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

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.

Synthesis and reactivity of a ruthenocene-type complex bearing an aromatic π-ligand with the heaviest group 14 element.

An anionic ruthenocene derived from a dilithioplumbole complex was prepared. In the complex, the plumbole ligand coordinates a ruthenium atom in an η5-fashion, similar to the cyclopentadienyl ligand in ferrocene. The ruthenocene that has the aromatic π-ligand with the heaviest group 14 element reacted with electrophiles to afford the plumbole complexes wherein the plumbole ligands show deviation from planarity, in contrast to the planar plumbole ring in the anionic ruthenocene. The bent angles of the plumbole ligands are dependent on the substituents on the lead atoms. Cyclic voltammetry measurements revealed that the plumbole complexes are oxidized more easily than the corresponding stannole complexes.

(η(4)-Butadiene)Sn(0) Complexes: A New Approach for Zero-Valent p-Block Elements Utilizing a Butadiene as a 4π-Electron Donor.

Research on zero-valent p-block elements is a recent hot topic in synthetic and theoretical chemistry because of their novel electronic states having two lone pairs in both the s- and p-orbitals. It is considered that σ-donating ligands bearing large substituents are essential to stabilize these species. Herein, we propose a new approach using butadiene as a 4π-electron donor to stabilize zero-valent group 14 elements. During our study to explore the coordination chemistry of stannacyclopentadienyl ligands, unexpected products, in which the tin atom is coordinated by a butadiene in a η(4)-fashion, were obtained. Because butadiene is a neutral 4π-electron donating ligand, the formal oxidation number of the tin atoms of the products should be zero, which is supported by X-ray diffraction analysis and theoretical calculations. A mechanism for the formation of the products is also described.

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

Reduction of THF-stabilized plumbacyclopentadienylidene with lithium afforded dilithioplumbole. On the other hand, oxidation of the dilithioplumbole provided the starting plumbacyclopentadienylidene. This is the unprecedented example of a reversible interconversion between group 14 M(II) and its dianionic species bearing organic substituents.