One-Bond Metal-Phosphorus Coupling Constants

The spin-spin scalar coupling between two nuclei has long since become a routine tool in the armament of chemists. This stems partially from the enormous number of empirical relations routinely in use as structure and hybridization probes and partially from the theoretically more tractable relationships which are thought to correctly describe this spin-spin interaction. There are several levels of sophistication commonly in use when discussing the theory of the one-bond metal-phosphorus coupling constant, J(M,P), and this topic, in combination with the question of metal-phosphorus bonding, will be considered first in 

The interactions which lead to a nuclear spin-spin coupling in fluids were first formulated by Ramsey [16] in terms of a contact (Fermi) mechanism, a spin-orbital- and a spin-polarization mechanism. Both McConnell [17] and Pople and Santry [18 19] have described modifications of Ramsey s equations which are suitable for use with molecular orbitals derived from LCAO methods. The Pople and Santry treatment has an advantage in that it is capable of producing both negative and positive coupling constants. The McConnell use of the mean excitation energy approximation, which we shall mention later, neces- 

If only one-center integrals involving valence s orbitals on A and B are retained then 

In the extended Hiickel (E.H.) method used by Pople and Santry this integral is omitted because of the neglect of the interelectronic repulsion. 

Finally, if the mean triplet excitation energy approximation is made, Eq.(2.3) can be further simplified and becomes Eq.(2.4) 

---

The magnitudes of the one-bond metal-phosphorus coupling constants represent a rich source of structural information. The anisotropy of the indirect spin-spin... 

Ill One-Bond Metal-Phosphorus Coupling Constants -A Survey... 

O.OOSA) is indeed very similar to the free ligand value. On the other hand, the nickel-phosphorus distance (2.099 O.OOSA) is very much shorter than the values reported in other phosphine-nickel complexes, which suggests that the metal-phosphorus bond in Ni(PF3)4 may indeed have significant -character. A u-bond order of one has been estimated from the magnitude of the Co- P coupling constant in the [Co(PF3)4] ion (191). ... 

---