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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 (nN) and the antibonding σ*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 nN → σ*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). [ABSTRACT FROM AUTHOR]

The article discusses the result of a study concerning synthesis and structure of a hexacoordinate carbon compound. The paper reported an example of hexacoordinate carbon with arguable hypervalence and characterized hexacoordinate carbon compounds. It was found that high-coordinate carbon compounds are electric-deficient, having three-center two electron bonds.