Insertion into phosphorus-oxygen bonds

Phosphorus(V) oxide, P4 Oio, contains the same triangular arrangement of phosphorus atoms as in P4, but an oxygen atom is inserted into each P—P bond. An additional terminal O atom is double-bonded to each P atom. 

A few final comments should be made on the insertions of substrates containing C-C multiple bonds into the bonds between a transition metal and an electronegative heteroatom. First, insertions of olefins into related thiolate and phosphide complexes are as rare as insertions into alkoxo and amido complexes. Reactions of acrylonitrile into the metal-phosphorus bonds of palladium- and platinum-phosphido complexes to give products from formal insertions have been observed, and one example is showm in Equation 9.90. However, these reactions are more likely to occur by direct attack of the phosphorus on the electrophilic carbon of acrylonitrile than by migratory insertion. Second, the insertions of alkynes into metal-oxygen or metal-nitrogen covalent bonds are rare, even though the C-C ir-bond in an alkyne is weaker than the ir-bond in an alkene. 

Analysis of both pathways A A-TS A-product and B B-TS B-product again suggested that the latter is clearly favorable from thermod3mamic reasons for acetylene insertion into the Pd-P(0)Me2 bond and it is also slightly favorable from kinetic reasons (Fig. 3). The relative stability of the products greatly depended on the orientation of the phosphorus group. Coordination of the oxygen atom to the metal center led to complex B-product, which was calculated to be more stable by 21.9 kcal/mol compared to the complex A-product. 

Theoretical calculations have been also carried out to study acetylene insertion into the Pd-P(0)(0Me)2 bond related to hydrophosphorylation process [39]. The activation barriers for alkyne insertion were calculated to be AG = 21.4 and 23.7 kcal/mol depending on the orientation of the phosphorus group. However, much smaller difference in the relative stability of the products was found. The presence of three oxygen atoms attached to the phosphorus center facilitated chelate coordination to the metal in any orientation of the phosphorus group. Thus, the influence of orientation of heteroatom group significantly depends on the number of bonded oxygen atoms (see also Scheme 8). 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

The oxazoliumcarboxylic acid (147) is easily decarboxylated via the ylide (148) the neutral compound (149) is much more stable due to the low equilibrium concentration of the zwitterionic tautomer (150 Scheme 7). Oxazolium salts lacking substituents at the 2-position react with dialkyl acylphosphonates in the presence of triethylamine to give mixtures of l,4-oxazin-3-ones and 2-azetidinones the reaction (see Scheme 8) proceeds by electrophilic attack of the phosphonate on an oxazolium ylide, e.g. (151), followed by insertion of oxygen into the carbon-phosphorus bond, ring-opening, and formation of the enolate anion (152) which can cyclize in two alternative ways with expulsion of the phosphonate group. 

Apart from studies of their properties as ligands in metal-catalysed processes in homogeneous solution, there have been other studies of the reactivity of aminophosphines in the past year. The first example of the insertion of a methylene group into a phosphorus(III)-nitrogen bond has been recorded. Treatment of the aminophosphine (112) with paraformaldehyde leads to the insertion of a methylene group into the P-N bond with subsequent oxygenation... 

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