Phosphirenes, Phospholes, and Phosphinines

A study of the reactivity of l-chloro-lH-phosphirenes 342 with nucleophiles has shown that the chlorine is easily replaced. Ab initio calculations suggest that IH-phosphirenes invert their configuration at phosphorus by a rotation of the PX group above the C2 moiety, rather than by the more usual trigonal inversion pathway involving a C2v-transition state. Related calculations on the aromaticity of IH-phosphirenium cations 343 have shown that the a ABMO associated with the P-X bond acts like an empty p-orbital. A facile route to the phosphirenium salts 344 is afforded by the reaction of the phosphiranium salt 345 with alkynes. The P -azaphosphirene system 346 has been obtained from the reaction of an iminophosphene with terminal alkynes.  

A theoretical study of the Diels-Alder reactions between 1,3-butadiene and, respectively, cyclopentadiene and 2H-phosphole, has revealed a remarkable similarity between the two reactions. Further studies of photocycloaddition reactions of phosphole moieties have also been reported. Transition metal complexes of phospholide anions continue to attract attention, and in particular the chemistry of phosphaferrocene systems remains a major interest . The past year has also seen significant activity in the chemistry of di- and tri-phospholes, related polyphospholide anions, and also heterodiphosphole systems. Routes have been developed to the diphosphonio-l,2-diphospholes 356, 

Yasuike, T. Kiharada, J. Kurita and T. Tsuchiya, Chem. Commm., 1996,2183. 

Cereghetti, R. Schmid, P. Schonholzer and A. Rageot, Tetrahedron Lett., 1996, 37, 5343. 

Benincori, E. Brenna, F. Sannicolo, L. Trimarco, P. Antognazza, E. Cesarotti, 

A new approach to the synthesis of 1-chlorophosphirenes is afforded by the reaction of the phosphirane complex (309), presumably acting as a source of a phosphinidene, with disubstituted alkynes to give the complexed P-aminophos-phirenes (310), which, on treatment with hydrogen chloride, are converted to the related complexed 1-chlorophosphirenes (311). A key step is their selective 

The influence of the heteroatom on the structure of a series of dinaphtho-fused five membered potentially aromatic ring systems (317), including the phosphorus and arsenic systems, has been studied by crystallographic techniques. A theoretical study has shown that the incorporation of two o, X -phosphorus atoms into the phosphole ring system decreases the ring strain and significantly lowers the inversion barrier about the phosphole pyramidal phosphorus. Pyramidalisation at phosphorus in phospholes has been shown to increase on 

A theoretical approach has been used to compare the proton affinities of phospha-, arsa-, and stiba-benzenes with that of pyridine, and other simpler organo-group 15 systems. The electronic excitation spectra of pyridine and phosphabenzene have also been studied by theoretical methods. A route to the 

Enders, T. Berg, G. Raabe, and J. Runsink, Helv. Chim. Acta, 1996,79,118. 

Guillaneux, A. Masson-Szymczak, F. Rebiere, 

The electronic structure and degree of aromaticity of 1,3-azaphospholes has received attention from the theoreticians. An alternative synthesis of the phospha-indolizine system (201), from the reaction of pyridinium salts with phosphorus trichloride, has undergone further development and has also been applied in the synthesis of fused 1,4,2-diazaphospholes, e.g., (234) , 2 (235). The 1,2,4,3-triazaphosphole system (236) has been isolated as an 

Yoshikawa, N. Yamamoto, M. Murata, K. Awano, T. Morimoto, and K. Achiwa, Tetrahedron Asymmetry, 1992,3, 13. 

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The addition of monochlorocarbenes to phospha-alkynes results initially in the formation of the transient 2H-phosphirenes (231), which then undergo rearrangement, with migration of chlorine from carbon to phosphorus, to give the stable P-halo-lH-phosphirenes (232). Unlike their nitrogen analogues, the latter cannot 

Metallation of phenyl isocyanide with t-butyl1ithium in the presence of TMEDA generates a difunctional reagent which, on treatment with dichlorophosphines, gives the 1,3-benzazaphosphole system (237). Flash vacuum pyrolysis of (237 R=Bu ) results in the formation of the lH-1,3-benzazaphosphole system (238). A route to the 3-hydroxy-l,2,4 -diazaphosphole (239) has been developed. This 

A simple one-pot synthesis of 2-chlorophosphinines (245) is afforded by the cycloaddition reactions with dienes of the phospha-alkene, ClP=CCl2, (generated by the action of triethylamine on dichloromethyldichlorophosphine). A route to 

YamashoJi, T.Matsushita, M.Tanaka, T.Shono, and M. Wada, Polyhedron, 

Tsumaki, H.Suzuki and N.Matsura, Jpn. Kokai Tokkyo Koho 62 234 089 (Chem. Abstr., 1988, 109, 54 956). 

Further progress has been made in the chemistry of 1,3-azaphospholes and related systems. Heinicke s group has developed a route to the new bulky A-substituted 1,3-benzazaphospholes (200). These workers have also carried out studies of the C-lithiation and subsequent phosphination of these systems. The first examples of pyrido[6]-annelated azaphosp-holes (201) have been prepared and a study of diastereo-and regio-se-lective Diels-Alder reactions of the 2-phosphaindolizines (202) has been described. Various alkali metal and samarium complexes of 1,2,4-diazaphospholide anions (203) have also been characterised. 

The synthesis and reactivity of the six membered ring, potentially aromatic, phosphinine system has received further attention. The first examples of a new class of axially chiral phosphorus ligands, the atropisomeric phosphinines (204), have been prepared and isolated in an enantiopure state. Also reported are syntheses of the wide-bite-angle diphosphinine (205) and the diphosphinine analogue of terpyridine (206), a new class of neutral, 7i-acceptor PNP-pincer ligand. Studies of the reactivity of phosphinines include the first observations of protonation, alkylation and silylation in systems usually viewed as extremely weak bases, the proto-desilylation of 2,6-disubstituted silylphosphinines, a theoretical study of 

Laitila, M. Haukka and J. Pursiainen, Eur. J. Inorg. 

Iwasawa, T. Kamei, S. Watanabe, M. Nishiuchi and Y. Kawamura, Tetrahedron Lett., 2008, 49, 7430. 

Phospholes bearing additional heteroatoms other than phosphorus have also been the subject of further study. Cycloaddition reactions of heterophospholes have received a theoretical treatment and these reactions have also been reviewed. Improvements in the synthesis of fused 1,3-azaphospholes via the reactions of N-alkyl-isoquinolinium salts with phosphorus trichloride have been described and their reactivity towards cycloaddition studied. New fused 

3- diazaphospholes, have also been reported. The phosphonio-l,2,4-di-azaphospholide (297) has been characterised and further studies of the coordination chemistry of 17/-l,3-benzazaphospholes, leading to complexes of the related benzazaphospholide anion, have been described. Routes to 

4- thiadiphospholes and their selenium and tellurium analogues (300) have received further study.  

Finally, it is of considerable interest to note the results of a theoretical treatment of the extent to which nine-membered monocycles can be aromatic, and which concludes that the phosphonide anion (309), as yet unknown, favours planar C2v symmetry.  

Baiget, M. Bouslikhane, J. Escudie, G.C. Nemes, I. Silaghi-Dumitrescu and L. Silaghi-Dumitrescu, Phosphorus, Sulfur, Silicon, 2003, 178, 1949. 

Trapping electrophilic phosphinidene complexes with alkynes has been used in the synthesis of the new phosphirene systems (341) and (342). In the latter, the phosphirene rings are coplanar and conjugated. The diphosphinines (343) are formed unexpectedly in a head to head dimerisation of l.ff-phosphir- 

The chemistry of the phosphole system, and that of related heterophos-pholes, has continued to be an active area. Treatment of unsymmetrical zirconacyclopentadiene reagents with phenyldichlorophosphine provides a route to the unsymmetrical phospholes (349). Organozirconium intermediates have also been used in routes to electropolymerisable heteroaryl-substituted phospholes, e.g. (350), and the bridged diphospholes (351). Routes 

Interest has continued in the extent to which factors affecting the planarity of the trivalent phosphorus atom have a bearing on the aromaticity and other properties of the phosphole ring system, and a review has appeared. A study of the coordination chemistry of phospholes bearing a sterically bulky substituent at phosphorus has shown that coordination to platinum results in increased pyramidality at phosphorus. In the same vein, an ab initio theoretical study of the triphosphole (357) has shown that the steric interac- 

The study of complexes of anionic phospholyl systems continues to develop. Heating l-t-butyl-3,4-dimethylphosphole in the presence of a pinene-fused cyclopentadienyl iron carbonyl complex results in the formation of the chiral 

Pickaert, M. Cesario, L. Douce and R. Ziessel, Chem. Commun., 2000,1125. 

Interest in potentially aromatic heterocyclic systems has continued at a similar level to the previous year, with most work again relating to the chemistry of fused ring phospholes and phospholyl anions. Activity in the phosphirene area, however, has again been minimal, the only significant 

Interest in the synthesis and reaetivity of the six-membered, potentially aromatic, , -phosphinine ring system has also continued, but at a fairly 

Sasaki, M. Izawa and M. Yoshifuji, Phosphorus, Sulfur Silicon Relat. Elem., 2014, 189, 1207. 

Noel-Duchesneau, N. Lugan, G. Lavigne, A. Labande and V. Cesar, Organometallics, 2014, 33, 5085. 

Suarez-Meneses, E. Bonilla-Reyes, E. A. Ble-Gonzalez, M. C. Ortega-Alfaro, R. A. Toseano, A. Cordero-Vargas and J. G. Lopez-Cortes, Tetrahedron, 2014, 70, 1422. 

Interest in potentially aromatic heterocyclic systems has continued at a similar level to the previous year, with most work again relating to the chemistry of fused ring phospholes and phospholyl anions. Activity in the phosphirene area, however, has again been minimal in the past year. Streubel s group has studied the thermal reactions of 2ff-phosphirene complexes (124) with primary and secondary amine deriwitives and alcohols, leading to the formation of aminophosphine and alkoryphosphine complexes, so as to explore the boundaries between complexed phosphanide, phosphinidenoid and transient phosphinidene intermediates. 

The chemistry of phospholide and related anions and their metallocene complexes also continues to generate interest. Of note is a commentary on the impact of Marianne Baudler s work in 1987 leading to the discovery of the pentaphosphacyclopentadienide ion, Recent 

Interest in the synthesis and reactivity of the six-membered, potentially aromatic, phosphinine ring system has also continued, but at a much lower level than in recent years. New synthetic work includes the application of the pyrylium salt route to phosphinine synthesis, this time starting from pyrylium salts bearing chiral substituents to give the related chiral phosphinines, and the development of new routes to the 2-phosphanaphthalene (137) ° and the phosphinine-2-aldehyde (138). Also reported is an approach to the synthesis of l,2-dihydro-l,4,2-benzo-diazaphosphinines, cationic gold(I) complexes of 2,4,6-tri-t-butyl-l,3,5-triphosphabenzene, and the synthesis of some X -phosphinines from phosphonium-iodonium ylides.  

MorisaM and Y. Chujo in Polymeric Chiral Catalyst Design and Chiral Polymer Synthesis , Ed. S. Itsuno, John Wiley Sons, Inc. Hoboken, NJ, 

Schaarschmidt, T. Riiffer and H. Lang, Dalton Trans., 2012, 41, 5377. 

The reactions of P-halophospha-alkenes with carbenes provide a new route to 1-chloro-lH-phosphirines (181). Such compounds are highly reactive, and a study of nucleophilic displacement reactions at phosphorus has been facilitated by preparation of the related P-W(CO)5 complexes.The first pentacoordinate systems derived from phosphirenes, (182), have been formed in the reactions of P-halo- or P-cyano-phosphirenes with tetrachloro-o-quinone. Evidence has been presented for the rearrangement of P-chlorophosphirenium ions (183) to the vinylphosphenium ions (184) 

A new approach to the phosphole ring system is provided by the reaction of terminal phosphinidene complexes with electron rich 

Cycloaddition of diazomethane to phospholes is a key step in the synthesis of the homophospholes (189). A simple route to phospholyl anions is offered by the reaction of the zircona-cyclopentadienide (190) with phosphorus trichloride, giving the intermediate chlorophosphole (191) which, on treatment with lithium metal, gives the related phospholyl derivative (192).  

The characterisation of phospholyl complexes has continued to attract attention.The reactions of bridging diphenyl-phosphido ligands with alkynes has led to the synthesis of 

TT-complexes involving quaternized phospholes. Treatment of the dilithiophosphide reagent (193) with carbon dioxide in the presence of trimethylsilyl chloride results in the formation of the benzodiphosphole (194). A related reaction of the diphosphide (193) with pivaloyl chloride gives the benzodiphospholyl complex (195), which on subsequent treatment with alkyl halides is converted to the benzodiphospholes (196). A new route to the 1,3-diphospholide anion (197) has been developed, and applied in 

The biphosphole (370) has been obtained in enantiomerically pure form by spontaneous resolution in the crystallisation of a racemic mixture, without the use of chiral auxiliaries. A new approach to -functionalised phospholes is afforded by metallation at a methyl group of l-phenyl-3,4-dimethylphosphole(in which both phosphorus and the diene unit are protected by coordination to an iron carbonyl acceptor), followed by treatment with electrophiles, to give C-substituted products, e.g., (371). Copper(II) oxidation of the intermediate lith-iomethyl derivative leads to the formation of bridged systems, e.g., (372).  

The coordination chemistry of phosphinines, including their polydentate and macrocyclic derivatives, has been reviewed. Valence isomerism of phosphinines has continued to attract attention. The structures, energetics, and vibrational spectra of valence isomers of the parent system, phosphinine, (CH)sP, have been studied by theoretical techniques. Phosphatriafulvenes (390) readily react with kinetically-stabilised phosphaalkynes to give, initially, 1,3-diphos-phinines, e.g., (391), which then undergo valence isomerism on heating in toluene 

Interest in X, -phosphinine systems has continued, the aromatic or ylidic state of these systems now having been evaluated using various magnetic property criteria. Much depends on the nature of the substituents at phosphorus, the more electron-withdrawing, the more aromatic is the molecule, but no evidence of d-orbital participation was found. A route to the X -diphosphinine (400) has been described. Studies of the protonation of the X. -triphosphinine (401) have also appeared.  

Clark and L. Jain, Indian. J. Chem., Sect A , Inorg., Bio-inorg., Phys., Theor. Anal. Chem., 2001,40A, 135. 

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