Low-coordination phosphorus species

X -systems, and other low coordination phosphorus species, in particular phosphenium ions, R2P , and phosphinidenes, RP . The reactions of phosphenium ions with isocyanides, 1,3-dienes and o-quinones, and amidines, have been investigated. The coordination chemistry of phosphenium ions also continues to stimulate interest.The thermal decomposition of phosphirene and phosphirane P-complexes provides a new approach for the synthesis of terminal phosphinidene complexes, e.g., (180), which can be trapped with a variety of reagents. Evidence of the formation of surface phosphinidene intermediates has been adduced in the heterogeneous dechlorination of alkyldi-chlorophosphines by magnesium metal at 600K. ... 

Our previous work has established techniques for the generation of four different types of low-coordination phosphorus species by ring fragmentation [some contributions made by other laboratories are summarized in a recent book (5)]. 

The Generation of Metaphosphoric Acid Derivatives. These are among the most reactive of low-coordinate phosphorus species, and are of great importance as reactive intermediates in some phosphorylation processes. The metaphosphate ion receives study as a possible intermediate in biological processes, a concept introduced in 1955 by the laboratories of F. H. Westheimer (6) and of C. A. Bunton (7). The... 

The two selenium atoms are attached to the low-coordinated phosphorus atom, with two lengthened dative bonds (2.788 and 2.637 A). Interestingly the phosphorus atom is here strongly pyramidalized, the Z SePSe angle was 80.6°. In other words the lone pair orbital at the electrophilic phosphorus atom remains stereo chemically active, as one would expect on the basis of the quantum chemical theory of bonding within this species. 

Phosphinidenes (R-P) differ from other low-coordinate organophosphorus compounds, such as phosphaalkynes (R-C=P), phosphaalkenes (R2C=PR), and phosphaaromatics, in that the phosphorus atom carries only a single a-bonded substituent [7-9]. They relate to carbenes, nitrenes, and silylenes and likewise can exist as singlet and triplet species. The advances that led to stable carbenes [10, 11] and silylenes [12] stimulated an exploration of the chemistry of phosphinidenes. 

The P-donor ligands we consider in this Part I are phosphoms(III) compounds. We avoid the classification difficulties of phosphine, PH3, as based on P-oxidation state —HI by referring throughout to tervalent phosphoms. Low-coordination number phosphorus species, such as RP, RCP, R2C=PR, and P , are presented in Part II. The P-donor ligands considered in Part I are covered by the generalized formula PR3 for a P-donor ligand. The PR3 ligands have a pyramidal shape due to their sterically active lone pair of electrons. In terms of a Valence Shell Electron Pair Repulsion Model model, the lone pair occupies the vacant tetrahedral site of the phosphoms center. 

Although species of the general formulation R-P=CR2 wherein trivalent phosphorus is bound to only two (carbon) atoms have been proposed for many years as intermediates in a variety of chemical reactions, it was not until 1978 thatastable compound of this class was isolated. This effort involved the generation of a sterically hindered system with three bulky aromatic rings bound around the P=C site (equation 9) that could reversibly add hydrogen chloride. The P NMR spectrum exhibited a signal at relatively low field in accord with the postulation of such trivalent doubly coordinated phosphorus. Approaches toward this type of species have been reviewed. ... 

Phosphabenzene, the phosphorus analogue of pyridine, is a species that, as with the methylenephosphines, formally contains a doubly coordinated phosphorus singly bound to one carbon and doubly bound to another. The first isolation of a phosphabenzene derivative was reported in 1966 using the reaction as shown below (equation 10). The parent phosphabenzene molecule was first isolated by the reaction (equation 11) of phosphorus tribromide with a staimane derivative, albeit in low yield.Further spectroscopic investigation of this parent molecule indicated it to be planar with indications of multiple bond character between phosphoms and carbon and aromatic delocalization. ... 

JOM(400)149 96BSCF33]. The complex 164 is the first known t] -phospholyl species. The tungsten atoms have a coordination number of 9, and the carbon atoms of the phospholyl ring are coplanar. The phosphorus atom deviates from the plane of carbon atoms by 0.015 nm. The basic difference between the Ti -cyclopentadienyl and ri -phospholyl complexes is the existence of a low-lying LUMO localized mainly at the phosphorus atom. 

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