The synthesis and characterisation of [Ru(H)(η5-3- phenylindenyl)(iBu-Phoban)2] 4 is reported ( iBu-Phoban = 9-isobutyl-9-phosphabicyclo-[3.3.1]-nonane). 4 is obtained via alcoholysis of metathesis pre-catalyst M11, in a process that was previously thought to be limited to analogous complex [RuCl 2(PPh3)2(3-phenylindenylidene)] (M 10). This journal is © The Royal Society of Chemistry.

Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance. © 2013 The Royal Society of Chemistry.

Density functional theory calculations were used to predict the behaviour of a potential novel architecture of olefin metathesis catalysts, in which one of the neutral ligands of classical Ru-based catalysts, e.g. a phosphine or an N-heterocyclic carbene, is replaced by an alkylidene group. Introduction of a second alkylidene ligand favors dissociation of the remaining phosphine and the overall energy profile for the metathesis using ethylene as the probe substrate reveals that the proposed bis-alkylidene complexes might match the requirements of a good performing olefin metathesis catalyst. © 2013 The Royal Society of Chemistry.

The distinctive characteristics of nanoparticles, resulting from properties that arise at the nano-scale, underlie their potential applications in the biomedical sector. However, the very same characteristics also result in widespread concerns about the potentially toxic effects of nanoparticles. Given the large number of nanoparticles that are being developed for possible biomedical use, there is a need to develop rapid screening methods based on in silico methods. This study illustrates the application of conceptual Density Functional Theory (DFT) to some carbon nanotubes (CNTs) optimized by means of static DFT calculations. The computational efforts are focused on the geometry of a family of packed narrow-diameter carbon nanotubes (CNTs) formed by units from four to twelve carbons evaluating the strength of the C-C bonds by means of Mayer Bond Orders (MBO). Thus, width and length are geometrical features that might be used to tune the electronic properties of the CNTs. At infinite length, partial semi-conductor characteristics are expected. © 2012 Bentham Science Publishers.

The reactivity of a new family of complexes with general formula [Ru IV(T)(R-D)(O)]2+ (T = trispyrazolylmethane (tpm); D = N-(1-hydroxy-3-methylbutan-(2S)-(-)-2-yl)-(4S)-(-)-4-isopropyl-4, 5-dihydrooxazole-2-carbimidate, R = Bz (1); iPr (2)) has been analyzed. There is a significant difference in regioselectivity between the two catalysts in the epoxidation of 4-vinylcyclohexene; 1 leads to the regioselective oxidation at the ring alkene position, whereas 2 leads to the oxidation at the terminal position. Although computational calculations indicate small energy differences, both the geometry through steric maps and the electronic parameters of the reactants via conceptual DFT, or charges via NPA, explain the reactivity differences found for the catalysts depending on the substituents of the oxazoline ligands. © 2013 Elsevier B.V. All rights reserved.

A DFT analysis of the strength of the Ru-halide bond in a series of typical olefin metathesis (pre)catalysts is presented. The calculated Ru-halide bond energies span the rather broad window of 25-43 kcal mol-1. This indicates that in many systems dissociation of the Ru-halide bond is possible and is actually competitive with dissociation of the labile ligand generating the 14e active species. Consequently, formation of cationic Ru species in solution should be considered as a possible event. © 2013 The Royal Society of Chemistry.

Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average ∼2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts. © 2014 Elsevier B.V.

Classical and frustrated Lewis pairs (LPs) of the strong Lewis acid (LA) Al(C 6F 5) 3 with several Lewis base (LB) classes have been found to exhibit exceptional activity in the Lewis pair polymerization (LPP) of conjugated polar alkenes such as methyl methacrylate (MMA) as well as renewable α-methylene-γ-butyrolactone (MBL) and γ-methyl- α-methylene-γ-butyrolactone (γ-MMBL), leading to high molecular weight polymers, often with narrow molecular weight distributions. This study has investigated a large number of LPs, consisting of 11 LAs as well as 10 achiral and 4 chiral LBs, for LPP of 12 monomers of several different types. Although some more common LAs can also be utilized for LPP, Al(C 6F 5) 3-based LPs are far more active and effective than other LA-based LPs. On the other hand, several classes of LBs, when paired with Al(C 6F 5) 3, can render highly active and effective LPP of MMA and γ-MMBL; such LBs include phosphines (e.g., P tBu 3), chiral chelating diphosphines, N-heterocyclic carbenes (NHCs), and phosphazene superbases (e.g., P 4- tBu). The P 4- tBu/Al(C 6F 5) 3 pair exhibits the highest activity of the LP series, with a remarkably high turn-over frequency of 9.6 × 10 4 h -1 (0.125 mol% catalyst, 100% MMA conversion in 30 s, M n = 2.12 × 10 5 g mol -1, PDI = 1.34). The polymers produced by LPs at RT are typically atactic (P γMMBL with ∼47% mr) or syndio-rich (PMMA with ∼70-75% rr), but highly syndiotactic PMMA with rr ∼91% can be produced by chiral or achiral LPs at -78 °C. Mechanistic studies have identified and structurally characterized zwitterionic phosphonium and imidazolium enolaluminates as the active species of the current LPP system, which are formed by the reaction of the monomer·Al(C 6F 5) 3 adduct with P tBu 3 and NHC bases, respectively. Kinetic studies have revealed that the MMA polymerization by the tBu 3P/ Al(C 6F 5) 3 pair is zero-order in monomer concentration after an initial induction period, and the polymerization is significantly catalyzed by the LA, thus pointing to a bimetallic, activated monomer propagation mechanism. Computational study on the active species formation as well as the chain initiation and propagation events involved in the LPP of MMA with some of the most representative LPs has added our understanding of fundamental steps of LPP. The main difference between NHC and PR 3 bases is in the energetics of zwitterion formation, with the NHC-based zwitterions being remarkably more stable than the PR 3-based zwitterions. Comparison of the monometallic and bimetallic mechanisms for MMA addition shows a clear preference for the bimetallic mechanism. This journal is © 2012 The Royal Society of Chemistry.

An olefin metathesis catalyst featuring a SIPr NHC and an ester chelating carbene ligand is introduced. In contrast to its previously published SIMes analogue, only the trans dichloro configurated isomer was obtained. The two counterparts are tested in various olefin metathesis reactions, revealing a striking superiority of the new complex in the cross metathesis of olefins with methyl vinyl ketone allowing for full conversion with only 500 ppm catalyst loading. © 2012 The Royal Society of Chemistry.

We discuss the impact of the nature of the heterocyclic carbene ring, when used as a complex forming ligand, on the relative stability of key intermediates in three typical Ru, Pd and Au promoted reactions. Results show that P-heterocyclic carbenes have a propensity to increase the bonding of the labile ligand and of the substrate in Ru-promoted olefin metathesis, whereas negligible impact is expected on the stability of the ruthenacycle intermediate. In the case of Pd cross-coupling reactions, dissociation of a P-heterocyclic carbene is easier than dissociation of the N-heterocyclic analogue. In the case of the Au-OH synthon, the Au-OH bond is weakened with the P-heterocyclic carbene ligands. A detailed energy decomposition analysis is performed to rationalize these results. © 2013 The Royal Society of Chemistry.