¹³C and ²⁰⁷Pb NMR Chemical Shifts of Dirhodio- and Dilithioplumbole Complexes: A Quantum Chemical Assessment

Abstract

Density functional theory (DFT) and zeroth-order regular approximation DFT calculations were performed to investigate the electronic structures and 13C and 207Pb nuclear magnetic resonance (NMR) chemical shifts of metal-coordinated plumboles, namely, mono­rho­dio­plumbole ([Rh–plumbole]−), di­rhodio­plumbole (Rh2–plumbole), and di­lithio­plumbole (Li2–plumbole), which have a five-membered ring containing lead. The molecular orbital correlation diagram and extended transition state–natural orbitals for chemical valence analysis of the [Rh–plumbole]− and Rh2–plumbole complexes showed that the plumbole is primarily a π-donor, with π-donation being dominant in the Rh2–plumbole complex. The present calculations show that the Pb–Cα internuclear distances are longer in the Rh2–plumbole complex than in [Rh–plumbole]− because of the combined effect of strong π-donation and weak π-back-donation in the Rh2–plumbole complex. The calculated 207Pb and 13Cα NMR chemical shifts agree with the experimental trends reasonably well. The influences of the relativistic effect, role of the functional, effect of the solvent, and dependence of the exact exchange admixture on the calculated 207Pb and 13Cα NMR chemical shifts were investigated. The NMR chemical shift trend of the 207Pb atom in the complexes originates from the paramagnetic and spin–orbit contributions. NMR component analysis revealed that the upfield shift of the 13Cα atoms of the [Rh–plumbole]− and Rh2–plumbole complexes compared to that of the Li2–plumbole complex is mainly due to the decrease in the paramagnetic term.

Lithium Salt of 2,5-Bis(trimethylsilyl)stannolyl Anion: Synthesis, Structure, and Nonaromatic Character

“…On the contrary, the 29 Si NMR signal of the aromatic silolyl anion reported by Kovács, Nyulászi, et al shifted to the lower field compared to that of its neutral precursor (δ 65.7 for the silolyl anion vs. 17.0 for its precursor) due to the π-electron delocalization [36]. A significant downfield shift was observed for the C α signal [from δ 148.5 (2) to 180.2 (3•(thf)], as was observed in stannolyl and plumbolyl anions, which can be explained by the substantial contribution of the paramagnetic term (σ para ) [49]. In the 7 Li NMR spectrum, a slightly broadened signal was observed at δ −1.47.…”

Benchmark Study on the Calculation of 207Pb NMR Chemical Shifts

“…16−20 Still, they all lack a thorough assessment of the underlying theoretical method based on a diverse set of lead-containing compounds that were measured in solution. [10][11][12][13][14][15]21 Due to the presence of unoccupied p-orbitals in group 14 elements, the 207 Pb nucleus has a huge SO heavy atom effect on the shielding of neighboring light atoms (HALA effects), especially in Pb II compounds. 22 Heavy atoms in the vicinity of the Pb nucleus can also have a heavy atom effect on the heavy atom Pb (HAHA).…”

“…Computations of 207 Pb NMR shifts have already been carried out for, e.g., dirhodioplumbole, organolead and halogen lead complexes, diarylplumbylenes, plumbacyclopentadienylidenes, and endohedral plumbaspherenes . Further studies include the computation of solid-state 207 Pb NMR chemical shifts that already reveal the importance of Fock exchange and spin–orbit (SO) effects. − Still, they all lack a thorough assessment of the underlying theoretical method based on a diverse set of lead-containing compounds that were measured in solution. − , Due to the presence of unoccupied p-orbitals in group 14 elements, the 207 Pb nucleus has a huge SO heavy atom effect on the shielding of neighboring light atoms (HALA effects), especially in Pb II compounds . Heavy atoms in the vicinity of the Pb nucleus can also have a heavy atom effect on the heavy atom Pb (HAHA).…”

“…Therefore, benchmark studies are essential for the choice of DFA. Computations of 207 Pb NMR shifts have already been carried out for, e.g., dirhodioplumbole, 10 organolead 11 and halogen lead complexes, 12 diarylplumbylenes, 13 plumbacyclopentadienylidenes, 14 and endohedral plumbaspherenes. 15 Further studies include the computation of solid-state 207 Pb NMR chemical shifts that already reveal the importance of Fock exchange and spin–orbit (SO) effects.…”

Computational NMR spectroscopy of 205Tl

“…14 In the case of heavy atoms, relativistic effects need to be accounted for, since they strongly influence the chemical shift mainly through spin-orbit coupling. 12,[15][16][17][18][19][20] Several heavy nuclei have been the subject of extensive theoretical works, including the closely related 199 Hg [21][22][23] and 207 Pb [24][25][26] (the previous and successive element in the periodic table, with respect to thallium) as well as other heavy nuclei such as 125 Te, 27-29 119 Sn, 30,31 113 Cd, 32 129 Xe, [33][34][35][36][37] just to mention a few. In contrast, computational studies of thallium NMR are quite scarce.…”