Biphilic Reactions

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 

Treatment of phosphorus trichloride with isoprene in the presence of acetone leads to 1-chlorophospholen 1-oxides (33).33 Evidence has been presented that the diene reacts first with the trichloride to produce (34), which then reacts with acetone.33 l-Bromo-3,4-dimethyl-A3-phospholen (35) does not form a spiro-compound with 2,3-dimethylbuta-l,3-diene, although the bisphospholen derivative (36) has been isolated after hydrolytic work-up.34 

Diphenylphosphinoisocyanate (37) undergoes a 1,3-dipolar addition to dimethyl acetylenedicarboxylate, but the adduct (38) could not be isolated in a pure state, and was further hydrolysed to (39).36 

Moedritzer, Synth. React. Inorg. Metal-Org. Chem., 1975, 5, 299. 

Chlorodi-t-butylphosphine (42) reacts with benzoates as shown, and evidence has been presented for the initial nucleophilic role of (42), with phosphorus attacking at 

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 

Bellucci, G. Ingrosso, F. Marioni, A. Marsili, and I. Morelli, Gazzetta, 91A, 104, 69. V. N. Volkovitskii, I. L. Knunyants, and E. G. Bykhovskaya, Zhur. Vsesoyuz. Khim. 

The phosphine (27) reacts as shown with chloral and with substituted 

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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 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 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... 

Diethyl disulfide is inserted by phenylphosphene (74), apparently involving a biphilic reaction. 

The sulfur abstraction from AT-alkylthiophthalimides (103) may be accomplished using a soft nucleophile such as (Mc2N)3P. A biphilic reaction occurs. 

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. 

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. " ... 

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. 

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... 

Before discussing the various aspects of phosphorus chemistry, one should keep in mind that the trivalent phosphorus compounds frequently exhibit biphilicity (2), as shown in the following reactions. 

It is plausible that the following reactions are biphilic rather than direct substitutive reactions. Both hardness and steric factors favor N-P bond formation in the last example. 

Semipolar oxygen may be removed by P(III) derivatives. However, the opposite reactivity order of these reagents to their usual nucleophilicities suggests that a biphilic process (78) is involved in the reaction. The two reactivity... 

There are two types of P(V) compounds, i.e., the pentacovalent and the ionic phosphonium salts. The most famUiar outcome of the attack at a pentacovalent phosphorus atom by nucleophiles is substitutive fragmentation. On the other hand, there are numerous ways for a nucleophile to attack R4P compounds direct Sn2 displacement, simple addition, and addition-elimination. Many reactions, especially the biphilic processes, involve formation of R4P compounds followed by a counterion-initiated decomposition. The Arbuzov and Perkov reactions are representative. 

The a-(alkylthio)ketones are dehydrogenated by phenylsulfenyl chloride (54). In this case chlorine transfer between the sulfur atoms of the reactants could be the initial and crucial step. There is little evidence asserting either a biphilic course or direct displacement at S during reaction of thiols with sulfenyl chlorides and acylsulfenyl chlorides (55). Both are soft interactions. 

A sulfur equivalent of the Perkov reaction has been reported (160). Whether the sulfinate ion attacks on the halogen (biphilic) or directly on the carbonyl oxygen remains to be clarified. 

The phosphorus atom can show biphilicity and be both nucleophilic and electrophilic in the same reaction, as, for example, in the formation of phosphoryl compounds RjI O, ylids R3P=CR2 and phosphinimines R3P=NR. In these reactions the P atom is nucleophilic in forming a bonds, but at the same time it shows electrophilic behaviour in accepting electrons by back donation to form n bonds. 

The failure to observe any radical products 7 or acetone) in the decomposition of 6 allows us to rule out a mec Hanism for the anchimerically accelerated homolysis of 3 which begins with a biphilic insertion of sulfenyl sulfur into the 0-0 bond of 3 to yield 6 directly with 6 serving as the precursor to radical products. "Analogous bipliilic insertion reactions have been used to produce sulfuranes from the reaction between sulfoxylates and dioxetanes (18). 

Prompted by earlier results which indicated that the rate law for substitution of Cl in square-planar rran -[Pt(PEt3)2(R)Cl] (R = phenyl, jp-tolyl, or mesityl) complexes included an associative as well as the normal dissociative path only in the case of substitution by strong biphilic ligands (e.g. CN, SeCN ), Ricevuto et al. have re-examined the reaction with weakly nucleophilic pyridine in methanol ... 

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