Phosphorus iodide carbonyl compounds

The addition of Grignard reagents to a-(diphenylphosphino)carbonyl compounds leads to alcoholates, which react with methyl iodide exclusively at phosphorus to yield betaines. Diphenylmethylphosphine is eliminated upon addition of strong base to yield isomerically pure alkenes (Scheme 8). ... 

The Wittig reagent is made by alkylation of the simplest ylid with the same silicon reagent. Notice that the leaving group (iodide) is on the carbon next to silicon, not on the silicon itself. Anion formation occurs next to phosphorus because PhsF is much more anion-stabilizing than MesSi. The ylid reacts with carbonyl compounds such as cyclohexanone in the usual way to produce the allyl silane with no ambiguity over which end of the allyl system is silylated. 

The reaction of phosphorus ylides with carbonyl compounds as a route to fluoro-olefins is prone to complications (see Vol. 2, p. 46), but excellent yields of olefins are obtained upon dehalogenation of fluoroiodomethyltriphenylphos-phonium iodide with zinc-copper couple, e.g, ... 

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