PPX/PXP-type ligands (X = O and S) and their transition metal complexes: synthesis, properties and applications

Short-bite diphosphines of the form R$_2$P–X–PR$_2$ (PXP; X = O, S; R = aryl, alkyl), incorporating an oxygen or sulphur atom as bridging unit X, are widely underexplored compared to their N- and C-containing PNP- and PCP-type counterparts. However, these PXP ligands undergo an interesting phosphorotropic equilibrium with the PPX (R$_2$P(vX)–PR$_2$) tautomer, which opens up a very versatile coordination chemistry. This article covers the impact of the ligand backbone in short-bite ligands on their coordination chemistry, reactivity and applications. Especially in PXP-type complexes, metallophillic interactions can be induced in the case of coinage metals, which lead to fascinating photo-optical properties. Furthermore, PPX/PXP-type complexes are believed to exhibit a promising behavior in catalysis, due to the potential hemilability of the ligand and the therewith involved availability of free active sites for substrate binding

Tripodal Inorganic 2-Pyridyl-phosphine Ligands and Unsymmetrical Analogues: Towards New Applications in Catalysis

Although a range of phosphorus-based ligands are used extensively in homogeneous catalysis, 2-pyridyl-phosphines have been largely overlooked in this field. However, such ligands offer great potential for catalytic applications through the combination of two ligand sites with different donating and accepting properties. In Chapter 1 previous studies of the structural and coordination chemistry of 2-pyridyl main group ligands are discussed, together with the applications of phosphine and tris-2-pyridyl ligands in catalysis which are relevant to the studies undertaken in the thesis. This chapter finishes with a statement of the aims of the thesis. Chapter 2 focuses on sterically-constrained C3-symmetric tris-2-pyridyl ligands and the effects of the substitution of the pyridyl rings at the 6-position on coordination to transition metal ions. The impact of such ligand modification is illustrated directly from the coordination studies of P(6-R-2-py)3 (R = H, Me) to iron(II). Whereas P(2-py)3 readily forms the cationic sandwich complex [{P(2-py)3}2Fe]2+, P(6-Me-2-py)3 forms only half-sandwich complexes of the type [{P(6-Me-2-py)3}FeX2] (X = Cl, OTf). In addition to C3-symmetric ligands, a range of unsymmetrical multidentate 2-pyridyl-phosphine ligands with tuneable electronic and steric character have been synthesised and are reported in Chapter 3. The stoichiometric reactions of (R2N)xP(2-py)3−x (R = Me, Et, x = 1, 2) with alcohols result in the formation of (alkoxy)-2-pyridyl-phosphines (RO)xP(2-py)3−x (R = Me, 2-Bu, Ph, x = 1, 2). This synthetic procedure also allows the introduction of enantiomerically pure alcohols, and as such provides a very convenient two-step route to chiral 2-pyridyl-phosphine ligands. Coordination studies towards CuI, NiII and RhI have shown that both the pyridyl-N and bridgehead-P atoms can be involved in coordination to the metal centres. In the case of nickel, an interesting in-situ reduction of the metal centre was observed. Different synthetic and computational approaches to quantify the donor properties of various 2-pyridyl-phosphines are presented in Chapter 4. The calculated Tolman electronic parameters give an overview of the donor properties of all investigated 2-pyridyl-phosphines with respect to PPh3 and P(tBu)3. In Chapter 5, the modification of the phosphorus bridgehead is reported. Air- and moisture-stable phosphorus(V) chalcogenides and fluorinated phosphines were synthesised. Also, a novel one-step procedure for the synthesis of fluorophosphonium salts was developed. Treatment of (Et2N)2P(2-py) with the bench-stable fluorinating reagent NFSI (N-fluorobenzenesulfonimide) leads to the selective formation [FP(NEt2)2(2-py)][N(SO2Ph)2]. Investigations of the applications of tris-2-pyridyl-phosphine complexes for hydrofunctionalisation reactions are explored in Chapter 6. Central to the study are the iron(II) complexes [{P(6-Me-2-py)3}FeCl2] and [{P(6-Me-2-py)3}FeCl(OTf)]. In-situ reduction of the iron complex [{P(6-Me-2-py)3}FeCl(OTf)] potentially results in the formation of Fe0 species, which are active in hydrogenation reactions of minimally functionalised alkenes

Transition metal complexes of the PPO/POP ligand: variable coordination chemistry and photo-luminescence properties

In the current work the tautomeric equilibrium between tetraphenyldiphosphoxane (Ph$_2$P–O–PPh$_2$, POP) and tetraphenyldiphosphine monoxide (Ph$_2$P–P([double bond, length as m-dash]O)Ph$_2$, PPO) in the absence and presence of transition metal precursors is investigated. Whereas with hard transition metal ions, such as Fe(II) and Y(III), PPO-type complexes, such as [FeCl$_2$(PPO)$_2$] and [YCl$_3$(THF)$_2$(PPO)], are formed, softer transition metals ions tend to form so-called coordination stabilised tautomers of the POP ligand form, such as [Cu$_2$(MeCN)$_3$(μ$_2$-POP)$_2$](PF$_6$)$_2$, [Au$_2$Cl$_2$(μ$_2$-POP)], and [Au$_2$(μ$_2$-POP)$_2$](OTf)$_2$. The photo-optical properties of the PPO- and POP-type transition metal complexes are investigated experimentally using photo-luminescence spectroscopy, whereby the presence of metallophillic interactions was found to play a crucial role. The dinuclear copper complex [Cu$_2$(MeCN)$_3$(μ$_2$-POP)$_2$](PF$_6$)$_2$ shows a very interesting thermochromic behavior and intense photo-luminescence with remarkable phosphoresence lifetimes at 77 K, which can probably be attributed to short intramolecular Cu–Cu distances

Support Engineering for the Stabilisation of Heterogeneous Pd3_{3}P‐Based Catalysts for Heck Coupling Reactions

Herein we report the use of a supported Pd$_3$P catalyst for Heck coupling reactions. For the stabilisation of Pd$_3$P and Pd, as reference system, the silica support material was modified via phosphorus doping (0.5 and 1 wt % P). Through this so-called support engineering approach, the catalytic activity of Pd$_3$P was clearly enhanced. Whereas an iodobenzene conversion of 79 % was witnessed for Pd$_3$P@SiO$_2$ in the coupling of styrene and iodobenzene in 1 h, 90 % conversion could be achieved using Pd$_3$P@1P-SiO$_2$. This improved catalytic activity probably stems from an electronic modulation of the support surface via the introduction of phosphorus. Simultaneously, the recyclability was boosted and the Pd$_3$P@1P-SiO$_2$ catalyst has shown to maintain its catalytic activity over several recovery tests. Hereby, metal leaching could almost be suppressed completely to 3 % by the use of a P-modified silica support

Current State of the Art of the Solid Rh-Based Catalyzed Hydroformylation of Short-Chain Olefins

The hydroformylation of olefins is one of the most important homogeneously catalyzed processes in industry to produce bulk chemicals. Despite the high catalytic activities and selectivity’s using rhodium-based homogeneous hydroformylation catalysts, catalyst recovery and recycling from the reaction mixture remain a challenging topic on a process level. Therefore, technical solutions involving alternate approaches with heterogeneous catalysts for the conversion of olefins into aldehydes have been considered and research activities have addressed the synthesis and development of heterogeneous rhodium-based hydroformylation catalysts. Different strategies were pursued by different groups of authors, such as the deposition of molecular rhodium complexes, metallic rhodium nanoparticles and single-atom catalysts on a solid support as well as rhodium complexes present in supported liquids. An overview of the recent developments made in the area of the heterogenization of homogeneous rhodium catalysts and their application in the hydroformylation of short-chain olefins is given. A special focus is laid on the mechanistic understanding of the heterogeneously catalyzed reactions at a molecular level in order to provide a guide for the future design of rhodium-based heterogeneous hydroformylation catalysts

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

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

How Research Data Management Plans Can Help in Harmonizing Open Science and Approaches in the Digital Economy

Within this perspective article, we intend to summarise definitions and terms that are often used in the context of open science and data-driven R&D and we discuss upcoming European regulations concerning data, data sharing and handling. With this background in hand, we take a closer look at the potential connections and permeable interfaces of open science and digital economy, in which data and resulting immaterial goods can become vital pieces as tradeable items. We believe that both science and the digital economy can profit from a seamless transition and foresee that the scientific outcomes of publicly funded research can be better exploited. To close the gap between open science and the digital economy, and to serve for a balancing of the interests of data producers, data consumers, and an economy around services and the public, we introduce the concept of generic research data management plans (RDMs), which have in part been developed through a community effort and which have been evaluated by academic and industry members of the NFDI4Cat consortium. We are of the opinion that in data-driven research, RDMs do need to become a vital element in publicly funded projects

A [HN(BH═NH)2]2– Dianion, Isoelectronic with a β-Diketiminate

Producción CientíficaThe 1:2 reaction of the Al(III) β-diketiminate dihydride [{DMPnacnac}AlH2] (DMPnacnac = HC{C(Me)N(2,6-Me2-C6H3)}2) (1) with ammonia–borane (NH3BH3) gives the new complex [{DMPnacnac}Al{NHBH)2NH}] (3), whose [HN(BHNH)2]2– dianion is isoelectronic with β-diketiminate anions.2019-03-15Ministerio de Economía, Industria y Competitividad - Agencia Estatal de Investigación (AEI)European Research Council (ERC) and the European Social Fund (ESF)European Social Fund (ESF)Ramón y Cajal contract (RG-R, RYC-2015–19035