Dicoordinated phosphorus compounds

Synthesis of New Dicoordinated Phosphorus Compounds with a P(III)=N Bond... 

In recent years, more and more varied dicoordinated phosphorus compounds have been isolated this has meant the appearance of a new and very interesting branch of phosphorus chemistry. 

Although the number of dicoordinated phosphorus compounds with a -Pxix=C bond is fairly large, compounds with a-Pxn=N bond are still few in number since only one heterocycle, namely 1,2,4,3-triazaphosphole ( 1 ), and two types of acyclic compounds, namely the diazaphosphapropenes (2) and the tetrazaphosphapentenes ( ), are known ... 

These oligomers, when heated in various solvents are in equilibrium with the monomer a dicoordinated phosphorus compound ... 

The percentage of dicoordinated phosphorus compound present depends equally on the substituent R, on the solvent and on the temperature. It has been possible to prepare these oligomers from monosubstituted aliphatic or aromatic diamines, from amidrazones, from semicarbazides, from substituted thiosemicarbazides, from 2-aminophenol, from 2-aminothiophenol and even from the monoimines of orthophenylediamine (Table I). It seems that these oligomers are generally the thermodynamic products of the reaction, except perhaps for the amidrazones, and the 1-phenyl semicarbazide in which case they would be kinetic products (the thermodynamic products being the triazaphospholes). 

If these oligomers are made to react with Lewis acids (BF, AICI3, ZnC etc...) the dicoordinated phosphorus compound is obtained quantitatively l.a. 

These compounds react with the amines to give the corresponding dicoordinated phosphorus compounds, a number of which may remain in the free state for a few hours before once again oligomerizing Particular notice should be given to the synthesis of the diaza-phospholes... 

It is known that dicoordinated phosphorus compounds can be obtained by the action of Lewis bases, such as triethylamine or DBU, on chlorophosphines ... 

The recorded shifts fall in the upper part of the range normally associated with neutral dicoordinated phosphorus compounds for comparison, in compoimd XXXV the... 

Si-P bonds in compounds with tetracoordinate silicon and dicoordinate phosphorus atoms... 

The chemistry of phosphorus compounds has shown a steady development in the last 30 years. The most interesting results can be related to those systems having 7t-elec-trons in the broadest sense. Recent books [1-3] and review papers [4,5] have appeared on the topic. Particularly noteworthy is the statement summarized by the title of the Mathey-Nixon-Dillon book Phosphorus The Carbon Copy [2], which emphasizes the analogy between compounds of multiply bonded dicoordinate phosphorus (r>v. -P, this notation has been used in [1]) and the unsaturated carbon (see Scheme 1). 

In the synthesis of specially substituted methylene diphosphines, made from secondary phosphines and carbonyl derivatives (7), a carbenium ion adjacent to trivalent phosphorus as the transition state has been discussed. The transfer of this reaction principle to primary phosphines and suitable carbonyl compound revealed a further pathway to derivatives of dicoordinated phosphorus (8). Aromatic phosphines react with carboxylic acid amide acetals under elimination of alcohol giving dialkylamino-alkylidene phosphines (Scheme 5). A modification of the synthesis... 

Ring expansion reactions Compound 91 was nucleophilically attacked at the dicoordinate phosphorus center when treated with -butyliso-cyanide in CH2CI2 at -50 °C. Ring enlargement of transient 165 afforded product 166, which was isolated as yellow crystals in 70% yield (Equation 23) <1994CC337>. 

The 177-1,2-azaphospholes are colorless to yellow solids or oils and are stable at ambient temperature <20008417, 1998ICA(270)273, 2003ZNB44>. Most of the reactions reported so far involve the dicoordinated phosphorus atom, which represents the reactive center of the molecule. l,3-Di(fet/-butyl)-5-phenyl-177-l,2-diazaphosphole reacts under mild conditions with alkyl triflates CF38O3R (R = Me, Et) to afford the P-alkylated 1,2-azaphospholium compounds la and lb in quantitative yields. With an equimolar amount of iron nonacarbonyl, the Tj -complex 2 was selectively formed in 63% yield (Scheme 1) <2002EJ01664>. 

A further method for the synthesis of cyclic compounds in the phosphinic acid series, and investigated within the last decade, is the clearly not unrelated cheletropic reaction which takes place between alka-1,3-dienes and phosphenium salts. The latter are based on dicoordinate phosphorus, [R R P ], the commonly encountered counter ion being the tetrachloroaluminate anion. Such salts are obtained in situ through the interaction of AICI3 and a hosphorus(III) chloride R R PCl, for which R = Cl, R = R2N, or R = R =... 

There are only five known X-ray crystal structures of compounds containing a tetracoordinate silicon atom that is bonded to a dicoordinate phosphorus atom. In three, 128-130, the phosphorus atom is singly bonded to silicon and doubly bonded to eitha- carbon or phosphorus atoms while in the remaining two, 131 and 132, the phosphorus atom is singly... 

The reaction of phosphorus trichloride with tgrt-bufylamine was reported to give a dicoordinate phosph(III)azene Bu N=P-NHBu which can be deprotonated to the [Bu NPNBu ] anion. The crystal structure ofK[Bu NPNBu ] has been determined. The anion has also been found in a gallium and a lithium complex. In monomeric form, the [RN P NMes] anion can be obtained when R = mesityl (Mes = 2,4,6-Me3C6H2), tert-butyl and 1-adamantanyl, as dimeric lithium ring compounds (3) ... 

For two of the compounds of Table 3, aromaticity indices were derived from the molecular dimensions (1,3-oxaphosphole 38, 1,3-thiaphosphole 55). According to them, aromaticity is not greatly reduced if dicoordinate nitrogen in a five-membered heterocycle is replaced by phosphorus <90T5697>. 

This chapter will be limited to the preparation and properties of compounds (2) with one or two P—C bonds, since only these compounds contain functional groups of phosphorus in the sense of the Patai series. Thus, important classes of tervalent phosphorus acid derivatives with three electronegative groups, e.g. phosphites (3), tris(dialkylamino)phos-phines (4) and phosphoramidites (5), will only be included for illustration of a reaction or property which is common to tervalent phosphorus acid derivatives but has not been sufficiently studied for compounds with a P—C bond. The chapter will cover the highly reactive, dicoordinated derivatives 6, but not diphosphines 1 (X = PR2) or diphosphenes 6 (X = PR). 

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