2-Alkylidenephosphiranes

Abstract

Three stable alkylidenephosphiranes have been synthesized from the addition of the terminal phosphinidene complex Ph-P-W(CO) 5 to allene, 1,1-dimethylallene, and tetramethylallene. Isopropylidenephosphirane 16b was characterized by a single-crystal X-ray structure determination. Demetalation of its W(CO) 5 group provides the uncomplexed compound. The addition reaction with tetramethylallene also yields vinylphosphirane epimers, which rearrange to phospholene 20. Ab initio MP2/6-31G* structures and energies are presented for the parent uncomplexed methylenephosphirane and its dimethyl derivatives.Ring strain augmented by the presence of an exocyclic double bond makes the heteroatom analogues of methylenecyclopropanes (1) fascinating compounds. 1,2 Strain underlies, for example, the biradical interconversion of the valence isomers 2 and 3, which consequently have received particular attention. [3][4][5] While synthesizing such systems is inherently challenging, their presence as reactive and versatile intermediates has been well established. Expectantly, the stability of the methylene derivatives of the aziridines, oxiranes, and thiiranes increases with bulky substituents on the heteroatom, ring, and/or double bond. These sterically congested systems are typically generated via ring closure reactions, either thermally or photochemically induced, rather then by, e.g., the epoxidation of or the nitrene addition to allenes. 1,6 Our interest in these heterocycles and their even more strained higher homologues, the radialenes 4, 7 arose because of the noticeable elusive phosphorus analogues. 8Only recently did Yoshifuji et al. 9 report the first synthesis of a congested methylenephosphirane, 5, via the addition of dichlorocarbene to a sterically protected 1-phosphaallene (eq 1). No structural details were provided. Subsequently, Manz and Maas 10 reported two similarly congested methylenephosphiranes 6a,b. These stable compounds were obtained from thermal N 2 -extrusion of diazaphosphole precursors, thereby extending the method explored in detail by Quast and coworkers 11 for the syntheses of the O-, S-, and N-analogues. Product formation is presumed to occur via ring closure of the reactive 2-phosphacumulene intermediates (eq 2). The yields are modest due to competing biradical H-abstractions. The difference between the ab initio geometry of the parent methylenephosphirane, C 3 H 5 P (7), 12 and the single-crystal X-ray structure of 6a emphasizes the effect of steric crowding (see also later). 10 These two synthetic routes are, however, rather limited in scope due to the high sensitivity of phosphaallene and 2-phosphacumulenes. 8 A third route has been attempted, Penn, R. E.; Ennis, M. D.; Owens, T. A.; Yu, S. L. J. Am. Chem. Soc. 1978, 100, 7436. Jongejan, E.; Buys, Th. S. V.; Steinberg, H.; de Boer, Th. Behr, H.; Adiwidjaja, G.; Tangerman, A.; Lammerink, B. H. M.; Zwanenburg, B.

Electrophilic Terminal-Phosphinidene Complexes: Versatile Phosphorus Analogues of Singlet Carbenes

“…Using substituted styrenes as a probe, they have measured the following Hammett reaction constants 1 : À 0. 76 5 ] towards a range of Me-substituted olefins produced somewhat erratic results that showed no predictable trends [68].…”

Phospha‐Organic Chemistry: Panorama and Perspectives

“…Another singlet biradical based upon a fourmembered P 2 C 2 ring (23) has been prepared by the Main synthesis: [158] Main reactions: alkenes: [155] conjugated dienes: [155,159] [ 160] allenes: [161,162] R = Me alkynes: [156] Scheme 2. Main reactions of [RPÀW(CO) 5 ].…”

Phospha[3]radialenes. Syntheses, Structures, Strain Energies, and Reactions

“…5 Recently, we reported on the synthesis and properties of phosphiranes containing one 6 and two spiroannelated rings 7 and those having one exocyclic double bond. 8 In the present study, we extend this work to phospha [3]radialenes and also report on new diphospha [4]radialenes.…”

“…10 and even the less electrophilic i Pr 2 NPFe(CO) 4 also react with allenes. 18 An X-ray crystal structure was reported not only for methylenephosphirane 12 8 but also for the strained phosphaspiropentane 13 6 and phospha [3]triagulene 14, 7 which result from the respective addition to alkylidenecyclopropane and bicyclopropylidene (Scheme 1). These compounds are surprisingly stable despite their significant strain energies (SE).…”