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, 2H, 19F, and/or 31P n.m.r. spectroscopy is used are only included when they make a non-routine contribution, but complete coverage of relevant papers is still attempted where nuclei other than these are involved. In view of the greater restrictions on space, and the ever growing numbers of publications, many more papers in marginal areas have been omitted. This is especially the case in the sections on solid-state n.m.r. spectroscopy, silicon and phosphorus.

Several relevant reviews have been published, including 'Ligand field interpretation of metal n.m.r. chemical shifts in octahedral d6 transition metal complexes, 'N.m.r. spectroscopy of the early transition metals', 'Nuclear magnetic resonance of transition metal compounds', which contains 95Mo n.m.r. spectroscopy, 'Metal cluster complexes containing heteroatom-substituted carbene ligands', which contains 13C n.m.r. spectroscopy, 'Metalloproteins', 'N.m.r. spectroscopy', which contains the use of Na n.m.r. spectroscopy for the determination of intracellular sodium, and 'Information obtained by liquid crystal n.m.r.', which contains its application to organic tin compounds.

A number of papers have been published which are too broadly based to fit into a later section and are included here. Anomalous scalar couplings of up to 1400 Hz in trihydrides such as [(η5-C5H 5)Ir(AsPh3)H3]+ have been explained as being due to quantum mechanical exchange. σ-Bond polarities in organometallic compounds have been studied by 19F n.m.r. spectroscopy and exchange equilibria methods. The structures of the hexamethylenecarbodithioates of transition metals and [M(Se2 C2S2CS) 2]2-, M = Ni, Pt, Zn, Cd, Hg, have been studied by 13C n.m.r. spectroscopy.

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. — The 7Li quadrupole coupling constants in Li12, LiMe, LiCH2X and related compounds have been calculated. A 13C spin-echo technique with gated 6Li decoupling has been developed for selective observation of different [RLi]n aggregates. J modulation of the 13C signals by 1 J (13C,6Li) has been used to characterise the multiplicity of n.m.r. signals of lithiated carbons in BunLi and PhLi by 13C(6Li) SEFT. [Li(tmeda)CH2PMe2-nRn] shows 1J(31-7Li) below -70 °C in the 7Li and 31P n.m.r. spectra. The 13C n.m.r. spectrum was also recorded. 77Se N.m.r. spectroscopy has been used to optimise α-selenoalkyl lithium synthesis. Li and 13C n.m.r. spectroscopy has been used to study the lithiation of some silyl ethers in hydrocarbon solvents by ButLi. Distinct 6Li, 7Li, 13C, and 31P n.m.r. signals have been observed in mixtures of LiBEt3Ph, LiBr, and LiPh in (Me2N)3PO. The ortho-metallation of C6H5-OMe by BunLi has been shown by 13C n.m.r. spectroscopy to be a tetrameric aggregate. 6Li, 1H HOESY has been used to demonstrate the solvation of BunLi by C6H5OMe. 13C n.m.r. spectroscopy has been used to show that 2-lithiobenzoselenophene-tmeda and lithiobenzothiophene-tmeda are dimeric with C2v symmetry. The 1Li, and 13C n.m.r. spectra of (1) show the presence of several aggregates. 13C n.m.r. data have also been reported for [PhC2Li(tmeda)], and [LiCNMeCH(CHN2 Me2)2]2.

The 7Li n.m.r. spectrum of [FBut2GePLi (C6H2But3-2,4,6)] shows 1J(31P-7Li). The 6 Li-1H HOESY two dimensional spectrum of [Li(OCBut =CH2)]4 has been recorded. The standard chemical potential of Li+ in 4-butyrolactone has been determined by a 7Li spin-lattice relaxation method. 13C N.m.r. spectroscopy has been used to perform the con-formational analysis of lithium complexes of dicyclohexano-12-crown-4 ethers. In arene solutions, [Li2Br2 {OP(NMe2)3}3] gives a 1:3:3:1 quartet in the 7Li n.m.r. spectrum due to P coupling. Nuclear quadrupole coupling constants of 2H, 7Li, and 35Cl have been calculated for HCl and LiCl. N.m.r. data have also been reported for [H2C(CH2)5NLi]6, (7Li), [Li(5,12,17-Me3-1,5,9,12,17-pentaazabicyclo [7.5.5]nonadecane)] +, (7Li, 13C), LiNPri2, (6Li, (13C, (15N), [Pr(n CHCBu(tNHLi(hmpa)(m]n, (7Li, (13C), [Li(pyrrolidide)](3, ((6Li, (7Li), [R2BOLi(tmeda)], (7Li, 11B, 13C), [1,2-{Li(thf)PH)2C6H4], (7Li, 13C), and [But2SiFPLi (mesityl)], (7Li, 13C, 29Si).

23Na n.m.r. spectroscopy has been used to discriminate between two possible structures for a piperazino-crown ether derived from adrenalin. A number of biological systems have been studied by 23Na n.m.r. spectroscopy, by H, 23Na, 35Cl, and 59Co n.m.r. spectroscopy, and by 87Rb n.m.r. spectroscopy. The nuclear electric hexapole coupling of 133Cs has been determined for Cs+ in a nematic lyotropic liquid crystalline solution. 133Cs n.m.r. spectra of oriented CsDNA have been reported.

1J (13C-1h) values for the α-hydrogen nuclei of organomagnesium compounds decrease by 20 Hz due to the presence of magnesium. One and two dimensional 1H and 13C n.m.r. spectroscopy has been used to investigate the solution conformations of CaCl2 and Ca(NO3)2 complexes of chiral tetramethyl 18-crown-6 macrocycles. 13C n.m.r. data have also been reported for [(Me3Si)2C(MgBr)2], unsaturated organo-Grignard compounds, the Mg complex of (2), [(Me3SiC5H4)2Ca(thf)], (29Si), [(Me5C5)Ca(μ-I)(thf>2] 2, a barium complex of a crown ether containing a Ni Schiff base, and barium and lead Schiff base complexes.

Complexes of Groups IIIA and IVA, the Lanthanides, and Actinides. — The 1H and 13C n.m.r. spectra of complexes such as [(η5-C5 H5)Fe<η-C5H4YbI)] and [η5-C5H5)Mo(CO)3-YbI] have been interpreted in terms of σ-versus π-bonding. In [Y(C[equivalent to]CBut)4Li(thf)], 1J (89Y-13C) = 96 Hz. The first high resolution 171Yb n.m.r. spectra have been reported for a series of Yb(II) complexes. 1J(171Yb-14N) = 117.6 Hz was observed from [Yb(NR2)2-(OEt2)2]. The 235U quadrupole spin relaxation...