rh, or Ir ) and [HMLJ+(M = NF, Pd , or Pt ), where L = PEtg or a trialkyl phosphite. The relevance to four-co-ordinate complexes is of course that these five-co-ordinate species can be regarded as models for transition states for associative substitution at four-co-ordinate species. Several quadridentate arsenic ligands are effective in stabilizing five-co-ordinate... 

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