New phosphabenzenes by [4 + 2] cycloaddition of stannoles to 1-phospha-1-alkynes - Determination of signs of coupling constants [nJ(31P, 13C), nJ(31P, 1H), 2J(31P, 29Si), 2J(119Sn, 31P)]

Article abstract of DOI:10.1016/0022-328X(96)06316-4

Stannoles bearing dialkylboryl groups in 3-position react with 1-phospha-1-alkynes P≡C-^tBu (1) and P≡C-CH₂ ^tBu (2) by [4 + 2] cycloaddition and elimination of stannylene to give phosphabenzenes in high yield. The stannylenes oligomerise to give [R¹₂Sn]_n with n ≥ 7 (R = Me, Et, -(CH₂)₅-or, in the case of R¹ = ^tBu, react with the stannole itself. All phosphabenzenes are characterised by their consistent sets of NMR data. The absolute signs of the coupling constants ⁿJ(³¹P, ¹H), ⁿJ(³¹P, ¹³C), ²J(³¹P, ²⁹Si) and ²J(¹¹⁹Sn, ³¹P) were determined by appropriate 1D and 2D NMR experiments.