An Assessment of the Parameters Relevant to the Subdivision of σ and Ω Electronic Effects in M-P Bonds

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Abstract
The origin of the σ and Ω controversy in inorganic and organometallic chemistry, particularly with respect to M-P bonds, is comprehensively analyzed. It is concluded that traditionally used physical parameters such as vco, δ(13CO), 1J(M-P), E° and r(M-P) of metal carbonyl complexes can not be used to resolve the σ and Ω controversy due to the parallel influence of weak σ and strong Ω bonding. In contrast, the parameters ΔE, bond strength and metal NMR isotropic chemical shift should be useful to distinguish σ and Ω effects because they respond to the weak σ and strong Ω effects in opposite directions. The metal NMR isotropic chemical shift is undoubtedly the best probe due to the high accuracy of experimental measurement. Its application in the separation of σ, Ω and steric effects in M-P bonding should be possible.