BINOL-3,3′-triflone N,N-dimethyl phosphoramidites: Through-space 19F31P spin-spin coupling with a remarkable dependency on temperature and solvent internal pressure

M. Kruck, M.P. Munoz, H.L. Bishop, C.P. Butts, G.C. Lloyd-Jones, C.G. Frost, C.J. Chapman, Gabriele Kociok-Kohn

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Abstract

A combined computational and experimental study of the effects of solvent, temperature and stereochemistry on the magnitude of the through-space spin–spin coupling between 31P and 19F nuclei which are six-bonds apart is described. The reaction of 3-trifluoromethylsulfonyl-2,′2-dihydroxy-1,1′-binaphthalene (3-SO2CF3-BINOL) with hexamethylphosphorous triamide (P(NMe2)3) generates a pair of N,N-dimethylphosphoramidites which are diastereomeric due to their differing relative configurations at the stereogenic phosphorous centre and the axially chiral (atropisomeric) BINOL unit. Through-space NMR coupling of the 31P and 19F nuclei of the phosphoramidite and sulfone is detected in one diastereomer only. In the analogous N,N-dimethylphosphoramidite generated from 3,3′-(SO2CF3)2-BINOL only one of the diastereotopic trifluoromethylsulfone moieties couples with the 31P of the phosphoramidite. In both cases, the magnitude of the coupling is strongly modulated (up to 400 %) by solvent and temperature. A detailed DFT analysis of the response of the coupling to the orientation of the CF3 moiety with respect to the P-lone pair facilitates a confident assignment of the stereochemical identity of the pair of diastereomers. The analysis shows that the intriguing effects of environment on the magnitude of the coupling can be rationalised by a complex interplay of solvent internal pressure, molecular volume and thermal access to a wider conformational space. These phenomena suggest the possibility for the design of sensitive molecular probes for local environment that can be addressed via through-space NMR coupling.
Original languageEnglish
Pages (from-to)7808-7812
Number of pages5
JournalChemistry - A European Journal
Volume14
Issue number26
Early online date17 Jul 2008
DOIs
Publication statusPublished - 8 Sep 2008

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