Trends in NMR chemical shifts of d0 transition metal compounds

NMR chemical shifts of d0 transition metal compounds show the following trends: (1) For single-bonded ligands such as M-H, M-CR3, M←NR3, M-SiR3 and M←PR3, 1H, 13C, 15N, 29Si and 31P shifts of these α atoms in the complexes of both first- and third-row transition metals are typically downfield from (or at higher frequencies than) those of second-row analogs with a “V-shape” (Trend 1). (2) For multiple-bonded ligands including those with d-p π bonds, such as M=CHR, M≡CR, M=NR, M=O and M F, 13C, 15N, 17O and 19F shifts of the α atoms in the complexes of first-, second- and third-row transition metals move consecutively upfield (or to lower frequencies) (Trend 2). NMR shifts of lanthanum(III) complexes help interpret Trend 1 in Group 3 congeners. Scandide (d-block) and lanthanide (f-block) contractions and relativistic effects are believed to contribute to the NMR shifts, leading to the observed trends. Comparisons are made with NMR chemical shifts of dn complexes and organic compounds. Since many chemical properties of the second- and third-row congeners such as Zr and Hf are similar, as a result of lanthanide contraction, the NMR chemical shifts are a rare property to distinguish compounds of the otherwise nearly identical congeners. The current paper points out the trends with our narrative interpretations of the trends.