Chiral HPLC Separation, Absolute Structural Elucidation, and Determination of Stereochemical Stability of trans-Bis[2-(2-pyridinyl)aminophenolato] Cyclotriphosphazene.

Chiral high-performance liquid chromatography (HPLC) separation of trans-bis[2-(2-pyridyl)aminophenolato] dichlorocyclotriphosphazene was achieved and the absolute configuration of was assigned to be S,S by single-crystal X-ray structural analysis. The optically pure 1,2-diphenyl-1,2-ethanediolate derivatives (+)- and (-)- were synthesized by the reactions of and with (R,R)-hydrobenzoin, respectively, in refluxing toluene in the presence of an excess amount of triethylamine and a catalytic amount of 4-(dimethylamino)pyridine. The racemization of the enantiomers of and the epimerization of diastereomers of 2 were not observed in refluxing toluene neither under acidic nor basic conditions. The stereochemistry of was confirmed by the crystal structure of (+)- and bis[(4-methyl-2-pyridyl)oxy]cyclotriphosphazene derived from . Chirality 28:556-561, 2016. © 2016 Wiley Periodicals, Inc.

Experimental determination of the nN --> sigma*P-O interaction energy of O-equatorial C-apical phosphoranes bearing a primary amino group.

The reaction of a chlorophosphorane (9-Cl) with primary amines produced anti-apicophilic spirophosphoranes (5, O-equatorial phosphoranes), which violate the apicophilicity concept, having an apical carbon-equatorial oxygen configuration, along with the ordinarily expected O-apical stereoisomers (6) with the apical oxygen-equatorial carbon configuration. Although the amino group is electronegative in nature, the O-equatorial phosphoranes were found to be stable at room temperature and could still be converted to their more stable O-apical pseudorotamers (6) when they were heated in solution. X-ray analysis implied that this remarkable stability of the O-equatorial isomers could be attributed to the orbital interaction between the lone-pair electrons of the nitrogen atom (n(N)) and the antibonding sigma(P-O) orbital in the equatorial plane. A kinetic study of the isomerization of 5 to 6 and that between diastereomeric O-apical phosphoranes 13b-exo and 13b-endo revealed that 5b bearing an n-propylamino substituent at the central phosphorus atom was found to be less stable than the corresponding isomeric 6b by ca. 7.5 kcal mol(-1). This value was smaller than the difference in energy (11.9 kcal mol(-1)) between the O-equatorial (1b) and the O-apical n-butylphosphorane (2b) by 4.4 kcal mol(-1). This value of 4.4 kcal mol(-1) can be regarded as the stabilization energy induced by the n(N) --> sigma(P-O) interaction. The experimentally determined value was in excellent agreement with that derived from density functional theory (DFT) calculations at the B3PW91 level (4.0 kcal mol(-1)) between the nonsubstituted aminophosphoranes (5g is less stable than 6g by 10.1 kcal mol(-1)) and their P-methyl-substituted counterparts (1a is less stable than 2a by 14.1 kcal mol(-1)).

Novel phosphoranido complex of rhodium(III) tetraphenylporphyrin. Synthesis and characterization.

A novel phosphoranido complex of rhodium(III) porphyrin was prepared by the reaction of a lithium phosphoranide, generated from a P-H phosphorane bearing two 8-oxy-1-naphthyl groups, with (TPP)RhCl (TPP = dianion of 5,10,15,20-tetraphenylporphyrin). The crystal structure of the complex was determined by X-ray structural analysis.

Characteristic reactions and properties of C-apical O-equatorial (O-cis) spirophosphoranes: effect of the sigma(P)(-)(O) orbital in the equatorial plane and isolation of a hexacoordinate oxaphosphetane as an intermediate of the Wittig type reaction of 10-P-5 phosphoranes.

Novel spirophosphoranes (O-cis) that exhibit reversed apicophilicity having an apical carbon-equatorial oxygen array in a five-membered ring showed enhanced reactivity toward nucleophiles such as n-Bu(4)N(+)F(-) or MeLi in comparison with the corresponding stable isomeric spirophosphoranes (O-trans) having an apical oxygen-equatorial carbon configuration. The enhanced reactivity of the O-cis isomer could be explained by the presence of a lower-lying sigma(P)(-)(O(equatorial)) orbital as the reacting orbital in the equatorial plane, whereas the corresponding orbital is a higher-lying sigma(P)(-)(C(equatorial)) in the O-trans isomer. Density functional theory (DFT) calculation on the actual compounds provided theoretical support for this assumption. In addition, we found that the benzylic anion alpha to the phosphorus atom in O-cis benzyl phosphorane is much more stable than that generated from the corresponding O-trans compounds. The experimental results were considered to be due to the n(C) --> sigma(P)(-)(O) interaction in the O-cis anion, and this was confirmed by DFT calculations. Furthermore, the hexacoordinate anionic species derived from the reaction of the benzylic anion from O-cis benzylphosphorane with an aldehyde was also found to be stabilized as compared with analogous species from the corresponding O-trans isomer. The first X-ray structural characterization of a hexacoordinate phosphate intermediate in the Wittig type reaction using pentacoordinate phosphoranes is reported.