β-Diketiminato Organolead Complexes: Structures, 207Pb NMR, and Hammett Correlations

Benchmark Study on the Calculation of 207Pb NMR Chemical Shifts

A benchmark set for the computation of 207Pb nuclear magnetic resonance (NMR) chemical shifts is presented. The PbS50 set includes conformer ensembles of 50 lead-containing molecular compounds and their experimentally measured 207Pb NMR chemical shifts. Various bonding motifs at the Pb center with up to seven bonding partners are included. Six different solvents were used in the measurements. The respective shifts lie in the range between +10745 and -5030 ppm. Several calculation settings are assessed by evaluating computed 207Pb NMR shifts for the use with different density functional approximations (DFAs), relativistic approaches, treatment of the conformational space, and levels for geometry optimization. Relativistic effects were included explicitly with the zeroth order regular approximation (ZORA), for which only the spin-orbit variant was able to yield reliable results. In total, seven GGAs and three hybrid DFAs were tested. Hybrid DFAs significantly outperform GGAs. The most accurate DFAs are mPW1PW with a mean absolute deviation (MAD) of 429 ppm and PBE0 with an MAD of 446 ppm. Conformational influences are small as most compounds are rigid, but more flexible structures still benefit from Boltzmann averaging. Including explicit relativistic treatments such as SO-ZORA in the geometry optimization does not show any significant improvement over the use of effective core potentials (ECPs).

Bis(imino)carbazolate lead(II) fluoride and related halides

The versatility of a bulky bis(imino)carbazolate ligand in lead(ii) chemistry is illustrated by the synthesis of a soluble, heteroleptic lead(ii) fluoride and several halide (Cl, Br and I), amide and hydrocarbyl congeners. All complexes have been structurally authenticated, and a full set of 207Pb NMR data is discussed.

The concept of substituent-induced force in the rationale of substituent effect

Controlling the thermochemistry and kinetics of chemical reactions is a central problem in chemistry. Among factors permitting this control, the substituent effect constitutes a remarkable example. Here, we develop a model accounting for the effect of a substituent on the potential energy surface of the substrate (i.e., substituted molecule). We show that substituents affect the substrate by exerting forces on the nuclei. These substituent-induced forces are able to develop a work when the molecule follows a given reaction path. By applying a simple mechanical model, it becomes possible to quantify this work, which corresponds to the energy variation due to the effect of the substituent along a specific pathway. Our model accounts for the Hammett equation as a particular case, providing the first non-empirical scale for the σ and ρ constants, which, in the developed model, are related to the forces exerted by the substituents (σ) and the reaction path length (ρ), giving their product (σ · ρ) the well-known variation on the reaction energy due to the substituent.

Aminofluoroalkoxide amido and boryloxo lead(ii) complexes

We report here on the utilisation of a readily available bidentate aminofluoroalkoxide in lead(ii) chemistry. Stable heteroleptic three-coordinate complexes can be produced in high yields, including a convenient amido synthetic precursor and a rare case of Pb^II-boryloxide.

Stable lead(ii) boroxides

The first examples of lead(ii) boroxides, [Pb(OB{CH(SiMe3)2}2)2] (1) and [{N^C}PbOB{CH(SiMe3)2}2] (5; N^C = 2-Me2NCH2C6H4), were prepared via simple protocols. These structurally characterised compounds are stable and, unlike lead(ii) alkoxides and siloxides, do not trigger uncontrolled formation of lead(ii) oxoclusters.