Addition products of a P(iii)-isothiocyanate to dialkyl acetylenedicarboxylates: a spirocyclic phosphinimine and a triphosphorus heterocycle with tetra- and penta-coordinate phosphorus

Abstract

Treatment of the P(III) isothiocyanate CH₂[6-t-Bu-4-Me-C₆H₂O]₂PNCS (1) with dimethyl acetylenedicarboxylate (DMAD) or diethyl acetylenedicarboxylate (DEAD) yields the spirocyclic phosphinimines CH₂[6-t-Bu-4-Me-C₆H₂O]₂P[NC(S)C(CO₂R)C(CO₂R)] [R = Me (2), Et (3)], in a reaction unlike those of organic isocyanates. From the reaction of 1 with DEAD, a second product, the triphosphorus compound 5, with the composition [2×1 + 3] but with a completely reorganized structure {CH₂[6-t-Bu-4-Me-C₆H₂O]₂PC(CO₂Et)C(CO₂Et)CN–}{CH₂[6-t-Bu-4-Me-C₆H₂O]₂P(NCS)}–SCN–P(S)[(OC₆H₂-6-t-Bu-4-Me)₂CH₂] with tetra- and penta-coordinate phosphorus, is also isolated. Structure and reactivity of these compounds are discussed. Addition of 2,2,2-trifluoroethanol to 2 or 3 leads to the pentacoordinate phosphorus compounds [CH₂(6-t-Bu-4-Me-C₆H₂O)₂P(OCH₂CF₃){C(CO₂R)C(CO₂R)–C(S)–NH–}] [R = Me (6), Et (7)]. The phosphonate [CH₂(6-t-Bu-4-Me-C₆H₂O)₂P(O)C(CO₂Et)C(CO₂Et)–C(S)–NH₂] (8) is obtained by evaporating a solution of 7 in open air.