3× Axial vs 3× Equatorial: The Δ Value Is a Robust Computational Measure of Substituent Steric Effects.

We define Δ as the free energy change for the formal equilibrium: [13]G-H + 1-X-adamantane → [13]G-X + adamantane, where [13]G-H is the CH fragment of all- graphane with 3-fold symmetry. This compares with a situation where the group X is equatorial to three cyclohexane rings with one where it is axial to three rings. Δ values vary from 2.

Catalytic mechanism of the colistin resistance protein MCR-1.

The mcr-1 gene encodes a membrane-bound Zn2+-metalloenzyme, MCR-1, which catalyses phosphoethanolamine transfer onto bacterial lipid A, making bacteria resistant to colistin, a last-resort antibiotic. Mechanistic understanding of this process remains incomplete. Here, we investigate possible catalytic pathways using DFT and ab initio calculations on cluster models and identify a complete two-step reaction mechanism.

Building a Toolbox for the Analysis and Prediction of Ligand and Catalyst Effects in Organometallic Catalysis.

Computers have become closely involved with most aspects of modern life, and these developments are tracked in the chemical sciences. Recent years have seen the integration of computing across chemical research, made possible by investment in equipment, software development, improved networking between researchers, and rapid growth in the application of predictive approaches to chemistry, but also a change of attitude rooted in the successes of computational chemistry-it is now entirely possible to complete research projects where computation and synthesis are cooperative and integrated, and work in synergy to achieve better insights and improved results. It remains our ambition to put computational prediction before experiment, and we have been working toward developing the key ingredients and workflows to achieve this.

Iron Catalyzed Double Bond Isomerization: Evidence for an Fe /Fe Catalytic Cycle.

Iron-catalyzed isomerization of alkenes is reported using an iron(II) β-diketiminate pre-catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H N⋅BH ). Reactivity with both allyl arenes and aliphatic alkenes has been studied.

Computational Mapping of Dirhodium(II) Catalysts.

The chemistry of dirhodium(II) catalysts is highly diverse, and can enable the synthesis of many different molecular classes. A tool to aid in catalyst selection, independent of mechanism and reactivity, would therefore be highly desirable. Here, we describe the development of a database for dirhodium(II) catalysts that is based on the principal component analysis of DFT-calculated parameters capturing their steric and electronic properties.

How Big is the Pinacol Boronic Ester as a Substituent?

The synthetically versatile pinacol boronic ester group (Bpin) is generally thought of as a bulky moiety because of the two adjacent quaternary sp -hydribized carbon atoms in its diol backbone. However, recent diastereoselective reactions reported in the literature have cast doubt on this perception. Reported herein is a detailed experimental and computational analysis of Bpin and structurally related boronic esters which allows determination of three different steric parameters for the Bpin group: the A-value, ligand cone angle, and percent buried volume.

Mapping the properties of bidentate ligands with calculated descriptors (LKB-bid).

We have extended the Ligand Knowledge Base (LKB) approach to consider a broad range of bidentate ligands, varying donors, substituents and backbones, which gives rise to a diverse set of 224 ligands in a new database, LKB-bid. Using a subset of steric and electronic parameters described previously for bidentate P,P-donor ligands (LKB-PP), here this approach has been applied to a wider set of bidentate ligands, to explore how these modifications affect the properties of organometallic complexes. The resulting database has been processed with Principal Component Analysis (PCA), generating a "map" of ligand space which highlights the contribution of donor atoms and bridge length to the variation in ligand properties.

Resistance to the "last resort" antibiotic colistin: a single-zinc mechanism for phosphointermediate formation in MCR enzymes.

MCR (mobile colistin resistance) enzymes catalyse phosphoethanolamine (PEA) addition to bacterial lipid A, threatening the "last-resort" antibiotic colistin. Molecular dynamics and density functional theory simulations indicate that monozinc MCR supports PEA transfer to the Thr285 acceptor, positioning MCR as a mono- rather than multinuclear member of the alkaline phosphatase superfamily.

On the Basicity of Carboranylphosphines.

Three new carboranylphosphines, [1-(1'--1',7'-CBH)-7-PPh--1,7-CBH], [1-(1'-7'-PPh--1',7'-CBH)-7-PPh--1,7-CBH], and [1-{PPh-(1'--1',2'-CBH)}--1,2-CBH], have been prepared, and from a combination of these and literature compounds, eight new carboranylphosphine selenides were subsequently synthesized. The relative basicities of the carboranylphosphines were established by (i) measurement of the NMR coupling constant of the selenide and (ii) calculation of the proton affinity of the phosphine, in an attempt to establish which of several factors are the most important in controlling the basicity. It is found that the basicity of the carboranylphosphines is significantly influenced by the nature of other substituents on the P atom, the nature of the carborane cage vertex (C or B) to which the P atom is attached, and the charge on the carboranylphosphine.

Computational mapping of redox-switchable metal complexes based on ferrocene derivatives.

DFT calculations were used to capture the properties of redox-switchable metal complexes relevant to the ring-opening polymerisation of cyclic esters by varying the metals, donors, linkers, and substituents in both accessible ferrocene oxidation states. A map of this chemical space highlights that modifying the ligand architecture and the metal has a larger impact on structural changes than changing the oxidation state of the ferrocene backbone.

Computational Ligand Descriptors for Catalyst Design.

Ligands, especially phosphines and carbenes, can play a key role in modifying and controlling homogeneous organometallic catalysts, and they often provide a convenient approach to fine-tuning the performance of known catalysts. The measurable outcomes of such catalyst modifications (yields, rates, selectivity) can be set into context by establishing their relationship to steric and electronic descriptors of ligand properties, and such models can guide the discovery, optimization, and design of catalysts. In this review we present a survey of calculated ligand descriptors, with a particular focus on homogeneous organometallic catalysis.

Asymmetric and Geometry-Selective α-Alkenylation of α-Amino Acids.

Both E- and Z-N'-alkenyl urea derivatives of imidazolidinones may be formed selectively from enantiopure α-amino acids. Generation of their enolate derivatives in the presence of K and [18]crown-6 induces intramolecular migration of the alkenyl group from N' to Cα with retention of double bond geometry. DFT calculations indicate a partially concerted substitution mechanism.

Inorganic Triphenylphosphine.

A completely inorganic version of one of the most famous organophosphorus compounds, triphenylphosphine, has been prepared. A comparison of the crystal structures of inorganic triphenylphosphine, PBaz (where Baz=B H N H ) and PPh shows that they have superficial similarities and furthermore, the Lewis basicities of the two compounds are remarkably similar. However, their oxygenation and hydrolysis reactions are starkly different.

Biocatalytic Routes to Lactone Monomers for Polymer Production.

Monoterpenoids offer potential as biocatalytically derived monomer feedstocks for high-performance renewable polymers. We describe a biocatalytic route to lactone monomers menthide and dihydrocarvide employing Baeyer-Villiger monooxygenases (BVMOs) from Pseudomonas sp. HI-70 (CPDMO) and Rhodococcus sp.

A Simple and Broadly Applicable C-N Bond Forming Dearomatization Protocol Enabled by Bifunctional Amino Reagents.

A C-N bond forming dearomatization protocol with broad scope is outlined. Specifically, bifunctional amino reagents are used for sequential nucleophilic and electrophilic C-N bond formations, with the latter effecting the key dearomatization step. Using this approach, γ-arylated alcohols are converted to a wide range of differentially protected spirocyclic pyrrolidines in just two or three steps.

Heavily Substituted Atropisomeric Diarylamines by Unactivated Smiles Rearrangement of N-Aryl Anthranilamides.

Diarylamines find use as metal ligands and as structural components of drug molecules, and are commonly made by metal-catalyzed C-N coupling. However, the limited tolerance to steric hindrance of these couplings restricts the synthetic availability of more substituted diarylamines. Here we report a remarkable variant of the Smiles rearrangement that employs readily accessible N-aryl anthranilamides as precursors to diarylamines.

Insights into the Mechanistic Basis of Plasmid-Mediated Colistin Resistance from Crystal Structures of the Catalytic Domain of MCR-1.

The polymixin colistin is a "last line" antibiotic against extensively-resistant Gram-negative bacteria. Recently, the mcr-1 gene was identified as a plasmid-mediated resistance mechanism in human and animal Enterobacteriaceae, with a wide geographical distribution and many producer strains resistant to multiple other antibiotics. mcr-1 encodes a membrane-bound enzyme catalysing phosphoethanolamine transfer onto bacterial lipid A.

Exploring Redox States, Doping and Ordering of Electroactive Star-Shaped Oligo(aniline)s.

We have prepared a simple star-shaped oligo(aniline) (TDPB) and characterised it in detail by MALDI-TOF MS, UV/Vis/NIR spectroscopy, time-dependent DFT, cyclic voltammetry and EPR spectroscopy. TDPB is part of an underdeveloped class of π-conjugated molecules with great potential for organic electronics, display and sensor applications. It is redox active and reacts with acids to form radical cations.

Spectroscopic, structural and computational analysis of [Re(CO)3(dippM)Br](n+) (dippM = 1,1'-bis(diiso-propylphosphino)metallocene, M = Fe, n = 0 or 1; M = Co, n = 1).

While the redox active backbone of bis(phosphino)ferrocene ligands is often cited as an important feature of these ligands in catalytic studies, the structural parameters of oxidized bis(phosphino)ferrocene ligands have not been thoroughly studied. The reaction of [Re(CO)3(dippf)Br] (dippf = 1,1'-bis(diiso-propylphosphino)ferrocene) and [NO][BF4] in methylene chloride yields the oxidized compound, [Re(CO)3(dippf)Br][BF4]. The oxidized species, [Re(CO)3(dippf)Br][BF4], and the neutral species, [Re(CO)3(dippf)Br], are compared using X-ray crystallography, cyclic voltammetry, visible spectroscopy, IR spectroscopy and zero-field (57)Fe Mössbauer spectroscopy.

Self-Assembly of a Functional Oligo(Aniline)-Based Amphiphile into Helical Conductive Nanowires.

A tetra(aniline)-based cationic amphiphile, TANI-NHC(O)C5H10N(CH3)3(+)Br(-) (TANI-PTAB) was synthesized, and its emeraldine base (EB) state was found to self-assemble into nanowires in aqueous solution. The observed self-assembly is described by an isodesmic model, as shown by temperature-dependent UV-vis investigations. Linear dichroism (LD) studies, combined with computational modeling using time-dependent density functional theory (TD-DFT), suggests that TANI-PTAB molecules are ordered in an antiparallel arrangement within nanowires, with the long axis of TANI-PTAB arranged perpendicular to the nanowire long axis.