Phosphorus bond, electronegativity

The number of terminal oxygen atoms, one, is exactly the same in all three acids, so that, according to (a), no great differences in acidity are expected. Since the electronegativities of P and H are almost the same, there is no tendency for the phosphorus-bonded H to ionize, nor to influence the ionization of the oxygen-bonded H s. 

Tertiary phosphines substituted at the -carbon by electronegative groups, e.g. (56), react with boron trihalides to give products derived from carbon-phosphorus bond cleavage. Phosphines containing only hydrocarbon groups do not react. 

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. 

Table 4. Properties and Electronegativity Differences of Phosphorus—Atom Bonds ...

Phosphorus and arsenic have nearly identical electronegativities, so in GaP Asi. , the dominant effect is the smaller atomic radius of P relative to As. Substituting P atoms for As atoms shrinks the dimensions of the semiconductor lattice. This leads to greater overlap of the valence orbitals, increased stability of the bonding orbitals (valence band), and an increased band gap. 

Cyclovoltammetric measurements were performed for the derivatives 15a and 15d. Interestingly, a reversible one-electron reduction was observed (—80°C, DME, Bu4NPF5) at E = - 1.81 (15a) and -1.74 V (15d).14 In contrast, the analogous arsasilenes (Si=As) undergo only irreversible reduction. Compounds 15a,d show a further one-electron reduction, which is irreversible. This remarkably different reduction behavior of Si=P and Si=As bonds is probably caused by the small, but significant difference in the electronegativities of phosphorus and arsenic. 

A variety of polar reagents add to P=C or P=N bond when more electronegative part is bonded to phosphorus. Addition of two water molecules on P=C bond in [l,4,2]diazaphospholo[4,5-a]pyridine (76) and P=N bond in [l,2,3]diazaphos-pholo[ 1,5-aIpyridinc (2) causes ring opening (Scheme 23) [16, 68], In the case of 76 (R=C02Et), further hydrolysis to pyridinium salt 78 was observed [73],... 

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