Novel Tetraphosphabarrelene and -semibullvalene Derivatives by Reactions of 2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene with Phosphaalkynes⋆

Abstract

2,4,6‐Tri‐tert‐butyl‐1,3,5‐triphosphabenzene 4 reacts with phosphaalkynes P≡C–R [R = tBu (5a), tPen (5b)] at room temperature in a formal [4 + 2] cycloaddition to yield the corresponding 1,3,5,7‐tetraphosphabarrelene derivatives 8a and 8b, respectively. The analogous reaction of 4 with the aminophosphaethyne P≡C–N(iPr)2 (9) unexpectedly leads to the 1,3,4,7‐tetraphosphasemibullvalene derivative 10 as the only product. The single‐crystal X‐ray analysis of 10 exhibits a diphosphirane unit with a very long PP distance of 2.274(1) Å together with a large extension of the PCP angle in the three‐membered ring to 75.3(1)°.

Homoaromaticity in aza‐ and phosphasemibullvalenes. A computational study

“…Attempted synthesis of derivatives of tetraazasemibullvalene 12 failed, giving 1,3,5,7‐tetrazocines instead 29. Derivatives of diphosphasemibullvalene30 and tetraphosphasemibullvalene31, 32 have been synthesized, but none of them were observed to undergo a Cope rearrangement. However, these phosphasemibullvalenes had a P atom in the bridge, i.e.…”

[1 + 4]-Cycloaddition of a stable silylene to 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene

“…The latter has only recently been synthesised by metal-induced cyclotrimerisation of the phosphaalkyne Bu t CP 12,13 and although its structure and PE spectrum have been reported, 14 its chemistry has not been studied in depth. Binger and coworkers 15 have described the synthesis of tetraphosphabarrelene and semibulvalene derivatives by addition of different phosphaalkynes to 2. The former products resulted from a conventional [4 + 2]-cycloaddition reaction and the latter most likely from nucleophilic attack at one of the ring C atoms, followed by ring closure.…”

Differing reactivities of PCMe and PCButtowards a triphosphabenzene and a tetraphosphabarrelene: synthesis of new phosphaalkyne pentamers (P5C5MenBut5−n, n = 0, 1 or 2)

“…Yield: 155 mg (66%). Mp: 206-208 • C; 1 H NMR (400 MHz, C 6 D 6 , 298 K): d 1.18 (s, 9H, Bu t ), 1.23 (s, 9H, Bu t ), 1.56 (s, 9H, Bu t ), 1.73 (v. tr, 3 J PH = 3 J PH = 19 Hz, 3H, Me on C(1)), 2.73 (ddd, 3 J PH = 30 Hz, 3 J PH = 14 Hz, 4 J PH = 7 Hz, 3H, Me on C(4)); 31 P{ 1 H} NMR (121.6 MHz, C 6 D 6 , 298 K): d −100.1 (br. d, 1 J PP = 176 Hz, P(3)), 9.4 (br.…”