Phosphorus dicoordinated

The iminophosphenium cation was also of interest for more physical investigations. It was noted to be a stable entity in gas phase experiments [52], the parameters were investigated in detail [53] and a systematic study of the nucleophilic addition of CH, NH and OH bonds was performed [54] with a concomitant interpretation of the chemical shifts (at the dicoordinate phosphorus centres). The latter authors also confirmed the loose interaction of a triphenylphosphine with the iminophosphenium cation (PP = 2.625 A). 

The following serves as one more example of the synthesis of a P,B-containing heterocycle (127) with a dicoordinated phosphorus atom [Eq. 

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). 

Recent Developments in the Chemistry of Dicoordinated Phosphorus Radicals and Cations... 

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... 

The application of further suitable carbenium salts offers a wide field of synthetic routes to derivatives of dicoordinated phosphorus. 

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 indole (78) and pyrrole (79) derivatives, containing phosphabenzene with a dicoordinated phosphorus atom as substituent, were obtained [76] in the reaction of indole- and pyrrole-substituted pyrrylium salts with trimethylolphosphine ... 

Dicoordinate phosphorus is present in the anion [RN-P-NR], which can be formulated with the aid of two resonance structures the anion can be also isolated in dimeric form, containing a P2N2 ring (Scheme 3) ... 

A phosphorus analog of benzimidazole (2), containing dicoordinate phosphorus, is mentioned as the reaction product between triethylphosphite, P(OEt)3, and ortho-phenylenediamine. ... 

The silylated aminoiminophosphine (MesSi)2N P=N SiMe3 reacts with anhydrons alnmtnum chloride at 40 °C with elimination of Me3SiCl to form a dicoordinate phosphorus-nitrogen ligand, in a four-membered chelate ring complex. Anhydrous aluminum chloride extracts a chlorine ion from [C1PNR]2 to form a cyclic cation with a dicoordinated... 

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

This difference between the a - and rf -P-containing rings may be rationalized by the nature of the orbitals involved in 7t-delocalization. In diphosphirenylium ions I with dicoordinate phosphorus atoms, these are one 2p(C) and two 3p(P) orbitals. In ions of type IV one 2p(C), one 3p(P), and one a (PX) orbital have to be considered for the cyclic dilocalization of two 7t-electrons. It is obvious that the Hiickel-type three-orbital two-electron interaction typical for the cyclopropenium cation is more favored in diphosphirenylium ions I than in the related diphosphir-enium systems IV. 

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>. 

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