Motivation and Methodology

Abstract

For almost a quarter of a century the words “nuclear magnetic resonance” were synonymous with proton measurements. During this period the literature abounded with a seemingly infinite variety of ¹H NMR studies concerned primarily with carbon chemistry. Occasionally a “novel” nucleus was studied and, even in those early days, the potential offered by ¹³C, ¹⁴N, ³¹P and ¹⁹F was clearly recognized. Despite the allure, the technical difficulties involved in measuring some of these nuclei were far from trivial. Small magnetic moments and low natural abundance in combination with spin-spin coupling from other nuclei, mostly protons, resulted in a signal-to-noise problem whose severity effectively excluded the study of metal complexes with unfavorable solubility characteristics. The first important breakthrough came with the advent of broad band ¹H-decoupling. For example, the featureless broad ³¹P resonance associated with the commonly used ligand triphenyl phosphine is converted to a sharp, more readily observed singlet when wide-band decoupling is employed (see Fig. 1). Despite this improvement investigation of more interesting molecules, such as catalytically active complexes was forced to await the development of Fourier Transform methods since only with relatively rapid signal averaging methods could sufficient signal-to-noise ratios be achieved.