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

Treatment of the P(III) isothiocyanate CH26-t-Bu-4-Me-C6H2O]2PNCS (1) with dimethyl acetylenedicarboxylate (DMAD) or diethyl acetylenedicarboxylate (DEAD) yields the spirocyclic phosphinimines CH26-t-Bu-4-Me-C6H2O]2PNC(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 2x1+3] but with a completely reorganized structure {CH26-t-Bu-4-Me-C6H2O]2P=C(CO2Et)C(CO2Et)=CN-}{CH26-t-Bu-4-Me-C6H2O]2P(NCS)}-SC=N-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.