Quinquecovalent Phosphorus Compounds

The formation of quinquecovalent PH species (2) from the addition of phenols to the phosphonamidite (1) has now been extended to the addition of alcohols, thiols. 

Hydroxyphosphoranes, which as such or as their conjugate bases have long been postulated as intermediates in nucleophilic substitutions at phosphoryl centres, are beginning to attract attention. Interconversion of the isomeric phosphinates (5) and (8), via the hydroxyphosphoranes (6) and (7), has been monitored by variable-temperature n.m.r. 17 kcal mol ) and the intermediates have been trapped as methoxyphosphoranes (9) on treatment with diazomethane. As expected, the 

The synthesis of phosphoranes from tervalent phosphorus compounds, 1,2- or 1,3-diols, and iV-chlorodi-isopropylamine according to equation (1) has been extended to 

X-Ray analysis has revealed essentially trigonal-bipyramidal geometry in the spiro-phosphorane (18) and distorted trigonal-bipyramidal geometry in the phosphor-anes (PhaFPNMe)2, (19), (20), (21),1 (22), (23), and (24). The nitrogen in (23) 

Analysis of the distortions of cyclic phosphoranes from ideal trigonal-bipyramidal geometry shows that these are towards square-pyramidal geometry, i.e. along the pathway followed in Berry pseudorotation. Ab initio calculations on the reaction of HgPO with H support a transition state or intermediate with distorted trigonal-bipyramidal geometry and equatorial 0.  

Perhaps the most surprising and potentially significant development in the year under review has been the preparation of stable, isolable, phosphoranes of the general formula (1). Examples include (2), formed from dineopentyl phosphonite and pinacol,1 and (3), formed by the addition of phenols to phosphorus(m) species.2-3 

Such phosphoranes are potential reducing agents mild oxidation of (4), or heating, gives the spirophosphorane (5) whereas (6) is slowly transformed into the spiro-phosphorane (7) at 0 °C.3 In general, cyclic PH-phosphoranes of structure (8) are in equilibrium in solution with the phosphorus(m) species (9).3 

Although the phosphoranes (1) so far detected are all stabilized by the presence of a ring, acyclic analogues presumably exist in solution, and there are clearly interesting 

X-Ray analysis has shown11 that the salt (16) is clearly trigonal bipyramidal round phosphorus. Vph for (16) is 791 Hz and the P—N distance 1.986 A. 

The year has been largely one of consolidation, with emphasis on the synthesis, structure, and properties of phosphoranes containing small (four- and five-membered) rings, especially the relatively stable compounds afforded by bi- and tri-cyclic structures. A new departure, however, has led to the first reports of five-co-ordinate phosphorus bound to transition-metal complexes vide infra) and these novel compounds may be the precursors of a new wave of chemistry in this area. 

An ingenious experiment involving irradiation (u.v. or JST-ray) of a single crystal of (1) produced two stereoisomeric phosphoranyl radicals (2) and (3) with the unpaired electron in the equatorial (2) or apical (3) positions. Although 

A single-crystal 2T-ray analysis of (6) [prepared from (4) and (5)] offers the first model of a five-co-ordinated structure containing the phosphole ring in which the distortion from trigonal-bipyramidal (tbp) towards rectangular-pyramidal (rp) is only 8.3 %, the lowest yet observed for a spirocyclic structure. The crystal 

In contrast, the geometry of the dioxadithiaspirophosphorane (8) is essentially rp (93% distorted from tbp) with the chalcogen atoms occupying the basal positions, a structure which represents the least distorted rp phosphorane on record. The paper re-emphasizes that no example of a rp structure for five-membered cyclic phosphoranes exists unless two rings are present, the rings contain unsaturation, and like atoms are present in any one ring bound to 

A new synthetic route from (9) and (10) gave the novel X P-X P spirophos-phorane (11), the A -ray analysis of which depicted a strongly distorted tbp with a X P-X P bond of similar length (221.4 pm) to numerous symmetrical and unsymmetrical diphosphorus compounds.  

Oxyphosphorane chemistry has been reviewed, with emphasis being placed on the importance of ligand sub-set symmetry in determining the relative stabilities of isomeric trigonal-bipyramidal phosphoranes, the effect being more pronounced for the equatorial than for the apical system. Applications of oxyphosphoranes in synthesis have also been reviewed.  

The spirophosphoranes (1 R = H or Me) and (2 R = Me) have been shown by JT-ray analysis to be essentially square-pyramidal while (2 R = F) is distorted trigonal-bipyramidal. Although reflecting on the usual assumption 

Ab initio calculations on PF5 and on a variety of substituted fluorophosphor-anes assign a significant role to p -d bonding and support the BPR route for ligand exchange in PFs and in PF3H2. 

The different Vfp coupling constants to apical and equatorial CFg groups allow the stable conformations at low temperatures of a variety of trifluoro-methylphosphoranes to be established. This leads to the partial apicophilicity series F, Cl CF3 OSiMes, OMe, SMe, NH2, H, Me. The phosphoranes (CFa)3pH2, CF3PF3H, and (CF3)aPFaH have been prepared by reduction of the corresponding fluorophosphoranes with trimethylsilane in the vapour phase. The stable conformations at low temperatures of the first two are (3) and (4) 

Non-equivaJent apical fluorines were observed in the low-temperature F n.m.r. spectra of the phosphoranes R PF3(OR ) when the alkoxy-group was asymmetric, e.g. R = MeEtCH, ClCHaMeCH, etc. The effect was not due to slowing of rotation lound the equatorial P—0 bond as it was not observed in the phosphoranes R gPF aCOR ). 

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The autoxidation of triphenylphosphine and phosphorus esters has been studied kinetically. After a short induction period the reaction gave the corresponding quinquecovalent phosphorus compounds. The intermediate (55) is probably formed by the addition of oxygen to perfluoroacyl-diarylphosphines. Subsequent decomposition afforded diarylphosphinates (56). The oxadiazine (57) has been prepared from the reaction of carbon dioxide and allyl isocyanate in the presence of tributylphosphine. ... 

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