Radical synthesis of trialkyl, triaryl, trisilyl and tristannyl phosphines from P4

Abstract

A reaction scheme has been devised according to 3 RX + 3 Ti(III) + 0.25 P 4 → PR 3 + 3 XTi(IV) wherein RX = PhBr, CyBr, Me 3 SiI, or Ph 3 SnCl with contrasting results in the case of more hindered RX; the scheme accomplishes direct radical functionalization of white phosphorus without intermediacy of PCl 3 .It is known that P 4 , white phosphorus, has excellent properties as a trap for carboncentered radicals in solution and under the mild conditions that are typical for organic synthesis. The most prominent example of this was the demonstration that phosphonic acids may be prepared from corresponding carboxylic acids by way of O-acyl derivatives of N-hydroxy-2-thiopyridone (Barton PTOC esters). 1 The latter provide carbon centered radicals in an oxygen-initiated chain reaction, and these are consumed upon combination with P 4 as the critical P-C bond-forming event; upon oxidative workup, any remaining P-P bonds are cleaved and the phosphonic acid RP(O)(OH) 2 is the end product. 2 It is also known that P-P bonds other than those in P 4 may serve as traps for organic radicals. This has been shown by Sato et al. in a scheme for radical phosphination of organic halides wherein ArX serves as a source of Ar· which in turn attacks For our part, we have previously shown that the three-coordinate titanium(III) complex Ti(N[ t Bu]Ar) 3 (Ar = 3,5-C 6 H 3 Me 2 ), 1, is a potent halogen-atom abstractor, capable of abstracting X· (X = Cl, Br, or I) from various donor molecules at room temperature or below, in aprotic organic media (Figure 1). With the present work, we sought to develop

The atomic level mechanism of white phosphorous demolition by di-iodine

“…21 The latter feature has never been observed by us, excluding such a possibility in our mechanism (vide infra). In other cases, the reaction is promoted by organic radicals 22 including a transition metal fragment such as Cp(CO) 2 Fe, originating from the homolysis of its dimeric precursor and carrying an unpaired spin at the d 7 metal. 23 In this regard, other authors have remarked how an unassisted P 4 + I 2 reaction excludes the access to any radical species.…”

Functionalization of P4 in the coordination sphere of coinage metal cations

“…Controlling direct P-C bond formation using P 4 as starting material is of interest in avoiding chlorinated intermediates, such as PCl 3 , for the production of organophosphorus compounds. Yet this task is extremely challenging due to the highly reactive nature of the P 4 tetrahedron.…”

“…Yet this task is extremely challenging due to the highly reactive nature of the P 4 tetrahedron. 1 Currently, several selective methods have been developed, like the use of ambiphilic carbenes pioneered by the group of Bertrand, 2 and the metal-mediated radical functionalization of P 4 reported by Scheer et al (A; R = Cp R , Scheme 1) 3 as well as by Cummins and co-workers (R = Dmp), 4 who also demonstrated facile P-functionalization chemistry by embedding photochemically generated P 2 fragments into organic frameworks (B). 5 In contrast, conventional methods for the formation of P-C bonds, 6 such as the use of organolithium and Grignard reagents, have been less fruitful due to the low selectivity and complex product distributions associated with their reactions with P 4 .…”

“…Commercially available IPrMCl (M = Cu, Au; IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene) in combination with Li + [Al(pftb) 4 ] À (pftb = perfluoro-tert-butoxy) 11,12 as chloride scavenger were found to be suitable starting materials allowing the isolation of readily available LA-P 4 adducts. The complexation of P 4 was achieved by dropwise addition of a solution of IPrMCl (1 equiv.…”

“…The formation of 3 could be optimized by using two equivalents of 1b, which allowed its isolation in 67% yield. Bis-gold complex 3 is likely formed via neutral exo,exo-ArP 4 AuIPr 2 (Scheme 3) that displaces a P 4 molecule from a second equivalent of gold complex 1b, which was computed to be energetically favorable by À43.1 kcal mol À1 , 27 1 H} resonances at À110.6 (P1), À119.9 (P4) and À314.5 (P2, P3) ppm (1 : 1 : 2 ratio), and an additional signal for free P 4 . The product could be isolated in 62% yield, and was confirmed to contain only one mesityl unit by mass spectrometry (ESI) and 1 H NMR spectroscopy, and two flanking IPrAu moieties.…”