Search

We isolate and characterize the gold(I)-iron(0) adducts [( i Pr 2 -bimy)Au-Fe(CO) 3 (PMe 3 ) 2 ][BAr F 4 ] and [Au-{Fe(CO) 3 (PMe 3 ) 2 } 2 ][BAr F 4 ] ( i Pr 2 -bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, BAr F 4 = tetrakis(pentafluorophenyl)borate). DFT analysis reveals that the gold-iron interaction in [( i Pr 2 -bimy)Au-Fe(CO) 3 (PMe 3 ) 2 ][BAr F 4 ] is predominantly a σ-donation from iron to gold. We further extend this class of compounds to include [( i Pr 2 -bimy)Au-Fe(CO) 3 (PR 3 ) 2 ][BAr F 4 ] (PR 3 = PPh 3 , PCy 3 , PCyPh 2 , PMePh 2 , PMe 2 Ph, P(4-C 6 H 4 F) 3 ) and [( i Pr 2 -bimy)Au-Fe(CO) 4 (PPh 3 )][BAr F 4 ] and correlate the i Pr 2 -bimy carbenic 13 C NMR signal with the relative donor strength of the iron(0) ligand. This approach allows for a fast and simple approach to gauge relative donor strength of Fe(0) donors.

The 'POCOP' pincer ligand, [2,6-(OPR 2 ) 2 C 6 H 3 ], has been attached to titanium in both Ti(III) and Ti(IV) complexes for the first time. Using a lithium-halogen exchange route [2,6-(OPR 2 ) 2 C 6 H 3 ]Li ([RPOCOP]Li) can be synthesised. Both the iso -propyl and tert -butyl derivatives can be made, but only the latter isolated. These can be reacted with the Ti(III) and Ti(IV) synthons to make a range of [POCOP]TiCl x species. In the presence of Ti(IV), THF and [RPOCOP]Li, an unprecedented ligand rearrangement occurs. ( t Bu POCOP)TiCl 2 , 1, can be derivatised with alkylating agents to make bis-methyl, phenyl and neopentyl complexes. The last of these can activate H 2 to make a rare example of a titanium chlorohydride, with the metal pincer fragment staying attached. EPR has been used to characterise the paramagnetic complexes and locate their electron spins, which is further validated with DFT calculations. This opens the door for this archetypical pincer ligand to be used with early transition metals.

Stimuli responsive anion transport is becoming an important aspect of supramolecular anion recognition chemistry. Herein, we report the synthesis of a family of anion receptors that incorporate a new anion binding motif, amidosquaramides. We show using experimental and computational methods that these receptors have p K a values close to physiological pH but also display intramolecular H-bonding interactions that affect anion recognition. Moreover, moderate activity in a Cl - /NO 3 - exchange assay is observed at physiological pH that can be effectively 'switched on' when repeated under acidic conditions. The reported findings provide synthetic methods that can be used for the construction of more complex squaramide based anion receptors and also provide insight into the importance of conformational analysis when considering receptor design.

Asymmetrically-bound pyrrolide-based bis-PNP pincer complexes of zirconium and hafnium have been formed. The [κ2-PNPPh][κ3-PNPPh]MCl2 species are in direct contrast to previous zirconium PNP pincer complexes. The pincer ligands are fluxional in their binding and the energy barrier for exchange has been approximated using VT-NMR spectroscopy and the result validated by DFT calculations.

Candida albicans is one of the most prevalent fungal pathogens involved in hospital acquired infections. It binds to glycans at the surface of epithelial cells and initiates infection. This process can be blocked by synthetic carbohydrates that mimic the structure of cell surface glycans. Herein we report the evaluation of a series of divalent glycosides featuring aromatic (benzene, squaramide) and bicyclic aliphatic (norbornene) scaffolds, with the latter being the first examples of their kind as small molecule anti-adhesion glycoconjugates. Galactosides 1 and 6 , built on an aromatic core, were most efficient inhibitors of adhesion of C. albicans to buccal epithelial cells, displacing up to 36% and 48%, respectively, of yeast already attached to epithelial cells at 138 μM. Remarkably, cis-endo -norbornene 21 performed comparably to benzene-core derivatives. Conformational analysis reveals a preference for compounds 1 and 21 to adopt folded conformations. These results highlight the potential of norbornenes as a new class of aliphatic scaffolds for the synthesis of anti-adhesion compounds., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

The pentamethylcyclopentadienyl (Cp*) antimony(iii) cations [Cp* 2 Sb][B(C 6 F 5 ) 4 ], [Cp 2 *Sb][OTf], [Cp*SbCl][B(C 6 F 5 ) 4 ] and [Cp*Sb][OTf] 2 have been isolated and structurally characterised. [Cp*SbCl] + forms dimers in the solid state via an intermolecular Sb-Cl interaction. Initial screening shows that [Cp*SbCl][B(C 6 F 5 ) 4 ] is significantly Lewis acidic and can catalyse the dimerisation of 1,1-diphenylethylene; [Cp 2 *Sb][B(C 6 F 5 ) 4 ] exhibits negligible Lewis acidity. Highly unstable [Cp*SbF][B(C 6 F 5 ) 4 ] could not be isolated, but stabilisation with the IMes ligand allowed isolation of [Cp*SbF(IMes)][B(C 6 F 5 ) 4 ]. Fluorodechlorination of CH 2 Cl 2 and PhCCl 3 was observed in the presence of crude [Cp*SbF][B(C 6 F 5 ) 4 ] in solution. A computational mechanistic investigation suggests that the latter proceeds via a carbocation intermediate.

The preparation of a range of tetraaryl-substituted bicyclo[4.2.0]octa-1,5,7-trienes using a one-pot procedure starting from terminal aryl alkynes and catalysed by a rhodium(i) complex is reported. This synthesis proceeds by a reaction sequence involving head-to-tail homocoupling of the terminal alkyne and zipper annulation of the resulting gem -enyne. The rhodium catalyst employed is notable for the incorporation of a flexible NHC-based pincer ligand, which is suggested to interconvert between mer - and fac -coordination modes to fulfil the orthogonal mechanistic demands of the two transformations. Evidence for this interesting auto-tandem action of the catalyst is provided by reactions of the precatalyst with model substrates, corroborating proposed intermediates in both component cycles, and norbornadiene, which reversibly captures the change in pincer ligand coordination mode, along with a DFT-based computational analysis., (This journal is © The Royal Society of Chemistry 2020.)

We report the direct carbonyl cleavage in a κ 3 -P',(η 2 -C,O),P'' ligand by a monomeric cobalt centre through metal-ligand cooperativity. C-O cleavage leads to the formation of a PC carbene P(O) pincer ligand with a central alkylidene anchor. A DFT analysis, supported by kinetic studies, suggests that decoordination of a pincer phosphino arm to generate a kinetically accessible free phosphine may be critical in transfer of the oxide to a phosphorus position. Thus, oxide transfer to bisphosphino bidentate co-ligands was also found to be viable, allowing access to the previously reported PC carbene P pincer complex (2), where bisphosphines were used as oxide sequestering agents.

Small titanium-oxo-alkoxide clusters, [TiO(OR)(O 2 PR' 2 )] 4 , synthesised by the stoichiometric reaction of Ti(O i Pr) 4 , phosphinic acid and water, undergo a photo-redox transformation under long-wave UV light. The photo-reaction generates blue coloured, mixed-valence Ti(iii)/Ti(iv)-oxo clusters alongside acetone and isopropanol by-products. This reactivity indicates the ability for photoactivated charge separation to occur in even the smallest of Ti-oxo clusters. EPR and NMR spectroscopic studies support a photo-redox mechanism that occurs via an intramolecular, two-electron pathway, directly relating to current doubling effects observed at TiO 2 photoanodes in the presence of alcohols. The rate of photo-reaction is solvent dependent, with donor solvents supporting the formation of low coordinate Ti(iii) sites. The nature of the electronic transition is identified by DFT and TDDFT calculations as an oxygen to titanium charge transfer and it is possible to finetune the UV absorption onset observed by changing the phosphinate ligand. A two-electron photo-reduced cluster, [Ti 4 O 4 (O 2 PPh 2 ) 6 ], forms spontaneously from the photo-reaction and its structure is identified by X-ray crystallography with supporting DFT calculations. These indicate that [Ti 4 O 4 (O 2 PPh 2 ) 6 ] is high-spin and contains two ferromagnetically coupled electrons delocalised over the Ti 4 core. [Ti 4 O 4 (O 2 PPh 2 ) 6 ] undergoes rapid oxidation in air in the solid-state and performs a remarkable single-crystal to single-crystal transformation, to form a stable cluster-superoxide salt.

We report the first example of a cobalt PC carbene P pincer complex ( 1 ) featuring a central alkylidene carbon donor accessed through the dehydration of an alcoholic POP proligand. Complex 1 shares bonding similarities with cobalt PBP and PNP pincer complexes where the donor atom engages in π-bonding with the cobalt centre, and thus completes the PXP (X = B, C, N) pincer ligand series for cobalt (for X donors that partake in M-L π-bonding). As compared to PBP and PNP pincer complexes, which are known to be good hydride and proton acceptors (respectively), complex 1 is found to be an effective hydrogen atom acceptor. Complex 1 partakes in cooperative ligand reactivity, engaging in several small molecule activations with styrene, bromine, carbon disulphide, phenyl acetylene, acetonitrile, hydrogen, benzaldehyde and water (through microreversibility). The mechanism for the formation of complex 1 is studied through the isolation and computational analysis of key intermediates. The formation of 1 is found to avoid C-H activation of the proligand, and instead proceeds through a combination of O-H activation, hydrogen atom transfer, β-hydride elimination and hydrogen activation processes.

Single-crystal to single-crystal solid/gas reactivity and catalysis starting from the precursor sigma-alkane complex [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(η 2 η 2 -NBA)][BAr F 4 ] (NBA = norbornane; Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ) is reported. By adding ethene, propene and 1-butene to this precursor in solid/gas reactions the resulting alkene complexes [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(alkene) x ][BAr F 4 ] are formed. The ethene ( x = 2) complex, [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(ethene) 2 ][BAr F 4 ]-Oct , has been characterized in the solid-state (single-crystal X-ray diffraction) and by solution and solid-state NMR spectroscopy. Rapid, low temperature recrystallization using solution methods results in a different crystalline modification, [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(ethene) 2 ][BAr F 4 ]-Hex , that has a hexagonal microporous structure ( P 6 3 22). The propene complex ( x = 1) [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(propene)][BAr F 4 ] is characterized as having a π-bound alkene with a supporting γ-agostic Rh···H 3 C interaction at low temperature by single-crystal X-ray diffraction, variable temperature solution and solid-state NMR spectroscopy, as well as periodic density functional theory (DFT) calculations. A fluxional process occurs in both the solid-state and solution that is proposed to proceed via a tautomeric allyl-hydride. Gas/solid catalytic isomerization of d 3 -propene, H 2 C[double bond, length as m-dash]CHCD 3 , using [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(η 2 η 2 -NBA)][BAr F 4 ] scrambles the D-label into all possible positions of the propene, as shown by isotopic perturbation of equilibrium measurements for the agostic interaction. Periodic DFT calculations show a low barrier to H/D exchange (10.9 kcal mol -1 , PBE-D3 level), and GIPAW chemical shift calculations guide the assignment of the experimental data. When synthesized using solution routes a bis-propene complex, [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(propene) 2 ][BAr F 4 ] , is formed. [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(butene)][BAr F 4 ] ( x = 1) is characterized as having 2-butene bound as the cis -isomer and a single Rh···H 3 C agostic interaction. In the solid-state two low-energy fluxional processes are proposed. The first is a simple libration of the 2-butene that exchanges the agostic interaction, and the second is a butene isomerization process that proceeds via an allyl-hydride intermediate with a low computed barrier of 14.5 kcal mol -1 . [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(η 2 η 2 -NBA)][BAr F 4 ] and the polymorphs of [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(ethene) 2 ][BAr F 4 ] are shown to be effective in solid-state molecular organometallic catalysis (SMOM-Cat) for the isomerization of 1-butene to a mixture of cis - and trans -2-butene at 298 K and 1 atm, and studies suggest that catalysis is likely dominated by surface-active species. [Rh(Cy 2 PCH 2 CH 2 PCy 2 )(η 2 η 2 -NBA)][BAr F 4 ] is also shown to catalyze the transfer dehydrogenation of butane to 2-butene at 298 K using ethene as the sacrificial acceptor., (This journal is © The Royal Society of Chemistry 2017.)

The bis(carboranyl)phosphines [μ-2,2'-PPh-{1-(1'-1',2'-closo-C 2 B 10 H 10 )-1,2-closo-C 2 B 10 H 10 }] (I) and [μ-2,2'-PEt-{1-(1'-1',2'-closo-C 2 B 10 H 10 )-1,2-closo-C 2 B 10 H 10 }] (1) have been prepared and spectroscopically and structurally characterised. Crystallographic and DFT computational studies of 1 suggest that the orientation of the ethyl group, relative to the bis(carborane), is the result of intramolecular dihydrogen bonding. This orientation is such that the magnitudes of the 2 J PH coupling constants are approximately equal but of opposite sign, and fast exchange between the methylene protons in solution leads to an observed 2 J PH close to zero. The steric properties of I, 1 and their derivatives [μ-2,2'-P(Ph)AuCl-{1-(1'-1',2'-closo-C 2 B 10 H 10 )-1,2-closo-C 2 B 10 H 10 }] (2) and [μ-2,2'-P(Et)AuCl-{1-(1'-1',2'-closo-C 2 B 10 H 10 )-1,2-closo-C 2 B 10 H 10 }] (3) have been assessed by Tolman cone angle and percent buried volume calculations, from which it is concluded that the bis(carboranyl)phosphines I and 1 are comparable to PCy 3 in their steric demands. The selenides [μ-2,2'-P(Ph)Se-{1-(1'-1',2'-closo-C 2 B 10 H 10 )-1,2-closo-C 2 B 10 H 10 }] (4) and [μ-2,2'-P(Et)Se-{1-(1'-1',2'-closo-C 2 B 10 H 10 )-1,2-closo-C 2 B 10 H 10 }] (5) have also been prepared and characterised. The 1 J PSe coupling constants for 4 and 5 are the largest reported so far for carboranylphosphine selenides and indicate that I and 1 are very weakly basic.

Metal hydrides are invoked as important intermediates in both chemical and biological H2 production. In the [NiFe] hydrogenase enzymes, pulsed EPR and high-resolution crystallography have argued that the hydride interacts primarily at the Ni site. In contrast, in [NiFe] hydrogenase model complexes, it is observed that the bridging hydride interacts primarily with the Fe. Herein, we utilize a combination of Ni and Fe X-ray absorption (XAS) and emission (XES) spectroscopies to examine the contribution of the bridging hydride to the observed spectral features in [(dppe)Ni(μ-pdt)(μ-H)Fe(CO)3](+). The corresponding data on (dppe)Ni(μ-pdt)Fe(CO)3 are used as a reference for the changes that occur in the absence of a hydride bridge. For further interpretation of the observed spectral features, all experimental spectra were calculated using a density functional theory (DFT) approach, with excellent agreement between theory and experiment. It is found that the iron valence-to-core (VtC) XES spectra reveal clear signatures for the presence of a Fe-H interaction in the hydride bridged model complex. In contrast, the Ni VtC XES spectrum largely reflects changes in the local Ni geometry and shows little contribution from a Ni-H interaction. A stepwise theoretical analysis of the hydride contribution and the Ni site symmetry provides insights into the factors, which govern the different metal-hydride interactions in both the model complexes and the enzyme. Furthermore, these results establish the utility of two-color XES to reveal important insights into the electronic structure of various metal-hydride species.

The product of the intermolecular 'frustrated Lewis pair' (FLP) B(C6F5)2(C6Cl5)/2,2,6,6-tetramethylpiperidine and H2 has been studied by single-crystal neutron diffraction. This is the first structurally characterised example of a geometrically unconstrained dihydrogen (H···H) bond within a hydrogenated FLP system.

The synthesis of a new endohedral ten-vertex Zintl ion cluster, [Fe@Sn10](3-), isoelectronic with [Fe@Ge10](3-), is reported. In an attempt to place this new cluster within the context of the known structural chemistry of the M@E10 family (M = transition metal, E = main group element), we have carried out a detailed electronic structure analysis of the different structural types: viz bicapped square antiprismatic ([Ni@Pb10](2-), [Zn@In10](8-)), tetra-capped trigonal prismatic ([Ni@In10](10-)) and the remarkable pentagonal prismatic [Fe@Ge10](3-) and [Co@Ge10](3-). We establish that the structural trends can be interpreted in terms of a continuum of effective electron counts at the E10 cage, ranging from electron deficient (<4n + 2) in [Ni@In10](10-) to highly electron rich (>4n + 2) in [Fe@Ge10](3-). The effective electron count differs from the total valence electron count in that it factors in the increasingly active role of the metal d electrons towards the left of the transition series. The preference for a pentagonal prismatic geometry in [Fe@Ge10](3-) emerges as a natural consequence of backbonding to the cage from four orthogonal 3d orbitals of the low-valent metal ion. Our calculations suggest that the new [Fe@Sn10](3-) cluster should also exhibit structural consequences of backbonding from the metal to the cage, albeit to a less extreme degree than in its Ge analogue. The global minimum lies on a very flat surface connecting D4d, C2v and C3v-symmetric minima, suggesting a very plastic structure that may be easily deformed by the surrounding crystal environment. If so, then this provides a new and quite distinct structural type for the M@E10 family.

Transition-metal complexes containing (C-C)→M σ-interactions have potential applications in both catalysis and the activation and cleavage of C-C bonds. Fully characterising the bonding and interactions in complexes containing such (C-C)→M σ-interactions is vital to understand their chemical behaviour. As a result a high-resolution experimental X-ray charge density study has been undertaken on [Rh(Binor-S)(PCy(3))][HCB(11)Me(11)] (Binor-S = 1,2,4,5,6,8-dimetheno-s-indacene) which contains a (C-C)→Rh interaction. The data are analysed using Bader's "Atoms in Molecules" (AIM) approach with particular attention paid to the interactions around the rhodium centre. The results provide clear evidence for the σ(C-C)→Rh interaction in the solid-state which is classified as a weak covalent interaction. These results are supported by theoretical calculations.

The electronic structure of so-called 'xenophilic' clusters, which contain both organometallic fragments and Werner-type paramagnetic transition metal centres, presents a challenge to simple theories of bonding. Density functional theory shows clearly that the cluster Mn(2)(thf)(4)(Fe(CO)(4))(2) is best described as an exchange-coupled Mn(II)(2) dimer, the closed-shell organometallic [Fe(CO)(4)](2-) fragments acting simply as bridging ligands. The high-spin configuration of the Mn(II) ions leads to single occupation of the Mn-Fe σ* orbitals and therefore substantially weaker metal-metal bonding than in conventional low-valent organometallic clusters. The transition metal fragments are effective mediators of superexchange (J(calc) = -44 cm(-1)), leading to the measured effective magnetic moment of ~5 μ(B) at 300 K, considerably lower than the limiting value of 8.37 μ(B) for two uncoupled S = 5/2 Mn(II) centres.

The isolation, structural chracterisation and electronic structure of a formally mixed-valent Rh(-I)-Rh(III) complex is described, along with its reaction with dioxygen leading to double arene hydroxylation of the coordinated ligands.