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Titanium (Ti) has two low sensitivity NMR active nuclei, ⁴⁷Ti and ⁴⁹Ti, with a very wide chemical shift range. It is unique in that their resonant frequency difference is only 267 ppm so both nuclei are generally observed at the same time (fig. 1).

Fig. 1. Ti-NMR spectrum of TiCl₄(neat) showing both nuclei in the same spectrum

⁴⁹Ti is the nucleus of choice because it is more sensitive and yields narrower lines than ⁴⁷Ti (fig. 2). Both nuclei yield moderately sharp lines in symmetric environments that become wider with increasing size of the complex and too broad to observe with a high-resolution NMR spectrometer for medium sized complexes. Ti-NMR is therefore restricted to the study of small complexes.

Fig. 2. Comparison of ⁴⁷Ti and ⁴⁹Ti for TiCl₄ (neat). ⁴⁹Ti yields greater sensitivity and narrower signals.

Each type of titanium compound has its characteristic chemical shift range (fig. 3). The NMR of Titanium can be observed in its (-II), (0), (II) and (IV) oxidation states. However, Ti(III) is paramagnetic and cannot be observed in high resolution NMR. Heteronuclear titanium spin-spin couplings have been observed with fluorine in TiF₆^2- (33 Hz) and with ¹³C in Ti(¹³CO)₆^2- (23 Hz).

Fig. 3. Chemical shift ranges for titanium NMR

⁴⁷Titanium NMR

⁴⁷Ti not as good an NMR nucleus as ⁴⁹Ti is because it is less sensitive and yields broader signals. However, its signals appear about 267 ppm downfield of those of ⁴⁹Ti unless they are too broad to observe. ⁴⁷Ti yields moderately sharp lines in small symmetric molecules but its signals become rapidly wider (fig. 4) (more rapidly than for ⁴⁹Ti) with increasing size of the complex and too broad to observe with a high-resolution NMR spectrometer for medium sized complexes. ⁴⁷Ti-NMR can only be observed in the smallest of complexes.

Fig. 4. Comparison of ⁴⁷Ti-NMR spectra of neat TiCl₄ and Ti(OⁱPr)₄ showing increasing line-width with molecular size

Properties of ⁴⁷Ti

(Click here for explanation)

Property	Value
Spin	5/2
Natural abundance	7.44%
Chemical shift range	2800 ppm, from -1400 to 1400
Frequency ratio (Ξ)	5.637534%
Reference compound	TiCl4 (90%) in C6D12*
Linewidth of reference	5.2 Hz
T1 of reference	0.06 s
Receptivity rel. to 1H at natural abundance	1.56 × 10-4
Receptivity rel. to 1H when enriched	2.10 × 10-3
Receptivity rel. to 13C at natural abundance	0.918
Receptivity rel. to 13C when enriched	12.3
Linewidth parameter	290 fm4

*Note that pure TiCl₄ resonates at 4.8 ppm in the ⁴⁷Ti-NMR spectrum.

⁴⁹Titanium NMR

⁴⁹Ti preferred as an NMR nucleus over ⁴⁷Ti because it is more sensitive and yields shaper signals. ⁴⁹Ti yields moderately sharp lines in small symmetric molecules but its signals become wider with increasing size of the complex (fig. 5) and too broad to observe with a high-resolution NMR spectrometer for medium sized complexes. ⁴⁹Ti-NMR can only be observed in small complexes.

Fig. 5. Comparison of ⁴⁹Ti-NMR spectra of neat TiCl₄ and Ti(OⁱPr)₄ showing increasing line-width with molecular size

Properties of ⁴⁹Ti

(Click here for explanation)

Property	Value
Spin	7/2
Natural abundance	5.41%
Chemical shift range	2800 ppm, from -1400 to 1400
Frequency ratio (Ξ)	5.639037%
Reference compound	TiCl4 (90%) in C6D12*
Linewidth of reference	2.4 Hz
T1 of reference	0.2 s
Receptivity rel. to 1H at natural abundance	2.05 × 10-4
Receptivity rel. to 1H when enriched	3.79 × 10-3
Receptivity rel. to 13C at natural abundance	1.20
Receptivity rel. to 13C when enriched	22.2
Linewidth parameter	83 fm4

*Note that pure TiCl₄ resonates at 4.6 ppm in the ⁴⁹Ti-NMR spectrum.

Safety note

Some of the materials mentioned here are very dangerous. Ask a qualified chemist for advice before handling them. Qualified chemists should check the relevant safety literature before handling or giving advice about unfamiliar substances. NMR solvents are toxic and most are flammable. Specifically, TiCl₄ reacts violently with moist air releasing toxic fumes (HCl) and many other Ti(IV) compounds are unstable and poisonous: wear protective gloves and work in a hood under nitrogen.

References

• R. G. Kidd, R. W. Matthews and H. P. Spinney, "Titanium-47 and titanium-49 nuclear magnetic resonance in titanium(IV)-halogen compounds" J. Am. Chem. Soc., 94, 6686 (1972).
• N. Hao, B. G. Sayer, G. Dénès, D. G. Bickley, C. Detellier and M. J. McGlinchey, "Titanium-47 and -49 Nuclear Magnetic Resonance Spectroscopy: Chemical Applications" J. Magn. reson., 50, 50-63 (1982).
• A. Dormond, M. Fauconet, J. C. Leblanc and C. Moise, "First NMR observation of ⁴⁷Ti and ⁴⁹Ti of cyclopentadienyl complexes" Polyhdron, 3, 897-900 (1984).
• K. M. Chi, S. R. Frerichs, S. B. Philson and J. E. Ellis, "Highly Reduced Organometallic. 23. Synthesis, Isolation, and Characterization of Hexacrbonyltitanate(2-), Ti(CO)₆^2-. Titanium NMR Spectra of Carbonyltitanates" J. Am. Chem. Soc., 110, 304-304 (1988).
• W. C. Finch, E. V. Anslyn and R. H. Grubbs, "Substituent Effects on the Cleavage Rates of Titanocene Metallacyclobutanes" J. Am. Chem. Soc., 110, 2406-2413 (1988).
• S. Berger , W. Bock, C. F. Marth, B. Raguse and M. T. Reetz, "^47/49Ti NMR of some titanium compounds" Magn. Reson. Chem., 28, 559-560 (1990).