From 2,4‐Diphospha‐3‐Thia‐ and ‐3‐Selenapentadienes [(Me₃Si)₂CP]₂E to Heteronorbornane Cage Compounds

Abstract

Highly unsaturated organophosphorus compounds are rich in energy, and tend to rearrange to more stable rings, cages, and polymers. Nieckes 2,3,4-triphosphapentadienide anion [{(Me 3 Si) 2 C = P} 2 P] À (1), [1] the only p-donor heteroatombridged bisphosphaalkene anion that allows electronic communication between the neighboring P=C bonds, is known to undergo thermal elimination/re-addition reactions to furnish anionic P 3 C 2 heterocyles, [1] but its synthetic potential remains unexplored. The uncharged isoelectronic sulfide [(Me 3 Si) 2 C= P] 2 S (2), however, might be a promising synthetic precursor. We began our studies with 2 and the related selenide 3 to evaluate if and how p communication through the heteroatoms sulfur and selenium might influence the reactivity of bifunctional phosphaalkenes.2,4-Diphospha-3-thia-and 2,4-diphospha-3-selenapentadienes 2 and 3 are formed in the reaction of (Me 3 Si) 2 C = PCl (4) [2] with bis(trialkylsilyl)chalcogenides [Eq. (1)]. Redbrown 3 crystallizes as a monomer. The W-shaped CPSePC moiety of 3 ( Figure 1) shows a close analogy to that of Nieckes anion 1.[1] The central angle PSeP of 3 is 90.78, whereas in the isoelectronic arsenide ion [{(Me 3 Si) 2 C=P} 2 As] À (5), the angle PAsP shrinks to 85.88.[3] The P = C bonds in 3 (1.664 and 1.668 ) are slightly shorter than in 1 (1.687 ), and the PÀSe bonds appear to be normal single bonds.Energies of isodesmic reactions of the model compound [(H 3 Si) 2 C = P] 2 S with H 2 S calculated at the B3LYP/6-31 + G* level (leading to 2 (H 3 Si) 2 C = PSH; + 0.1 kcal mol À1 ) and with PH 3 (leading to (H 3 Si) 2 C = PH and (H 2 P) 2 S; + 17.6 kcal mol À1 ) [4] suggest that in the C=P-S unit there is p stabilization (ca. 9 kcal mol À1 for each P=C moiety), but there is no further energy gain when the second P=C unit is attached to sulfur.Two equivalents of elemental sulfur or selenium add to compounds 2 and 3, respectively, in a surprising fashion: [5] norbornane-type P 2 Se 5 -related [6] [(Me 3 Si) 2 CP] 2 E 3 cages (E = S, Se) are formed. Bisphosphiranes (Scheme 1, type III), or thermodynamically somewhat less stable bis-s 3 ,l 5 -phosphoranes (V), are not observed.31 P NMR spectra of the reaction mixture of 2 with sulfur (see Experimental Section) exhibit a weak AX pattern at early stages of the reaction (d( 31 P) = + 353.3, À25.0 ppm; J = 276.3 Hz); this AX pattern is assigned to a P-(phosphaalkenylthio)thiaphosphirane (6, type I, see Scheme 1).[7] The main product is the C 2 -symmetric compound [(Me 3 Si) 2 C] 2 P 2 S 3 (7; P III ,P III ) [Eq. (2)], accompanied by partially oxidized [(Me 3 Si) 2 C] 2 P 2 S 4 (8; P III ,P V ), which has an AB pattern (J31 P 31 P = AE 17.0 Hz) in the 31 P NMR spectrum, and C 2 -symmetric [(Me 3 Si) 2 C] 2 P 2 S 5 (9, P V ,P V ). Compound 9 was isolated as a few single crystals. In a similar way, compound 3 reacts smoothly with two equivalents of selenium to give [(Me 3 Si) 2 C] 2 P 2 Se 3 (10, P III , P III ) in high yield [Eq. (3)] which is however not further oxidized by selenium. Crude 10 is

Diastereoselective Reactions of Sulfur- and Selenium-Bridged Bisphosphaalkenes with Tetrachloro-o-benzoquinone

“…Recently it was observed that 1a and 1b add elemental sulfur and selenium in a surprising way, different from the behavior of comparable monofunctional phosphaalkenes. 2 In the following, we report our first experiments on reactions of 1a and 1b with cyclopentadiene and with tetrachloro-o-benzoquinone (TOB), both of which are typical reagents for [2+4] cycloadditions to phosphaalkenes. [3][4][5] TOB also adds oxidatively to other shortlived or persistent compounds of low-coordinated phosphorus, [6][7][8] and-in a [4+1] fashion-to P(σ 3 λ 3 )-compounds, 6,[9][10][11][12] 2 C=P-E-PR 2 (R = tBu, iPr) with cyclopentadiene, the initially formed endo-isomers usually rearranged to the more stable exo-isomers within 24 h 4 ; we therefore assume that both diastereomers of 2a and 2b were isolated as the exo,exo-isomers, as depicted in Scheme 1.…”

Oxygen, sulfur, selenium, tellurium and polonium

“…Du Mont et al reported that reaction of {(Me 3 Si) 2 CQP} 2 E (E = S, Se) with elemental S or Se generates a heteronorbornane cage compound (below left). 47 Reversible chalcogen exchange is observed and excess sulfur leads to sequential oxidation of the P III centre (below centre and right).…”

Deoxygenation of chalcogen oxides EO2 (E = S, Se) with phospha-Wittig reagents

“…In general, the oxi-dation of diphosphenes with elemental sulphur (or selenium) is the most established route to synthesize P 2 Ch (Ch = S, Se) rings (Scheme 3). [58][59][60][61][62][63][64][65][66] A handful of other routes have also been reported, [67][68][69][70][71] among them a combined dechlorinationelementation strategy using (Me 3 Sn) 2 E and (tBuPCl) 2 to access (tBuP) 2 E (E = S, Se) (Scheme 3, middle). 72 In here we show that Scheme 2 Phospha-Wittig reagents as phosphinidene precursors and their diverse reactivity toward selected nucleophiles.…”