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The Ligand‐Exchange Process of P–H apical Phosphoranes and the Thermal Formation and Pseudorotation of Anti‐Apicophilic Spirophosphoranes
Author(s) -
Kojima Satoshi,
Kajiyama Kazumasa,
Nakamoto Masaaki,
Matsukawa Shiro,
Akiba Kinya
Publication year - 2006
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200500510
Subject(s) - pseudorotation , chemistry , ligand (biochemistry) , denticity , hexacoordinate , nucleophile , substituent , stereochemistry , agostic interaction , homoleptic , carbon group , ring (chemistry) , crystallography , group (periodic table) , crystal structure , organic chemistry , catalysis , biochemistry , receptor , silicon , metal
Monocyclic P–H apical phosphoranes 10 bearing a ring‐opened Martin ligand are formed upon treatment of the P–H equatorial spirophosphorane 7 with more than 2 equiv. of alkyllithium compounds. A ligand‐exchange process of these phosphoranes 10 involving the interconversion of the bidentate Martin ligand with the monodentate Martin ligand was found to proceed, probably through a hexacoordinate phosphorus atom. Heating of 10 in nondonating solvents furnished alkylspirophosphoranes 5 , whereas heating of 10 in donor solvents led to the formation of anti‐apicophilic phosphoranes 6 , a new class of phosphoranes in which the less apicophilic carbon substituent occupies an apical position and the more apicophilic oxygen atom occupies an equatorial position. These phosphoranes 6 were found to completely convert into their energetically more stable C equatorial ,O apical stereoisomers 5 upon heating. On the basis of kinetic examinations of the cyclization process of 10 , the formation of 6 can be rationalized by the enhanced nucleophilicity of the hydroxy group in the donor solvents. The isomer 5b was estimated to be more stable than 6b (R = n Bu) by 12 kcal mol –1 from kinetic studies on the pseudorotation of 6b to 5b . This is in good agreement with theoretical calculations with analogous 5a and 6a (R = Me), which estimate the difference in energy to be 14.1 kcal mol –1 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)