CHAPTER 1
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 proton 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.
A number of reviews have appeared including 'N.m.r. and inorganic chemistry', 'N.m.r. of metal nuclides. Part II: the transition metals', 'Scalar spin-spin interactions of nuclei in diamagnetic coordination compounds', 'Steady state techniques for low sensitivity and slowly relaxing nuclei, 'Effect of substituents in RnM organometallic compounds and changes in direct constants of the 1J (M,13C) spin-spin interaction', 'Nuclear magnetic resonance spectroscopy of organic analytical reagents and their metal complexes,' 'Nuclear magnetic resonance spectroscopy of chlorophylls and corrins', 'Structural properties of calmodulin, an intracellular calcium ion-modulator protein, as revealed by different n.m.r. techniques, and 'Elucidation of the structure and metal sequestering properties of metallothionein by nuclear magnetic resonance'.
A number of papers have been published which are too broadly based to fit into a later section and are included here. The general magnitudes of n.m.r. isotope shifts have been discussed. Recycled flow n.m.r. spectroscopy has been used to investigate 13C, 15N, 29Si, 31P, and 113Cd n.m.r. spectra of model compounds. Scalar relaxation of heteronuclear multiple quantum coherences and relative\ signs of nuclear spin-spin coupling constants have been examined and applied to J(35Cl,1H) and J(35Cl,29Si), which have opposite signs in SiHC3. The 13C magnetic shielding in cyclopentadienyl complexes has been calculated by eliminating effects due to charge. The results for the first overlapping sphere Zα-SW chemical shift calculations reproduce the trends in 13C n.m.r. measurements for the CO, CS, CN, and C5H5 ligands in Ni(CO)4, Cr(CO)5CS, and Fe(5CH 5)(CO)2CN. 13C n.m.r. spectra of RN=CHCH=NR in various coordination modes have been discussed with particular reference to the Ru3(CO)12 /RN=CHCH=NR system. Metal-allyl bonding has been studied by using 1J(13C,13C). 1J (13C,13C) varies between 59 Hz for Li or K(C3H5) down to 40 Hz for some transition-metal complexes. N.m.r. data have also been reported for complexes of ethylenediphosphinetetraacetic acid (31P), 1,3-bis(2-hydroxyphenyl)-1,3-propanedione (13C), and 7-methylguanosine (13C).
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. — 1H, 7Li, and 13C n.m.r. spectroscopy has been used to show that Li[Ph2CCLiCPh] has this structure. A similar investigation has been carried out using J(13C, 13C) and J(13C,6Li) on isotopically enriched materials. Solutions of alkylaryllithium salts chelated by Me2NCH2CH2NMe 2 or Me2N(CH2CH2 NMe)3Me have been studied by 7Li n.m.r. spectroscopy. Good correlations between the chemical shift and the pK of the parent hydrocarbon were found. The 13C n.m.r. spectrum of 6Li-benzovalene shows 1J (13C,6Li), 1H, 7Li, and 13C n.m.r. spectra of MSiMenPh3-n M = Li, K, have been discussed in terms of π-polarization of the phenyl rings. At low temperatures J(29Si,6 Li) and J(29Si,7Li) in Ph3-n MenSiLi are observed. A wide range of unsaturated hydrocarbons have been reduced by alkali metals in liquid ammonia, and detected in situ by 13C n.m.r. spectroscopy. K- in [K(15-crown-5)2]+K- in Me2O has been observed by 39K n.m.r. spectroscopy. The 7Li and 31P n.m.r. spectra of LiPR2 show 1J(31P, 7Li). The relaxation times T1 of free Na+ and Na+ bound to macromolecules have been determined simultaneously by the two-dimensional n.m.r. method by using 23Na n.m.r. spectroscopy. The 39K n.m.r. spectrum of K/Cs alloy dissolved in 12-crown-4 or 15-crown-5 shows the presence of K-. N.m.r. data have also been reported for EtCMeCHCH2Li (13C), 1-(Me2N)-3-lithiopropane [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]
A 13C n.m.r. study of the biosynthesis of bacteriochlorophyll using 18O has shown that 18O is incorporated into all possible sites. Similarly the incorporation of 1-[1-13C]glutamate and [2-13C]-glycine into bacteriochlorophyll has been studied by 113C n.m.r. spectroscopy. The structure of a bacteriochlorophyllide dimer in solution has been determined by 1H n.m.r. spectroscopy. 13Ca and 113Cd n.m.r. spectroscopy has been used to investigate structural differences in the two calcium-binding sites of the porcine intestinal calcium-binding protein. Shift reagents have been employed for 43Ca n.m.r. studies of calcium-binding proteins. Quadrupole coupling constants have been determined for 43Ca and 25Mg in M(acac)2, M = Ca, Mg. 13C T1 measurements were also performed. N.m.r. data have also been reported for Mg(C5H5)(CH2Bu t) (13C), Mg(C5H3 R1R2)2 (13C), [Mg(anthracene)]n (13C), 1,2-dimethylanthracenemagnesium (13C), Mg-inosine-5-monophosphate (13C), Be(R1 COCHCOR2)2 (13C, 19F), and MUO2(OAc)4 (M = Mg, Ba, Co, Zn; 19F).
Complexes of Groups IIIA and IVA, the Lanthanides, and Actinides. The 89Y n.m.r. spectra of some organoyttrium complexes such as (MeC5H4)3Y(thf) have been reported, and vary over a range of 400 p.p.m. For (MeC5 H4)3Y(thf), J(89Y,1 H) = 27 Hz. The 17O chemical shifts are related to the lowest electronic transition energies of UO2 complexes. 1H, 17O, and 79Br n.m.r. spectra have been recorded for aqueous-organic solutions of the perbromates of uranyl and neptunyl and the coordination of water and anion investigated. The 19F relaxation in gaseous UF6, WF6, and MoF6 is consistent with relaxation dominated by spin-rotation interaction. The possibility of the use of 19F n.m.r. spectra in 235U enrichment determination in UF6 (gas) has been investigated. The linewidth modification induced by various 235U enrichments is related to the 19F-235U indirect scalar interaction, modulated by rapid 235U quadrupole relaxation. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
The 1H n.m.r. spectrum of [FORMULA NOT REPRODUCIBLE IN ASCII] has been reported. The titanium analogue has a thermally accessible paramagnetic state, and hence the shifts are temperature dependent. 1H n.m.r. spectroscopy has been used to show exchange in [(C5Me5)2 Hf (N2)]2<μ-N2), and the 13C n.m.r. spectrum of (C5Me5) 2Hf2(CO) was recorded. In (C5 H5)2Ti(μ-CH2)M(C5 H5>2, M = Ti, Zr, Hf, both 1H and 13C n.m.r. spectra show high-frequency shifts for the methylene groups, which were discussed in relation to metal-carbene or metal-metal bonding in those complexes. 47Ti and 49Ti n.m.r. chemical shifts, recently reported for (C5H5) 2TiX2 have been reassigned. In R2 Si(C5H4)2MCl2, M = Ti, Zr, the 13C n.m.r. signal of the bridgehead carbon is substantially to low-frequency from the other ring carbon atoms. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
Complexes of V, Nb, and Ta. — 51V chemical shifts vary over a range of 1400 p.p.m. with a temperature coefficient of up to +1.2 p.p.m. deg-1 for [(C5H5)V(SnCl3)(C0) 3]3. 1J(117,119 Sn,51V) and 1J(51V,-13C) were determined. For [V(CO)5L]- the shielding of the 51V nucleus decreases in the order alkene > alkyne - N2 > SO2 > CS2 > {O}. Compared to n1-coordination, n2-coordination gives rise to a deshielding contribution of 100-280 p.p.m. In (C5H4Me)Nb(n2-RC2 R)Cl2 the 13C n.m.r. chemical shifts of the acetylenic carbon atoms suggest that the alkyne donates four electrons to the niobium atoms. The 13C isotope effect in the 51V n.m.r. spectra of [V(CO)6]- has been determined. The 13C n.m.r. spectrum was also recorded. In [V(CO)5PR3 the 51V shift trends correlate with the integral ligand strength as quantified by Graham's σ- and π-parameters. The 31P n.m.r. spectra were also recorded. 51V and 55Mn chemical shifts of analogous compounds have been compared for [V(CO)5L]-, V(NO) (CO)4L, and Mn(NO)3L. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
A decrease of 51V shielding in the order [VO2 Cl2]- > [VOCl4]- > [VX3(N3S2]22- (X = N3 > Cl) has been reported. For V(OR1) 3- (=NR2) the 51V n.m.r. spectrum shows 1J(51V,14N), [VO4H] 2 has been investigated by 51V n.m.r. spectroscopy in a mixed lyotropic mesophase. For a series of oxovanadium(V) compounds, linear relations exist between 6( V) and substituent parameters such as the electronegativity, Pearson's hardness parameter, and Taft's electronic and steric constants. High-field 51V and 17O n.m.r. spectra have been determined for peroxyvanadates in aqueous soluttion; five new species, including four which are dimeric, were identified. [HPV14O42]8- shows a pH-dependent oxygen exchange, which correlates with 17O, 31P, and 51V chemical shifts. Mixed vanadium-tungsten polyoxo complexes in aqueous solutions have been identified by 17O and 51V n.m.r. spectra. 31P and 51V n.m.r. spectroscopy has been used to study vanadotungstophosphate heteropoly acids in solution. The influence of 51V, 93Nb, 181Ta, 95Mo, 97Mo, and 183W coupling on 17O line widths has been determined. Only 51V and 93Nb coupling affects 17O linewidths. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
Complexes of Cr, Mo, and W. — The 95Mo T1 and T2 have been measured for a number of compounds. Quadrupolar relaxation is the only significant mechanism involved, allowing T1 values to be interpreted in terms of the electric field gradient, molecular size and shape, solution viscosity, temperature, and solvent-solute interactions. 97Mo relaxation times were also reported. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
13C and 31P n.m.r. spectra have been used to show that W(CO)3- {P(OMe)3} (n4 -C8H8) is a mixture of fac- and mer-isomers. The effect of slippage of the cyclopentadienyl ring on n.m.r. parameters has been investigated for (indenyl)Mo(CO)2 (1-Me-allyl) and [(indenyl)IrH(PPh3)2]+. For a number of molybdenum compounds such as [(C5 H5)Mo(CO)2(NR1=CR2 C5H4N)]+, the 95Mo signal shows the presence of diastereomers. A study of the aryl 13C chemical shifts and 1J(13C, 1H) for (3-8-n-[2.2]paracyclophane)chromium and some related complexes has shown that they correlate with chromium-carbon distances. The geometric configuration of (n6-9-RCl 3H9)-Cr(CO)3 has been determined using 1H ASIS. It has been shown that the enantiomeric purity of (arene)Cr(CO)3 complexes bearing an aldehyde group can be determined using Eu(hfc)3. A comparison of the 1H n.m.r. spectra of veratrole and (veratrole)Cr(CO)3 shows that protons ortho to MeO are less shielded upon complexation and this was discussed in terms of relative regioselectivity. 1H and 13C n.m.r. spectroscopy, including two-dimensional techniques, has been used to distinguish between the two isomers of Cr(n6 -es-tradiol)(CO)3. The 31P chemical shift of the n6-bonded ligand in Mo(n6-PhPR2) (PPhR2)(dppe) correlates with the sum of the cone angles of the three π-bonded ligands in each complex. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
Spin-lattice relaxation times of 95Mo, 97Mo, 17O, and 13C for Mo(CO)6 have been reported. The rotational correlation time of the molecule was obtained from the c.s.a. relaxation of 13C. Quadru-polar coupling constants were calculated for 17O, 95Mo, and 97Mo. The 95Mo n.m.r. parameters have been measured for Mo(CO)6-n(py)n. T1 was determined for 95Mo and 13C for some complexes. The ^Mo chemical shift range of some seven coordinate molybdenum(II) isocyanide complexes is about 1100 p.p.m. 13C, 14N, and 31P n.m.r. spectra were also recorded where relevant. 19F and 31P chemical shift data support the σ-donor/π-acceptor model of the Cr-P bond in Cr(CO)5L and cis-Cr(CO) 4L2, L = RPSCH2CH2S. 95Mo chemical shifts have been reported for a range of complexes, [Mo{CO)5X]-. The chemical shift values extend over 1000 p.p.m. and reflect the importance of ligand field strength, polarizability, and electronegativity factors in determining the 95Mo chemical shifts. The decreasing shielding effect is in the order [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and 31P n.m.r. spectra of (OC)4Mo(Ph2PO)2 SiMeR have been studied. The chemical shift ranges of the carbonyl 13C and 17O, the phenyl C(1) 13C and 31P resonance are relatively large, and, with the exception of the cis CO 17O chemical shifts, the correlations between the chemical shifts of the various resonances are excellent. For Mn(CO)4(substituted bipy) the influence of the solvent on the chemical shifts of the bipyridine ring increases significantly as a result of coordination to the metal. Complexes of the type Mo(CO)4(Ph2PO) SiMeR exhibit two 13C resonances for the cis-CO and phenyl carbon atoms. The differences between the chemical shifts of the two resonances can be correlated with the Taft steric parameters of the R groups. The 31P n.m.r. spectrum of Mo(CO)3{P(OCMe2CH2) 2N}3 shows 1J(95Mo, 31P) = 210 Hz. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
15N T1 and 15N-{1H} n.O.e. measurements have been reported for 15N in N2 complexes of Mo, W, Re, and Os, together with 13C and 31P n.m.r. data. It was found that the relaxation is predominantly due to c.s.a. and the rotational correlation times were determined. The Nα in the rhenium complex is also relaxed by Re. The 14N linewidths were also determined. The 31P relaxation is fully dipolar. 95MO and 14N n.m.r. studies of seven coordinate molyb-denum(VI) monoxo, nitride, and phenylimido complexes have been reported. The chemical shifts of the complexes increase in the order L = NPh < NO < N < O < NS, while the linewidths of these compounds increase in the order L = O < N << NPh < NS < NO. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
