The impact of ion pair association upon the ¹H NMR spectra of cationic complexes akin to Grubbs catalysts

Abstract

A reconsideration of the (1)H NMR spectra of cationic transition metal complexes exhibiting the features of cyclophanes on the basis of Mislow's classification of topic groups arrives at the conclusion that the spectral changes triggered by chiral counterions reflect an intracationic diastereotopication of enantiotopic protons rather than the existence of pairs of long-lived diastereomeric ion pairs.

Ion‐Pairing of Phosphonium Salts in Solution: CH⋅⋅⋅Halogen and CH⋅⋅⋅π Hydrogen Bonds

“…The CÀH stretch bands CD 2 Cl 2 ) [9] were rationalized to be predominantly caused by the ring current of the BPh 4 À anions phenyl rings, which reside above the C(a) À H protons of the phosphonium ion due to Coulomb attraction between the two ions. [9,10,16,17] Based on this effect, many applications of the BPh 4 À anion as shift reagent in NMR spectroscopy have been described. [9,[11][12][13][14][15]18] One of the examples used by Schiemenz to illustrate the usefulness of the "BPh 4 À effect" was the possibility to determine 2 J H,P for the a proton of Ph 2 CH À PPh 3 + (2 a).…”