The metal-perfluorocarbon bond

Periluorocarbon-a-transition metal complexes are likely to be thermodynamically unstable on account of the high lattice energies of metal fluorides. It seems reasonable that the relatively high thermal stability of M—Rf complexes, compared to that of M—Rj, complexes, arises from an increased stability to dissociation of the M—Rf bond. A relative increase in the M—Rf bond strength could be due both to an increase in the or-bonding and, possibly, there could be si-bonding in the M—Rf bond [246, 247, 248]. 

The Mo-C.fC2 angle in jr-C5HsMo(CO)3CH2CH3 is also large (120°) [56] (see 7.15). These increases above the tetrahedral angle may be due to steric repulsion of the Ci-substituents by the metal orbitals (a )S-efFect). It has been suggested also that in the above M—Rf complexes the increased 

All these arguments for the stability of the M—Rf complexes are speculative and they neglect considerations which may be significant, such as the relative free energies of the fluorocarbon and hydrocarbon radicals. It should be noted that generally very little is known about the importance of factors which affect the stability of transition metal complexes and that a very small change in bond energy may have a marked effect on thermal stability. 

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