Diphosphine monoxides, formation

Phosphine-containing ally lie alcohols 301 undergo facile [2,3]-sigmatropic rearrangements with chlorophosphines, furnishing highly enantioenriched (dr 25 1) or enantiopure, crystalline diphosphine monoxides boranes 302, which were deprotected by treatment with DABCO with formation of 303. The configuration at the newly-formed stereocenter is opposite to that expected based on prior studies, and an ab initio computational evaluation of the possible transition states was performed to explain the stereochemical course of the reaction (Scheme 101) [199]. 

Carbon monoxide insertion in a palladium-carbon bond is a fairly common reaction [21]. Under polymerization conditions, CO insertion is thought to be rapid and reversible. Olefin insertion in a palladium-carbon bond is a less common reaction, but recent studies involving cationic palladium-diphosphine and -bipyridyl complexes have shown that olefin insertion also, particularly in palladium-acyl bonds, appears to be a facile reaction [22], Nevertheless, it is likely that olefin insertion is the slowest (rate-determining) and irreversible step vide infra) in polyketone formation. 

In the hydrogenolysis of (diphosphine)aryl methyl ethers catalysed by nickel, a Ni(0) complex featuring Ni-arene interactions adjacent to the aryl-O bond is formed, which on heating leads to a nickel aryl methoxide complex by aryl-O bond activation. Formal -elimination from this species produces a nickel aryl hydride which undergoes reductive elimination in the presence of formaldehyde to generate a carbon monoxide adduct of Ni(0). Hydrogen is necessary for the formation of the active catalyst but not for the actual catalytic fransformation (Scheme 38). ... 

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