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This study describes the synthesis and characterization of a new class of ferrocene-containing carbon monoxide-releasing molecules (CORMs, 1–3). The ferrocenyl group is both a recognized therapeutically viable coligand and a handle for informative infrared spectroelectrochemistry. Deoxymyoglobin CO-release assays and in situ infrared spectroscopy confirm compounds 2 and 3 as photoCORMs and 1 as a thermal CORM, attributed to the increased sensitivity of the Mn–ferrocenyl bond to protonation in 1. Electrochemical and infrared spectroelectrochemical experiments confirm a single reversible redox couple associated with the ferrocenyl moiety with the Mn tetracarbonyl center showing no redox activity up to +590 mV vs Fc/Fc+, though no concomitant CO release was observed in association with the redox activity. The effects of linker length on communication between the Fe and Mn centers suggest that the incorporation of redox-active ligands into CORMs focuses on the first coordination sphere of the CORM. Redox-tagg...

Signal Amplification By Reversible Exchange (SABRE) is a hyperpolarisation technique that commonly uses [Ir(H)2(carbene)(substrate)3]Cl complexes to catalytically transfer magnetisation from para-hydrogen derived hydride ligands to coordinated substrates. Here, we explore the reactivity of a novel class of such catalysts based on sulfoxide containing [IrCl(H)2(carbene)(DMSO)2], which are involved in the hyperpolarisation of pyruvate using SABRE. We probe the reactivity of this species by NMR and DFT and upon reaction with sodium pyruvate establish the formation of two isomers of [Ir(H)2(η2-pyruvate)(DMSO)(IMes)]. Studies with related disodium oxalate yield [Ir2(H)4(IMes)2(DMSO)2(η2-κ2-Oxalate)] that is characterised by NMR and X-ray diffraction.

Oxazolidinone synthesis through the coupling of carbon dioxide and aziridines was catalysed by an aluminium(salphen) complex at 50-100 °C and 1-10 bar pressure under solvent-free conditions. The process was applicable to a variety of substituted aziridines, giving products with high regioselectivity. It involved the use of a sustainable and reusable aluminium-based catalyst, used carbon dioxide as a C

NaNO3 is used in oxidative Pd-catalyzed processes as a complementary co-catalyst to common oxidants, e.g., CuII salts, in C–H bond activation and Wacker oxidation processes. NaNO3 and NaNO2 (with air or O2) assist the sp3-C–H bond acetoxylation of substrates bearing an N-directing group. It has been proposed previously that a redox couple is operative. The role played by NOx anions is examined in this investigation. Evidence for an NOx anion interaction at PdII is presented. Palladacyclic complexes containing NOx anions are competent catalysts for acetoxylation of 8-methylquinoline, with and without exogenous NaNO3. The oxidation of 8-methylquinoline to the corresponding carboxylic acid has also been noted at PdII. 18O-Labeling studies indicate that oxygen derived from nitrate appears in the acetoxylation product, the transfer of which can only occur by interaction of 18O at Pd with a coordinating-acetate ligand. Nitrated organic intermediates are formed under catalytic conditions, which are converted to ...

A new class of carbon monoxide-releasing molecules (CO-RMs) are reported based on a previously known tetracarbonyl phenylpyridine manganese(I) motif. A pre-functionalized CO-RM undergoes a direct Pd-catalysed Suzuki–Miyaura cross-coupling with phenylboronic acid to give a π-extended three-ring CO-RM. Cross-coupling conditions were modified to allow coupling of a morpholine-containing boronic acid on to a CO-RM, introducing drug-like functionality. An LED system was used to facilitate controlled CO-release. Irradiation using an LED (400 nm or 365 nm) gives rise to faster CO-release, with lower overall input power than traditional use of a TLC lamp (365 nm), as measured by an assay based on the conversion of deoxymyoglobin to carbonmonoxymyoglobin.

Manganese‐catalyzed C−H bond activation chemistry is emerging as a powerful and complementary method for molecular functionalization. A highly reactive seven‐membered MnI intermediate is detected and characterized that is effective for H‐transfer or reductive elimination to deliver alkenylated or pyridinium products, respectively. The two pathways are determined at MnI by judicious choice of an electron‐deficient 2‐pyrone substrate containing a 2‐pyridyl directing group, which undergoes regioselective C−H bond activation, serving as a valuable system for probing the mechanistic features of Mn C−H bond activation chemistry.

N-Substituted derivatives of cantharimide and norcantharimide represent a promising but underutilized motif for therapeutic applications. Herein, we report a divergent strategy for the preparation of secondary amides and norcantharimide-resembling spirocyclic imides from a biomass-derived oxanorbornene and assess their biological activity. Computational modelling suggests these compounds fall perfectly within lead-like chemical space (200 Da

Well-controlled and extremely rapid ring-opening metathesis polymerization of unusual oxanorbornene lactam esters by Grubbs third-generation catalyst is used to prepare a range of bio-based homo- and copolymers. Bio-derived oxanorbornene lactam monomers were prepared at room temperature from maleic anhydride and secondary furfuryl amines by using a 100 % atom economical, tandem Diels–Alder lactamization reaction, followed by esterification. Several of the resulting homo- and copolymers show good control over polymer molecular weight and have narrow molecular weight distributions.

Cu(II), Mn(II) and Zn(II) complexes of metronidazole with benzoic acid derivatives formulated as [Cu2(met)4(4-nba)4] (1), [Mn(met)2(2bba)2(H2O)2] (2) and [Zn(met)2(3,5-dnba)2] (3) [met = metronidazole, 4-nba = 4-nitrobenzoic acid, 2-bba = 2-bromobenzoic acid and 3,5-dnba = 3,5-dinitrobenzoic acid] were synthesized and characterized by elemental analysis and spectroscopic techniques and two of them by single crystal X-ray crystallography. Single crystal X-ray crystallography revealed a five-coordinate, trigonal bipyramidal arrangement in compound 1, while compound 2 is six coordinate octahedral geometry. The molar conductance indicates the complexes are non-electrolytes in solution. The EPR spectra of 1 and 2 showed broad signals centered on g = 2.125, 2.116 and 1.970, 2.005. A hyperfine quartet was observed in the solid state for 1 typical of Cu(II) ion, I = 3/2; while a hyperfine sextet characteristic of 55Mn nucleus, I = 5/2 was observed for 2. Cyclic voltammetry revealed a one-step redox couple for 1 at a potential range of −0.4 to +0.1 V assigned to the reduction peak of Cu(II)/Cu(I). The linearity of Randles-Sevcik plot (R2 = 0.999) suggests a diffusion-controlled redox couple.

A range of iridium complexes, Ir(η3-C3H5)(CO)(PR2R')2 (1a-1e) [where 1a, PR2R' = PPh3, 1b P(p-tol)3, 1c PMePh2, 1d PMe2Ph and 1e PMe3] were synthesized and their reactivity as stoichiometric hydroformylation precursors studied. Para-hydrogen assisted NMR spectroscopy detected the following intermediates: Ir(H)2(η3-C3H5)(CO)(PR2R') (2a-e), Ir(H)2(η1-C3H5)(CO)(PR2R')2 (4d-e), Ir(H)2(η1-C3H5)(CO)2(PR2R') (10a-e), Ir(H)2(CO-C3H5)(CO)2(PR2R') (11a-c), Ir(H)2(CO-C3H7)(CO)2(PR2R') (12a-c) and Ir(H)2(CO-C3H5)(CO)(PR2R')2 (13d-e). Some of these species exist as two geometric isomers according to their multinuclear NMR characteristics. The NMR studies suggest a role for the following 16 electron species in these reactions: Ir(η3-C3H5)(CO)(PR2R'), Ir(η1-C3H5)(CO)(PR2R')2, Ir(η1-C3H5)(CO)2(PR2R'), Ir(CO-C3H5)(CO)2(PR2R'), Ir(CO-C3H7)(CO)2(PR2R') and Ir(CO-C3H5)(CO)(PR2R')2. Their role is linked to several 18 electron species in order to confirm the route by which hydroformylation and hydrogenation proceeds.

Photochemical reactions of germane and diphenylgermane with Ru(PP) 2 H 2 (PP = R 2 PCH 2 CH 2 PR 2 or DuPhos, R = Ph dppe, R = Et depe, R = Me dmpe) are reported. Reaction with GeH 4 generates a mixture of cis and trans isomers of Ru(PP) 2 (GeH 3 )H except for the DuPhos complex which yields the product only in the cis form. In situ laser photolysis (355 nm) demonstrates that the initial product is the cis isomer that undergoes thermal isomerization to the trans isomer. The complex cis-[Ru(dppe) 2 (GeH 3 )H] crystallizes selectively, allowing determination of its X-ray structure as a germyl hydride with a long Ru-H···Ge separation of 2.64(3) Å indicating that no residual interaction between the RuH and Ge is present. DFT calculations are also consistent with full oxidative addition. The structure of cis-[Ru(DuPhos) 2 (GeH 3 )H] reveals significant distortion from an octahedral geometry. The major species in the crystal (95%) exhibits a structure with a Ru-H···Ge distance of 2.42(5) Å suggesting negligible interaction between these centers. DFT calculations of the structure are consistent with the experimental determination. The reactions of Ru(PP) 2 H 2 with diphenylgermane yield cis-[Ru(PP) 2 (GePh 2 H)H] exclusively for PP = dmpe and depe, while the cis isomer is dominant in the case of dppe. A photochemical competition reaction between Ru(dppe) 2 (H) 2 and the two substrates Ph 2 SiH 2 and Ph 2 GeH 2 results in both Si-H and Ge-H oxidative addition activation with a kinetic preference (0.18:1) for the germyl hydride product. Thermal conversion of Ru(dppe) 2 (SiPh 2 H)H to Ru(dppe) 2 (GePh 2 H)H is observed on heating.

The chemistry of phosphorus(III) ligands, which are of key importance in coordination chemistry, organometallic chemistry and catalysis, is dominated by relatively electron-rich species. Many of the electron-poor P(III) ligands that are readily available have relatively small steric profiles. As such, there is a significant gap in “ligand space” where more sterically bulky, electron-poor P(III) ligands are needed. This contribution discusses the coordination chemistry, steric and electronic properties of P(III) ligands bearing highly fluorinated alkoxide groups of the general form PRn(ORF)3-n, where R = Ph, RF = C(H)(CF3)2 and C(CF3)3; n = 1-3. These ligands are simple to synthesize and a range of experimental and theoretical methods suggest that their steric and electronic properties can be “tuned” by modification of their substituents, making them excellent candidates for large, electron-poor ligands.

Hyperpolarised NMR allows the tracking of the DFT-rationalised outer sphere hydrogenation of quinazoline., PHIP and SABRE hyperpolarized NMR methods are used to follow the unexpected metal-catalysed hydrogenation of quinazoline (Qu) to 3,4-dihydroquinazoline as the sole product. A solution of [IrCl(IMes)(COD)] in dichloromethane reacts with H2 and Qu to form [IrCl(H)2(IMes)(Qu)2] (2). The addition of methanol then results in its conversion to [Ir(H)2(IMes)(Qu)3]Cl (3) which catalyses the hydrogenation reaction. Density functional theory calculations are used to rationalise a proposed outer sphere mechanism in which (3) converts to [IrCl(H)2(H2)(IMes)(Qu)2]Cl (4) and neutral [Ir(H)3(IMes)(Qu)2] (6), both of which are involved in the formation of 3,4-dihydroquinazoline via the stepwise transfer of H+ and H–, with H2 identified as the reductant. Successive ligand exchange in 3 results in the production of thermodynamically stable [Ir(H)2(IMes)(3,4-dihydroquinazoline)3]Cl (5).

It has been shown for the first time that the PtIV complex cis‐[Pt(N^C‐tolpy)2Cl2] (tolpy=2‐(4‐tolyl)pyridinyl) can be prepared in a one‐pot reaction from K2[PtCl4], although analogous complexes containing 2,5‐bis(4‐dodecyloxyphenyl)pyridine (=HL) could be prepared using existing routes. The resulting complexes cis‐[Pt(N^C‐L)2Cl2] are liquid crystals and small‐angle X‐ray scattering suggests formation of a lamellar mesophase. Surprisingly, heating [Pt(κ2‐N^C‐L)2Cl(κ1‐N^C‐LH)] also leads to a mesomorphic compound, which results from thermally induced oxidation to cis‐[Pt(N^C‐L)2Cl2] and what is presumed to be another geometric isomer of the same formula. The PtIV complexes are quite strongly luminescent in deoxygenated solution, with φ≈10 % and show vibrationally structured emission spectra, λmax(0,0)=532 nm, strongly displaced to the red compared to cis‐[Pt(N^C‐tolpy)Cl2]. Long luminescence lifetimes of 230 μs are attributed to a lower degree of metal character in the excited state accompanying the extension of conjugation in the ligand. There is no significant difference between the emission properties of the bromo‐ and chloro‐complexes, in contrast with the known complexes cis‐[Pt(N^C‐ppy)X2], where the quantum yield for X=Br is some 30 times lower than for X=Cl (ppyH=2‐phenylpyridine). The lower energy of the excited state in the new complexes probably ensures that deactivating LLCT/LMCT states remain thermally inaccessible, even when X=Br.

Dihydrolevoglucosenone (Cyrene®) has been successfully utilised as a bio-based platform molecule for the synthesis of pharmaceutically relevant intermediates through aldol condensation reactions. Utilising sustainable synthetic methodologies, the self-aldol condensations reaction of Cyrene was achieved in high purity, with isolated yields of 81.3%. Claisen-Schmidt reactions with a range of aromatic and heteroaromatic aldehydes yielded novel cyrene-based compounds, characterised by single-crystal X-ray diffraction, FT-IR, NMR and MS.

A new oxa-norbornene bio-based lactone obtained from the 100% atom economic reaction of furfuryl alcohol and itaconic anhydride via a tandem Diels–Alder addition and lactonisation is presented. Esterification of the resulting acid gives a monomer for the production of a bio-based polymer with low polydispersity and well controlled molecular weight via ring-opening metathesis polymerisation (ROMP).

A computational study of the C(methyl)–O bond activation of fluorinated aryl methyl ethers by a platinum(0) complex Pt(PCyp3)2 (Cyp = cyclopentyl) (N. A. Jasim, R. N. Perutz, B. Procacci and A. C. Whitwood, Chem. Commun., 2014, 50, 3914) demonstrates that the reaction proceeds via an SN2 mechanism. Nucleophilic attack of Pt(0) generates an ion pair consisting of a T-shaped platinum cation with an agostic interaction with a cyclopentyl group and a fluoroaryloxy anion. This ion-pair is converted to a 4-coordinate Pt(II) product trans-[PtMe(OArF)(PCyp3)2]. Structure-reactivity correlations are fully consistent with this mechanism. The Gibbs energy of activation is calculated to be substantially higher for aryl methyl ethers without fluorine substituents and higher still for alkyl methyl ethers. These conclusions are in accord with the experimental results. Further support was obtained in an experimental study of the reaction of Pt(PCy3)2 with 2,3,5,6-tetrafluoro-4-allyloxypyridine yielding the salt of the Pt(η3-allyl) cation and the tetrafluoropyridinolate anion [Pt(PCy3)2(η3-allyl)][OC5NF4]. The calculated activation energy for this reaction is significantly lower than that for fluorinated aryl methyl ethers.

The synthesis of bis-oxindoles via the copper(II)-mediated double cyclisation of linear bis-anilides is described. Cu(OAc)2·H2O was identified as an efficient and inexpensive catalyst for this process. In contrast to previous methods, which rely on the synthesis of the central core from existing oxindole building blocks, this new approach focusses on concurrent formation of both oxindole rings from a simple linear precursor, allowing the formation of bis-oxindoles containing a diverse range of cyclic and acyclic linkers using a single synthetic method.

The effect of fluorine substituents on the regioselectivity of intramolecular reactions of mono- and difluorinated N,N-dimethylbenzylamines (1a–f) at palladium, to form palladacycles di-μ-acetatobis[o-dimethylaminomethyl-n-fluorophenyl-C,N)dipalladium(II) (2a–f) and di-μ-chlorobis[o-dimethylaminomethyl-n-fluorophenyl-C,N)dipalladium(II) (3a–e), has been investigated. When fluorinated substrates with two sites available for the C–H functionalization (1c and 1e) undergo cyclopalladation via a CMD mechanism (acetate-bridged palladacycles), they do not exhibit regioselectivity. In contrast, the same substrates exhibit complete regioselectivity for the C–H functionalization para to fluorine in cyclopalladation reactions that proceed via an SEAr mechanism (involving chloride-bridged palladacycles). X-ray crystal structures were obtained for all the palladacycles synthesized, and a structural analysis showed that the number and the position of the fluorine atoms on the aromatic ring have a marked effect on the “...

The development of inexpensive and sustainable aluminum(salen) complexes as catalysts for the kinetic resolution of terminal epoxides is described. The kinetic resolution is carried out under mild conditions (0–25 °C and 1 bar of CO2 pressure) in the presence of tetrabutylammonium bromide as co-catalyst in the absence of solvent. The relative rate of reaction of the two epoxide enantiomers (krel) is substrate dependent, and the highest krel obtained was 15.4, using N-(2,3-epoxypropyl)diphenylamine as substrate.

A dinuclear, butadiene-bridged complex, trans-μ2:η2,η2-1,3-butadiene-bis(trichloroplatinate(ii)) (1) was unexpectedly obtained on photolysis of acetone solutions of (NBu4)2[PtCl6].

A new family of linear metal polymers of formula [M(isn-κNpy)4(μ-SiF6-κF,F′)]n (M = Cu, Co, Ni; isn = isonicotinamide) have been synthesized and characterized. The authenticities of these polymers were characterized by elemental analysis, IR and electronic absorption spectroscopy and magnetic susceptibility, which suggested that all the three complexes possess a similar structure. The crystal structure of the Cu-complex was determined by single crystal X-ray diffraction, showing that the compound is a backbone metal chain in which the metals are linked by a SiF62− bridges.

The pincer complex [(C5H3N(CH2P(tBu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange., The short lived pincer complex [(C5H3N(CH2P(tBu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange. This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine. When the catalysts 1H nuclei are replaced by 2H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals. The ligand exchange pathways of [(C5H3N(CH2P(tBu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P(tBu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P(tBu)2)2)Ir(H)2(H2)]BF4.

We report a study of the photocatalytic reduction of CO2 to CO by zinc porphyrins covalently linked to [ReI(2,2′-bipyridine)(CO)3L]+/0 moieties with visible light of wavelength >520 nm. Dyad 1 contains an amide C6H4NHC(O) link from porphyrin to bipyridine (Bpy), Dyad 2 contains an additional methoxybenzamide within the bridge C6H4NHC(O)C6H3(OMe)NHC(O), while Dyad 3 has a saturated bridge C6H4NHC(O)CH2; each dyad is studied with either L = Br or 3-picoline. The syntheses, spectroscopic characterisation and cyclic voltammetry of Dyad 3 Br and [Dyad 3 pic]OTf are described. The photocatalytic performance of [Dyad 3 pic]OTf in DMF/triethanolamine (5 : 1) is approximately an order of magnitude better than [Dyad 1 pic]PF6 or [Dyad 2 pic]OTf in turnover frequency and turnover number, reaching a turnover number of 360. The performance of the dyads with Re–Br units is very similar to that of the dyads with [Re–pic]+ units in spite of the adverse free energy of electron transfer. The dyads undergo reactions during photocatalysis: hydrogenation of the porphyrin to form chlorin and isobacteriochlorin units is detected by visible absorption spectroscopy, while IR spectroscopy reveals replacement of the axial ligand by a triethanolaminato group and insertion of CO2 into the latter to form a carbonate. Time-resolved IR spectra of [Dyad 2 pic]OTf and [Dyad 3 pic]OTf (560 nm excitation in CH2Cl2) demonstrated electron transfer from porphyrin to Re(Bpy) units resulting in a shift of ν(CO) bands to low wavenumbers. The rise time of the charge-separated species for [Dyad 3 pic]OTf is longest at 8 (±1) ps and its lifetime is also the longest at 320 (±15) ps. The TRIR spectra of Dyad 1 Br and Dyad 2 Br are quite different showing a mixture of 3MLCT, IL and charge-separated excited states. In the case of Dyad 3 Br, the charge-separated state is absent altogether. The TRIR spectra emphasize the very different excited states of the bromide complexes and the picoline complexes. Thus, the similarity of the photocatalytic data for bromide and picoline dyads suggests that they share common intermediates. Most likely, these involve hydrogenation of the porphyrin and substitution of the axial ligand at rhenium.

The coordination modes of the [Au(PPh3)](+) cation to metal alkynyl complexes have been investigated. On addition to ruthenium, a vinylidene complex, [Ru(η(5)-C5H5)(PPh3)2([double bond, length as m-dash]C[double bond, length as m-dash]CPh{AuPPh3})](+), is obtained while addition to a gold(iii) compound gives di- and trinuclear gold complexes depending on the conditions employed. In the trinuclear species, a gold(i) cation is sandwiched between two gold(iii) alkynyl complexes, suggesting that coordination of multiple C-C triple bonds to gold is facile.

This study describes the synthesis and characterization of a new class of ferrocene-containing carbon monoxide-releasing molecules (CORMs, 1-3). The ferrocenyl group is both a recognized therapeutically viable coligand and a handle for informative infrared spectroelectrochemistry. Deoxymyoglobin CO-release assays and in situ infrared spectroscopy confirm compounds 2 and 3 as photoCORMs and 1 as a thermal CORM, attributed to the increased sensitivity of the Mn-ferrocenyl bond to protonation in 1. Electrochemical and infrared spectroelectrochemical experiments confirm a single reversible redox couple associated with the ferrocenyl moiety with the Mn tetracarbonyl center showing no redox activity up to +590 mV vs Fc/Fc

Reaction of the alkenyl-substituted carbene complex [Ru(κ2-O2CMe)(OC{Me}O(═CCH═CH2)(PPh3)2]+ with PPh3 results in the formation of the vinylidene-containing species [Ru(κ1-O2CMe)(κ2-O2CMe)(═C═CHCH2PPh3)(PPh3)2]+, among other products. This complex could also be obtained by reaction of [Ru(κ2-O2CR)(PPh3)2] (R = Me, Ph) with [HC≡CCH2PPh3]+ although in this instance competitive formation of allene-containing [Ru(κ1-O2CR)(κ2-O2CR)(η2-H2C═C═CHPPh3)(PPh3)2] occurred. Reaction of [Ru(κ2-O2CMe)2(PPh3)2] with [H2C═C═CHPPh3]+ gives this allene complex in a selective fashion. Similar results were obtained when [RhCl(PiPr3)2]2 was used as the metal precursor. The reaction with [H2C═C═CHPPh3]+ gave [RhCl(η2-H2C═C═CHPPh3)(PiPr3)2]+, whereas treatment with [HC≡CCH2PPh3]+ afforded a mixture of the same complex and [RhCl(η2-HC≡CCH2PPh3)(PiPr3)2]+, which subsequently isomerized to vinylidene-containing [RhCl(═C═CHCH2PPh3)(PiPr3)2]+ via the alkynyl hydride complex [RhCl(H)(C≡CCH2PPh3)(PiPr3)2]+. Consistent with previous fin...

The intramolecular arylation of 2-pyrones, 2-pyridones, coumarins and quinolones is reported using PdII precatalyst sources without added phosphine ligands. The excellent yields and convenient reagents enables the formation of various analogues containing these moieties, and access to potential biologically active candidates. Stoichiometric studies were carried out to provide an insight into the oxidation addition step. A switch in regioselectivity, together with a hydrodebromination process, was observed in the case of a 3-bromo-2-pyrone.

A double C-H, Ar-H coupling process for the conversion of bis-anilides into spirocyclic bis-oxindoles, enabling the concomitant formation of two all-carbon quaternary centers at oxindole 3-positions in a diastereoselective manner, is described. The optimum cyclization conditions utilize stoichiometric Cu(OAc)2·H2O/KOtBu in DMF at 110 °C and have been applied to prepare a range of structurally diverse bis-spirooxindoles in fair to good yields (28-77%); the method has also been extended to prepare bis-oxindoles linked by a functionalized acyclic carbon chain.

Experimental results have long suggested that catalyst optimization is an inherently multivariate process, requiring the screening of reaction conditions (temperature, pressure, solvents, precursors, etc.), catalyst structure (metal and ligands), and substrate scope. With a view to demonstrating the feasibility and utility of multivariate computational screening of organometallic catalysts, we have investigated the structural and electronic properties of a library of transition-metal-coordinated alkyne and vinylidene tautomers in different coordination environments. By varying the substituents on the organic moiety of 60 alkyne/vinylidene pairs we were able to capture and quantify the key structural and electronic effects on tautomer preference. For a carefully selected subset of substituents, the effects of metal and ancillary ligands were then explored. We have been able to formulate a protocol for assessing the stabilization of vinylidenes in transition-metal complexes, suggesting that the d6 square-ba...

Irradiation of CpRh(PMe3)(C2H4) (1; Cp = η5-C5H5) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable η2-C,C-coordinated pentafluoropyridine complex, CpRh(PMe3)(η2-C,C-C5NF4) (2). The molecular structure of 2 was determined by single-crystal X-ray diffraction, showing coordination by C3–C4, unlike previous structures of pentafluoropyridine complexes that show N-coordination. Corresponding experiments with 2,3,5,6-tetrafluoropyridine yield the C–H oxidative addition product CpRh(PMe3)(C5NF4)H (3). In contrast, UV irradiation of 1 in hexane, in the presence of 4-substituted tetrafluoropyridines C5NF4X, where X = NMe2, OMe, results in elimination of C2H4 and HF to form the metallacycles CpRh(PMe3)(κ2-C,C-CH2N(CH3)C5NF3) (4) and CpRh(PMe3)(κ2-C,C-CH2OC5NF3) (5), respectively. The X-ray structure of 4 shows a planar RhCCNC-five-membered ring. Complexes 2–5 may also be formed by thermal reaction of CpRh(PMe3)(Ph)H with the respective pyridines at 50 °C.

Reaction of hydroxyvinylidene complexes [Ru(κ1-OAc)(κ2-OAc)(═C═CHC{OH}R1R2)(PPh3)2] (R1 = R2 = Ph; R1 = R2 = Me; R1 = Ph, R2 = Me) with [CPh3]BF4 results in the formation of the cationic carbene species [Ru(κ2-OAc)(OC{Me}OCC{H}═CR1R2)(PPh3)2]BF4. In these complexes, the κ1-acetate ligand has changed its binding mode in order to stabilize the resulting cationic species. The carbene complexes may be deprotonated, although the outcome of the reaction depends markedly on the substituent present. In the case in which R1 = R2 = Ph, the hydrogen on the β-carbon of the organic ligand is removed to afford an allenylidene complex [Ru(κ1-OAc)(κ2-OAc)(═C═C═CPh2)(PPh3)2]. An examination of the structural and spectroscopic parameters for the allenylidene complex indicates that the electronic influence of this ligand is very similar to the corresponding vinylidene and isonitrile analogues. In the cases where R1 = R2 = Me and R1 = Me, R2 = Ph deprotonation occurs at a methyl group to afford vinylvinylidene complexes [Ru(...

Pd(0)2(dba)3 (dba = E,E-dibenzylidene acetone) is the most widely used Pd(0) source in Pd-mediated transformations. Pd(0)2(dba-Z)3 (Z = dba aryl substituents) complexes exhibit remarkable and differential catalytic performance in an eclectic array of cross-coupling reactions. The precise structure of these types of complexes has been confounding, since early studies in 1970s to the present day. In this study the solution and solid-state structures of Pd(0)2(dba)3 and Pd(0)2(dba-Z)3 have been determined. Isotopic labeling ((2)H and (13)C) has allowed the solution structures of the freely exchanging major and minor isomers of Pd(0)2(dba)3 to be determined at high field (700 MHz). DFT calculations support the experimentally determined major and minor isomeric structures, which show that the major isomer of Pd(0)2(dba)3 possesses bridging dba ligands found exclusively in a s-cis,s-trans conformation. For the minor isomer one of the dba ligands is found exclusively in a s-trans,s-trans conformation. Single crystal X-ray diffraction analysis of Pd(0)2(dba)3·CHCl3 (high-quality data) shows that all three dba ligands are found over two positions. NMR spectroscopic analysis of Pd(0)2(dba-Z)3 reveals that the aryl substituent has a profound effect on the rate of Pd-olefin exchange and the global stability of the complexes in solution. Complexes containing the aryl substituents, 4-CF3, 4-F, 4-t-Bu, 4-hexoxy, 4-OMe, exhibit well-resolved (1)H NMR spectra at 298 K, whereas those containing 3,5-OMe and 3,4,5-OMe exhibit broad spectra. The solid-state structures of three Pd(0)2(dba-Z)3 complexes (4-F, 4-OMe, 3,5-OMe) have been determined by single crystal X-ray diffraction methods, which have been compared with Goodson's X-ray structure of Pd(0)2(dba-4-OH)3.

The effects of substituting (pseudo)halide for anionic imidate ligands in Au(I) and Au(III) (i.e. [AuBr(NHC)] and [AuBr3(NHC)]) complexes have been investigated. [Au(N-imidate)(NHC)] and [AuBr2(N-imidate)(NHC)] complexes were prepared and the structure and bonding of the complexes examined spectroscopically and crystallographically. The [AuBr2(N-imidate)(NHC)] complexes, in combination with Ag salts, were tested for catalytic activity in the cycloisomerization of 1,5-enynes and found to be more effective than the tribromide analogues (e.g. [AuBr3(NHC)]). Subtle changes to the anionic imidate ligand structure had a pronounced effect on the catalytic activity of the Au(III) complexes.

The facile synthesis of a stable and isolable compound with a fluoroalkynyl group, M−C≡CF, is reported. Reaction of [Ru(C≡CH)(η5-C5Me5)(dppe)] with an electrophilic fluorinating agent (NFSI) results in the formation of the fluorovinylidene complex [Ru(=C=CHF)(η5-C5Me5)(dppe)][N(SO2Ph)2]. Subsequent deprotonation with LiN(SiMe3)2 affords the fluoroalkynyl complex [Ru(C≡CF)(η5-C5Me5)(dppe)]. In marked contrast to the rare and highly reactive examples of fluoroalkynes that have been reported previously, this compound can be readily isolated and structurally characterized. This has allowed the structure and bonding in the CCF motif to be explored. Further electrophilic fluorination of this species yields the difluorovinylidene complex [Ru(C=CF2)(η5-C5Me5)(dppe)][N(SO2Ph)2].

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Reaction of cis-[RuCl2(DMSO-S)3(DMSO-O)] with cis-1,3,5-triaminocyclohexane (tach) results in the formation of [RuCl(tach)(DMSO-S)2]Cl, a valuable precursor for a wide range of other tach-containing Ru complexes. Reaction of [RuCl(tach)(DMSO-S)2]Cl with the chelating nitrogen-based ligands (N-N = bipyridine, phenanthroline, and ethylenediamine) affords [Ru(N-N)(DMSO-S)2(tach)][Cl]2. A similar reaction between [RuCl(tach)(DMSO-S)]Cl with the chelating phosphorus-based ligands (P-P = dppm, dppe, dppp, dppb, dppv, and dppben) leads to the formation of [RuCl(P-P)(tach)]Cl. The structures of 10 examples of the tach-containing complexes have been determined by single crystal X-ray diffraction. An examination of the structural metrics obtained from these studies indicates that the tach ligand is a strong sigma donor. In addition, the presence of the NH2 groups in the tach ligand allow for participation in hydrogen bonding further modulating the coordinative properties of the ligand.

A multidentate and flexible diolefin-diphosphine ligand, based on the dibenzylidene acetone core, namely dbaphos (1), is reported herein. The ligand adopts an array of different geometries at Pt, Pd and Rh. At Pt(II) the dbaphos ligand forms cis- and trans-diphosphine complexes and can be defined as a wide-angle spanning ligand. (1)H NMR spectroscopic analysis shows that the β-hydrogen of one olefin moiety interacts with the Pt(II) centre (an anagostic interaction), which is supported by DFT calculations. At Pd(0) and Rh(I), the dbaphos ligand exhibits both olefin and phosphine interactions with the metal centres. The Pd(0) complex of dbaphos is dinuclear, with bridging diphosphines. The complex exhibits the coordination of one olefin moiety, which is in dynamic exchange (intramolecular) with the other "free" olefin. The Pd(0) complex of dbaphos reacts with iodobenzene to afford trans-[Pd(II)(dbaphos)I(Ph)]. In the case of Rh(I), dbaphos coordinates to form a structure in which the phosphine and olefin moieties occupy both axial and equatorial sites, which stands in contrast to a related bidentate olefin, phosphine ligand ("Lei" ligand), in which the olefins occupy the equatorial sites and phosphines the axial sites, exclusively.

The dimeric di-μ-chlorido anion hexachloridopalladate(II)platinate(II) has been prepared as a mixture with hexachloridodipalladate(II) and hexachloridodiplatinate(II) and has been identified by using a combination of X-ray crystallography and 195Pt NMR spectroscopy. This is the first report of a heterodinuclear dimer of this type.

A concise synthesis of the AB rings of samaderine C (12 steps, 8 isolation steps, 7.8% overall yield), a quassinoid with antifeedant and insecticidal activity, is described. The development of the first general approach to the trans-1,2-diol A-ring motif in samaderine C and other quassinoids is a key feature. The trans-1,2-diol is crafted via stereoselective α-hydroxylation (of a silyl enol ether) and reduction, a strategy that has much potential for quassinoid synthesis.

A regioselective Pd-mediated C–H bond arylation methodology for tryptophans, utilizing stable aryldiazonium salts, affords C2-arylated tryptophan derivatives, in several cases quantitatively. The reactions proceed in air, without base, and at room temperature in EtOAc. The synthetic methodology has been evaluated and compared against other tryptophan derivative arylation methods using the CHEM21 green chemistry toolkit. The behavior of the Pd catalyst species has been probed in preliminary mechanistic studies, which indicate that the reaction is operating homogeneously, although Pd nanoparticles are formed during substrate turnover. The effects of these higher order Pd species on catalysis, under the reaction conditions examined, appear to be minimal: e.g., acting as a Pd reservoir in the latter stages of substrate turnover or as a moribund form (derived from catalyst deactivation). We have determined that TsOH shortens the induction period observed when [ArN2]BF4 salts are employed with Pd(OAc)2. Pd(OTs)2(MeCN)2 was found to be a superior precatalyst (confirmed by kinetic studies) in comparison to Pd(OAc)2.

EPR spin-trapping, although a powerful, sensitive technique for the study of free radicals, can be susceptible to artefacts; one of the most intractable to determine has been the non-radical addition of a substrate to a spin-trap followed by oxidation of the product to an EPR-detectable nitroxide. This work details how differentially isotopically labelled spin-traps (either nitroso or nitrone) may be used to determine the presence (or absence) of such artefacts, and provide a semi-quantitative measure of the extent of their contribution to the total EPR spectra in spin-trapping reactions. Artefactual 'ene' addition of the nitroso spin-trap 3,5-dibromo-4-nitroso-benzenesulphonic acid (DBNBS) to tryptophan followed by oxidation to EPR-detectable products has been confirmed, as has its nucleophilic addition to the thiol of glutathione to give non-EPR detectable products. The nitrone α-phenyl-N-tert-butylnitrone (PBN) exhibited no such reactivity.

With the increasing restriction and control of hazardous solvents, safer alternatives need to be identified. Here a contemporary approach to solvent selection and substitution is presented that offers a more scientific alternative to the simple “like-for-like” exchange. A new family of levoglucosenonederived compounds is proposed, modeled to determine their solvent properties, synthesized, and tested. These new molecules show promise as replacements for polar aprotic solvents that have chronic toxicity issues, such as dichloromethane, nitrobenzene, and N-methylpyrrolidinone. The success of this approach makes it possible for academia and industry to make calculated, intelligent choices for solvent substitution in the future.

The luminescent and mesomorphic properties of a series of metal complexes based on hexacatenar 2,2′:6′,2′′-terpyridines are investigated using experimental methods and density functional theory (DFT). Two types of ligand are examined, namely 5,5′′-di(3,4,5-trialkoxyphenyl)terpyridine with or without a fused cyclopentene ring on each pyridine and their complexes were prepared with the following transition metals: ZnII, CoIII, RhIII, IrIII, EuIIIand DyIII. The exact geometry of some of these complexes was determined by single X-ray diffraction. All complexes with long alkyl chains were found to be liquid crystalline, which property was induced on complexation. The liquid-crystalline behaviour of the complexes was studied by polarising optical microscopy and small-angle X-ray diffraction. Some of the transition metal complexes (for example, those with ZnIIand IrIII) are luminescent in solution, the solid state and the mesophase; their photophysical properties were studied both experimentally and using DFT methods (M06-2X and B3LYP). Bright ideas: The luminescent and mesomorphic properties of a series of metal complexes based on hexacatenar 2,2′:6′,2′′-terpyridines (see figure) are investigated using experimental methods and density functional theory. The ligands in this study show a remarkable ability to promote liquid crystal behaviour when complexed to a wide range of metals where the liquid crystallinity extends over a very wide temperature range. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The preparation is described of bimetallic complexes of the multidentate ligand, H6TTHA – triethylenetetraamine-N,N′,N″,N‴-hexaacetic acid. Attempts to use a stepwise approach systematically to prepare heterobimetallic complexes were unsuccessful and led in most cases to homobimetallic complexes or to heterobimetallic complexes whose stoichiometry did not reflect the stoichiometry of the preparation. Nonetheless, on one occasion a monodisperse heterobimetallic complex of rhodium and zinc was isolated, which represents the first properly characterised heterobimetallic complex of TTHA.

Reaction of PPh2H with UrI (Ur = uracil) in the presence of Pd(OAc)2 affords PPh2Ur. In the solid state, PPh2Ur crystallises as a methanol solvate in the monoclinic space group P21/c. Reaction of PPh2Ur with CuI in dry and deoxygenated THF solution results in the formation of [Cu4(μ3-I)4(PPh2Ur)4]. A single crystal X-ray diffraction study demonstrated that this species contains a distorted tetrahedral core of copper atoms, with facially-capping iodides. The uracil groups in the clusters are engaged in hydrogen bonding to groups on neighbouring molecules to form an extended array. A similar reaction between PPh2Ur and CuI in unpurified THF allows for the isolation of the phosphine oxide P(O)PPh2Ur. The synthesis of the benzyl-protected phosphine PPh2UrP is also described [UrP = 2,4-bis(benzyloxy)pyrimidine]. Reaction of PPh2UrP with [Ru(η5-C5H5)(NCMe)3]PF6 allows for isolation of [Ru(η5-C5H5)(NCMe)(PPh2UrP)2]PF6.

We report the syntheses of imprinted polymers using iron-oxo-hydroxo clusters as templates. Three new iron clusters, [Fe6O2(OH)2(O2CC(Cl)CH2)12(H2O)2] (1), [{Fe(O2CC(Cl)CH2)(OMe)2}10] (2) and [Fe6O2(OH)2(O2C–Ph–(CH)CH2)12(H2O)2] (3) have been prepared from commercially-available carboxylic acids. Cluster-imprinted-polymers (CIPs) of 1, 2 and 3 were prepared with ethylene glycol dimethacrylate monomer, and of 1 with methyl methacrylate monomer. The imprinted sites within the CIPs were examined using EXAFS and diffuse reflectance UV/vis spectroscopy, demonstrating that the clusters 1, 2 and 3 were incorporated intact within the polymers. Extraction of the clusters from the CIPs imprinted with 1 and 3 gave new polymers that showed evidence of an imprinting effect.

Reaction of cis-Ru(κ2-OAc)2(PPh3)2 with two-electron donor ligands L results in the formation of complexes trans-[Ru(κ1-OAc)(κ2-OAc)L(PPh3)2] (L = CO, NO+, CNtBu). Vinylidene complexes (L = C=CHR) may be prepared from the corresponding reaction with terminal alkynes HC≡CR, and species containing hydroxyvinylidene ligands (L = C=CHCR1R2{OH}) may be prepared from related reactions with propargyl alcohols HC≡CCR1R2{OH}. Treatment of cis-Ru(κ2-OAc)2(PPh3)2 with ω-alkynols HC≡C(CH2)nOH (n = 2–4) results in the formation of oxacyclocarbene complexes [L = CCH2(CH2)nO]. An analysis of the spectroscopic data and the structural metrics (as determined by X-ray crystallography) of this series of complexes allows for the relative donor/acceptor properties of the ligand L to be evaluated. This comparison indicates that the vinylidene ligand behaves in a similar fashion to the isocyanide ligand.

A study is presented of the thermodynamics of the halogen-bonding interaction of C(6)F(5)I with a series of structurally similar group 10 metal fluoride complexes trans-[Ni(F)(2-C(5)NF(4))(PCy(3))(2)] (2), trans-[Pd(F)(4-C(5)NF(4))(PCy(3))(2)] (3), trans-[Pt(F){2-C(5)NF(2)H(CF(3))}(PR(3))(2)] (4a, R = Cy; 4bR = iPr) and trans-[Ni(F){2-C(5)NF(2)H(CF(3))}(PCy(3))(2)] (5a) in toluene solution. (19)F NMR titration experiments are used to determine binding constants, enthalpies and entropies of these interactions (2.4 ≤ K(300) ≤ 5.2; -25 ≤ ΔH(o) ≤ -16 kJ mol(-1); -73 ≤ ΔS(o) ≤ -49 J K(-1) mol(-1)). The data for -ΔH(o) for the halogen bonding follow a trend Ni < Pd < Pt. The fluoropyridyl ligand is shown to have a negligible influence on the thermodynamic data, but the influence of the phosphine ligand is significant. We also show that the value of the spin-spin coupling constant J(PtF) increases substantially with adduct formation. X-ray crystallographic data for Ni complexes 5a and 5c are compared to previously published data for a platinum analogue. We show by experiment and computation that the difference between Pt-X and Ni-X (X = F, C, P) bond lengths is greatest for X = F, consistent with F(2pπ)-Pt(5dπ) repulsive interactions. DFT calculations on the metal fluoride complexes show the very negative electrostatic potential around the fluoride. Calculations of the enthalpy of adduct formation show energies of -18.8 and -22.8 kJ mol(-1) for Ni and Pt complexes of types 5 and 4, respectively, in excellent agreement with experiment.

Reaction of [MoCl(η5-C5H5)(CO)3] with propargyl alcohols HC≡CCR1R2OH in the presence of catalytic amounts of CuI and using NEt2H as solvent results in the formation of alkynyl complexes [Mo(C≡CCR1R2OH)(η5-C5H5)(CO)3]. The structure of the complexes where R1 = R2 = Me and R1 = Me, R2 = Ph were confirmed by single-crystal X-ray diffraction. The method could be extended to a range of propargyl ethers and propargyl esters, which allowed for the preparation of molybdenum complexes containing pendant salicylate and β-d-fructopyranose groups. The alkynyl complex [Mo(C≡CCH2OH)(η5-C5H5)(CO)3] undergoes a further reaction with NEt2H to give the substituted allyl complex [Mo(η3-H2CC{NEt2}CHC{O}NEt2)(η5-C5H5)(CO)3]. Similar products could be obtained from the reaction of [MoCl(η5-C5H5)(CO)3] with HC≡CCH2OH in the presence of CuI using pyrrolidine or piperidine as solvent. In the case of the reaction with piperidine a further product could be isolated that has arisen from the coupling of two propargyl alcohol molecule...