Phosphorus, hypervalent

Investigations of hypervalent phosphorus compounds have tended to concentrate on the more stable bicyclic systems. Elegant studies of spirophosphoranes and a thorough investigation of permutational isomerisations within amidinium fluorphosphates are worth noting. 

Phosphorus also bears a significant (positive) partial charge in neutral compounds. By expanding formally its valence shell, hypervalent bonding structures are formed, which can conveniently be described by the 3c-4e model [34, 35], (Note that there is no need to consider the involvement of rf-orbitals in the bonding for the hypervalent phosphorus compounds [36, 37].)... 

Holmes RR (2004) Phosphoryl transfer enzymes and hypervalent phosphorus chemistry. Acc... 

Introduction - The subject has received a stimulus this year from the publication of the proceedings of the Xlth International Conference on Phosphorus Chemistry at Tallinn, Estonia in July 1989. Among the huge variety of papers presented at the conference, there were niimerous contributions in the field of hypervalent phosphorus chemistry, several of which are mentioned later in the article. 

In conclusion, the realm of hypervalent phosphorus chemistry is becoming ever more complicated as it expands into the chemistry of As, Sb and Bi and as the coordination of phosphoranes with Lewis Acids and transition metal elements adds another facet to the burgeoning field of asymmetric synthesis. 

The year has seen yet another diminution in the number of publications dealing with hypervalent phosphorus chemistry but the quality of work... 

Needed hypervalent phosphorus species have not yet been formed with trilithio species 13. Recently considered methods for making needed phosphoranide species are now being tried, and will be reported later. 

The year has seen a considerable extension of the principles of hypervalent phosphorus chemistry into the fields of other elements notably Si, Sn, Ge and Sb and in this context the well-known Martin ligand has proved to be especially valuable. Particularly interesting contributions have been provided by Ju et al on the relative rates of reaction of pentoses and hexoses with pentacoordinate phosphorus, by Bentrude et on the mechanism of the reaction of hy-dridophosphoranes with dimethyl disulfide and by Kawashima et alP on the isolation of two carbaphosphatranes containing covalent P-C bonds. Holmes et al report on the fluxional properties of propeller shaped phosphoranes and Buono et have also demonstrated the utility of hydridophosphoranes in some highly diastereoselective reactions with isocyanates. In summary, although the number of reports was small, the year was noteworthy for some very sophisticated contributions to the field. 

Introduction - The year has again seen a consolidation of knowledge in the area of hypervalent phosphorus chemistry with emphasis on the synthesis and properties of monocyclic and bicyclic phosphoranes. A considerable effort has been made to resolve the mechanism of the Mitsunobu Reaction (see Section 3) and the principles established by studies of pentaco-ordinate phosphorus compounds have again been extended to hypervalent compounds of other elements (e.g. As, Sb, and Si). A comprehensive review of the reactions of phosphorus acids with chlorine includes a number of examples of acyclic, monocyclic and bicyclic phosphoranes prepared by this route together with a useful catalogue of their 31p 5-values. 

Although interest in pn-bonded compounds continues at a high level the pace of advance seems to be slackening, perhaps reflecting that the most interesting chemistry in this area has now been revealed. The year has seen a further consolidation of knowledge in the area of hypervalent phosphorus chemistry and the principles established in this area have expanded further into the chemistry of As, Sb, Bi and Si. Notable contributions have appeared on the importance of the conformational transmissions effect to ligand... 

Introduction - It is gratifying to report that interest in hypervalent phosphorus chemistry has been maintained, especially with regard to structural studies and the synthetic utility of pentaco ordinate phosphorus compounds. A novel departure has appeared in the area of hexaco-ordinate phosphorus with the synthesis of further phosphorus derivatives of the porphyrin ring system containing hypervalent phosphorus coordinated by the tetrapyrrole unit. The chapter will take its usual format, however, and the details of this small nugget will therefore appear in the last section. 

Finally a new departure in an unusual aspect of hypervalent phosphorus chemistry has been provided by the synthesis of water-stable dialkoxy phosphorus(V)-tetraphenylporphyrins (125) from (124). The six-co-ordinate phosphorus porphyrin (125) with R=Et, has... 

Comparison of the various ab initio basis sets has been made to resolve the question of the best basis set for a particular application. It was concluded that of the lower-level basis sets (STO-3G, 4-3IG, STO-3G ), STO-3G provides the best electronic representation of hypervalent phosphorus and sulphur species (Collins et al 1976). Of the higher-level basis sets (3-2IG, 3-21G( ), 6-31G ), it was concluded that the 6-31G and 3-21G( ) sets give good representation of such species (Pietro et al., 1982). A major conclusion of both these studies is that d-orbital functions are essential for calculations on species containing hypervalent second-row elements and bonds involving two heavy atoms. 

Bonding natnre in hypervalent phosphorus compounds has been of widespread interest in the last years, especially in phosphine and amine oxides [1-11]. In addition, the P-O bond has been of particular interest and it has been discussed in a general review [12]. However, there are still several points of controversy in the P-O bond description. Experimental results [12,13] show that the phosphoryl bond is strong, short and polar. For years, the theoretical description of the P-O bonding was connected to the involvement of virtual d orbitals in the phosphorus atom. Nevertheless, recently evidence against this involvement appeared [2,14-26], as reviewed by Gilheany [13], leading to the exclusion of dorbital participation. 

Despite the overall decline in output, the year has produced ftirther interesting developments in the fteld of hypervalent phosphorus chemistry. These include phosphoranes containing acetylenic links, the synthesis and enantiomeric separation of a bicyclic phosphorane with chirality only at phosphorus, and a wide range of phosphoranes incorporated within macrocyclic ring systems (Houlla et al). In addition Lattman has reported on phosphoranes bound to transition metals or enclosed within calixarene skeletons and Holmes and his co-workers have made further substantial contributions on the X-ray crystal structures of phosphoranes containing eight-membered rings. 

During last year the majority of researches in this area has been focused on the synthesis and structural determination of novel hypervalent phosphorus compounds as well as on the stereochemistry of pentacoordinated chiral spirophosphoranes. In these studies, Mironov et al. obtained tricyclic pentacoordinated spirophosphoranes containing a phosphorus-carbon bond with high regio- and stereo-selectivity whereas Kawashima presented the synthetic route to perfectly anti-apicophilic carba-phosphatranes. ... 

It is well known that the coordination ability of phosphorus to form hypervalent compound, mainly penta- and hexacoordinated, is the driving force in describing the mechanistic action of phosphoryl transfer enzymes. On the other hand, organophosphorus compounds play also a fundamental role in inorganic, organic and applied chemistry as a key species, reaction intermediates or final products. Therefore, the utility of hypervalent phosphorus compounds in many chemical processess is indisputable and in some cases facilitate the outcome of the reaction to be defined. Recently, some achievements on the role of hypervalent phosphoranes in various chemical processess have been described. 

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