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Spectroscopic Properties of Inorganic and Organometallic Compounds Volume 7
A Review of Literature Published during 1973
By N. Greenwood The Royal Society of Chemistry
Copyright © 1974 The Chemical Society
All rights reserved.
ISBN: 978-1-84755-491-8
CHAPTER 1
Nuclear Magnetic Resonance Spectroscopy
BY B. E. MANN
1Introduction
The structure of this chapter has been modified in several ways. The introductory section has been considerably shortened with the omission of discussion of techniques, coupling constants, chemical shifts, and relaxation measurements. Papers relevant to this review have been absorbed into the rest of the text. Readers who are interested in these sections are referred to the excellent Specialist Periodical Report on 'Nuclear Magnetic Resonance' where these sections are covered in much greater depth than has been possible in earlier volumes of this review. The use of the Chemical Society's n.m.r. Macroprofile (UKCIS) has again been changed. It is now used as a source of references in non-chemical or obscure journals which are included in the main text and consequently there is no bibliography. As a result of this change, many more biochemical papers have been abstracted and a new section on metals in biological systems has been added. There is also a change of terminology introduced this year. Following recommendations, the use of the phrase 'magnetic field' has been discontinued and magnetic flux density is used instead.
1H N.m.r. spectroscopy continues to be the principal n.m.r. nucleus. However, interest in other nuclei has continued to grow and includes 2H, 6Li, 7Li, 10B, 11B, 13C, 14N, 15N, 19F, 23Na, 25Mg,27Al, 29Si, 31P, 35Cl, 39K, 45Sc, 51V, 55Mn, 59Co, 69Ga, 71Ga, 73Ge, 75As, 77Se, 81Br, 85Rb, 87Rb, 93Nb, 105Pd, 113Cd, 113In, 115In, 119Sn, 121Sb, 127I, 133Cs, 183W, 199Hg, and 205T1. There has been a marked increase in the use of C n.m.r. spectroscopy with 13C n.m.r. spectrometers becoming more readily accessible, and 29Si n.m.r. spectroscopy is also becoming popular.
Volume 5B of Annual Reports on N.M.R. Spectroscopy has appeared, and is devoted to 'N.M.R. Studies of Phosphorus Compounds (1965 – 1969)' by G. Mavel. It is split into three chapters on Chemical Shifts, Coupling Constants, and Applications.
A number of books devoted to aspects of n.m.r. spectroscopy have been published. McFarlane and White's book is principally concerned with experimental and instrumental aspects of n.m.r., and the one by Batterham contains details of phosphorus, arsenic, selenium, tellurium, boron, and silicon heterocycles. Two new student texts have appeared. 'N.M.R. and Chemistry' is especially welcome being written by a previous reporter of this chapter, J. W. Akitt. It is one of the few student texts on n.m.r. which acknowledges that inorganic chemistry exists. 'Magnetic Resonance and Related Phenomena', edited by V. Hovi, contains the proceedings of the XVIIth Congress Ampere, Turku, August, 1972.
Other books have appeared which contain sections or chapters devoted to n.m.r. spectroscopy. Books have also been published containing chapters on high-resolution n.m.r. theory and n.m.r. spectra of sulphur compounds. 'Dictionary of Spectroscopy', 'Organic Analysis', 'Spectroscopic Problems in Chemistry', and 'Atlas of Spectral Data and Physical Constants for Organic Compounds' have also been published
A large number of reviews on n.m.r. spectroscopy have been published this year ranging from the very general reviews, 'Introduction to N.M.R. Spectroscopy' and 'Nuclear Magnetic Resonance' via 'Troublesome Concepts in N.M.R. Spectroscopy' to specialized reviews such as 'Chemistry and Applications of Liquid Crystals' and 'The Solvent Dependence of Nuclear Spin-Spin Coupling Constants'. Other reviews to appear include 'Progress of N.M.R. and its Application. Fourier Transform N.M.R.', 'Fourier Transform Spectroscopy', 'Applications of 1H N.M.R. Spectroscopy', 'Double Resonance', a review of transition-metal hydrides which contains discussion of hydride chemical shifts, and 'Applications of 19F N.M.R. Spectroscopy'. 13C N.m.r. spectroscopy has received much attention from reviewers, and in addition to articles on 13C n.m.r. spectroscopy in general, reviews have appeared on 'Current Applications of 13C N.M.R. Spectroscopy in the Petroleum Industry', 'Application of N.M.R. to the Food Industry', 'New Analytical Instruments', 'Experimental Techniques', 'Principles and Instrumental Assumptions in Carbon-13 N.M.R. Spectroscopy', '13C Spin-Lattice Relaxation Studies and Their Application to Organic Chemical Problems', and '13C-13C, 13C-15N, and 13C-31P N.M.R. Coupling Constants; Classification and Analysis'. Other reviews have appeared on 'Stereochemical Studies of Metal Carbonyl-Phosphorus Trifluoride Complexes', 'Spectroscopic Studies of Metal-Phosphorus Bonding in Co-ordination Complexes', 'The trans-Influence', 'The cis- and trans-Effects of Ligands', '29Si N.M.R. Spectroscopy', 'Applications of 31P N.M.R. Spectroscopy', and 'Nuclear Magnetic Resonance Studies of Organophosphorus Extractants'.
In addition to these books and reviews, papers have appeared which are too broadly based to fit into any of the later sections of this chapter and are included here. The dependence of the paramagnetic component of the magnetic shielding constant for RnAZ4-n has been studied and good agreement between theory and experiment was found for third and fourth group elements. A detailed examination of the relation between chemical shifts in ESCA and n.m.r. spectroscopies has been presented. It was shown that even for related compounds, a linear correlation cannot be expected. A close relationship between chemical shifts in ESCA and n.m.r. spectroscopies and spin rotation constants of molecules has been pointed out. 136C N.m.r. chemical shifts of [M(CN)n]m- have been determined and cover a range of 53 p.p.m. In complexes having the central transition-metal ion with the same electronic configuration, the heavier the metal, the more positive is the chemical shift. 13C N.m.r. spectra of a wide range of π-complexes have been studied. An increase in 13C shielding and 1J(13C-1H) was observed. For π-cyclopentadienyl complexes a correlation between the shielding of the ligand and the structure of the valence shell of the transition metal and geometry was found.
2 Stereochemistry
This section is subdivided into nine parts, which contain n.m.r. information about lithium, beryllium, magnesium, calcium, and transition-metal complexes, presented by groups according to the Periodic Table. Within each group classification is by ligand type. As far as possible, cross-references are given at the beginning of each sub-group to compounds discussed elsewhere in this chapter. In this cross-referencing, it has not proved possible within the space available to include the many compounds that occur within the sections on dynamic systems, paramagnetic systems, and solid-state n.m.r. spectroscopy. Thus many more compounds of relevance to this section appear elsewhere.
Complexes of Li, Be, Mg, Ca, Sc, Y, La, Ce, Er, and U. — A review entitled 'N.M.R. Study of Organolithium and Organomagnesium Compounds' has appeared.
1H N.m.r. spectroscopy has been used to investigate the lithiation of arenes, and the 1H n.m.r. spectrum of (1) has been measured in various solvents to investigate the structure and conformation. o-LiC6H4CH2-NMe2 reacts with AgBr to give 6H4CH2NMe2)4 Ag2Li2. On the basis of 1H and 13C n.m.r. spectroscopies, structure (2) was proposed. It is interesting to note that J(1H-107,109]Ag), J(13C-7Li), and J(13C-Ag107,109) were observed. 1H N.m.r. spectroscopy has also been used to investigate the complex between LiCl and MeSi(CH2-2-pyridyl)3, and the observation of two CH resonances for LiCH2CO2But suggests that the compound is in the enol form. Data have also been reported for Me2NCH2CH2NMe2-LiBun.
The methyl signal of (ButBeMe)3 is broad and temperature invariant, whereas the 1H n.m.r. spectrum of bis-3-(2-thenoyl)-1,1,1 -trifluoroaceto-natoberyllium(II) is AMX. Bun2 reacts with BunK to give Bun3MgK and the α-CH2 moves from τ 10.57 to τ 10.74. The basicity of solvents with respect to Et2Mg has been determined by measuring the chemical shift separation of the CH3 and CH2 resonance in various solvents. At – 100 °C, the 1H n.m.r. spectrum of PhCN and Me2Mg shows signals attributable to (PhMeC=NMgMe)2 and the presence of two isomers, (3) and (4), was suggested. 1H N.m.r. spectroscopy has been used to show that RCH=CHCH2MgCl exists in solution as rapidly interconverting cis-trans isomers even at – 80 °C. On the basis of coupling constants the percentage of cis-isomer decreases as the size of the alkyl substituent increases. 1H N.m.r. spectroscopy has also been used to determine the ratio of EtMgBr to EtOCHMePr, to characterize XMgCH2CHCMe2CMe2, and to demonstrate meso deuteriation of magnesium porphyrins. The 13C n.m.r. spectrum of chlorophyll a has been assigned and T1 determined. The 1H n.m.r. spectrum of (4-RO-pyridyl)2MgBr2, reported as A2B2 rather than [AB]2, shows deshielding of the pyridine signals. From 1H n.m.r. spectroscopy, the structure of calcium benzylcyanide is thought to be a mixture of (PhCH=C=N)2Ca and (PhC[equivalent to]CNH)2Ca, and data have been reported for (C5H5)2Ca(solvent)2, and {PhCH=C(OEt)O}2Ca.
It is interesting that [FORMULA NOT REPRODUCIBLE IN ASCII] or Y) shows 2J(Y-1H) = 2.5 Hz when M2 = Y. Data have also been reported for Sc(8-hydroxyquinoline)3-n(OAc)n, La(acac)3L (L = en, pn, or phen), Ce(Acfp)a, Er2(Acfp)4(OH)2(MeCONH2) [Acfp = MeCONH-CO(CF3)2], uranyl-thiamine derivatives, and UO2-L2L1 (L = acac and related compounds, L1 = Ph2SO or Bz2SO).
Complexes of Ti, Zr, Hf, V, Nb, and Ta. — The 11B n.m.r. spectrum of XTi(BH4)3 is a quintet and hence the molecule is fluxional. The 1H n.m.r. spectrum of (C6H6)2Ti, prepared via matrix isolation, has been reported. The thermal stability of [FORMULA NOT REPRODUCIBLE IN ASCII] has been measured by 1H n.m.r. spectroscopy by determining the time taken for 50% decomposition. The order Ti < Zr < Hf was found. The 1H n.m.r. chemical shifts of (Cp)2TiXY (X, Y = Ph, Bz, or Cl) have been examined in a wide range of solvents and some previous work has been shown to be wrong because of decomposition. Data have also been reported for [FORMULA NOT REPRODUCIBLE IN ASCII]
1H N.m.r. spectroscopy has proved useful in demonstrating the presence of an asymmetric centre at the titanium in complexes such as [FORMULA NOT REPRODUCIBLE IN ASCII] , and [FORMULA NOT REPRODUCIBLE IN ASCII]. When titanium is linked to ferrocene in compounds such as [FORMULA NOT REPRODUCIBLE IN ASCII], the 13C n.m.r. signal of the substituted carbon moves to low frequency by 40 p.p.m. 1H N.m.r. spectrum of Me3Al and (ButO)4Ti showed (Me2AlOBut)2 and MeT(OBut)3. MeTiC(OBut)3 is stable at 75 °C, contrary to previous reports. Data have also been reported for [FORMULA NOT REPRODUCIBLE IN ASCII] or Hf;X = Cl, Me, Ph, or C6F6) and some indenyl derivatives, [FORMULA NOT REPRODUCIBLE IN ASCII] , or I), (6) and related compounds, [FORMULA NOT REPRODUCIBLE IN ASCII] or 3), and [FORMULA NOT REPRODUCIBLE IN ASCII] .
The 1H n.m.r. spectrum of (RO)3TiL (L = Me2NCH2CH2NMe2 and related ligands) shows that both NMe2 groups are co-ordinated and hence the complexes are five-co-ordinate. However, the equivalence of alkyl protons of (R2NCS2)TiX even at – 80 °C was attributed to non-rigid behaviour. The reaction of β-diketones, L, with [FORMULA NOT REPRODUCIBLE IN ASCII] and [FORMULA NOT REPRODUCIBLE IN ASCII] gives and [FORMULA NOT REPRODUCIBLE IN ASCII] and [FORMULA NOT REPRODUCIBLE IN ASCII]. The 19F n.m.r. spectra of the titanium compounds are A2X2 or ABX2, depending on the symmetry of L. The 19F n.m.r. spectra of TiF4 and TiOF2,H2O in H2O2 show the presence of fluorinated species not found in aqueous solution. 19F N.m.r. spectroscopy has been used to demonstrate the existence of fluoride-bridged polymeric fluoroanions of TiIV and SnIV in liquid SO2, e.g. [Ti2F11]. Data have also been reported for [TiCl2-NSiMe3]4, [FORMULA NOT REPRODUCIBLE IN ASCII], [FORMULA NOT REPRODUCIBLE IN ASCII], Ti(α-benzoin-oxime)2, Ti complexes of (7), TiCl2(OAc)(OR), and [(3)-1,N-B9C2H11] [M4(acac)9(OH)11]12 (M = Zr or Hf; N = 2 or 7).
The 1H n.m.r. spectrum of [FORMULA NOT REPRODUCIBLE IN ASCII] shows a quintet and the molecule remains fluxional down to -140 °C. When Et3Al is added to [(C5H5)(C5H4)NbH]2 or to (C5H5)2Nb(C2H4)H the hydride signals move 5 and 7 p.p.m., respectively, to high magnetic flux density. For (C5H5)TaH3, only the A resonance of the AB2, hydride, spectrum shows any interaction. These results were interpreted as the Et3Al co-ordinating to the hydride. 1H N.m.r. spectroscopy has been used to follow the reaction of Me3MNMe2 (M = Si, Ge, or Sn) with transition-metal hydrides to form species such as [FORMULA NOT REPRODUCIBLE IN ASCII] and [FORMULA NOT REPRODUCIBLE IN ASCII] (M = Mo or W). [FORMULA NOT REPRODUCIBLE IN ASCII] dissolves in CS2 to give [FORMULA NOT REPRODUCIBLE IN ASCII] and the 1H n.m.r. spectrum shows a static σ-allyl. This reacts with RI to give [FORMULA NOT REPRODUCIBLE IN ASCII] (1H n.m.r. data). Data have also been reported for [FORMULA NOT REPRODUCIBLE IN ASCII] (M = Nb or Ta; M1 = Ti or Zr), and MCl4(CCl=NMe)CNMe, (M = Nb or Ta). hexahalogenoniobate anions in the series [NbClnBr6-n]- have been prepared and 93Nb n.m.r. spectra measured. [NbCl2Br4]- and [NbCl4Br2]- are cis-isomers, while [NbCl3Br3]- is the fac-isomer. The pairwise additivity model for predicting chemical shifts has been extended from four- to six-co-ordinate complexes. It provides a powerful technique for identifying in solution the presence of specific geometric isomers. Chlorine substitution causes a shift of the 93Nb resonance to high flux density. 1H and 19F n.m.r. data have also been reported for [FORMULA NOT REPRODUCIBLE IN ASCII] and related compounds.
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Excerpted from Spectroscopic Properties of Inorganic and Organometallic Compounds Volume 7 by N. Greenwood. Copyright © 1974 The Chemical Society. Excerpted by permission of The Royal Society of Chemistry.
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