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 REPRODUCIBLE IN ASCII]) have been reported, and the quadrupole-coupling constants of 47,49Ti in TiCl4, were estimated as 2.8 and 2.4 MHz, respectively. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

Complexes of V, Nb, and Ta. — 13C n.m. r. data have been used to indicate that CS2 in NbCp2Bun(η2-CS2) has a larger σ-donor/π-acceptor ratio than CO. In Ta(C2H4)(Np)C12(PMe3)2 the high-frequency chemical shift for the neopentyl α-carbon atom δ139) and the low value for J(13C,1H) of 98 Hz have been interpreted in terms of one α-hydrogen atom interacting with the metal. The 31P n.m.r. spectrum was also recorded. For CpV(NO)2L the 5tV chemical shift varies between δ-1300 and -500, depending on the nature of L, whereas δ(13C) of the cyclopentadienyl ring varies only over 98 — 102 p.p.m. The isotope effect (1H/2H) on δ(93Nb) and temperature dependence of δ(93Nb) and T1(93Nb) for [CpNbX(CO)3]- have been discussed. Variations of δ(93V), δ(55Mn), and δ(93Nb) with the paramagnetic-deshielding contributions to the overall shielding have been discussed in terms of influences imposed by the ligand-field splitting, the nephelauxetic effect, and the covalency of the metal-to-ligand bond, for a wide range of organometallic compounds. e2qQ/h values have been obtained from 51V n.m.r. spectra of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] using 51V and 35Cl linewidths and 35Cl n.q.r. data. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] derivatives of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

Complexes of Cr, Mo, and W. — A book entitled 'Proton Magnetic Resonance in Hydrates of Molybdates and Tungstates' has appeared.

2H n.m.r. spectroscopy has been used to characterize D4M(dppe)2 (M = Mo or W) and reaction products with olefins. In µ-H[W(CO)4PR3]2-, 1J(183W, 1H) has been interpreted in terms of electronic and/or steric asymmetry. 13C n.m.r. data were also reported. For M2R2(NMe2)4(,M = Mo or W

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] n.m.r. studies have revealed the existence of a mixture of anti and gauche rotamers; as the bulkiness of the alkyl group increases, the gauche rotamer becomes increasingly favoured. A systematic study has been made on the effect of substituent-induced chemical shifts in [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] compounds using 13C and 95MO n.m.r. shifts. The 95Mo chemical shifts are extremely sensitive to the effects of distant substituents. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

For (2–5:9,10-{eta]-9-methylenebicyclo[4.2.1)nona-2,4,7-triene)Cr (CO)3 an unusual low-frequency shift for the quaternary 13C resonance of the semi-olefinic carbon atom (106 p.p.m., cf. free olefin) has been attributed to shielding effects. The 13C n.m.r. spectrum of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] is too simple owing to fluxiona1ity. For [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] the isocyano carbon atom of the σ+π-bonded isocyanide ligand occurs at δ215. For CpM(CO)2(LL) (M = Mo or W, LL = α-amino-acid) the diastereomers can be distinguished by their 1H and 13C n.m.r. spectra. The 1H and 13C n.m.r. spectra of (η6-naphthalene)Cr and (8) have been used to assess the bonding. 95MO n.m.r. spectra of (arene)Mo(CO)3 have been reported and the shift has been related to the Mo–arene bond strength. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

13C n.m.r. spectroscopy has been used to characterize [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], the product from the reaction of trans- Cr(CO)4(PPh3)2 and cis-Cr(CO)4(PPh3)2 with 13CO. The 31P n.m.r. spectrum of (19) (M = Cr, Mo, or W) is to very high frequency, δ 200–260. The 17O chemical shifts of RMn(CO)5 and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] have been explained in terms of substituent electronegativity which increases the paramagnetic shielding as the charge density at the oxygen 2p-orbitals decreases. The 31P and 199Hg n.m.r. spectra of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] have been reported, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] being the lowest observed for Hg-P bonds. The 19F and 31P n.m.r. spectra of some [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] complexes of Mo(CO)6 and W(CO)6 have been analysed to give 1J (31P,19F), 2J(31P, 31P), 3J(31P,19F), and in a few cases 4J(19F, 19F). N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

The effect of solvent polarity on the 1H n.m.r. spectra of Mo(CO)4(4,4'-disubstituted bipy) has been determined from measurements in CDCl3 and [2H6]DMSO. In all cases there are large changes in the chemical shift of the ring protons H3, H3', H6, and H6' as the solvent polarity increases. 95MO and 183W n.m.r. spectra of 65 derivatives of Mo(CO)6 and W(CO)6 with mainly phosphorus derivatives have been reported. W chemical shifts are ca. 1.7 times more sensitive than 95MO chemical shifts. The chemical shifts are temperature dependent. The 31P n.m.r. spectra, including 1J(95Mo, 31P) or 1J(183W, 31P), have been determined for [FORMULA NOT REPRODUCIBLE IN ASCII]. Several groups have determined 95MO chemical shifts for Mo(CO)5L and Mo(CO)4L2 compounds. A low-frequency shift is found in the order PPh3 > AsPh3 > SbPh3. When L = PF31, 97MO n.m.r. spectra were also recorded. For the 7-co-ordinate MoII carbonyl halide species there is a very large shift to high frequency for a carbonyl group in the capping position, thus permitting 13C n.m.r. spectroscopy to distinguish between possible isomers. The 31P INEPT spectra of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] have been recorded with considerable enhancement of the metal nuclei. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

17O n.m.r. chemical shifts of the MoO3-ligand complexes are much more sensitive to trans influences than crystal-structure measurements. 95MO and 13C chemical shifts were also reported. 13C n.m.r spectroscopy has been used to study oxotungsten(VI) complexes with aminopolycarboxylic acid ligands. Extremely sharp δ-sensitive spectra have demonstrated the importance of 183W n.m.r. spectroscopy for the polytungstate field. An excellent linear relation was found between δ(183W) and the wavelength of the lowest-energy optical absorption. 11B and 14N n.m.r. spectra were also recorded. 14N.m.r. data have also been reported for [FORMULA NOT REPRODUCIBLE IN ASCII].

Complexes of Mn, Tc, and Re. — 1H and 13C n.m.r. spectra have shown that [FORMULA NOT REPRODUCIBLE IN ASCII] is static. A two-dimensional δ/J31P n.m.r. spectrum of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] has been determined. The 13C n.m.r. spectrum was also recorded. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

The temperature dependence of the relaxation of 99Tc in [TcO4]- has been studied and the quadrupole moment of 99Tc estimated as +0.50 [+ or -] 0.05 barns. [TcO4] has an 18O isotopic shift of the 99Tc resonance of 0.43 p.p.m., and [FORMULA NOT REPRODUCIBLE IN ASCII] is 133.3 [+ or -] 0.5 Hz or 131.4Hz. For [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] were also characterized by 17O, 19F, and 99Tc n.m.r. 13C n.m.r. data have been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

Complexes of Fe, Ru, and OS. — 99RU and 101Ru n.m.r. spectra have been reported for a selection of compounds, covering a chemical-shift range in excess of 7000 p.p.m. The observation of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] has been shown to be useful as an aid to determining structure and dynamic behaviour and to indicate the presence of a tetrahedral interstitial hydride in [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

The 1H n.m.r. spectrum of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] shows one cyclopentadienyl signal, even at -90°C. For CpFeL2R (R = a silyl group) 29Si chemical-shift and NOE data have been related to the chemical bonding and molecular motion of the complexes. 115Sn, 117Sn, and 115Sn n.m.r. spectra have been recorded for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. The spectra revealed [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and very large [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

The complexation-induced changes of 13C chemical shifts of CH2 = CHSiR3 in (CH2=CHSiR3)Fe(CO) 4 result from rehybridization of the olefrnic carbon atoms to sp3. 1H and 13C n.m.r. has been used to determine the stereochemistry of (C6H8)Fe(CO)3 derivatives. In μ-(butatriene)-Fe2(CO)6 complexes the 13C resonances were assigned using the 1H-coupled n.m.r. spectrum. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

The SCCC MO theory, applied to the Pople-Karplus equation, predicts a low-frequency shift of the complexed ring carbon atoms in [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] relative to free l,3-cyclohexadienyl. The 13C-{57Fe} n.m.r. spectra of 57FeCp(CO)2X have been studied. The shielding of the 57Fe nucleus shows the normal dependence on the nature of the halogen. The structure of [CpFeC5H4CHR]+ has been investigated by 1H n.m.r. spectroscopy and discussed in terms of steric hindrance of R. 1H n.O.e. and 13C n.m.r. spectra of (31) have been used to investigate conformation. 11B and 19F n.m.r. spectra of [FORMULA NOT REPRODUCIBLE IN ASCII] have been used to demonstrate ion pairing. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

13C n.m.r. data have indicated that alkylation of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] occurs at a bridging CO and not on the carbide. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].

1H n.m.r. spectroscopy has been used to show 3,3' deuteriation of [Ru(bipy)3]2+ by CD3ONa/CD3OD. Additivity has been found in the C chemical shifts in 2,2'-bipyrimidine monometallic and bimetallic complexes of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. Spin-lattice relaxation times have been measured for diphenylphosphinous acid, dimethyl phosphite, and a series of RuII and PtII complexes of their anions. N.m.r. data have also been reported for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].