All-electron scalar relativistic basis sets for the elements Rb-Xe.

Segmented all-electron relativistically contracted (SARC) basis sets are presented for the elements 37 Rb-54 Xe, for use with the second-order Douglas-Kroll-Hess approach and the zeroth-order regular approximation. The basis sets have a common set of exponents produced with established heuristic procedures, but have contractions optimized individually for each scalar relativistic Hamiltonian. Their compact size and loose segmented contraction, which is in line with the construction of SARC basis sets for heavier elements, makes them suitable for routine calculations on large systems and when core spectroscopic properties are of interest. The basis sets are of triple-zeta quality and come in singly or doubly polarized versions, which are appropriate for both density functional theory and correlated wave function theory calculations. The quality of the basis sets is assessed against large decontracted reference basis sets for a number of atomic and ionic properties, while their general applicability is demonstrated with selected molecular examples.

Where Is the Fluoro Wall?: A Quantum Chemical Investigation.

Despite their isoelectronic properties, fluoro and oxo ligands exhibit completely different chemical behavior. Formally speaking, the first is known to exclusively form single bonds, while the latter is generally observed to form double (or even triple) bonds. The biggest difference, however, lies in what is known among inorganic chemists as the Oxo Wall: the fact that six-coordinate tetragonal transition metal oxo complexes are not observed beyond group 7 elements. While the Oxo Wall was explained a few decades ago, some questions regarding the nature of the Oxo Wall remain unanswered. For example, why do group 8 oxo complexes with high oxidation states not violate the Oxo Wall? Moreover, why are transition metal fluoro complexes observed through the whole transition metal series? In order to understand how the small difference between these two isoelectronic ligands can give rise to such different chemical behaviors, we conducted an extensive computational analysis of the geometric and electronic properties of model fluoro and oxo complexes with metals around the Oxo Wall. Among many insights into the details of the Oxo Wall, we mostly learned that the oxygen 2p orbitals are prone to meaningfully interact with transition metal d orbitals, because they match not only spatially but also energetically, while for fluorine the p orbital energies are lower to an extent that interaction with transition metal d orbitals is much reduced. This in turn implies that in those instances where the metal d orbitals principally accessible for interaction are occupied, the oxygen 2p orbitals are too exposed to be stable.

Palladium-catalysed electrophilic aromatic C-H fluorination.

Aryl fluorides are widely used in the pharmaceutical and agrochemical industries, and recent advances have enabled their synthesis through the conversion of various functional groups. However, there is a lack of general methods for direct aromatic carbon-hydrogen (C-H) fluorination. Conventional methods require the use of either strong fluorinating reagents, which are often unselective and difficult to handle, such as elemental fluorine, or less reactive reagents that attack only the most activated arenes, which reduces the substrate scope. A method for the direct fluorination of aromatic C-H bonds could facilitate access to fluorinated derivatives of functional molecules that would otherwise be difficult to produce. For example, drug candidates with improved properties, such as increased metabolic stability or better blood-brain-barrier penetration, may become available. Here we describe an approach to catalysis and the resulting development of an undirected, palladium-catalysed method for aromatic C-H fluorination using mild electrophilic fluorinating reagents. The reaction involves a mode of catalysis that is unusual in aromatic C-H functionalization because no organometallic intermediate is formed; instead, a reactive transition-metal-fluoride electrophile is generated catalytically for the fluorination of arenes that do not otherwise react with mild fluorinating reagents. The scope and functional-group tolerance of this reaction could provide access to functional fluorinated molecules in pharmaceutical and agrochemical development that would otherwise not be readily accessible.