Quantum‐chemical analyses of aromaticity, UV spectra, and NMR chemical shifts in plumbacyclopentadienylidenes stabilized by Lewis bases

Abstract

We carried out a series of zeroth-order regular approximation (ZORA)-density functional theory (DFT) and ZORA-time-dependent (TD)-DFT calculations for molecular geometries, NMR chemical shifts, nucleus-independent chemical shifts (NICS), and electronic transition energies of plumbacyclopentadienylidenes stabilized by several Lewis bases, (Ph)2 ((t) BuMe2 Si)2 C4 PbL1 L2 (L1, L2 = tetrahydrofuran, Pyridine, N-heterocyclic carbene), and their model molecules. We mainly discussed the Lewis-base effect on the aromaticity of these complexes. The NICS was used to examine the aromaticity. The NICS values showed that the aromaticity of these complexes increases when the donation from the Lewis bases to Pb becomes large. This trend seems to be reasonable when the 4n-Huckel rule is applied to the fractional π-electron number. The calculated (13)C- and (207)Pb-NMR chemical shifts and the calculated UV transition energies reasonably reproduced the experimental trends. We found a specific relationship between the (13)C-NMR chemical shifts and the transition energies. As we expected, the relativistic effect was essential to reproduce a trend not only in the (207)Pb-NMR chemical shifts and J[Pb-C] but also in the (13)C-NMR chemical shifts of carbons adjacent to the lead atom.

A reversible two-electron redox system involving a divalent lead species

“…Such dissociation behaviour was already supported by theoretical calculations. 6,8 Dilithioplumbole 3 is regarded as a dianionic equivalent of 1, and therefore two-electron reduction of 1 occurred, which is a novel reduction mode of a tetrylene.…”

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

“…Recently, hybrid functionals such as B3LYP and PBE0 have been widely used in NMR calculations of metal complexes. ,− We investigated the performance of the B3LYP and PBE0 functionals in determining the 207 Pb, 13 C α , and 13 C β NMR chemical shifts for the rhodio- and lithioplumbole complexes (Figures , , and S6 and Tables S2–S4 and S6). The B3LYP functional reproduces the experimental trend of the increasing 207 Pb NMR chemical shifts of [Rh–plumbole] − < Li 2 –plumbole < Rh 2 –plumbole reasonably well, whereas the PBE0 functional fails to determine the trend because it underestimates the chemical shift of the Rh 2 –plumbole complex.…”

“…The initial structures used for the optimization of the geometry were obtained from the X-ray crystallographic data. , The molecular geometries were optimized in the gas phase using the B3LYP functional , with and without dispersion correction . The B3LYP functional was chosen on the basis of previous reports of the plumbole complexes . In the optimization procedure, the basis sets used were cc-pVTZ-pp for Rh and Pb, , TZP for Li and O in tetrahydrofuran (THF), C in the five-membered ring and cyclooctadiene ring, DZ for H, and DZP for Si and the other atoms.…”

“…Plumba­cyclo­penta­dienyl­idenes stabilized by ligands such as THF, pyridine, and N -heterocyclic carbene were subsequently synthesized and characterized . Even though plumbacyclopentadienylidene is antiaromatic, coordination with Lewis bases significantly decreases the antiaromaticity owing to occupation of the vacant 6p orbital of the Pb atom by the lone pair on the ligand . Recently, it was reported that the plumbole dianion ((SiC 6 H 15 ) 2 (C 6 H 5 ) 2 –C 4 Pb) 2– ([plumbole] 2– ) can coordinate to rhodium to form mono­rhodio­plumbole ([Rh–plumbole] − ) and di­rhodio­plumbole (Rh 2 –plumbole) complexes (Figure ).…”

Anisotropic Crystals Based on a Main-Group Coordination Polymer with Alignment of Rigid π Skeletons

“…We envisaged that a vacant p orbital in a divalent atom would be coordinated through its vacant p orbital by a Lewis base that has two coordinating sites to construct a coordination polymer with the alignment of the π skeletons. We chose a plumbacyclopentadienylidene, where a plumbylene unit is incorporated into a π skeleton . Another interesting feature of coordination polymers is their potential application as nonlinear optical (NLO) materials, which should have anisotropy without inversion symmetry in the solid state.…”