Synthesis and luminescent properties of hetero-bimetallic and hetero-trimetallic Ru( ii )/Au( i ) or Ir( iii )/Au( i ) complexes

A series of Ru(ii) and Ir(iii) based photoluminescent complexes were synthesised that incorporate an ancillary 2,2′-bipyridine ligand adorned with either one or two pendant N-methyl imidazolium groups. These complexes have been fully characterised by an array of spectroscopic and analytical techniques. One Ir(iii) example was unequivocally structurally characterised in the solid state using single crystal X-ray diffraction confirming the proposed formulation and coordination sphere. These complexes were then transformed into their heterometallic, Au(i)-containing, analogues in two steps to yield either bi- or trimetallic complexes that integrate {Au(PPh3)}+ units. X-ray diffraction was used to corroborate the solid state structure of the hetero bimetallic complex, based upon a Ru(ii)–Au(i) species. The heterometallic complexes all displayed red photoluminescent features (λem = 616–629 nm) that were consistent with the parent Ru(ii) or Ir(iii) lumophores in each case. The modulation of the emission from the Ru(ii)–Au(i) complexes was much more strongly evident than for the Ir(iii)–Au(i) analogues, which is ascribed to the inherent differences in the specific triplet excited state character of the emitting states within each heterometallic species

Synthesis and Reactivity of a Bis-Strained Alkyne Derived from 1,1'-Biphenyl-2,2',6,6'-tetrol.

The novel "double strained alkyne" 3 has been prepared and evaluated in strain-promoted azide-alkyne cycloaddition reactions with azides. The X-ray crystallographic structure of 3, which was prepared in one step from 1,1'-biphenyl-2,2',6,6'-tetrol 4, reveals the strained nature of the alkynes. Dialkyne 3 undergoes cycloaddition reactions with a number of azides, giving mixtures of regiosiomeric products in excellent yields. The monoaddition products were not observed or isolated from the reactions, suggesting that the second cycloaddition proceeds at a faster rate than the first, and this is supported by molecular modeling studies. Dialkyne 3 was successfully employed for "peptide stapling" of a p53-based diazido peptide, whereby two azides are bridged to give a product with a stabilized conformation

Synthesis and cycloaddition reactions of derivatives of strained alkynes derived from 2,2’-dihydroxy-1,1’-biaryls

A series of strained alkynes, based on the 2,2’-dihydroxy-1,1’-biaryl structure, were prepared in a short sequence from readily-available starting materials. These compounds can be readily converted into further derivatives including examples containing fluorescent groups with potential for use as labelling reagents. The alkynes are able to react in cycloadditions with a range of azides without the requirement for a copper catalyst, in clean reactions with no observable side reactions

Asymmetric transfer hydrogenation of acetophenone derivatives using 2-benzyl-tethered ruthenium (II)/TsDPEN complexes bearing η6-(p-OR) (R = H, iPr, Bn, Ph) ligands

A series of 4′-OR (R = H, iPr, Bn, Ph) substituted ruthenium (II) biphenyl TsDPEN complexes are described; the complexes are accessed via an operationally simple and reliable two-step ligand synthesis followed by ligation to the ruthenium (II) centre. We report the preliminary asymmetric transfer hydrogenation (ATH) results on a range of primarily acetophenone derivatives with these new complexes using FA/TEA (5:2) as a reducing agent; the results confirm that these catalysts are capable of reducing the substrates within 48 h with excellent enantioselectivities

A strained alkyne-containing bipyridine reagent ; synthesis, reactivity and fluorescence properties

We report the synthesis of a bipyridyl reagent containing a strained alkyne, which significantly restricts its flexibility. Upon strain-promoted alkyne-azide cycloaddition (SPAAC) with an azide, which does not require a Cu catalyst, the structure becomes significantly more flexible and an increase in fluorescence is observed. Upon addition of Zn(II), the fluorescence is enhanced further. The reagent has the potential to act as a fluorescent labelling agent with azide-containing substrates, including biological molecules

Polycationic Ru(II) luminophores: syntheses, photophysics, and application in electrostatically driven sensitization of lanthanide luminescence

A series of photoluminescent Ru(II) polypyridine complexes have been synthesized in a manner that varies the extent of the cationic charge. Two ligand systems (L1 and L2), based upon 2,2′-bipyridine (bipy) mono- or difunctionalized at the 5- or 5,5′-positions using N-methylimidazolium groups, were utilized. The resulting Ru(II) species therefore carried +3, +4, +6, and +8 complex moieties based on a [Ru(bipy)3]2+ core. Tetra-cationic [Ru(bipy)2(L2)][PF6]4 was characterized using XRD, revealing H-bonding interactions between two of the counteranions and the cationic unit. The ground-state features of the complexes were found to closely resemble those of the parent unfunctionalized [Ru(bipy)3]2+ complex. In contrast, the excited state properties produce a variation in emission maxima, including a bathochromic 44 nm shift of the 3MLCT band for the tetra-cationic complex; interestingly, further increases in overall charge to +6 and +8 produced a hypsochromic shift in the 3MLCT band. Supporting DFT calculations suggest that the trend in emission behavior may, in part, be due to the precise nature of the LUMO and its localization. The utility of a photoactive polycationic Ru(II) complex was then demonstrated through the sensitization of a polyanionic Yb(III) complex in free solution. The study shows that electrostatically driven ion pairing is sufficient to facilitate energy transfer between the 3MLCT donor state of the Ru(II) complex and the accepting 2F5/2 excited state of Yb(III)

Potassium binding adjacent to cationic transition metal fragments: unusual heterobimetallic adducts of a calix[4]arene-based thione ligand

The synthesis of cationic rhodium and iridium complexes of a bis(imidazol-2-thione) functionalised calix[4]arene ligand and their surprising capacity for potassium binding is described. In both cases uptake of the alkali metal into the calix[4]arene cavity occurs despite adverse electrostatic interactions associated with close proximity to the transition metal fragment (Rh+∙∙∙K+ = 3.715(1) Å, Ir+∙∙∙K+ = 3.690(1) Å). The formation and constituent bonding of these unusual heterobimetallic adducts has been interrogated through extensive solution and solid-state characterisation, examination of the host-guest chemistry of the ligand and its upper-rim unfunctionalised calix[4]arene analogue, and computationally using DFT-based energy decomposition analysis (EDA)

Synthesis of enantiomerically-pure and racemic benzyl-tethered Ru (II)/TsDPEN complexes by direct arene substitution : further complexes and application

The use of a direct arene-exchange method for the synthesis of benzyl-tethered arene/Ru/TsDPEN complexes for use in asymmetric transfer hydrogenation is reported. A series of complexes tethered through a three-carbon linear chain was also prepared. The arene-exchange approach significantly simplifies the synthetic approach to this class of catalyst and permits the ready formation of modified analogues. The approach also provides a route to racemic catalysts for use in general reductions with either hydrogen or transfer hydrogenatio

Lanthanide appended rotaxanes respond to changing chloride concentration

Lanthanide appended rotaxanes have been prepared by the CuAAC ‘click’ reaction between an azide appended rotaxane and lanthanide complexes of propargyl DO3A. The resulting complexes are luminescent, and exhibit chloride responsive luminescence behavior consistent with the existence of two independent halide binding pockets, one in the rotaxane cavity and one on the ninth (axial) coordination site of the lanthanide. Strong halide binding to europium gives rise to changes in the relative intensity of the hypersensitive ΔJ = 2 transition compared to the rest of the europium emission spectrum, combined with quenching of the overall intensity of emission as a consequence of non-radiative quenching by the bound halide. The weaker interaction with the rotaxane pocket mediates a subsequent recovery of intensity of the europium centered luminescence despite the considerable separation between the lanthanide and the rotaxane binding pocket

Luminescent Pt(II) complexes using unsymmetrical Bis(2-pyridylimino)isoindolate analogues

A series of ligands based upon a 1,3-diimino-isoindoline framework have been synthesized and investigated as pincer-type (N∧N∧N) chelates for Pt(II). The synthetic route allows different combinations of heterocyclic moieties (including pyridyl, thiazole, and isoquinoline) to yield new unsymmetrical ligands. Pt(L1–6)Cl complexes were obtained and characterized using a range of spectroscopic and analytical techniques: 1H and 13C NMR, IR, UV–vis and luminescence spectroscopies, elemental analyses, high-resolution mass spectrometry, electrochemistry, and one example via X-ray crystallography which showed a distorted square planar environment at Pt(II). Cyclic voltammetry on the complexes showed one irreversible oxidation between +0.75 and +1 V (attributed to Pt2+/3+ couple) and a number of ligand-based reductions; in four complexes, two fully reversible reductions were noted between −1.4 and −1.9 V. Photophysical studies showed that Pt(L1–6)Cl absorbs efficiently in the visible region through a combination of ligand-based bands and metal-to-ligand charge-transfer features at 400–550 nm, with assignments supported by DFT calculations. Excitation at 500 nm led to luminescence (studied in both solutions and solid state) in all cases with different combinations of the heterocyclic donors providing tuning of the emission wavelength around 550–678 nm