Biphilicity

Biphilic Reactions with Dienes or Carbonyl Compounds. Stereochemical details have appeared of the reactions between substituted 1,3-dienes and halogenophosphines, such as dichloromethylphosphine (21a) and dibromo-phenylphosphine (21b). In general, both cis- and /ra/i5-adducts are formed, and they are not interconvertible via quinquecovalent intermediates. The conversion of these adducts to A -phospholens or to A -phospholen-l-oxides produces cis-trans mixtures. 

Biphilic Reactions.—A most thorough investigation into the cycloaddition of buta-1,3-diene with dichloro(methyl)phosphine (30) has revealed some of the factors which influence the composition of the final products.32 Thus the A3-phospholen 1-oxide (31) is the product of the cycloaddition at room temperature, but at 90 °C the isomeric A2-phospholen 1-oxide (32) predominates after work-up. The yields of (31) and (32) are improved by a new work-up involving methanolysis rather than hydrolysis of the intermediate salts.32... 

The reaction of a diphosphine with a dihalo compound, resulting in the formation of a di- or tetra-phosphonium salt2c, is a special case because if fits well with a cyclization on phosphorus, but also at the same time with a cyclization between two chains already linked to the second phosphorus (reaction 102). Another kind of ring closure on the phosphorus results from the biphilic character of halophosphines toward dienic392 or acetylenic28,393 systems (reaction 105). 

The following example is a good illustration of these two facts the spirophosphorane 70 (Scheme 9), with a TBP structure, is a racemate of the enantiomers x and x, which can both be in tautomeric equilibrium with 70a, a derivative of tricoordinated phosphorus. The pentacoordinated P is electrophilic and can therefore undergo a number of reactions with nucleophilic reagents, whereas the tricoordinated P atom of 70a is nucleophilic or even biphilic, and 70a itself, with its OH group, has a nucleophilic protic centre with all its specific chemical properties. 

Since charge effects are also important in affecting substitution rates, a recent suggestion has been made that the complex [PtCl(NH3)en]+ be used as a reference for npt with complexes of this charge type.1992-1994 In particular, before comparison can be made it is emphasized that kinetic data must be collected under the same ionic strength conditions, and care must be exercised when fitting data for biphilic nucleophiles. 

It has been suggested that when the trans ligand is a strong o-donor with no x-acidity the role of transition state stabilization is taken up by any biphilic species, such as thiourea.488 Such potential Jt-acceptors seem to be more capable than others in making use of the direct substitution pathway. 

The energy levels of the pertinent intermediates in the photoreactions of chloranil (acceptor) and tetramethylphenylenediamine (donor), respectively, with the am-biphilic phenylpropene isomers are compared in Fig. 10. 

The results obtained in this study have been believed to be consistent with a biphilic insertion of the group V atom into the peroxy bond of the dioxetane. 

Hence, a new method is developed for formation of NBF by adsorption of a surfactant from a gas phase. It offers new options for the production of such films from insoluble substances with biphilic structure. 

Gas diffusion through NBF is of particular interest, since this film represents a model of biphilic bilayer the permeability of which is of principle importance for biological membranes. 

Recently, this reaction was extended to include triphenylarsine and triphenyl-antimony.The fact that the relative reactivity was PhsP PhaSb >PhaAs confirms that the mechanism involves biphilic insertion into the peroxide bond rather than nucleophilic displacement, leading first to the pentacovalent intermediate. 

An unstable adduct between triphenylphosphine and a photochemically-generated dimethylgermylene has been characterised spectrophotometrically.The first 2,3-dihydro-l,3,2-X -benzodiazaphospholes (73) have been formed in the reactions of triphenylphosphine with g-benzoquinone di-imines stabilised by coordination.A complex of phenylnitrene with a tungsten pentacarbonyl acceptor has been trapped using triphenylphosphine. A kinetic study of the reactions of diazoalkanes with triphenylphosphine, leading to the phosphazenes (74), indicates a biphilic mechanism, the dominant interaction in the transition state involving the diazoalkane as a net electron donor,... 

Studies of the kinetics of the reactions of A -phospholens (108) with diethyl peroxide are consistent with a mechanism involving rate-determining biphilic attack of the phospholen on the peroxide, followed by a fast fragmentation of the intermediate phosphorane. " ... 

Biphilic Reactions with Carbonyl Compounds.—The dichlorophosphine (34) undergoes a standard chloromethylation when heated with paraformaldehyde, and a good yield of the phosphinic chloride (37) is obtained. At temperatures below 100 °C, the ester (38) is isolated, and the authors discuss, somewhat speculatively, the mechanism of the reaction see Scheme 3. 

Biphilic Reactions. Reactions between carbonyl compoimds and halogenophosphines continue to be prominent in the literature. Thus hexafluoro-acetone has been converted into halogenophosphoranes by reaction with (45), chlorodi-n-propylphosphine (49), or l-chloro-2,2,3,4,4-pentamethyl-phosphetan (50). By contrast, the analogous reactions of benzaldehyde with... 

Hexafluoroacetone alkoxycarbonylimines 29, exhibiting biphilic properties, act as 1,3-heterodienes or as dienophiles in [2 + 4] cycloadditions. With cyclopentadiene they react as dienophiles forming [2 + 4] cycloadducts, for example, 2-alkoxy-carbonyl-3,3-bis(trifluormethyl)-2-azabicyclo[2.2.1]hept-5-ene 30 (95IZV1809)... 

Further kinetic investigations of the reactions of phosphites with a-diketones are held to support the previously suggested mechanism in which the first and slow step involves nucleophilic attack of phosphorus on carbonyl carbon. The relative rates of reaction of a series of phosphines with diethyl peroxide to give diethoxyphosphoranes are in the reverse order of those for reaction with ethyl iodide. The differences involved are small but are consistent with a concerted biphilic addition to the peroxide. 

Biphilic Reactions with Dienes and with Unsaturated Carbonyl Compounds. The Diels-Alder reactions of the aj8-unsaturated lactone (40) have been described. The lactone is prepared by treatment of chloro-methyldichlorophosphine (41) with propiolic acid and then hot acetic... 

Further evidence for a biphilic insertion mechanism is derived from a study of the reaction of the bicyclic phosphoramidites (115) and (116) with diethyl peroxide to form (117) and (118), respectively. The strained 1-phosphabi-cyclo[3.3.0]octane (115) reacts much faster than its l-phosphabicyclo[4.4.0]-decane analogue (116), but the opposite reactivity is found towards diphenyl disulphide. At room temperature (116) produced (120) within seconds, presumably via an intermediate phosphonium salt, whereas (115) gave (119) [S 3ip = —19 p.p.m.] after 1 h at 58 °C. As mentioned earlier, the latter appears to be the only phosphorane reported so far with two exocyclic P-S bonds. 

Nucleophilic Attack on Oxygen or Sulphur.— The reactions of two bicyclic phosphoramidites, (35) and (36), with diethyl peroxide or diphenyl disulphide have been studied. Based on ring-strain arguments, the higher rate of (35) with diethyl peroxide, and of (36) with diphenyl disulphide, is considered support for a biphilic insertion mechanism for the addition of diethyl peroxide, and an... 

Kinetic data, activation parameters, and Hammett p values have been reported for the reaction of trico-ordinate phosphorus compounds with diphenyl trisulphide, and the results discussed in terms of a biphilic mechanism.A dithymidyl 3 -S phosphorothioate (33) has been prepared from a thymidin-3 -yl disulphide and a dimethyl 5 -thymidyl phosphite. ... 

When the platinum nucleophilicity scale was first proposed it was implied that one np, scale was applicable to all substrates and that plots of logk2 against npt°(Y) were linear, taking the form log 10 2 = S np, (Y) + C, where S is termed the nucleophilic discrimination factor of the substrate and C its intrinsic reactivity. Discussions of mechanism based on a comparison of nucleophilic discrimination factors are frequently encountered. Nucleophiles that do not retain their positions in the nucleophilicity scale, e.g. NO2", SeCN and SC(NH2)2, were termed biphilic by Cattahni since their behaviour could be explained by their n-acceptor properties. When the Pt reaction centre had a greater n-basicity than the standard complex (for example a smaller effective nuclear charge) the substrate was more reactive than predicted and vice versa. This concept had been deduced some years earlier by Bosnich from his work with octahedral Ru complexes... 

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