Dimers phosphorus compounds

The reason for this behavior in the case of the double-bonded structures ( A -type phosphorus) is the easy dimerization of the P=C bond. Tricoordinate planar (or nearly planar) phosphorus ( B - and C -type bonding) can be stabilized by repyramidalization when the cyclic electron delocalization is disturbed or lost (e.g., in a chemical reaction). The fine balance between these energetic effects cannot easily be predicted by using analogies or other simple models. Such predictions, however, can be made by using the sophisticated methods of computational chemistry, leaving the field of the chemistry of the aromatic phosphorus compounds an interesting research area with unexpected results in the future. 

Remarkable enhancements of the unimolecular c-t isomerization of c-S with p-MeO and oxidation of S with -MeO are explained by charge-spin separation in such S Unimolecular c-t isomerization of such c-S proceeds with a chain mechanism, while regioselective oxidation occurs in such S because of the spin localization. Cycloreversion of t,c,t-TPCB occurs to give a a-St 2, while the photochemical cycloreversion of TPCB and t,t,t-TPCB gives Tr-St 2 and t-St /t-St pair, respectively. Radical cations of phosphorus compounds (9 and 10 form intramolecular rr-dimer between two Nps from which Np 2 forms. Formation of intermolecular a-dimer of aromatic acetylene (11 - and 12 -) and intramolecular dimer of 13 and diarylmethanoT was observed, and the n = 3 rule is not effective for intramolecular dimer -. 

The addition of a molecule X—Z (often with Z = H) to a P=0, P=N, P=C or P=S double bond can always be a possibility. The reaction may occur with a distinct molecule, or it may even be intramolecular when XH is a constitutive part of the phosphorusbearing molecule. Structures such as A, A, A", C and C in Scheme 28 are representative of a large proportion of phosphorus compounds of (mono)phosphazenes, and of their cyclophosphazane dimers (over 1000 literature references ). 

A series of four-membered Si- or P-containing heterocycles was produced in various yields by electrocyclization or [2-t-2]-dimerization of compounds with multiple carbon-silicon or carbon-phosphorus bonds. These unsaturated species are formed under photolysis of diazo compounds containing a P or Si atom in an a position with respect to the diazo group, following a [l,2]-sigmatropic shift in the intermediate carbene. 

Unlike cyclic silicon-phosphorus compounds, which occur as dimers and/or trimers, the cyclic silicon-arsenic ring of (Me2SiAsMe)4 is eight-membered. It results from MeAsHLi and Me2SiCl2 along with polymer, and occurs in solution as a mixture of conformers (equation 90)no. 

Organophosphorus compounds (OPs) are utilized on a large scale as flame retarding agents and plasticizers in a variety of products, such as plastic materials, rubbers, varnishes, lubricants, hydraulic fluids, and other industrial applications. This family of chemicals consists of alkylated and arylated phosphate or phosphonate esters and related compounds such as phosphites, phosphines, and related dimeric forms as well as ionic forms (Figure 31.2). " The low volatility of phosphoric acid and derivatives makes it the preferred choice of the phosphorus based FRs. These FRs are most effective in polymers that char readily. Also halogenated phosphate esters, such as tris(l-chloroisopropyl) phosphate (TCPP), and tris(2-chloroethyl) phosphate (TCEP), are widely used. These combine the properties of both the halogen and the phosphorus compounds. 

Secondary phosphites and thiophosphites react with silylketens to give vinylphosphonates (58), presumably through rearrangement of (59). The reactions of keten dimers with tervalent phosphorus compounds are much more complicated and have been the subject of extensive study by Bentrude... 

Here, Ihe emission occurs in llie blue wiih niaximii 111, W4 iind 1 )4 nni. The clieniMuniinescem intensity is proportional to the concenlralion of the excited sulfur dimer. Similarly, combustion of phosphorus compounds in a hydro.ccn flame gi es emission due to HPO at S2(i nm. Linear working curves over four decades of concentraiion arc reported. Both of these flame ehemiluntinescence techniques have been employed for detection of sulfur aitti phosphorus species in the effluent from gas chromatographic columns. 

Phosphorus Compounds.—Treatment of the dioxaphospholen (635) with sulphur yields a mixture of the oxathiole (636) and fran -dibenzoylstilbene, PhCOCPh=CPhCOPh." 2-Phenyl-l,3,2-dioxaphospholan (637 R = Ph) dimerizes in solution to a ten-membered-ring compound, which was isolated as (638) by sulphurization." The cyclic thiophosphorous acid (639) exists in equilibrium with the betaine (640) in aqueous ethanol/ The spiro-compound (641), which contains a phosphorus-hydrogen bond, is formed by the action of (637 R = Cl) on diethyl tartrate. The phosphazene (642) spontaneously cyclizes to the spiro-compound (643). " Stable derivatives (645) and (646 R = Br) of five-co-ordinate phosphorus have been obtained by the action of bromine on the o-phenylene phosphite (644)/ The chlorine analogue (646 R Cl) reacts with 3,5-dimethylpyrazole to give the corresponding pyrazole derivative (646 R = 3,5-dimethylpyrazol-l-yl), which reversibly dimerizes to the zwitterion (647). ... 

The generation of an aryl phosphenite (150) from a 7-phospha-norbornene derivative (151) by thermolysis or photolysis has been investigated. Thermolysis gave a condensate containing some (150) besides dimers and trimers photolysis, however, gave no fragmentation products from (151) or from similar phospha-norbornenes unless alcohols were present. Photolysis of 7-phospha-norbomenes is therefore not a route to two-co-ordinate phosphorus compounds, as assumed earlier. 

Like phosphinic acids, phosphonic acids or their acid esters readily form dimers as in (6.287a) or other hydrogen-bonded arrangements. Dialkylphosphonates may also form dimers as in (6.287b) but in this case the H bonding is much weaker (in all phosphorus compounds with P-H bonds the H bonding is generally weak or absent (Chapter 13.1)). 

The compound so obtained in 1877 by Michaelis [27] was considered to be a dimer and was wrongly given the formula Ph-P=P-Ph, analogous to that of azobenzene, Ph-N=N-Ph. Most phosphorus compounds of this type, and their arsenic analogues, are now known to have ring structures and are devoid of double bonds (but see Section 6.19). Examples are... 

In principle, the preparation of these compounds should be similar to the chemistry of carboxylic acids and sulfonic acids, but it is more complex and there are synthetic routes that are specific for the phosphorus compounds. For example, the reaction of phosphoric acid and an alcohol may give the ester, but the reaction is slow and this is not a good preparative method. An alternative is the reaction of phosphorous pentoxide with an excess of an alcohol to give a mixture of phosphate esters. The reaction of ethanol and P4O10 (the dimeric form of phosphorus pentoxide), for example, gives a mixture of 207 and 208. They are separable based on differences in solubility in alkaline earth salts.The hydrolysis of pyrophosphate esters such as 209 gives the phosphate ester 208. 

Although most of the macrocycles that contain phosphorus or arsenic which have thus far been prepared, are primarily transition metals binders, two compounds have been prepared which are essentially crown ethers containing phosphorus. Kudrya, Shtepanek and Kirsanovhave prepared two compounds which are essentially polyoxygen macrocycles but which contain one or two methylphosphonic acid esters as part of the ring. These two macrocycles are shown below as 7d and 17 and are both prepared by the reaction of 2,2 [oxybis(ethyleneoxy)] bisphenolate with methylphosphonic dichloride in a mixture of acetonitrile and benzene. The crystalline monomer 16) and dimer 17) were isolated in 17% and 11% yields respectively as indicated in Eq. (6.13). 

The products from the reactions with phosphorus pentachioride vary even with the nature of the aryl group. Thus, the p-chlorophenyl compound gave a product analogous to (6), but it was accompanied by the dimeric phosphazene, [p-ClCeHiNPClsJa. 

Compound 132 was formed from 0,0-diphenyldiamine with hexaethyltriamide of phosphorus acid (HEPA), as outlined in Scheme 9. This reaction was found to be nonselective and dependent on the reaction conditions employed. Heating the reaction mixture to 90-100 °C without solvent for an hour resulted in a mixture that upon sulfurization yielded compounds 132 and 133 <1997PS(123)89>. When the above reaction was carried out in xylene and heated to 120-130 °C, compound 134 was formed. Equilibrium was established between compound 134 and the dimer, compound 135, in a ratio of 3 2 (Equation 12). 

Reviews covering the chemistry of group 2 metal complexes with phosphorus-stabilized carbanions,279 and of molecular clusters of magnesium dimetallated primary phosphanes, are available.2 u Magnesium phosphanes remain rare compounds.281 Lithiation of bromide 98 with BuLi in the presence of tmeda in pentane produces a lithium phosphine dimer subsequent treatment with MgCl2 in EtzO gives the phosphane 99 in 69% overall yield (Equation (19)). The centrosymmetric 99 has Mg-C = 2.217 A Mg-P = 2.77 A (av.).282... 

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