Facile Rearrangement of a Bis(N-heterocyclic carbene)borate Chelate Ligand and Access to [:GeX]+Complexes (X = H, Cl)

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

Isomerization Reactions in Anionic Mesoionic Carbene-Borates and Control of Properties and Reactivities in the Resulting CoII Complexes through Agostic Interactions

We present herein anionic borate-based bi-mesoionic carbene compounds of the 1,2,3-triazol-4-ylidene type that undergo C-N isomerization reactions. The isomerized compounds are excellent ligands for CoII  centers. Strong agostic interactions with the "C-H"-groups of the cyclohexyl substituents result in an unusual low-spin square planar CoII  complex, which is unreactive towards external substrates. Such agostic interactions are absent in the complex with phenyl substituents on the borate backbone. This complex displays a high-spin tetrahedral CoII  center, which is reactive towards external substrates including dioxygen. To the best of our knowledge, this is also the first investigation of agostic interactions through single-crystal EPR spectroscopy. We conclusively show here that the structure and properties of these CoII complexes can be strongly influenced through interactions in the secondary coordination sphere. Additionally, we unravel a unique ligand rearrangement for these classes of anionic mesoionic carbene-based ligands.

NHCs in Main Group Chemistry

Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

Unexpected Photodegradation of a Phosphaketenyl-Substituted Germyliumylidene Borate Complex

The first zwitterionic borata-bis(NHC)-stabilized phosphaketenyl germyliumylidene [(L₂ (O=C=P)Ge:] 2 (L₂ =(p-tolyl)₂ B[1-(1-adamantyl)-3-yl-2-ylidene]₂ ) has been synthesized by salt-metathesis reaction of [L₂ (Cl)Ge:] 1 with sodium phosphaethynolate [(dioxane)_n NaOCP]. Unexpectedly, its exposure to UV light affords, after reductive elimination of the entire PCO group, the unprecedented [L₂ Ge-GeL₂ ] complex 3 in 54 % yields bearing the Ge₂²⁺ ion with Ge in the oxidation state +1. In addition, the 1,3-digermylium-2,4-diphosphacyclobutadiene [L₂ Ge(μ-P)₂ GeL₂ ] 4 and bis(germyliumylidenyl)-substituted diphosphene [(L₂ Ge-P=P-GeL₂ )] 5 could also be obtained in moderate yields. The formation of 3-5 and their electronic structures have been elucidated with DFT calculations.

New Insight into the Nature of Bonding in the Dimers of Lappert's Stannylene and Its Ge Analogs: A Quantum Mechanical Study

The strength and nature of the connection in Lappert's stannylene dimer ({Sn[CH(SiMe3)2]2}2) and its smaller analogs, simplified stannylenes, as well as similar Ge complexes were studied by means of DFT-D3 calculations, energy decomposition analysis (EDA), electrostatic potential (ESP), and natural population analysis. The trans-bent structure of the investigated molecules was rationalized by means of EDA, ESP, and molecular orbital (MO) analyses. The different ESPs for the monomers studied are a result of different hybridization of the Sn (Ge) atoms. The comparably strong stabilization in the largest and the smallest systems with a dramatically different substituent size is explained by the different nature of the binding between monomers. For all complexes, it has been found that the total attractive interaction is mostly provided by the electrostatic component (>50%), followed by orbital interaction and dispersion. In the largest molecule (Lappert's stannylene), the dispersion interaction plays a more significant role in stabilization and its magnitude is comparable to that of orbital interaction; on the other hand in the smallest molecule (SnH2), where bulky substituents are replaced by H only, the dispersion energy is less important and the E-E bond is more of a charge-transfer character, caused by donor-acceptor orbital interactions. The charge transfer in Ge dimers is greater than in the Sn ones due to shorter distances between monomers, which cause better ⟨HOMO/LUMO⟩ overlaps. The easier dimerization of Lappert's stannylene as compared to Kira's ({Sn[(Me3Si)2CHCH2CH2CH(SiMe3)2-κ(2)C,C']}) stannylene is explained by the different orientation of their substituents-asymmetry promotes dimerization.

Group 14 inorganic hydrocarbon analogues

This Review article deals with the synthesis and properties of inorganic hydrocarbon analogues: binary chemical species that contain heavier Group 14 elements (Si, Ge, Sn or Pb) and hydrogen as components. Rapid advances in our general knowledge of these species have enabled the development of industrially relevant processes such as the hydrosilylation of unsaturated substrates and the chemical vapor deposition of semi-conducting films.