Earth abundant element compounds in homogeneous catalysis

Welcome to this themed issue of Dalton Transactions in the area of earth abundant element (EAE) compounds in homogeneous catalysis. This collection contains 40 contributions from international leaders in these areas from around the world. It encompasses a range of new developments summarised in two Perspective review articles, seven preliminary communications, and thirty one full papers.

The aim of this special issue is to showcase the latest research in the development of highly active and selective homogeneous catalysts utilizing earth abundant elements from across the periodic table. This reflects a recent trend in catalysis that seeks to find alternatives to catalysts based on precious metals like Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, or Au, and toxic elements like Hg, Bi, In and Pb. This issue therefore contains contributions from researchers utilizing catalysts based on elements from both the s and p blocks, the more abundant first row transition metals, and the lanthanides as catalysts for commodity chemical, fine chemical and polymer synthesis, to emphasise the broad range of activity in this area.

We have organised this issue as follows. As usual the Perspective review articles are found at the front of the collection. These are followed by the communications and then the full papers. Within these overall categories we have grouped together as far as possible articles dealing with similar catalytic transformations or themes.

The Perspective review by Hannedouche et al. (DOI: 10.1039/c5dt00280j) on recent advances in hydroamination and other EAE-catalysed hydroelementation reactions sets the scene for a major theme in this issue, namely the catalysed addition of H–X bonds to unsaturated substrates (X = p-block element or H), or elimination from saturated substrates (X = H). Two communications (Waterman et al. (DOI: 10.1039/c5dt00108k), Hill et al. (DOI: 10.1039/c5dt00178a)), and an article from Beweries et al. (DOI: 10.1039/c5dt00275c) report on Group 1 or transition metal dehydrocoupling reactions of amine–boranes. Wright et al. (DOI: 10.1039/c5dt00662g) also describe a novel dehydrogenative Si–N bond forming process using amines and silanes. Articles from Morris et al. (DOI: 10.1039/c4dt02799j) and Guan et al. (DOI: 10.1039/c5dt00161g) report on iron-based asymmetric transfer hydrogenation and nickel based hydrogenation catalysts, respectively. Trifonov et al. (DOI: 10.1039/c5dt00129c), Doye et al. (DOI: 10.1039/c4dt03916e) and Tobisch (DOI: 10.1039/c5dt00121h) all report on the hydrophosphination and/or hydroamination of C=C bonds using EAE catalysts drawn from across the periodic table. A communication from Piers et al. (DOI: 10.1039/c4dt03902e) describes nickel-catalysed, selective hydration of nitriles to the corresponding organic amides.

C–C, C–N and other EAE-catalysed coupling reactions are also featured in this issue. Ogoshi et al. (DOI: 10.1039/c5dt00640f) present a review on nickel-catalysed transformations, and Han and Shyu et al. (DOI: 10.1039/c5dt00151j) and Yun et al. (DOI: 10.1039/c5dt00144g) communicate copper-catalysed C–O coupling and borylation reactions, respectively. Copper catalysis also features in Zhang and Su et al.'s article (DOI: 10.1039/c4dt03782k) on catalytic alkene cyclopropanation. Webster et al. (DOI: 10.1039/c5dt00112a) describe iron-catalysed Negishi cross-coupling with pro-ligands which are themselves prepared using iron-catalysed hydrophosphination chemistry. Copper-based systems feature in the catalytic aerobic oxidation of phenols to ortho-quinones in Ottenwaelder et al.'s communication (DOI: 10.1039/c5dt00822k) on this topic. The theme of EAE-catalysed oxidation is continued in articles by Bouwman et al. (DOI: 10.1039/c5dt01041a) for copper and Yin and Hubin et al. (DOI: 10.1039/c5dt00742a) for manganese and iron systems. Roberts and Bullock et al. (DOI: 10.1039/c5dt00162e) complete this group of contributions with their paper on the development of new catalysts supported on glassy carbon electrodes, in the context of electrocatalytic hydrogen oxidation.

In a more biological context, Avidan-Shlomovich and Gross (DOI: 10.1039/c5dt00086f) describe a detailed mechanistic study of the iron-catalysed decomposition of the potent toxin peroxynitrite. Davenport and Tilley (DOI: 10.1039/c4dt02727b) report on a series of dinuclear and tetranuclear first-row transition metal complexes of the dinucleating ligand DPFN from the point of view of multinuclear catalysis. In the context of catalytic transformations utilising fluorophosphonium cations, Stephan et al. (DOI: 10.1039/c5dt00217f) describe a series of such salts prepared from phosphine/borane frustrated Lewis pairs with XeF₂.

EAE compounds continue to be of considerable importance in polymerisation catalysis as represented by two groups of contributions, firstly on olefin polymerisation and then on ring-opening polymerisation (ROP) to form oxygenated polymers. In the first grouping, four papers from Coates (DOI: 10.1039/c5dt01104c), Nomura (DOI: 10.1039/c4dt04026k), Sun (DOI: 10.1039/c5dt00052a) and Redshaw (DOI: 10.1039/c5dt00376h) and their coworkers all describe new first-row transition metal-catalysts for ethylene homo- and co-polymerisation, continuing the well-established use of these elements for this type of transformation. Cipullo et al. (DOI: 10.1039/c5dt01514f) present an elegant quenched-flow kinetics study addressing some of the fundamental questions still challenging researchers in this area. Apart from these transition metal systems, Bonnet and Mountford et al. (DOI: 10.1039/c5dt00252d) describe lanthanide borohydride precatalysts for the polymerisation and coordinative chain transfer polymerisation of styrene and isoprene using a dialkyl magnesium activator and chain transfer agent.

Finally, one communication (Kerton et al., DOI: 10.1039/c5dt00220f) and ten full papers describe a range of ROP catalysts and their applications. The electropositive EAEs in these systems are drawn from across all of the periodic table: pre- and post-transition metals, transition metals, Group 3 and the lanthanides. The monomers employed were typically the cyclic esters rac- and L-lactide, ε-caprolactone and β-butyrolactone, but also cyclohexene oxide and trimethylene carbonate and α-methyltrimethylene carbonate. In the case of rac-lactide polymerisation, both isoselective and heteroselective catalysts are reported (e.g. contributions from Long and Williams et al. (DOI: 10.1039/c5dt00192g), and Ma et al. (DOI: 10.1039/c5dt00158g)). In addition to those forming linear polyesters, catalysts for the controlled synthesis of cyclic polyesters are also reported (Phomphrai et al., DOI: 10.1039/c5dt00139k). Block co-polymers are also obtained using Schafer et al.'s (DOI: 10.1039/c5dt01162k) titanium-based catalysts. The theme of using lanthanide borohydride complexes in polymerisation catalysis is continued in the contribution from Guillaume and Roesky et al. (DOI: 10.1039/c4dt04034a).

In concluding our editorial we would like to sincerely thank all of the contributors for submitting their new research and reviews to Dalton Transactions. Without their high-quality work and willingness to join in this venture this themed issue would obviously not exist. We also would like to extend our thanks to all the Dalton Transactions editorial team for their hard work and typical professionalism in handling all the manuscripts.

---