Nuclear Magnetic Resonance Spectroscopy

BY B. E. MANN

1 Introduction

Following the criteria established in earlier volumes. only books and reviews directly relevant to this chapter are included. and the reader who requires a complete list is referred to the Specialist Periodical Reports 'Nuclear Magnetic Resonance', where a complete list of books and reviews is given. Reviews which are of direct relevance to a section of this Report are included in the beginning of that section rather than here. Papers where only 1H n.m.r. spectroscopy is used are only included when the 1H n.m.r. spectra make a non-routine contribution, but complete coverage of relevant papers is still attempted where nuclei other than the proton are involved.

Only one relevant book has appeared. namely N.M.R., Basic Principles and Progress; Oxygen-17 and Silicon-29. Several reviews have appeared including 'N.m.r. of metal nuclides. Part 1. The main group metals' 'Multinuclear n.m.r. studies of transition metal carbonyl clusters'. 'Applications of phosphorus-31 n.m.r. to the study of metal-phosphorus bonding' 'Conformational analysis of chelate ring systems by n.m.r.' 'N.m.r. spectroscopy of oriented molecules and its applications to inorganic chemistry', and 'N.m.r. of metal ions: biochemical investigations'.

A number of papers have been published which are too broadly based to fit into a later section and are included here. 1J(13C, 13C) coupling constants for some simple ally1 compounds of Ni, Cr. Mg, and Li have been determined. In transition-metal complexes, 1J (13C, 13C) is reduced to 41 Hz (Ni) whilst in C3H5Li it is 58.7 Hz. The 13C and 15N n.m.r. spectra have been measured for 13 metal cyano complexes. The coupling constants increase in most cases with increasing 13C and/or 15N shifts to higher field. The Pople-Karplus paramagnetic screening equation has been reinterpreted in an attempt to account for the opposite trends with π-back-bonding observed for 13C and 17O chemical shifts in transition-metal carbonyl complexes. The results support the conclusion that metal-to-CO π-back-bonding decreases QAB resulting in a low-frequency chemical shift for the carbonyl carbon atom. A 13C and 19F n.m.r. study of 24 Ru, Rh, Pd, and Pt complexes of R1CSCH2COR2 has been reported and the chemical shifts have been discussed. 13C/12C-isotope-induced 15N chemical shifts of 0.06–0.10 p.p.m. have been observed for the cyanide ion in several transition-metal cyanides. The influence of hard and soft metals on the 13C n.m.r. spectrum of guanosine and inosine under both neutral and basic conditions has been determined. 1J(M, 13C) for elements with other elements having a constant hybridization should be linearly related. This concept was applied when M = 1H, 29Si, 119Sn, or 207Pb. Diamagnetic-metal-ion-nucleoside 15N n.m.r. DEPT has been used to observe enhanced 29Si and 195Pt n.m.r. signals." Analytical expressions for n.m.r. lineshapes of I = 5/2 and 2/7 nuclei have been derived.

2 Stereochemistry

This section is subdivided into ten parts which contain n.m.r. information about Groups IA and IIA and transition-metal complexes presented by Groups according to the Periodic Table. Within each Group, classification is by ligand type.

Complexes of Groups IA and IIA. — Studies of chlorophyll a in model and natural membrane systems' has been reviewed and includes 13C and 31P n.m.r. measurements.

The nature of oligoisoprenyl-lithium complexes with NNN'N'- tetramethylethylenediamine or pentamethyldiethylenetriamine has been investigated. 2J(13C, 1H) has been used to assign % s-character in the CH bonds of allyl and pentadienyl Li,Na, K,and MgBr. The solvent effect on the 13C n.m.r. chemical shifts of indenyl-lithium has been measured. For (1), 1J(13C, 7Li) has been measured as 20 Hz. 13C spin-lattice relaxation times of the cryptands 2.1.1, 2.2.1, and 2.2.2 and complexes with Li+, Na+, and K+ have been measured and interpreted in terms of molecular compression and desolvation effects. N.m.r. data have also b reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

1H n.m.r. spectroscopy, including NOE measurements, has been used to study the shape, motion, and flexibility of the quinone-capped porphyrins and their Mg derivatives. The nature of the metalloporphyrin ligand complexes produced by Zn, Mg, and Co porphyrins with basic ligands has been studied using the diamagnetic ring-current shifts of the porphyrin on the ligand protons. A double-dipole model of the macrocycle ring current in the dihydroporphyrin ring of chlorophyll derivatives has been presented and parameterized. 13C n.m.r. data have been presented which show that tetracyclin undergoes a major conformational change upon addition of H2O. 43Ca spin-lattice relaxation times have been measured for calcium complexes with EDTA, EGTA, and a cyclic ligand. The 43Ca quadrupole-coupling constants were calculated for each complex and increase by a factor of four on going from the EDTA to the EGTA complex. A summary of fundamental Mg relaxation parameters has been presented for magnesium complexes with AMP, VMP, and DNA. 1H NOE experiments have been used to determine torsion angles in Mg2+ complexes of ATP and ADP. 43Ca n.m.r. signals have been reported from Ca2+ bonded to parvalbumin, troponin C, and calmodulin. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]).

Complexes of Groups IIIA and IVA, the Lanthanides, and the Actinides. — 139La n.m.r. linewidths vary greatly over various complexes. The chemical shifts and linewidths are useful in determining the structure of compounds. La(fod), diamagnetic complexation shifts have been used as a sensitive probe to the extent and pattern of π-electron delocalization in aromatic and olefinic aldehydes and ketones in 13C n.m.r. spectroscopy.'

The 19F transverse relaxation rate in liquid UF6 has been investigated as a function of U enrichment revealing a linear dependence on the enrichment. The result was explained in terms of the 19F-235U indirect scalar interaction which provides an efficient relaxation mechanism. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]).

The 31P n.m.r. spectrum of [Cp2ZrC1(CH2PPh2)]2Rh(CO)Cl shows the presence of three isomers due to restricted rotation about the phosphorus-rhodium bond. The 13C n.m.r. spectrum was also given. J(13C,1H) has been measured in (2). 47,49Ti n.m.r. spectra of [MATHEMATICAL EXPRESSION NOT...