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, 13C, 19F, and/or 31P NMR 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 number of publications, many more papers in marginal areas have been omitted. This is especially the case in the sections on solid-state NMR spectroscopy, silicon and phosphorus.

Two books relevant to this review have been published, namely, 'Advanced Applications of NMR to Organometallic Chemistry', and 'NMR Spectroscopy of the Non-metallic Elements'.

Several reviews have been published which are relevant to this review:- 'Ab initio calculations of the NMR chemical shift' 'Structure and physical properties of transition metal nitrosyls', which contains 15N NMR spectra, 'NMR and EPR spectroscopic characterisation of the reactive intermediates of transition-metal-catalysed oxidations', which contains C0 NMR spectroscopy, 'Nuclear magnetic resonance: a non-invasive technique in the study of life processes in situ', 'The binding of transition metal ions to DNA oligonucleotides studied by nuclear magnetic resonance spectroscopy', 'Stereochemistry of chelate complexes of fluorides of tantalum(V) and phosphorus(V) in solutions according to NMR data', and 'NMR experiments of magnetic compounds below 1K'.

A number of papers have been published which are too broadly based to fit into a later section and are included here. The relationship between 1J(2H1H) and internuclear distance in H2 complexes has been examined. Molecular orbital calculations have been used to explain the 1H chemical shifts of titanium, chromium, molybdenum and tungsten bis(fluorene) complexes in terms of px electronic density. A general theoretical formalism for describing the high-order effects of the dipolar coupling between I = 1/2 and quadrupolar nuclei has been reported. The optimal conditions for the NMR observation of nuclei other than 1H and 13C have been discussed according to receptivity and the factors governing the relaxation processes. An easy way to investigate reactions with gases in the liquid phase has been described and applied to the formation of a zirconacyclopentene from a zirconium-alkyne complex and ethene and investigations on rhodium-catalysed olefin hydrogenation. The NMR rotational correlation equations for dipolar relaxation between 1H and the nuclei, 1H, 13C, 31P, and 113Cd have been solved for viscous solutions using the R2/R1 dipolar ratio. The technique was applied to determine the 27Al nuclear quadrupole coupling constants in 1:2 LiCl-EtAlCl2 melts and neat EtAlCl2, and used to characterise Cd2+ and inorganic phosphate binding sites in yeast inorganic pyrophos-phatase. Rovibrationally averaged nuclear magnetic shielding tensors have been calculated at the coupled-cluster level for H2, HF, N2, CO and F2. The effect of a libration or hopping motion of the η2+-dihydrogen ligand in transition metal complexes on T1 has been investigated. The application of T1 and T2 of metallic hydrides in the structural investigation of hydride complexes and clusters has been reported. The effect of net charge and π-backbonding contribution of ML5 fragments containing FeII, RuII, OsII, CoIII and RhIII on the 1H NMR shifts of coordinated N-heterocycles has been studied. The 17O shielding in [MO4]n-, M = Cr, Mo, W, Mn, Tc, Re, Ru, Os, and the 53Cr, 95MO, and 183W chemical shifts in [M(CO)6]], M = Cr, Mo, W, have been calculated.' The calculation of 13C chemical shifts of [M(CO)6], M = Hf, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Ir, have been reported. The 31P NMR chemical shifts of [(OC)4,M(μ-PMe2)]2, M = V, Cr, Mn, have been calculated and correlated with the metal-metal bond. Extensive use has been made of 1H, 17O, 51V, 59CO, and 95Mo to investigate reactions, and species such as [VO(acac)2 (OCMe2Ph)], [Co3O(OAc)5, (OH)(AcOH)3]+, and [MoO(O2)2(HMPA)] have been identified.

2 Stereochemistry

Complexes of Groups 1 and 2 – The dimeric structure of [(2-Me2NCH2-4,6-Me2C6 H2)Li]2 has been confirmed by the seven line 13C NMR signal due to 1J(13C 7Li). The 6Li and 7Li NMR chemical shifts of lithium salts of cyclopentadienyl, indenyl, and fluorenyl have been calculated. The 1H, 6Li, and 13C NMR data of cyclopropenyl cation and its lithium derivatives indicate that the chemical shifts increase with increasing lithium substitution on the ring. 6Li and 7Li NMR spectroscopy has been used to show that [6LiCHPhNArC(=O) OBut] is monomeric. 1J(15N 6Li) has been detected in (1). A 6Li6Li INADEQUATE experiment was carried out and J(6Li 6Li) observed. A Si-HLi agostic interaction has been observed by 1H, 6Li, and 29Si NMR spectroscopy in (2), but none detected in the 1H -6Li HOESY spectrum of [Li(Me2SiHNBut)]. The 7Li NMR spectrum of (3) shows two signals and the 29Si NMR spectrum shows J(29Si7Li). A two-dimensional HMQC experiment has been performed for the first time to correlate 6Li and 29Si resonances using scalar 6Li, 29Si coupling in 1, 4-diyl-1,4-diphenyl-1,2,3,4-tetrakis(trimethylsilyl)butane, where 2J(29Si6Li) and 3J(29Si6Li) are 0.3 and 0.7 Hz respectively. NMR data have also been reported for [Li2(CH2NPh2)2(THF) 3], (7Li), [LiCH2SR], (7Li), [C4H4MLi2], (M = C, Si, Ge, Sn, Pb; 7Li), (4), (6Li), [7Li (CHPMe2NSiMe3)3(OSiMe2 Bun)]2, (29Si),[LLi] 2, [L2Pb], {L = (5); 7Li, 207Pb}, [Li{N(SiMe3)CPhCHPR2=NSiMe3}], (7Li), [{LiC6H3-3,5-But2}6], (7Li), N,C-dilithio-2-allylpyrrole, (7Li), [Me2Si-(fluorenyl)2Li2], (7Li), [LiC(SiMe3)3], (29Si), [MC(SiMe3)3-n-(SiMe2Ph)n], (M = Li, Cs; 7Li, 29Si, 133Cs), [LiC = CSiMe2C6H4-2-OMe], (29Si), [MeBut2SiNLiN-LiSiBut2Me], (7Li), [But3SiLi], (7Li, 29Si), [MSi(SiMe33], (M = Li, Na, K, Rb, Cs; 29Si), [MeSi{Me2SiN(4-tol)}3SnLi (OEt2)], (7Li, 29Si), (6), (7Li, 29Si),[(Et2N)Ph2SiLi], (29Si), (7), (6Li, 29Si), and [Me(PhMe2Si)2SiLi], (7Li, 29Si).

6Li and 15N NMR spectroscopic studies of lithium diisopropylamide have established...