Search

Combining a sterically bulky, electron-deficient cyclometalating C∧N ligands with an electron rich, highly rigidified N∧N ligand gives an iridium complex, that achieves extraordinarily bright blue emission (Φ PL = 90%; λ max = 459 nm in MeCN) for a cationic iridium complex., Combining a sterically bulky, electron-deficient 2-(2,4-difluorophenyl)-4-(2,4,6-trimethylphenyl)pyridine (dFMesppy) cyclometalating C∧N ligand with an electron rich, highly rigidified 1,1′-(α,α′-o-xylylene)-2,2′-biimidazole (o-xylbiim) N∧N ligand gives an iridium complex, [Ir(dFMesppy)2(o-xylbiim)](PF6), that achieves extraordinarily bright blue emission (Φ PL = 90%; λ max = 459 nm in MeCN) for a cationic iridium complex. This complex is compared with two reference complexes bearing 4,4′-di-tert-butyl-2,2′-bipyridine, and solution-processed organic light emitting diodes (OLEDs) have been fabricated from these materials.

The scope of dihydropyranone and dihydropyridinone products accessible by isothiourea‐catalyzed processes has been expanded and explored through the use of 2‐N‐tosyliminoacrylates and 2‐aroylacrylates in a Michael addition‐lactonization/lactamization cascade reaction. Notably, to ensure reproducibility it is essential to use homoanhydrides as ammonium enolate precursors with 2‐aroyl acrylates, while carboxylic acids can be used with 2‐N‐tosyliminoacrylates, delivering a range of 3,5,6‐substituted dihydropyranones and dihydropyridinones with high enantioselectivity (typically >90 % ee). The derivatization of the heterocyclic core of a 3,5,6‐substituted dihydropyranone through hydrogenation is also reported.

The relationship between the NMR chemical shifts of phosphinidene and selenourea compounds and the π-accepting ability of the related carbene ligands has been investigated., The electronic nature of the interaction of NHCs with metal centres is of interest when exploring their properties, how these properties influence those of metal complexes, and how these properties might depend on ligand structure. Selenourea and phosphinidene complexes have been proposed to allow the measurement of the π-accepting ability of NHCs, independent of their σ-donating ability, via the collection of 77Se or 31P NMR spectra, respectively. Herein, the synthesis and characterisation of selenoureas derived from a range of imidazol-2-ylidenes, 4,5-dihydroimidazol-2-ylidenes and triazol-2-ylidenes are documented. Computational studies are used to explore the link between the shielding of the selenium centre and the electronic properties of the NHCs. Results show that δ Se is correlated to the energy gap between a filled lone pair orbital on Se and the empty π* orbital corresponding to the Se–NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital σ-contribution to bonding and the chemical shielding, while a good correlation was found between the π-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept π-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between δ Se and δ P and π-back bonding ability clearly established, these compounds represent useful ways in which to fully understand and quantify this aspect of the electronic properties of NHCs.

EZ-C acknowledges the University of St Andrews for financial support. EZ-C and AKP thank EPSRC (EP/M02105X/1) for funding. The authors would like to thank the Engineering and Physical Sciences Research Council for financial support for Adam Henwood: EPSRC DTG Grants: EP/J500549/1; EP/K503162/1; EP/L505097/1 and the European Research Council (HetIridium, CIG-322280). The Valencian team acknowledges the financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) via the Unidad de Excelencia Mara de Maeztu MDM-2015-0538 and MAT2014-55200, PCIN-2015-255 and the Generalitat Valenciana (Prome-teo/2016/135). C. M. thanks MINECO for her predoctoral contract. The synthesis, structural and photophysical characterisation of four novel, cationiciridium(III) complexes is reported. These complexes were designed to emit in the blue region of the visible spectrum, without employing sp2 carbon-fluorine bonds, which have been shownto be electrochemically unstable. Two different C^N (where C^N is a bidentate cyclometalating ligand possessing an nitrogen-carbon chelate) ligands [5-(4-methylpyridin-2-yl)-2,4-dimethoxypyrimidine (Mepypyrm) and 5-(5-(trifluoromethyl)pyridine-2-yl)-2,4-dimethoxypyrimidine (CF3pypyrm)] combine electron-withdrawing pyrimidyl nitrogen atoms (in a para relationship with respect to the metal) with methoxy groups in meta relationship with respect to the metal, which both inductively withdraw electron density from the metal centre,stabilizing the highest occupied molecular orbital. The result is highly efficient (φPL = 73 –81%) green to blue (λPL = 446 – 515 nm) emission for complexes 1 – 4 in MeCN solution.Complex 1 exhibits a broad, unstructured charge transfer (CT) emission profile, while complexes 2 – 4 exhibit structured, vibronic emission profiles. Density Functional Theory (DFT) calculations corroborate these findings, with spin density calculations predicting a T1 state that is metal-to-ligand and ligand-to-ligand (C^N to N^N) charge transfer (3MLCT/3LLCT) in nature for complex 1 , while complexes 2 – 4 are predicted to exhibit ligand-centred (3LC) states with spin density localised exclusively on the C^N ligands. These complexes were used as emitters in sky-blue and blue-green light-emitting electrochemical cells (LEECs). The bluest of these devices (CIE: 0.23, 0.39) is among the bluest reported for any iridium-based LEEC. Noteworthy is that although the electroluminescence intensity decreases rapidly with time (t1/2 = 0.1 – 20 min), as is typical of blue-green LEECs, for devices L1 , L3 and L4 we have observed for the first time that this decay occurs without an accompanying red-shift in the CIE coordinates over time, implying that the emitter does not undergo any chemical degradation processes in the non-doped zones of the device. Publisher PDF

EZ-C acknowledges the University of St Andrews and EPSRC (EP/M02105X/1) for financial support. DE thanks funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 700961. DJ acknowledges the European Research Council (Marches grant n°278845) and the RFI Lumomat for financial support. Synthetic self-assembly is a powerful technique for the bottom-up construction of discrete and well-defined polyhedral nanostructures resembling the spherical shape of large biological systems. In recent years, numerous Archimedean-shaped coordination cages have been reported based on the assembly of bent monodentate organic ligands containing two or more distal pyridyl rings and square planar PdII ions. The formation of photoactive PdII metallamacrocycles and cages, however, remain rare. Here we report the first examples of emissive and homochiral supramolecular cages of the form of [Ir8Pd4]16+. These cages provide a suitably sized cavity to host large guest molecules. Importantly, encapsulation and energy transfer have been observed between the blue-emitting NBu4[Ir(dFppy)2(CN)2] guest and the red-emitting Δ8-[Ir8Pd4]16+ cage. Publisher PDF

EZ-C acknowledges the University of St Andrews for financial support. The authors are grateful to the EPSRC for financial support from grant EP/M02105X/1, DTG grants: EP/J500549/1, EP/K503162/1, EP/L505097/1. The authors are also grateful to the European Research Council (321305) for support. IDWS is a Royal Society Wolfon Research Merit Award holder. A structure-property relationship study of neutral heteroleptic ( 1 and 2 , [Ir(C^N)2(L^X)]) and homoleptic ( 3 and 4 , fac-[Ir(C^N)3]) Ir(III) complexes [where L^X = anionic 2,2,6,6-tetramethylheptane-3,5-dionato-κO3,κO6 (thd) and C^N = a cyclometalating ligand bearing a pentafluorosulfanyl (-SF5) electron-withdrawing group (EWG) at C4 (H L1 ) and C3 (H L2 ) positions of the phenyl moiety] is presented. These complexes have been fully structurally characterised, including by single crystal X-ray diffraction, and their electrochemical and optical properties have also been extensively studied. While complexes 1 ([Ir( L1 )2(thd)]), 3 (Ir( L1 )3) and 4 (Ir( L2 )3) exhibit irreversible first reduction waves based on the pentafluorosulfanyl substituent in the range of -1.71 V to -1.88 V (vs. SCE), complex 2 ([Ir( L2 )2(thd)]) exhibits a quasi-reversible pyridineC^N-based first reduction wave that is anodically-shifted at -1.38 V. The metal+C^N ligand oxidation waves are all quasi-reversible in the range of 1.08-1.54 V (vs. SCE). The optical gap, determined from the lowest energy absorption maxima, decreases from 4 to 2 to 3 to 1 and this trend is consistent with the Hammett behaviour (σm/σp with respect to the metal-carbon bond) of the –SF5 EWG. In degassed acetonitrile, for complexes 2 - 4 , introduction of the -SF5 group produced a blue-shifted emission (λem = 484-506 nm) compared to reference complexes [Ir(ppy)2(acac)], R1 (where acac = acetylacetonato) (λem = 528 nm in MeCN), [Ir(CF3-ppy)(acac)], R3 (where CF3-ppy = 2-(4-(trifluoromethyl)phenyl)pyridine) (λem = 522 nm in DCM) and [Ir(CF3-ppy)3], R8 (λem = 507 nm in MeCN). The emission of complex 1 , by contrast, was modestly red-shifted (λem = 534 nm). Complexes 2 and 4 , where the –SF5 EWG is substituted para to the Ir-Cppy bond are efficient phosphorescent emitters, with high photoluminescence quantum yields (ΦPL = 58-79% in degassed MeCN solution) and microsecond emission lifetimes (τε = 1.35-3.02 μs). Theoretical and experimental observations point towards excited states that are principally ligand-centered (3LC) in nature, but with a minor metal-to-ligand charge-transfer (3MLCT) transition component, as a function of the regiochemistry of the pentafluorosulfanyl group. The 3LC character is predominant over the mixed 3CT character for complexes 1 , 2 and 4 while in complex 3 , there is exclusive 3LC character as demonstrated by unrestricted Density Functional Theory (DFT) calculations. The short emission lifetimes and reasonable ΦPL values in doped thin film (5 wt% in PMMA), particularly for 4 , suggest that these neutral complexes would be attractive candidate emitters in organic light-emitting diodes. Publisher PDF

The authors are grateful to the University of St Andrews and EPSRC for financial support from grant EP/M02105X/1. The authors also thank the Spanish Ministry of Economy and Competitiveness (MINECO) via the Unidad de Excelencia María de Maeztu MDM-2015-0538, MAT2014-55200 and PCIN-2015-255 and the Generalitat Valenciana (Prometeo/2012/053). C. M. thanks MINECO for her predoctoral contract. Two cationic Ir(III) complexes bearing 2-phenylpyridinato cyclometalating ligands and bithiazole-type ancillary ligands have been synthesized and optoelectronically characterised. These emitters exhibit unusually deep red-to-Near-infrared emission at room temperature, thereby rendering them as attractive emitters in solution-processed light emitting electrochemical cell (LEEC) electroluminescent devices. Publisher PDF

EZ-C acknowledges the University of St Andrews for financial support. We thank Johnson Matthey and Umicore AG for the gift of materials. We would like to thank the Engineering and Physical Sciences Research Council for financial support for Adam Henwood: EPSRC DTG Grants: EP/J500549/1; EP/K503162/1; EP/L505097/1. We thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. DJ thanks the LumoMat RFI project for support. This research used computational resources of (i) the GENCI-CINES/IDRIS; (ii) CCIPL (Centre de Calcul Intensif des Pays de Loire); (iii) a local Troy cluster. The first examples of phosphorescent platinum(II) complexes bearing pentafluorosulfanyl (-SF5) substituted cyclometalating ligands (C^N) are reported. These complexes are of the form [Pt(C^N)(pivacac)], where pivacac is 2,2’,6,6’- tetramethylheptane-3,5-dionate. Modifying the phenyl ring of the C^N ligand to incorporate one strongly electron-withdrawing -SF5 group has important effects on the photophysical and electrochemical properties of the complex that are dependent on the regiochemistry of the substituent. In a meta position with respect to the Pt-CC^N bond, the substituent exerts a predominantly stabilising effect on the lowest triplet excited state that red-shifts the emission of the complex compared to the reference [Pt(ppy)(pivacac)], 1 , where ppy is 2-phenylpyridinato. When the -SF5 group is located para to the Pt-CC^N bond, it does not affect the triplet state directly, and the electron-withdrawing group stabilises the metal-based orbitals, resulting in a blue-shift of the emission. In the solid-state all three complexes are mechanochromic, and can display excimeric emission originating from intermolecular π-π* interactions, but the relative emission intensities of the monomeric and dimeric excited states correlate with the steric congestion of the metal centre, and in particular the regiochemistry of the -SF5 group. We correlate these findings with observations in the crystal structures. Publisher PDF

A new family consisting of three luminescent neutral Ir(III) complexes with the unprecedented [Ir(C^N^C)(N^N)Cl] architecture, where C^N^C is a bis(six-membered) chelating tridentate tripod ligand derived from 2-benzhydrylpyridine (bnpy) and N^N is 4,4′-di-tert-butyl-2,2′-bipyridine (dtBubpy), is reported. X-ray crystallography reveals an unexpected and unusual double C–H bond activation of the two distal nonconjugated phenyl rings of the bnpy coupled with a very short Ir–Cl bond trans to the pyridine of the bnpy ligand. Depending on the substitution on the bnpy ligand, phosphorescence, ranging from yellow to red, is observed in dichloromethane solution. A combined study using density functional theory (DFT) and time-dependent DFT (TD-DFT) corroborates the mixed charge-transfer nature of the related excited states., An unprecedented tridentate tripod C^N^C ligand resulting from an unusual double C−H bond activation of 2-benzhydrylpyridine (bnpyH2) opens access to a new class of bis-cyclometalated Ir(III) luminophores. X-ray crystal structures reveal an unstrained geometry thanks to the formation of two six-membered chelate rings. The complexes display a yellow to red emission attributed to mixed charge-transfer excited states.

We report the synthesis of nine new N-heterocyclic carbene gold bifluoride complexes starting from the corresponding N-heterocyclic carbene gold hydroxides. A new methodology to access N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) fluoride starting from N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) hydroxide and readily available potassium bifluoride is also reported. These gold bifluorides were shown to be efficient catalysts in the hydrofluorination of symmetrical and unsymmetrical alkynes, thus affording fluorinated stilbene analogues and fluorovinyl thioethers in good to excellent yields with high stereo- and regioselectivity. The method is exploited further to access a fluorinated combretastatin analogue selectively in two steps starting from commercially available reagents.

The authors thank the EPSRC Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT, grant code EP/L016419/1, RMNP) for funding.The European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013) ERC Grant Agreement No. 279850 is also acknowledged. ADS thanks the Royal Society for a Wolfson Research Merit Award The catalytic enantioselective 6-exo-trig Michael addition-lactonization of enone-acid substrates to form cis-chromenones with high diastereo- and enantiocontrol was developed using the commercially available isothiourea tetramisole. An acidic workup proved necessary to minimize product epimerization and maximize product er, providing cis-chromenones in excellent yield, and with excellent diastereo- and enantioselectivity. Publisher PDF