Role of the conformation in the reactivity of 1,3‐diphosphapropenes

Abstract

The symmetrical and unsymmetrical I ,3-diphosphapropenes 3 and 4 were obtained from the cowesponding diphosphiranes 1 and 2. The chemical behavior of these compounds has been studied. Phosphoniumphosphaalkenes 7a and 10a have been obtained in the reactions with aluminium trichloride. Whereas the symmetrical diphosphaallene 13 can be obtained by reaction of 1 or 3 with lithio compounds, the unsymmetrical diphosphaallene 14 cannot be prepared by a similar route. Reduction of 3a and 4a (obtained with a different conformation) by lithium aluminum hydride afforded phosphino-phosphaalkenes 17a and 18a (with a similar conformation); further dehydrochlorination with amines led to the symmetrical and unsymmetrical diphosphaallenes 13 and 14, respectively. The formation of allenes strongly depends on the conformation of the starting diphosphapropenes.

Heavy Allenes and Cumulenes ECE‘ and ECCE‘ (E = P, As, Si, Ge, Sn; E‘ = C, N, P, As, O, S)

“…114 cannot be obtained from diphosphirane 115 (prepared from diphosphene ArPdPTsi and CCl 2 ) 119 nor from 116 by reaction with lithium compounds as its symmetrical isologue ArPdCdPAr since only unidentified products are obtained in these cases. 118 A mechanistic study shows that a suitable conformation of the diphosphapropene is necessary for the formation of the diphosphaallene. Reduction of 116 to 113 involves a change in the conformation, as proved by the great variation of 2 J PP from 457 to 89 Hz.…”

“…Thus, it seems that the allene 114 can be prepared only from a diphosphapropene in the suitable conformation 113 close to that of allene. 118…”

“…The 2,3-dihalodiphosphapropenes 120 obtained by photolysis of the corresponding 3,3-dihalo-1,2-diphosphiranes 121 are good precursors of the diphosphaallene 111 by reaction with methyllithium in Et 2 O 118,119 (eq 39). The mechanism of ring opening of diphosphiranes 121 (thermal, 121 photolytic, 122 with Grignard reagents, 123 or with Lewis acids 124 ) and the stereochemistry of this reaction, leading to 2,3-dihalo-1,3-diphosphapropenes 120, have been very well studied by Koenig.…”

Group 14 and 15 Heteroallenes ECC and ECE‘

“…1 σ 2 ,3 σ 2 -Diphosphaallenes. The preparation of stable 1σ 2 ,3σ 2 -diphosphaallenes can be achieved by starting from differently substituted 1,3-diphosphapropenes by HX abstraction with bases, 75b, dehalogenation, lithium silanolate elimination, 75a,b or photochemical extrusion of carbon disulfide . Peterson olefination-like reactions involving a phosphaketene 75a or intermediate phosphathioketene and ring-opening reactions of functionalized diphosphiranes , also have provided stable 1σ 2 ,3σ 2 -diphosphaallenes (Scheme ).…”

New stable 2,3-dichloro,1,3-diphosphapropenes; synthesis and characterization

“…The chemistry of unsaturated compounds containing the phosphaalkenyl -P=C< moiety maintains its scientific interest due to the applications of these compounds, especially in obtaining coordinative compounds with applications in catalysis. 1,2 If the symmetric carbodiphosphiranes with the general formula R 3 P=C=PR 3 (where R is a bulky organic group) are well represented in the literature, [3][4][5][6][7] the unsymmetrical derivatives containing a bicoordinated trivalent and a tricoordinated pentavalent phosphorus atom namely diphosphapropenes containing the P=C-P(=E) backbone (when E is a group 16 element) are less studied. 8 Almost unknown remain 2,3-dihalogenated,1,3-diphosphapropenic derivatives, which represent effective building blocks for the synthesis of new organometallic and coordination compounds due to multiple reaction centers: the electron lone pairs, the halogen atoms and also the P=C double bond.…”