Bonded Phosphorus Compounds

This area of phosphorus chemistry continues to grow rapidly. A new route to the diphosphene (150) (and confirmation of the structure of the product by X-TAy studies) has been reported which involves the reaction of 2,4,6-tri-t-butylphenyldichlorophosphine with tris(trimethylsilyl)silyl-lithium. Apart from a chemical shift for this compound of +493 p.p.m., the physical properties are similar to those published in 1981 by Yoshifuji and his co-workers for the product [formulated as (150)] of the reaction of the above dichloro-phosphine with magnesium, for which a phosphorus chemical shift of —59 p.p.m. was reported. This work has now been reinvestigated by Cowley s group, and the desired phosphene isolated and shown to have 8( P) = +494 p.p.m. The compound responsible for the signal at 8 = —59 p.p.m. has been 

Yoshifuji, K. Shibayama, N. Inamoto, and T. Watanabe, Chem. Lett., 1983, 585. 

Gonbeau, G. Pfister-Guillouzo, J. Escudie, C. Couret, and J. Satge, J. Organomet. 

Chromatographic separation of the products of reaction of mixtures of two dichlorophosphines with either sodium-naphthalene or magnesium has led to the isolation of (153) and (154). The reaction of a primary phosphine and a dichlorophosphine in the presence of a base has also been used to prepare compounds of these types, - The less sterically crowded (and therefore less stable) diphosphenes (155) have been prepared by the reactions of dichlorophosphines with bis(trimethylsilyl)phosphines and trapped as cycloadducts with dimethylbutadiene. In the absence of a trapping agent, these systems rapidly undergo cyclopolymerization.  

Base-induced elimination of hydrogen chloride from the diphosphine (156) has given a new class of diphosphenes (157). Reduction of dialkylamino-dichlorophosphines with lithium aluminium hydride also affords these systems, which are reported to be pyrophoric, red liquids that are stable in solution for 

Activity in the phospha-alkyne area has again continued at a high level. The applications of these compounds as building blocks in inorganic and organo- 

New approaches for the generation of reactive p -bonded phosphorus compounds have been developed, and the systems (299) and (300) characterised by trapping experiments. Evidence for the involvement of the alkylidene-oxophosphorane (301) has been adduced from studies of nucleophilic substitution reactions on a 9-fluorenylphosphonamidic chloride, which appear to 

Studies of the reactivity of diphosphenes and phospha-arsenes which bear a complexed transition metal substituent at phosphorus (or arsenic) continue to appear.Aspects of the coordination chemistry of diphosphenes also continue to receive attention.The phosphorus and arsenic analogues of cyclobutadiene, cyclo-P and cyclo-As, have been stabilised as ligands at a niobium centre. 

The reaction of cyanomethyllithium with 2,4,6-tri-t-butylphenyl-dichlorophosphine enables a one-step preparation of the functionalised phospha-alkene (144). A new route to phospha-alkenes is provided by nucleophilic attack at the vinylic CH2 of the halogenophosphine (145), with displacement of halogen from phosphorus. Thus, with DABCO as nucleophile, the novel system (146) is formed.Treatment of the phosphino-substituted ylides (147) with Lewis acids results in the 2-phosphonio-l-phospha-alkenes (148), reported to be sufficiently stable for X-ray analysis, but also undergoing various addition reactions. 

Routes to the dihalomethylene systems (149) have been developed which involve the reactions of halogenophosphines with tetrahalo-genomethanes in the presence of phosphines,and also phosphine-induced dechlorinations of trichloromethylchloro- 

The diphosphetene-complex (154) undergoes a reversible, conrotatory ring-opening on treatment with maleic anhydride or N-phenylmaleimide, to form the complexed diphosphadiene (155). The reactions of P-halofunctional phospha-alkenes with N-trimethyl-silylimines and related compounds have given a series of azaphosphadienes (156). The first unsymmetrical 1,3-diphospha- 

Addition reactions of phospha-alkenes continue to be explored. The thermally unstable 1,2,3,4-triazaphospholine system 

This area continues to generate interest across the range of p -bonded phosphorus compounds. Whereas long-established topics such as the chemistry of diphosphenes and phosphaall nes have again received comparatively little study, the chemistry of phosphaalkenes (and related P=C=X compounds), and the less-developed groups of low coordination number phosphorus compounds, in particular phosphenium ions, phosphinidenes, and their complexes with carbenes and metal ions, has again dominated the area. 

A new route to phosphaalkenes is provided by treatment of dichloro-phenylphosphine with two equivalents of carbonyl-functional carbenes, resulting in a two-electron reduction of the phosphorus centre coupled with carbene oxidation. A range of amido-functional phosphaalkenes, e.g., (112), (alternatively viewed as carbene-phosphinidene adducts), was prepared using this approach, followed by full spectroscopic and structural characterisation. A related diamino-functional phosphaalkene has also been described and its coordination chemistry studied. Among other new phosphaalkene systems reported is a series of phosphaalkene-phospholes, e.g., (113), the monoanionic phos-phaalkenyl-phosphido ligand (114), alkali metal salts of the phosphaalkene radical anion (115), ° and new 1,3-diphosphacyclobutadiene 

The chemistry of phosphinidenes, RP , and terminal phosphinidene complexes, RP - [M], has also continued to be explored. A review of the conversion of allenes to strained three-membered heterocycles includes work on the reactions of phosphinidenes leading to phosphiranes. A route to oxaphosphirane complexes (and also, following a 

The literature on this area up to 1990 has been reviewed in a major volume. The ability of complex metal hydride acceptors to stabilise p,-bonded phosphorus compounds, but without diminishing their reactivity, has also been reviewed.  

In a review, largely of the work of his own group, Mathey has expanded on the analogy between P=C and C=C bonds. The difficulties inherent in the attempted preparation of phospha-alkene systems by the condensation of primary phosphines with carbonyl compounds 

The reactions of the halogenophospha-alkene (183) with complex metallo-anions have given a range of P-metallophospha-alkenes, e.g., (184), which are found to be metastable, undergoing gradual dimerisation and subsequent transformation. Mathey s group has shown that rhodium complex-promoted catalytic hydrogenation of prochiral complexes of phospha-alkenes offers a route to related complexes of chiral secondary phosphines. The reactivity 

A new route to the phospha-alkyne (199, R=2,4,6-Bu 3C H2) is provided by the reaction of the readily available phospha-alkene (173, X=Y=C1) with a triphenylphosphine-palladium (0) complex. The low temperature Lewis base-induced rearrangement of primary 

A review of lone pair effects involving multiple bonds between heavier main group elements contains much of relevance to pj -bonded phosphorus systems. The diphosphene (295) has been shown to undergo cycloaddition reactions with isocyanides, to give the iminodiphosphiranes (296). A thirtyfive-fold excess of methyl triflate is needed to convert the diphosphene (297) to the salt (298), which is unstable in non-polar solvents. Experimental data show that the P=P bond becomes stronger on alkylation as is the case for N=N compounds. 

Cyclic triphosphenium ions, e.g. (299), have been obtained from the reactions of bis(diphenylphosphino)alkenes with phosphorus trichloride in the presence of tin(ii) chloride in dichloromethane. The simple phospha-alkene 

A study of the reactivity of the carbonyl-functional phospha-alkenes (305) has also been reported. The triphospha-Dewar-benzene (306) has been shown to undergo cycloaddition reactions with alkynes to form the triphosphabishomo-prismane system (307). Cycloaddition of t-butylphospha-ethyne to the phosphatriafulvene (308) results in the formation of a single isomer of the diphosphaisobenzene (309), having an allene system within the ring. This 

Phospha-alkyne systems have continued to attract interest. The phosphino-phospha-alkyne (324) arises as a transient intermediate in the thermolysis of a phosphino-phosphiranyl-diazo system.A convenient synthetic route to substituted phosphavinyl Grignard reagents (325) is provided by the regio- and stereo-selective addition of Grignard reagents to the phospha-alkyne 

Bu C = P. Whereas the latter phospha-alkyne does not react with sulfur or selenium, the related system Pr 2NC = P yields the diphosphetene system (326). Also reported in this study is a slow cycloaddition of Bu C = P with carbon disulfide, eventually yielding a l-thia-2,4-diphosphole. Interest in the dimer- 

Activity in this area has remained at a similar level to that reported for 2007. Well-established topics such as the chemistry of diphosphenes, phos-phaalkenes and phosphaalkynes have continued to attract attention, as also has work on the less-developed classes of low coordination number phosphorus compounds, in particular phosphenium ions and phosphinidenes, and their metal complexes. Recent work on kinetically-stabilised doubly bonded systems involving two of the heavier Group 15 elements has been 

A successful protocol has been developed for the introduction of stable phosphaalkene units into oligoalkynes, leading to compounds of types (162) and (163), a new class of 71-conjugated molecules. Also reported are routes to the planar chiral l-phosphaethenyl-2-phosphinoferrocenes (164), from the reactions of optically active 2-phosphinoferrocenecarboxaldehydes with Mes P(Li)SiMe3 in and the bidentate ligands (165), in- 

This area has undergone yet another year of rapid development, with a significant increase in the volume of published work. A number 

Diphosphenes stabilised by bulky groups, e.g. (157, R = 2,4,6-tri-t-butylphenyl), can be isolated in high yield from the reactions of alkyl- or aryl-(trichlorogermyl)phosphines with an excess of the base DBU. The formation of less sterically crowded systems, e.g. (157, R = t-butyl), is also possible by this route, 

R = t-butyl, 23 phenyl, 2 or trimethylsilyl2 ) have been characterised as Ti-complexes of various transition metal acceptors. 

A novel mode of coordination of diphosphenes is seen in the ligand 

The highly reactive diphosphene (157, R = trifluoromethyl), accessible from the reaction of trifluoromethyldiiodophosphine 

A detailed study of the vibrational spectra of phosphaalkenes has appeared, which includes studies of the influence of structural effects on the P--C bond.  

The first report of the gas-phase generation of the ds-isomer of the iminophos-phene (345) (and the related iminoarsene) has appeared. NMR and theoretical techniques have been used to study the /Z-isomerism of the aminoiminophos-phenes (346). The stabilisation of singlet nitrenes by N-iminophosphene substituents has been studied from a theoretical standpoint. The phos-phadiazonium cation (347) has been shown to form complexes involving the phosphorus atom as acceptor, on treatment with 2,2 -bipyridyl.  

Although this area continues to attract considerable interest, the pace of advance seems to be slackening. Compared with recent years, there has been a significant reduction in the number of publications in the period under review. 

6-tris(trifluoromethyl)phenyl group provides another 

These molecules form the usual complexes with metal acceptors. Photolysis of the E-isomer of the diphosphene (163) using a mercury lamp with a pyrex filter results in the formation of a mixture of and Z- isomers in equilibrium. However, photolysis 

The diphosphiranes also rearrange in solution, or in the presence of silica gel, to form the new 1,3-diphosphapropenes (167), in 

The metallated phospha-alkenes (172) and (173) offer considerable potential for the synthesis of P=C compounds. Treatment of (172) with carbonyl compounds has given the 1-phospha-allenes (174), and 

Treatment of the diphosphenium salt (223) with lithium diisopropylamide results in a high yield conversion into the diphosphirane (224), alkylation of which gives a diphosphiranimn salt. EPR techniques have been used to study the products of sodium reduction of the bis(diphosphene) (225) and related phosphaalkenes.  

3- diseletanes (232), and reactions of this type have also been reviewed.  

3- diene systems. The diphosphabutadiene (244) has been shown to undergo an unusual [2+4] cyclodimerisation to form (245). The diphosphinidenecyclobutenes (246) continue to attract interest as diphosphabutadiene ligands for transition metal ions and related catalyst systems. Metal complexes of 1,4-diphosphabutadienes, 2,3-diphosphabutadienes, and l-phospha-buta-l,3-dienes have also been investigated. 

Interest in the chemistry of phosphaalkynes has continued, although perhaps at a slightly lower level than in recent years. Theoretical studies include consideration of the gas-phase acidities of HC=P, CHsC P (and the related arsaalkynes), isomerism in the FCH2C=P system,and calculation of the indirect nuclear spin-spin coupling constants A review has 

Although strictly outside the remit of this chapter, it is appropriate to note continued activity in the chemistry of c X -p -bonded phosphorus compounds that do not possess a lone pair of electrons at phosphorus. A monomeric metaphosphonate species (262, X=0) has been stabilised by coordination via the P=0 bond), and Harger s group has provided evidence of the intermediacy of metathiophosphonates (262, X=S) in the reactions of phosphonami-dothioic acids with alcohols.The cation (263) has been stabilised by coordination at phosphorus with 4-dimethylaminopyridine and the reactivity of bis(methylene)phosphoranes (264) and related phosphoranylidene car-benoids has been investigated.  

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Although this chapter is somewhat shorter than last year s, it is encouraging to note that several papers have appeared which deal with the synthesis and chemistry of / -bonded phosphorus compounds. 

Synthesis of multiply bonded phosphorus compounds using silylphosphines and silylphosphides... 

Bis(trialkylsilyl)phosphines have been used as the starting materials for the preparation of phosphaethenes as well as other types of multiply bonded phosphorus compounds. For example, r-butyl[bis(trimethylsiIyl)]phosphine (2) and phenyl[bis(trimethylsilyl)]phosphine (3) afforded phosphaethenes in various manners. Some typical reactions of 2 and 3 leading to phosphaethenes are shown in equations 10-128,30 31. 

Multiply bonded phosphorus compounds are often reactive as heterodienophiles. However, diis is a diffuse area of research and little systematic study of these Diels-Alder reactions has been done. A complete listing of the various types of phosphorus dienophiles is beyond the scope of diis review. Some of this material is available in previous summaries. Selected representative examples of recent activity in this area is given in equations (109), (110), (111) and (112). ... 

The Reporter notes an overall decrease in the number of papers in this area published during the year, although the number dealing with p -bonded phosphorus compounds continues to increase. The reactions of disulphides with tervalent phosphorus compounds have been reviewed. ... 

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