PHOSPHORANES .10. BARRIERS TO 5-COORDINATE PERMUTATIONS AND-OR ROTATION OF THE THIOMETHYL GROUP IN (FLUOROMETHYL)PHOSPHORANE AND (TRIFLUOROMETHYL)PHOSPHORANE BY MEANS OF DYNAMIC NMR-STUDIES

Line-shape analyses of the proton-decoupled 31P NMR spectra of F4P(SCH3), CF3PF3(SCH3) (including in this case 19F dynamic behavior of the CF3 region), (CF3)2PF2(SCH3), and (CF3)3PF(SCH3) have been carried out. Two processes can be distinguished in CF3PF3(SCH3): the five-coordinate permutation (i.e., Berry pseudorotation (BPR)) and the rotation of the SCH3 group about the P-S bond. Respective barriers (AG298‡) are 12.8 (±0.6) and 10.2 (±0.3) kcal. The ΔG298‡ values of 10.0 (±0.2) and 11.0 (±0.3) kcal/mol obtained for the observable process in (CF3)2PF2(SCH3) and CH3(C-F3)PF2(SCH3), respectively, are attributed to a pure rotation process since there is no spectral evidence to support CF3-F positional interchange. The processes which equilibrate the three distinguishable fluorine environments in F4P(SCH3) (a pair of equatorial fluorine atoms and two distinct axial environments) yield only one barrier of 11.0 (±0.3) kcal, larger than that reported for F4PN(CH3)2. Detailed analysis of the line shapes and the above behavior of CF3PF3(SCH3), wherein the processes are separable, strongly suggest that the permutational process in F4P(SCH3) is not concerted (i.e., BPR is not intimately coupled with rotation about the P-S bond) but rather involves uncorrelated independent rotation and pseudorotation processes represented by an overall barrier. The barrier to exchange (permutation of CF3 groups) in (CF3)3PF(SCH3) is 11.5 kcal. © 1979, American Chemical Society. All rights reserved.