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 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 [2x1+3] but with a completely reorganized structure {CH2[6-t-Bu-4-Me-C6H2O]2P=C(CO2Et)C(CO2Et)=CN-}{CH2[6-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.

Novel reactions of phosphorus(III) azides and isocyanates: unusual modes of cycloaddition with dipolarophiles and an unexpected case of ring expansion.

New modes of 1,3-dipolar cycloaddition are uncovered by the isolation of [CH2(6-t-Bu-4-Me-C6H2O)2]P(C(CO2Me)C(CO2Me)N[NP(N3)(OC6H2-6-t-Bu-4-Me)2CH2]N) (3) and [CH2(6-t-Bu-4-Me-C6H2O)2]P(C(CO2Me)C(CO2Me)C(O)N) (4) on treating [CH2(6-t-Bu-4-Me-C6H2O)2]P-X [X = N3 (1) and NCO (2)] with the dipolarophile MeO2CC identical to CCO2Me; compound 4 undergoes an unprecedented ring expansion upon addition of 2-(methylamino)ethanol to afford the spirocycle [CH2(6-t-Bu-4-Me-C6H2O)2]P(OCH2CH2N(Me)CH(CO2Me)CH(CO2Me)C(O)N) (5).

Apical versus equatorial disposition of substituents in tetraoxyphosphoranes bearing a 1,3,2-dioxaphosphocin ring: implications on apicophilicity in trigonal bipyramidal phosphorus.

New spirocyclic (amino/amido)tetraoxyphosphoranes CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)P(NRR')(O(2)C(6)Cl(4)) [R = Me, R' = Ph (1), R = R' = i-Pr (2); R = R' = H (3); R = H, R' = Ph (4)] and the isothiocyanatotetraoxyphosphorane CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)P(NCS)(O(2)C(6)Cl(4)) (5) have been synthesized. X-ray crystallography for these compounds reveals that -N(Me)Ph, -N(i-Pr)(2), and -NCS groups occupy an apical position whereas -NH(2) and -NHPh groups occupy an equatorial position in a trigonal bipyramidal geometry around phosphorus. These results are in contrast with the common assumption that a sterically bulky and less electronegative substituent [e.g. -N(i-Pr)(2)] should be less apicophilic than a sterically small and more electronegative substituent (e.g. -NH(2)). The possible rationalization for these results is discussed. Variable-temperature ((1)H, (31)P) NMR spectra of these compounds show some unusual features not reported before for pentacoordinate phosphorus. Probable intramolecular processes involving (i) apical-equatorial <--> equatorial-apical exchange, (ii) apical-equatorial <--> equatorial-equatorial exchange, and (iii) boat-chair <--> tub (for the eight-membered ring) interconversion as well as cessation of the P-N bond rotation have been invoked to explain the spectral features.