Phosphorus and Arsenic Derivatives

MeaSiPPha forms 1 1 adducts with CSa, RNCS, and RNCO, with silyl migration to S or N. With (MeaSi)aPR (31) (R=Ph) and /j-ClCeHiNCO, CO insertion 

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E. Reactions with Sulfui , Selenium, Tellurium, Phosphorus, and Arsenic Derivatives.. . 171... 

E. Reactions with Sulfur, Selenium, tellurium. Phosphorus, AND Arsenic Derivatives... 

Heterocycles that contain a pyramidal heteroatom may exhibit pyramidal inversion as well as the conformational inversion processes outlined in the previous section. Pyramidal inversion barriers have been measured for a number of phosphorus and arsenic derivatives and have been shown to be considerably higher than their nitrogen analogs (258). 

A comparison of these compounds with the corresponding zinc derivatives should clarify the influence of the empty d orbitals involved in the bonding situation of the alkaline earth metal bis(phosphanides). Whereas zinc bis[bis(trimethylsilyl)amide] is monomeric due to the steric demand of the bulky amide ligand [6], the trimethylsilyl substituted phosphanide leads to oligomers such as dimers or trimers [7], The influence of the pnicogen atom is small, thus the phosphorus and arsenic derivatives (Fig. 5.) look very similar [8] or even crystallize isotypically. In contrast to the d metals calcium, strontium and barium, zinc derivatives solely build up monocyclic ring systems. 

The sulphonic acids are now known to be stronger than was supposed up to ten years ago. Methane-sulphonic acid has a pKg of —1 20, as determined by proton magnetic resonance (Covington and Lilley, 1967), or —1 86, as determined by Raman spectrometry (Clarke and Woodward, 1966) both values were obtained in water at 25°. Thus this substance is comparable in strength to nitric acid (Table 8.12). Similarly p-toluenesulphonic acid was shown to have a pKg of - 1 - 34 (Dinius and Choppin, 1962) by p.m.r. measurements in water at 25° (cf. —1 06 for Raman measurement by Bonner and Torres, 1965). Table 8.5 contains values for these substances, and organic sulphinic and boric acids (see Table 8.6 for corresponding phosphorus and arsenic derivatives). 

Nitrogen, phosphorus and arsenic form more than one hydride. Nitrogen forms several but of these only ammonia, NHj, hydrazine, N2H4 and hydrogen azide N3H (and the ammonia derivative hydroxylamine) will be considered. Phosphorus and arsenic form the hydrides diphosphane P2H4 and diarsane AS2H4 respectively, but both of these hydrides are very unstable. 

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. 

Pyridyl-phosphorus and -arsenic compounds have also been made by nucleophilic displacement reactions with, for example, 3-pyridinediazonium salts (74HC(14-2)489). Organomercury derivatives can be converted into bromides and iodides by standard methods, e.g. Scheme 147 (59JPR(8)156). 

The use of hypervalent iodine reagents for heteroatom-heteroatom bond forming reactions is well established in the context of classical oxidation chemistry [1-11]. For example, oxidations of anilines to azobenzenes, thiols to disulfides, and sulfides to sulfoxides with aryl-A3-iodanes were documented decades ago [1-5]. During the last ten years, particular attention has also been given to oxidative transformations of compounds derived from heavier elements, including the interception of reaction intermediates or initially formed products with external nucleophiles. A second important development is the utilization of sulfonyliminoiodanes, ArI = NS02R, for heteroatom-nitrogen bond formation, especially for imidations of sulfur, selenium, phosphorus and arsenic com-... 

When this method is applied to compounds of phosphorus and arsenic, the components undergo an entirely different reaction, and alkylidene trialkyl derivatives of these elements (ylides) are obtained 102, 104). Thus, instead of the introduction of an additional alkyl substituent at the central element, as observed with antimony, a deprotonation at one of the a-carbon atoms adjacent to phosphorus and arsenic occurs ... 

Mass spectra of pentaphenylarsorane and some compounds of type V have been reported and compared with the corresponding derivatives of group VA elements (92, 94, 96). The mass spectra of some of the phosphorus- and arsenic-substituted biphenyl systems show doubly charged parent ions of higher abundance than the singly charged molecular ions (92). Characteristic IR bands of compounds of type V have been summarized in Table II. 

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