Novel tetraphosphabarrelene and -semibullvalene derivatives by reactions of 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene with phosphaalkynes

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] cycl oaddition to yield the corresponding 1,3,5,7-tetraphosphabarrelene derivati ves 8a and 8b, respectively. The analogous reaction of 4 with the aminophos phaethyne P=C-N(iPr)(2) (9) unexpectedly leads to the 1,3,4,7-tetraphosphas emibullvalene derivative 10 as the only product. The single-crystal X-ray a nalysis of 10 exhibits a diphosphirane unit with a very long PP distance of 2.274(1) Angstrom together with a large extension of the PCP angle in the three-membered ring to 75.3(1)degrees.