Ulrich Hintermair

• PhD
• Research Associate at University of Bath

FlowNMR spectroscopy is an excellent technique for non-invasive real-time reaction monitoring under relevant conditions that avoids many of the limitations that bedevil other reaction monitoring techniques. With the recent commercial availability of FlowNMR hard-and software solutions for high resolution spectrometers it is enjoying increased popul...

Real‐time Small Angle X‐Ray Scattering (SAXS) has been used to investigate the homogeneity of a series of molecular iridium complexes during water oxidation catalysis in aqueous NaIO4 solution through a continuous flow cell. The results obtained for the unstable [Cp*Ir(OH2)3]²⁺ precursor forming amorphous IrOx nanoparticles (NPs) in‐situ validate a...

While a number of reports have established the unique structures and electronic properties of mono- and dinuclear pentalenide complexes of s, p, d and f block elements, access to these intriguing compounds is restricted by synthetic challenges. Here we review various strategies for the synthesis, functionalisation and (trans)metalation of pentaleni...

Synthesis of a chelating phosphite-phosphine ligand from a tris(quinoxaline) extended resorcin[4]arene and its application in the rhodium-catalyzed hydroformylation of terminal alkyl alkenes are reported. Rhodium complexes are formed within the cavity of the macrocycle and branched-selective hydroformylation of 1-octene with a b/l ratio of 5.9 has...

The solid‐state structures of the first rubidium and caesium pentalenides, [Rb(THF)]2[Ph4Pn] and [Cs(THF)]­­2[Ph4Pn] have been determined by single crystal X‐ray diffraction. Both were found to be polymeric in the solid state through interactions of the cations with the phenyl substituents, in contrast to their lighter group 1 congeners which are m...

The application of Mg[Ph4Pn] and Li·K[Ph4Pn] in transmetalation reactions to a range of Rh(I) precursors led to the formation of “half-baguette” anti-[RhI(L)n]2[µ:η5:η5Ph4Pn] (L = 1,5-cyclooctadiene, norbornadiene, ethylene; n = 1,...

We report the development of a versatile Ru-porphyrin catalyst system which performs the aerobic epoxidation of aromatic and aliphatic (internal) alkenes under mild conditions, with product yields of up to 95% and turnover numbers (TON) up to 300. Water is shown to play a crucial role in the reaction, significantly increasing catalyst efficiency an...

The catalytic anti-Markovnikov addition of carboxylic acids to propargylic alcohols to furnish unsaturated esters is an appealing transformation due to its mild conditions, high selectivity and atom economy. Treatment of...

1,3,4,6-Tetraphenylpentalene (Ph4Pn) has been synthesised by chemical oxidation of the corresponding pentalenide complex Mg[Ph4Pn] with iodine. Ph4Pn is a rare example of a room-temperature stable hydrocarbon that is antiaromatic by Hückel's rule and has been fully characterised by NMR and UV-vis spectroscopy, mass spectrometry as well as single-cr...

The first magnesium pentalenide complexes have been synthesized via deprotonative metalation of 1,3,4,6-tetraphenyldihydropentalene (Ph4PnH2) with magnesium alkyls. Both the nature of the metalating agent and the reaction solvent influenced the structure of the resulting complexes, and an equilibrium between Mg[Ph4Pn] and [ⁿBuMg]2[Ph4Pn] was found...

Ever since its first report over 60 years ago the 10π dianionic hydrocarbon pentalenide and its intriguing organometallic chemistry has remained a rare curiosity due to the exceptional difficulty of precursor synthesis and associated limitations in ligand design. Here we report the first example of systematic tuning of the electronic properties of...

Phosphites are industrially important ligands for the Rh‐catalysed hydroformylation of olefins because they produce more active catalysts than phosphines, which is mainly due to their strong π‐acceptor properties facilitating CO dissociation from the metal centre. Herein, the effect of three prominent phosphite ligands (triphenylphosphite, Alkanox...

This work examines the palladium( ii ) catalysed oxidation of terminal alkenes to their corresponding methyl ketones using tert -butyl hydroperoxide (TBHP) as the oxidant.

In search of novel pentalenide ligands for use in organometallic chemistry and homogeneous catalysis, we report the scope of a straightforward base-promoted Michael annulation of cyclopentadienes with α,β-unsaturated ketones that allows the introduction of symmetrical as well as unsymmetrical aryl and alkyl substitution patterns including electron-...

We report new insights into the fate of the precious metal during hydroformylation catalysis of 1-hexene with Rh/PPh3 complexes using multi-nuclear operando FlowNMR spectroscopy. By applying selectively excited ¹H and ³¹P{¹H} NMR pulse sequences we were able to characterise and quantify key hydrido-rhodium and acyl-rhodium intermediates formed duri...

FlowNMR spectroscopy has become a popular and powerful technique for online reaction monitoring. DOSY NMR is an established technique for obtaining information about diffusion rates and molecular size on static samples. This work extends the FlowNMR toolbox to include FlowDOSY based on convection compensation and use of a low-pulsation pump or flow...

Chemical solution-phase equilibria such as acid/base reactions and complex formation are typically investigated by titration studies that either use in situ analysis of a continuously changing sample with techniques that measure single attributes (e.g. pH or UV-vis absorbance at a specific wavelength) or ex situ analysis of multiple samples with hi...

We report a high-yielding solution phase synthesis of 1,3,4,6-tetraphenyl-dihydropentalene based on a simple annulation reaction of cyclopentadiene with a chalcone. Deprotonative metalation of 1,3,4,6-tetraphenyl-dihydropentalene with alkali metal bases (Li, Na, K) of moderate basicity (pKa > 15) cleanly yields the corresponding hydropentalenide co...

Noyori-Ikariya type [(arene)RuCl(TsDPEN)] (TsDPEN, sulfonated diphenyl ethylenediamine) complexes are widely used C=O and C=N reduction catalysts that produce chiral alcohols and amines via a key ruthenium-hydride intermediate that determines the stereochemistry of the product. Whereas many details about the interactions of the pro-chiral substrate...

In this article we review some fundamental engineering concepts and evaluate components and materials required to assemble and operate safe and effective FlowNMR setups that reliably generate meaningful results.

The selective catalytic synthesis of limonene‐derived monofunctional cyclic carbonates and their subsequent functionalisation via thiol–ene addition and amine ring‐opening is reported. A phosphotungstate polyoxometalate catalyst used for limonene epoxidation in the 1,2‐position is shown to also be active in cyclic carbonate synthesis, allowing a tw...

From oranges to sustainable coatings, foams and adhesives: turning natural terpenes into renewable chemical building blocks has been achieved via a telescoped catalytic system consisting of an epoxidation–carbonation sequence. This work discusses the stereochemical considerations and cooperative effects in selectively making valuable mono‐carbonate...

High-resolution FlowNMR was coupled to a continuous flow reactor to monitor polymer molecular weight evolution online by diffusion ordered NMR spectroscopy. Polymers were synthesized by reversible addition fragmentation chain transfer polymerization in continuous flow. The setup allows to target various polymer chain lengths in a dynamic manner wit...

The hydroformylation of 1-hexene with 12 bar of 1:1 H2/CO in the presence of the catalytic system [Rh(acac)(CO)2]/PPh3 was successfully studied by real-time multinuclear high-resolution FlowNMR spectroscopy at 50 °C. Quantitative reaction progress curves that yield rates as well chemo- and regioselectivities have been obtained with varying P/Rh loa...

A tungsten-based polyoxometalate catalyst employing aqueous H2O2 as a benign oxidant has been used for the solvent free catalytic epoxidation of the trisubstituted alkene bonds of a wide range of biorenewable terpene substrates. This epoxidation protocol has been scaled up to produce limonene oxide, 3-carene oxide and a-pinene oxide on a multigram...

Transfer hydrogenation of acetophenone from formic acid / triethylamine mixtures catalysed by the Ikariya-Noyori complex [(mesitylene)RuCl(R,R)-(TsDPEN)] has been investiated by simultaneous high-resolution FlowNMR and FlowUV-Vis spectroscopies coupled with on-line sampling head-space mass spectrometry and chiral high-performance liquid chromatogra...

The structure of a highly active pyridine-alkoxide iridium water oxidation catalyst (WOC) is examined by X-ray absorption spectroscopy (XAS). A detailed comparison with IrO2 points to a rigid molecular unit...

Metal-halide perovskites have been widely investigated in the photovoltaic sector due to their promising optoelectronic properties and inexpensive fabrication techniques based on solution processing. Here we report the development of inorganic CsPbBr3-based photoanodes for direct photoelectrochemical oxygen evolution from aqueous electrolytes. We u...

Catalytic hydrogen transfer from basic iso-propanol to aryl-ketones mediated by [(arene)(TsDPEN)RuCl] complexes has been investigated by operando 1H NMR spectroscopy using a recirculating flow setup. Selective excitation pulse sequences allowed fast and quantitative monitoring of the key [(mesitylene)(TsDPEN)Ru-H] intermediate during catalysis, whi...

The Cover Feature illustrates the reaction mechanism of Cp*IrIII complexes with varying pyridine‐alkoxide ligands in the oxygen evolution reaction (OER). In their Full Paper, E. V. Sackville et al. demonstrate there are electronic ligand effects at play and describe a dimer‐monomer equilibrium of the IrIV resting state preceding a proton‐coupled el...

We report the solution‐phase electrochemistry of seven half‐sandwich iridium(III) complexes with varying pyridine‐alkoxide ligands to quantify electronic ligand effects that translate to their activity in catalytic water oxidation. Our results unify some previously reported electrochemical data of Cp*Ir complexes by showing how the solution speciat...

We demonstrate how FlowNMR spectroscopy can readily be applied to investigate photochemical reactions that require sustained input of light and air to yield mechanistic insight under realistic conditions. The Eosin Y mediated photo-oxidation of N-allylbenzylamine is shown to produce imines as primary reaction products from which undesired aldehydes...

Six novel derivatives of pyridine-alkoxide ligated Cp*IrIII complexes, potent precursors for homogeneous water and C–H oxidation catalysts, have been synthesized, characterized, and analyzed spectroscopically and kinetically for ligand effects. Variation of alkoxide and pyridine substituents was found to affect their solution speciation, activation...

It is shown that a crystalline metal-organic framework (HKUST-1) can be rapidly synthesized from DMSO/MeOH solution with greatly reduced amounts of organic solvents using a supercritical CO2 (scCO2) solvent expansion technique. The precursor solution is stable for months under ambient condi-tions, and CO2-driven MOF crystallization is achieved unde...

Oxygen-deficient iron oxide thin films, which have recently been shown to be highly active for photoelectrochemical water oxidation, were surface-functionalized with a monolayer of a molecular iridium water oxidation co-catalyst. The iridium catalyst was found to dramatically improve the kinetics of the water oxidation reaction at both stoichiometr...

Three highly porous Zr(iv)-based metal-organic frameworks, UBMOF-8, UBMOF-9, and UBMOF-31, were synthesized by using 2,2'-diamino-4,4'-stilbenedicarboxylic acid, 4,4'-stilbenedicarboxylic acid, and combination of both linkers, respectively. The mixed-linker UBMOF-31 showed excellent hydrogen uptake of 4.9 wt% and high selectivity for adsorption of...

Solution-phase catalysis using molecular transition metal complexes is an extremely powerful tool for chemical synthesis and a key technology for sustainable manufacturing. However, as the reaction complexity and thermal sensitivity of the catalytic system increase, engineering challenges associated with product separation and catalyst recovery can...

Molecular catalysts are known for their high activity and tunability, but their solubility and limited stability often restrict their use in practical applications. Here we describe how a molecular iridium catalyst for water oxidation directly and robustly binds to oxide surfaces without the need for any external stimulus or additional linking grou...

Organometallic iridium complexes bearing oxidatively stable chelate ligands are precursors for efficient homogeneous water oxidation catalysts, but their activity in oxygen evolution has so far been studied almost exclusively with sacrificial chemical oxidants. In this report, we study the electrochemical activation of Cp*Ir complexes and demonstra...

Hydrogenation of CO2 to formic acid (HCO2H) and methanol (MeOH) provides access to valuable products in a low-carbon economy. The development of effective processes for the production of pure HCO2H is still in progress. Hydrogenation of CO2 to MeOH is thermodynamically much more favorable (DG= 9.5 kJ/mole). However, homogeneous catalysts were kinet...

The activity of the two related complexes [Cp*Ir(IMe)2X]BF4 (X = Cl (1), H (2)) in transfer hydrogenation from isopropyl alcohol to acetophenone was investigated. The results suggest that the commonly accepted monohydride mechanism for transfer hydrogenation mediated by cyclopentadienyl iridium species does not apply to chloride 1. We have found ev...

Fourteen Cp*IrIII complexes, bearing various combinations of N- and C-spectator ligands, are assayed in hydrogen-transfer catalysis from isopropyl alcohol to acetophenone under various conditions to investigate ligand effects in this widely used reaction. The new cationic complexes bearing monodentate pyridine and N-heterocyclic carbene (NHC) ligan...

Sodium periodate (NaIO4) is added to Cp*Ir(III) (Cp* = C5Me5(-)) or (cod)Ir(I) (cod = cyclooctadiene) complexes, which are water and C-H oxidation catalyst precursors, and the resulting aqueous reaction is investigated from milliseconds to seconds using desorption electrospray ionization, electrosonic spray ionization, and cryogenic ion vibrational...

A series of Cp*Ir(III) dimers have been synthesized to elucidate the mechanistic viability of radical oxo-coupling pathways in iridium-catalyzed O2 evolution. The oxidative stability of the precursors toward nanoparticle formation and their oxygen evolution activity have been investigated and compared to suitable monomeric analogues. We found that...

A series of Cp*IrIII dimers have been synthesized to elucidate the mechanistic viability of radical oxo-coupling pathways in iridium-catalyzed O2 evolution. The oxidative stability of the precursors toward nanoparticle formation and their oxygen evolution activity have been investigated and compared to suitable monomeric analogues. We found that pr...

We present evidence for Cp* being a sacrificial placeholder ligand in the [Cp*IrIII(chelate)X] series of homogeneous oxidation catalysts. UV-vis and 1H-NMR profiles as well as MALDI-MS data show a rapid and irreversible loss of the Cp* ligand under reaction conditions, which likely proceeds through an intramolecular inner-sphere oxidation pathway r...

A continuous-flow process based on a chiral transition-metal complex in a supported ionic liquid phase (SILP) with supercritical carbon dioxide (scCO2 ) as the mobile phase is presented for asymmetric catalytic transformations of low-volatility organic substrates at mild reaction temperatures. Enantioselectivity of >99 % ee and quantitative convers...

Sodium periodate (NaIO4) is shown to be a milder and more efficient terminal oxidant for C-H oxidation with Cp*Ir (Cp* = C5Me5) precatalysts than ceric(IV) ammonium nitrate. Synthetically useful yields, regioselectivities, and functional group tolerance were found for methylene oxidation of substrates bearing a phenyl, ketone, ester, or sulfonate g...

Dual role for CO(2): Pure formic acid can be obtained continuously by hydrogenation of CO(2) in a single processing unit. An immobilized ruthenium organometallic catalyst and a nonvolatile base in an ionic liquid (IL) are combined with supercritical CO(2) as both reactant and extractive phase.

The invention relates to a continuous method for producing formic acid from CO2, extracting the formic acid using compressed CO2.

Real-time monitoring of light scattering and UV-vis profiles of four different Cp*Ir(III) precursors under various conditions give insight into nanoparticle formation during oxidation catalysis with NaIO(4) as primary oxidant. Complexes bearing chelate ligands such as 2,2'-bipyridine, 2-phenylpyridine, or 2-(2'-pyridyl)-2-propanolate were found to...

A compact and versatile continuous reaction system for supercritical fluids as mobile phase was realised using commercially available components where possible. All process parameters of particular importance to the specific properties of near- or supercritical fluids such as pressure, temperature, and composition (p, T, x) can be accurately contro...

Organometallic catalysis is a powerful tool for chemical synthesis, and the field still evolves at a high pace continuously improving efficiencies and opening up new possibilities. However, despite increasing use in specialty and fine chemical production issues of catalyst recovery still hamper broader application and prevent tapping the full poten...

The synthesis of N-heterocyclic carbene (NHC) complexes of silver is an established techniquefor their use ascarbenetransferreagents. Whileitis known that both mono-NHC Ag(I) and bis-NHC Ag(I) complexes are accessible, different reactivities of these species have not been explored synthetically. Whereas the commonly used mono-NHC Ag(I) complexes ac...

A supported ionic liquid phase (SILP) catalyst prepared from [PrMIM][Ph(2)P(3-C(6)H(4)SO(3))] (PrMIM = 1-propyl-3-methylimidazolium), [Rh(CO)(2)(acac)] (acacH = 2,4-pentanedione) [OctMIM]NTf(2) (OctMIM = 1-n-octyl-3-methylimidazolium, Tf = CF(3)SO(2)) and microporous silica has been used for the continuous flow hydroformylation of 1-octene in the p...

Two processes are described for improving reaction rates for relatively hydrophobic substrates in aqueous biphasic systems. In the first, 1-octyl-3-methylimidazolium bromide ([Octmim]Br) increases the rate of hydroformylation of 1-octene from 8% conversion in 24h to full conversion of 1.5h. Phase separation is fast and catalyst retention is good. 1...

The sections in this article are 4.1 A Practical Classification of Biphasic Systems Consisting of Liquids and Compressed Gases for Multiphase Catalysis 4.2 Physical Properties of Expanded Liquid Phases 4.2.1 Volumetric Expansion 4.2.2 Density 4.2.3 Viscosity 4.2.4 Melting Point 4.2.5 Interfacial Tension 4.2.6 Diffusivity 4.2.7 Polarity 4.2.8 Gas S...

Highly efficient continuous-flow asymmetric catalysis was achieved by combination of supported ionic liquid phase (SILP) catalysts with supercritical CO2 (scCO2) as the mobile phase, as demonstrated for enantioselective hydrogenation in the presence of a molecular rhodium–QUINAPHOS complex. The integrated reaction and separation process yielded che...

a b s t r a c t A direct synthetic route to cationic N-heterocyclic carbene (NHC) complexes of rhodium and iridium from neat dialkyl-imidazolium ionic liquids (ILs) has been found. The method uses complexes bearing basic anionic ligands, [M(COD)(PPh 3)X], X = OEt, MeCO 2 , which react with the inactivated imidazolium cation in the absence of extern...

Rapid hydroformylation of 1-octene (rates up to 800 h(-1)) with the catalyst remaining stable for at least 40 h and with very low rhodium leaching levels (0.5 ppm) is demonstrated when using a system involving flowing the substrate, reacting gases and products dissolved in supercritical CO(2) (scCO(2)) over a fixed bed supported ionic liquid phase...

A discussion covers the different methods for the separation of the aldehyde products from the catalyst and any solvent during or after hydroformylation reactions of long chain alkenes (octene, hexene, pentene); aqueous, fluorous, and ionic liquid biphasic systems as well as systems involving scCO2 sometimes in conjunction with one or other of the...