Steric Effects on the Structures, Reactivity, and Coordination Chemistry of Tris(2-pyridyl)aluminates.

Introducing substituents in the 6-position of the 2-pyridyl rings of tris(pyridyl)aluminate anions, of the type [EtAl(2-py')3 ](-) (py'=a substituted 2-pyridyl group), has a large impact on their metal coordination characteristics. This is seen most remarkably in the desolvation of the THF solvate [EtAl(6-Me-2-py)3 Li⋅THF] to give the monomer [EtAl(6-Me-2-py)3 Li] (1), containing a pyramidal, three-coordinate Li(+) cation. Similar monomeric complexes are observed for [EtAl(6-CF3 -2-py)3 Li] (2) and [EtAl(6-Br-2-py)3 Li] (3), which contain CF3 and Br substituents (R). This steric influence can be exploited in the synthesis of a new class of terminal Al-OH complexes, as is seen in the controlled hydrolysis of 2 and 3 to give [EtAl(OH)(6-R-2-py)2 ](-) anions, as in the dimer [EtAl(OH)(6-Br-2-py)2 Li]2 (5). Attempts to deprotonate the Al-OH group of 5 using Et2 Zn led only to the formation of the zincate complex [LiZn(6-Br-py)3 ]2 (6), while reactions of the 6-Br substituted 3 and the unsubstituted complex [EtAl(2-py)3 Li] with MeOH give [EtAl(OMe)(6-Br-2-py)2 Li]2 (7) and [EtAl(OMe)(2-py)2 Li]2 (8), respectively, having similar dimeric arrangements to 5. The combined studies presented provide key synthetic methods for the functionalization and elaboration of tris(pyridyl)aluminate ligands.We thank the EU for a Marie Curie Intra European Fellowship within the seventh European Community Framework Programme for R.G.-R. and an Advanced Investigator Award for D.S.W.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/chem.20150215

Stoichiometric and catalytic Si-N bond formation using the p-block base Al(NMe2)3.

The aluminium amide Al(NMe2)3 acts as a stoichiometric or catalytic reagent in dehydrogenic Si-N bond formation using amines and silanes. Although of limited substrate scope, this represents the first p-block metal catalytic system for N-H/Si-H dehydrocoupling. The observed catalytic rate law for the formation of aminosilane products in a model study of one of the catalytic reactions suggests a mechanism involving the silane component in the deprotonation of the amine (possibly in the form of a hypervalent silicon hydride).We thank The EU (ERC Advanced Investigator Grant for D.S.W., studentship for L.K.A.) and The EU (Marie Curie Intra European Fellowship for R.G.-R).This is the author accepted manuscript. The final published version is available from the Royal Society of Chemistry at http://pubs.rsc.org/en/Content/ArticleLanding/2015/DT/c5dt00662g#!divAbstract

The Coordination Chemistry of the N-Donor-Substituted Phosphazanes.

Phosph(III)azanes, featuring the heterocyclobutane P2 N2 ring, have now been established as building blocks in main-group coordination and supramolecular compounds. Previous studies have largely involved their use as neutral P-donor ligands or as anionic N-donor ligands, derived from deprotonation of amido-phosphazanes [RNHP(μ-NR)]2 . The use of neutral amido-phosphazanes themselves as chelating, H-bond donors in anion receptors has also been an area of recent interest because of the ease by which the proton acidity and anion binding constants can be modulated, by the incorporation of electron-withdrawing exo- and endo-cyclic groups (R) and by the coordination of transition metals to the ring P atoms. We observed recently that the effect of P,N-chelation of metal atoms to the P atoms of cis-[(2-py)NHP(μ-Nt Bu)]2 (2-py=2-pyridyl) not only pre-organises the N-H functionality for optimum H-bonding to anions but also results in a large increase in anion binding constants, well above those for traditional organic receptors like squaramides and ureas. Here, we report a broader investigation of ligand chemistry of [(2-py)NHP(μ-t NBu)]2 (and of the new quinolyl derivative [(8-Qu)NHP(μ-Nt Bu)]2 (8-Qu=8-quinolyl). The additional N-donor functionality of the heterocyclic substituents and its position has a marked effect on the anion and metal coordination chemistry of both species, leading to novel structural behaviour and reactivity compared to unfunctionalized counterparts.Cambridge Trus

Regioselective 1,4-hydroboration of pyridines catalyzed by an acid-initiated boronium cation

The reaction of the commercially available ammonium salt NH4BPh4 with a pyridine-activated pinacolborane species generates a boronium cation that facilitates the 1,4-selective hydroboration of pyridines in polar solvents. This catalytic reaction is amenable to a host of reactive functional groups and provides access to sterically bulky hydroboration products, previously inaccessible by metal-free routes. Further, the regioselectivity of this reaction can be altered by reducing the polarity of the reaction solvent, resulting in greater proportions of the 1,2-hydroboration product.E. N. K. thanks NSERC of Canada for a PGSD as well as the Cambridge Commonwealth, European, and International Trust and Gonville and Caius College for funding

Multiple deprotonation of primary aromatic diamines by LiAlH4.

Reaction of LiAlH4 with 1,2-phenylenediamine (1H4) in THF results in formation of the metallocyclic amido-/imido complex [{Al(1H2)}2{Al(1H)2}2][Li(THF)2]4 (3), while in the presence of various Lewis base ligands 1,8-diaminonaphthalene (2H4) gives the amido-('ate') complexes [Al(2H2)2](-)[Li(LL')](+) [L = THF, L' = PMDETA (N,N,N',N',N''-pentamethyldiethylenetriamine) (4); L = L' = TMEDA (N,N,N',N'-tetramethylethylenediamine) (5)]. The latter complexes provide evidence of intermediates in the proposed reaction pathway for formation of the cyclic framework of the tetraanion [{Al(1H2)}2{Al(1H)2}2](4-) of 3.We thank the EU (ERC Advanced Investigator Grant for D.S.W.), the EU (R.J.L. and L.K.A.). We also thank Dr. J. E. Davies for collecting X-ray data on 3, 4 and 5.This is the author accepted manuscript. The final version is available via RSC at http://pubs.rsc.org/en/Content/ArticleLanding/2015/DT/c4dt03802a#!divAbstract

Novel properties and potential applications of functional ligand-modified polyoxotitanate cages.

Functional ligand-modified polyoxotitanate (L-POT) cages of the general type [TixOy(OR)z(L)m] (OR = alkoxide, L = functional ligand) can be regarded as molecular fragments of surface-sensitized solid-state TiO2, and are of value as models for studying the interfacial charge and energy transfer between the bound functional ligands and a bulk semiconductor surface. These L-POTs have also had a marked impact in many other research fields, such as single-source precursors for TiO2 deposition, inorganic-organic hybrid material construction, photocatalysis, photoluminescence, asymmetric catalysis and gas adsorption. Their atomically well-defined structures provide the basis for the understanding of structure/property relationships and ultimately for the rational design of new cages targeting specific uses. This highlight focuses on recent advances in L-POTs research, with emphasis on their novel properties and potential applications.EPSRCThis is the final version of the article. It first appeared from Royal Society of Chemistry via https://doi.org/10.1039/C6CC03788G

The influence of halides in polyoxotitanate cages; dipole moment, splitting and expansion of d-orbitals and electron-electron repulsion

Metal-doped polyoxotitanate (M-POT) cages have been shown to be efficient single-source precursors to metal-doped titania [TiO$_2$(M)] (state-of-the-art photocatalytic materials) as well as molecular models for the behaviour of dopant metal ions in bulk titania. Here we report the influence halide ions have on the optical and electronic properties of a series of halide-only, and cobalt halide-‘doped’ POT cages. In this combined experimental and computational study we show that halide ions can have several effects on the band gaps of halide-containing POT cages, influencing the dipole moment (hole–electron separation) and the structure of the valance band edge. Overall, the band gap behaviour stems from the effects of increasing orbital energy moving from F to I down Group 17, as well as crystal-field splitting of the d-orbitals, the potential effects of the Nephelauxetic influence of the halides and electron–electron repulsion.We thank the EPSRC (Doctoral Prize for P. D. M.), A*STAR Singapore (Scholarship for N. L.), the Studienstiftung des deutschen Volkes, Fonds of the Chemical Industry (S. H.) for funding. The authors would like to acknowledge the use of the EPSRC UK National Service for Computational Chemistry Software (NSCCS) at Imperial College London and contributions from its staff in carrying out this work

The use of mixed-metal single source precursors for the synthesis of complex metal oxides

Complex metal oxides, defined as metal oxide materials with multiple metals, phases or including dopants, are used in a huge variety of modern applications ranging from photocatalysis, transparent conductive materials, supercapacitors and battery components. In this feature article, the use of mixed-metal single source precursors to synthesise complex metal oxides is explored. The structures and decomposition/reaction pathways of various precursors including mixed-metal alkoxides, complexes with chelating ligands, clusters, polyoxometallates, and metal-organic frameworks are discussed. The advantages and opportunities of using a single source precursor strategy are investigated and highlighted

An experimental and theoretical study of the coordination and donor properties of tris-2-pyridyl-phosphine ligands

Producción CientíficaThe coordination characteristics and donor/acceptor properties of a series of 2-pyridyl substituted phosphine ligands have been investigated using structural, spectroscopic and DFT calculational studies. A range of different coordination modes are observed in Mo and W carbonyl complexes of tris-2-pyridyl-phosphine ligands of the type P(2-py’) (2-py’ = substituted or unsubstituted 2-pyridyl group), including an unprecedented example exhibiting N,N′,μ2-π coordination. DFT calculations were used to assess the relative donor/acceptor properties of a range of related 2-pyridyl-phosphine ligands with respect to PPh3 and PtBu3.Ministerio de Ciencia, Innovación y Universidades (PGC2018-096880-A-I00. AEI / FEDER, UE

Formation of a unique 'unsupported' hydridic stannate(II).

The reaction of the amido-stannate LiSn(NMe2)3 with the phosphine-borane (t)Bu2PHBH3 gives the Sn(II) hydride [(Me2NH)2Li{BH3P((t)Bu)2}2Sn(H)]; the first example of a hydridic stannate(ii) that is not supported by transition metal or ligand bonding.This is the author accepted manuscript. The final version is available from Royal Society of Chemistry via http://dx.doi.org/10.1039/C6CC01885H