N. Satish Kumar

Structurally diverse penta- and hexacoordinate phosphorus compounds from the reaction of diethyl or diisopropyl azodicarboxylates with phosphorus(III) compounds

The reaction of diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD) with cyclic phosphites/phosphoramidites has been examined in an effort to delineate the structural preferences in spirocyclic penta- and tricyclic hexacoordinate (amino)oxyphosphoranes. It is shown that the familiar Bent’s or apicophilicity rules referred to in standard books give an oversimplified picture. Thus the reaction of CH2(6-t-Bu-4-Me–C6H2O)2PCl (19) with DEAD/DIAD leads to the chlorophosphoranes CH2(6-t-Bu-4-Me–C6H2O)2PCl[N(COOR)–NC(OR)O–] [R = Et (21a), i-Pr (21b)]. Treatment of 21a–b with pyrazole or imidazole leads to CH2(6-t-Bu-4-Me–C6H2O)2P(NRR′)[N(COOR)–NC(OR)O–] [NRR′ = pyrazolyl (12a–b), imidazolyl (13a–b)] that have trigonal bipyramidal phosphorus with ‘reversed apicophilicity’. Compound S(6-t-Bu-4-Me–C6H2O)2P(NH–i-Pr) (20b) affords the pentacoordinate derivative S(6-t-Bu-4-Me–C6H2O)2P(NH–i-Pr)[N(COOR)–NC(OR)O–] (15), but S(6-t-Bu-4-Me–C6H2O)2PCl (20a) gives the hexacoordinate phosphorane S(6-t-Bu-4-Me–C6H2O)2PCl[N(COOR)–NC(OR)O–] (16) with the shortest known S→P coordinate bond. Compound 15 also exhibits the ‘reversed apicophilicity’ phenomenon, but the disposition of substituents is different from that in 12–13. The compound S(6-t-Bu-4-Me–C6H2O)2PPh[N(COOR)–NC(OR)O–] (17) is prepared similarly. Reaction of 16 with imidazole gives S(6-t-Bu-4-Me–C6H2O)2P(imidazolyl)[N(COOR)–NC(OR)O–] (18). Both 17 and 18 show distorted octahedral geometry with S→P coordination, but the sulfur is trans to the phenyl/imidazolyl group (while it is cis to –Cl in 16). The variable temperature 31P NMR spectra of 15 exhibit four totally distinct signals showing a dynamic behaviour with isomeric pentacoordinate species present. Theoretical calculations suggest that the compound as isolated is the favoured one for S(6-t-Bu-4-Me–C6H2O)2P{(N-t-Bu)[N(CO2Et)NH(CO2Et)]} (2, previously reported) as well as 15 and 16.

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).

Unusual products in the reactions of phosphorus(III) compounds with N=N, C≡C or conjugated double-bonded systems

The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction.

Chemistry of selected cyclic P(III) compounds possessing a P -Cl bond

The compounds [CH2(6-t-Bu-4-Me-C6H2O)2]PCl (1), (OCH2CMe2CH2O)-PCl (2), and [ClPN(t-Bu)]2 (3) have been utilized as precursors in the synthesis of (i) new pentacoordinate phosphorus compounds [e.g. CH2(6-t-Bu-4-Me-C6H2O)2 P(NRR′)(O2C6C14), CH2(6-t-Bu-4-Me-C6H2O)2PX[OC(O-i-Pr)N=N(C(O)O-i-Pr)],(ii) cyclic phosphates and their complexes [e.g. imidazolium+CH2(6-t-Bu-4-Me-C6H2O)2PO2-.MeOH], (iii) new cycloaddition products [e.g. CH2(6-t-Bu-4-Me-C6H2O)2PC(CO2Me)C(CO2Me)C(O)N, (iv) macrocyclic compounds [e.g. [(t-BuN)P]2[-OCH2CMe2CH2O-]h2] and (v) phosphonates [e.g. (OCH2CMe2CH2O)P (O)CH2C(CN)=CHC5H4FeC5H5]. The synthetic and structural aspects of these new products are discussed.