Template Synthesis of Cyclometalated Macrocycle Iridium(III) Complexes Based on Photoinduced C-N Cross-Coupling Reactions In Situ.

The synthesis of metal macrocycle complexes holds paramount importance in coordination and supramolecular chemistry. Toward this end, we report a new, mild, and efficient protocol for the synthesis of cyclometalated macrocycle Ir(III) complexes: [Ir(L1)](PF6) (1), [Ir(L2)](PF6) (2), and [Ir(L3)](PF6) (3), where L1 presents 10,17-dioxa-3,6-diaza-2(2,8),7(8,2)-diquinolina-1,8(1,4)-dibenzenacyclooctadecaphane, L2 is 10,13,16,19,22,25-hexaoxa-3,6-diaza-2(2,8),7(8,2)-diquinolina-1,8(1,4)-dibenzenacyclohexacosaphane, and L3 is 4-methyl-10,13,16,19,22,25-hexaoxa-3,6-diaza-2(2,8),7(8,2)-diquinolina-1,8(1,4)-dibenzenacyclohexacosaphane. This synthesis involves the preassembly of two symmetric 2-phenylquinoline arms into C-shape complexes, followed by cyclization with diamine via in situ interligand C-N cross-coupling, employing a metal ion as a template. Moreover, the synthetic yield of these cyclometalated Ir(III) complexes, tethered by an 18-crown-6 ether-like chain, is significantly enhanced in the presence of K+ ion as a template. The resultant cyclometalated macrocycle Ir(III) complexes exhibit high stability, efficient singlet oxygen generation, and superior catalytic activity for the aerobic selective oxidation of sulfides into sulfoxides under visible light irradiation in aqueous media at room temperature. The photocatalyst 2 demonstrates recyclability and can be reused at least 10 times without a significant loss of catalytic activity. These results unveil a new and complementary approach to the design and in situ synthesis of cyclometalated macrocycle Ir(III) complexes via a mild interligand-coupling strategy.

Solvent-Induced Umpolung Reaction from Dioxygenation to C-S Coupling in Bis(2-phenylquinoline) Iridium(III) Thiolate Complexes.

The construction of C-S bonds is of great importance in the field of synthetic and medicinal chemistry. Herein, solvent-induced umpolung reactions from dioxygenation to interligand C-S cross-coupling in bis(cyclometalated) Ir(III) thiolate complexes are reported in good to excellent yields at room temperature. Specifically, the reaction of rac-[Ir(pq)2(aet)] (where pq is 2-phenylquinoline and aet is 2-aminoethanethiolate) can be selectively switched to dioxygenation in acetonitrile solution in the presence of O2, resulting in the formation of a sulfinato complex rac-[Ir(pq)2(aes)] (where aes is 2-aminoethanesulfinato). Alternatively, the reaction in trifluoroethanol solution leads to interligand C-S cross-coupling, affording a rac-[Ir(pq)(pqaet)](PF6) [where pqaet is 2-((2-phenylquinolin-8-yl)thio)ethan-1-amine] complex, which generates a new tetradentate ligand in situ. Mechanistically, the formation of electrophilic metal thiyl radicals is proposed as a key intermediate in the interligand C-S coupling reaction. Furthermore, the sequential oxidation of a thioether complex into a sulfoxide complex is also observed at room temperature using H2O2 as an oxidant. Additionally, a new approach for the synthesis of a hexadentate ligand is developed through sequential C-S and C-N interligand coupling of metal thiolate complexes in situ under visible light irradiation in the presence of O2.

Switching the Photoreactions of Ir(III) Diamine Complexes between C-N Coupling and Dehydrogenation under Visible Light Irradiation.

The selective photoreactions under mild conditions play an important role in synthetic chemistry. Herein, efficient and mild protocols for switching the photoreactions of Ir(III)-diamine complexes between the interligand C-N coupling and dehydrogenation are developed in the presence of O2 in EtOH solution. The photoreactions of achiral diamine complexes rac-[Ir(L)2(dm)](PF6) (L is 2-phenylquinoline or 2-(2,4-difluorophenyl)quinoline, dm is 1,2-ethylenediamine, 1,2-diaminopropane, 2-methyl-1,2-diamino-propane, or N,N'-dimethyl-1,2-ethylenediamine) are competitive in the oxidative C-N coupling and dehydrogenation at room temperature, which can be switched into the interligand C-N coupling reaction at 60 °C, affording hexadentate complexes in good to excellent yields, or the dehydrogenative reaction in the presence of a catalytic amount of TEMPO as an additive, affording imine complexes. Mechanism studies reveal that 1O2 is the major reactive oxygen species, and metal aminyl is the key intermediate in the formation of the oxidative C-N coupling and imine products in the photoreaction processes. These will provide a new and practical protocol for the synthesis of multidentate and imine ligands in situ via the postcoordinated strategy under mild conditions.

Discrepancy between Proline and Homoproline in Chiral Recognition and Diastereomeric Photoreactivity with Iridium(III) Complexes.

The chiral-recognition processes of homoproline (hpro) and [Ir(pq)2(MeCN)2](PF6) (pq is 2-phenylquinoline; MeCN is acetonitrile) are investigated, in favor of formation of the thermodynamically stable diastereomers Λ-[Ir(pq)2(d-hpro)] and Δ-[Ir(pq)2(l-hpro)]. Moreover, the diastereoselective photoreactions of Δ-[Ir(pq)2(d-hpro)] and Δ-[Ir(pq)2(l-hpro)] are reported in the presence of O2 at room temperature. Diastereomer Δ-[Ir(pq)2(l-hpro)] is dehydrogenatively oxidized into imino acid complex Δ-[Ir(pq)2(hpro-2H2)] (hpro-2H2 is 3,4,5,6-tetrahydropicalinate), while diastereomer Δ-[Ir(pq)2(d-hpro)] occurs by interligand C-N cross-coupling and dehydrogenative oxidation reactions, affording three products: Δ-[Ir(pq)(d-pqh)] [pqh is N-(2-phenylquinolin-8-yl)homoproline], Δ-[Ir(pq)2(hpro-2H2)], and Δ-[Ir(pq)2(d-hpro-2H6)] [hpro-2H6 is 2,3,4,5-tetrahydropicalinate]. The C-N cross-coupling and dehydrogenative oxidation reactions are competitive, and the dehydrogenative oxidation reactions are regioselective. By optimization of the photoreaction parameters such as the diastereomeric substrate, solvent, and temperature as well as base, each possible competitive product is selectively controlled. In addition, density functional theory calculations are performed to elucidate the distinctly chiral recognition between proline and hpro with an iridium(III) complex.

Visible-Light-Induced Amination of Quinoline at the C8 Position via a Postcoordinated Interligand-Coupling Strategy under Mild Conditions.

The postcoordinated interligand-coupling strategy provides a useful and complementary protocol for synthesizing polydentate ligands. Herein, diastereoselective photoreactions of Λ-[Ir(pq)2(d-AA)] (Λ-d) and Λ-[Ir(pq)2(l-AA)] (Λ-l, where pq is 2-phenylquinoline and AA is an amino acid) are reported in the presence of O2 under mild conditions. Diastereomer Λ-d is dehydrogenatively oxidized into an imino acid complex, while diastereomer Λ-l mainly occurs via interligand C-N cross-dehydrogenative coupling between quinoline at the C8 position and AA ligands at room temperature, affording Λ-[Ir(pq)(l-pq-AA)]. Furthermore, the photoreaction of diastereomer Λ-l is temperature-dependent. Mechanistic experiments reveal the ligand-radical intermediates may be involved in the reaction. Density functional theory calculations were used to eluciate the origin of diastereoselectivity and temperature dependence. This will provide a new protocol for the amination of quinoline at the C8 position via the postcoordinated interligand C-N cross-coupling strategy under mild conditions.

Cyclometalated Ir-Zr Metal-Organic Frameworks as Recyclable Visible-Light Photocatalysts for Sulfide Oxidation into Sulfoxide in Water.

Aerobic photo-oxidation of sulfide into sulfoxide in water is of great interest in green chemistry. In this study, three highly stable Ir(III)-Zr(IV) metal-organic frameworks (Ir-Zr MOFs), namely Zr6-Irbpy (bpy is 2,2'-bipyridine), Zr6-IrbpyOMe (bpyOMe is 4,4'-dimethoxy-2,2'-bipyridine), and Zr6-Irphen (phen is 1,10-phenanthroline), are constructed by using [Ir(pqc)2(L)2]Cl complexes (where pqc is 2-phenylquinoline-4-carboxylic acid and L is an ancillary ligand bpy, bpyOMe, or phen) as linkers and Zr6 cluster as nodes. The constructed Ir-Zr MOFs present high catalytic activity on aerobic photo-oxidation of sulfide into sulfoxide under visible light irradiation in water at room temperature. Moreover, the reaction is high chemoselectivity and functional group tolerance. The catalyst can be readily recycled and reused at least 10 times without loss of catalytic activity. Mechanism studies demonstrate that superoxide radical is the reactive oxygen species in the sulfoxidation, which is generated by electron transfer from the excited triplet photosensitizer 3[Ir-Zr-MOF]* to O2. The high activity of photocatalytic sulfoxidation in water may be attributed to the stabilization of the persulfoxide intermediate by hydrogen bond formation with water solvent, which accelerates the conversion of persulfoxide into sulfoxide and prevents further oxidation of sulfoxide into sulfone. This work provides a new strategy for the green synthesis of sulfoxides under ambient conditions.

Thermodynamic Resolution and Enantioselective Synthesis of C2-Symmetric Bis-sulfoxides Based on Chiral Iridium(III) Complexes.

Enantiopure Λ-[Ir(dfppy)2(MeCN)2](PF6) and Δ-[Ir(dfppy)2(MeCN)2](PF6) (where dfppy is (4,6-difluoropheny)pyridine) were demonstrated to preferentially react with (S,S)-1,2-bis(arylsulfinyl)ethane and (R,R)-1,2-bis(arylsulfinyl)ethane, respectively, under thermodynamic equilibrium. Sequential treatment of Λ-[Ir(dfppy)2(MeCN)2](PF6) and Δ-[Ir(dfppy)2(MeCN)2](PF6) with C2-symmetric bis-sulfoxides led to diastereoselective formation of the corresponding diastereomers Λ-[Ir(dfppy)2(R,R)-bis-sulfoxide)](PF6) in 90-92% and Δ-[Ir(dfppy)2(S,S)-bis-sulfoxide)](PF6) in 88-90%, respectively. The uncoordinated (R,S)-bis-sulfoxides were afforded in 45% with >97% de values. Enantiopure (S,S)-bis-sulfoxides and (R,R)-bis-sulfoxides were respectively obtained by the release of sulfoxide ligands from the corresponding complexes in the presence of glycine in yields of 20-21% with 97-99% ee values. The enantioreceptors Λ-[Ir(dfppy)2(MeCN)2](PF6) and Δ-[Ir(dfppy)2(MeCN)2](PF6) can be recycled and reused in the next reaction cycle. Moreover, a protocol for asymmetric oxidation of prochiral bis-sulfide into enantiopure C2 symmetric bis-sulfoxide was also developed in a high enantioselectivity. The absolute configurations at the metal centers and sulfur atoms were determined by X-ray crystallography.

Efficient Generation of Singlet Oxygen and Photooxidation of Sulfide into Sulfoxide via Tuning the Ancillary of Bicyclometalated Iridium(III) Complexes.

With 2-phenylquinoline (pq) as a cyclometalated ligand, a series of cationic Ir(III) complexes [Ir(pq)2(L1)2](PF6) (L1 is pyridine (1a), 4-methoxypyridine (1b), 4-dimethylaminopyridine (1c), and 4-acetylpyridine (1d)) and [Ir(pq)2(L2)](PF6) (L2 is 2,2'-bipyridine (1e), 2,2'-bipyrimidyl (1f), 4,4'-dimethyl-2,2'-bipyridine (1g), and 4,4'-dimethoxy-2,2'-bipyridine (1h)) were synthesized and characterized. The influence of the metal-based highest occupied molecular orbital on triplet-state lifetime, triplet-state quantum yield, and 1O2 generation quantum yield as well as aerobic photo-oxidation of sulfide into sulfoxide was evaluated via tuning the ancillary ligand of Ir(pq)2 complexes. The results revealed that 1h with chelate ancillary ligand bearing electron-donating group possesses a high 1O2 generation quantum yield (0.90) and photocatalytic activity for sulfide oxidation with high chemoselectivity and a low catalyst loading (0.5 mol %) under mild conditions. Moreover, one-pot two-step procedure for preparation of enantiopure sulfoxides, including aerobic photo-oxidation of sulfide using 1h as a photosensitizer and chiral resolution of sulfoxide via a chiral-at-metal strategy, was also developed.

Efficient Conversion of CO2 via Grafting Urea Group into a [Cu2(COO)4]-Based Metal-Organic Framework with Hierarchical Porosity.

The assembly of mixed [1,1';3',1'']terphenyl-4,5',4''-tricarboxylic acid (H3TPTC) and [1,1'-biphenyl]-4,4'-dicarboxylic acid (H2BPDC), 2,2'-diamino-[1,1'-biphenyl]-4,4'-dicarboxylic acid (H2BPDC-NH2), or 6-oxo-6,7-dihydro-5H-dibenzo[ d, f][1,3]diazepine-3,9-dicarboxylic acid (H2BPDC-Urea) with Cu2+ ion generated the corresponding copper-paddlewheel-based metal-organic framework (MOF) [Cu5(TPTC)3(BPDC)0.5(H2O)5] (1), [Cu5(TPTC)3(BPDC-NH2)0.5(H2O)5] (1-NH2), or [Cu5(TPTC)3(BPDC-Urea)0.5(H2O)5] (1-Urea). They are isostructural with hierarchical porosity, consisting of zero-dimensional cage (19.2 Å × 18.9 Å) and one-dimensional pillar channel (29.7 Å × 15.1 Å) in a manner of face sharing. Platon analyses revealed the porous volume ratios are 80.2%, 80.0%, and 77.8% for 1, 1-NH2, and for 1-Urea, respectively. Thermogravimetric measurements suggested 53, 51, and 48 wt % guest molecules in 1, 1-NH2, and 1-Urea, respectively. 1-NH2 and 1-Urea were precisely functionalized via the introduction of amino and urea functional groups into the pillar channels. The constructed MOF 1-Urea, incorporating both exposed copper active sites and accessible urea functional groups to substrates, presents high efficiency on catalytic CO2 cycloaddition with propene oxide to produce cyclic carbonate in the yield of 98% with a TOF value of 136 h-1 at 1 atm and room temperature. This synergic effect provides a new strategy for designing high-efficient catalysts for CO2 chemical conversion under ambient conditions.

Diastereoselective Photooxidation and Reduction of Chiral Iridium(III) Complexes.

A diastereoselective photooxidation of α-amino acid (AA) complexes into imino acid complexes using a chiral iridium(III) complex as a photosensitizer and stereo-controller under visible light irradiation and oxygen was developed. It was found that the oxidative rate of Δ-[Ir(pq)2( L-AA)] (pq is 2-phenylquinoline) diastereomer is significantly higher than that of the corresponding Δ-[Ir(pq)2( D-AA)] diastereomer, providing a new protocol for kinetic resolution of AAs via a nonenzymatic pathway. Moreover, the thermodynamic controlled strategy offered a complemental method for the diastereoselective hydrogenation of imine bonds using NaBH4 as a reductant under the chiral Ir(III) complex as a stereo-controller. The combination of diastereoselective photooxidation and reduction processes results in a new protocol for deracemization of α-amino acids under mild conditions. Mechanism study strongly indicates that singlet oxygen is a key participant in the reaction and the α-C-H bond cleavage of AAs is the rate-determining step.

Discrimination and Enantiomeric Excess Determination of Chiral Primary Amines Based on a Chiral-at-Metal Ir(III) Complex Using NMR Spectroscopy.

A three-component protocol involving enantiopure Δ-[Ir(ppy)2(MeCN)2](PF6) (ppy is 2-phenylpyridine) and salicylaldehyde as chiral auxiliaries was successfully applied to discriminate the absolute configuration and determine the enantiopurity of primary amines and amine alcohols via 1H NMR spectroscopy. The assembly reaction is rapid and quantitative, generating a pair of diastereomers that can be determined directly without physical separation. Single crystal structural analyses indicate that the shielding effects on the ligands imposed by a pair of diastereomers are different and generate sufficient resolution NMR signals for identification. The enhancement of stability via chelating coordination to Ir(III) ion and more than one pair of diastereotopic resonances in different detection regions of the three-component protocol ensure a high degree of accuracy in quantifying the ee value of chiral amines. The absolute errors in the ee determinations by 1H NMR spectroscopy in different detection windows are within 2.0%. The linear relationship between the experimentally measured ee values and the gravimetrically prepared samples is found to be excellent. This finding would provide a complementary method for the discrimination and determination of the enantiopurity of chiral primary amines and amine alcohols in the screening of asymmetric reactions.

Chiral Recognition and Dynamic Thermodynamic Resolution of Sulfoxides by Chiral Iridium(III) Complexes.

The optically active Ir(III) complex Λ-[Ir(ppy)2(MeCN)2](PF6) (ppy is 2-phenylpyridine) with a chiral-at-metal was first demonstrated to preferentially react with (R)-configuration sulfoxides 2-(alkylsulfinyl)phenol (HLO-R, R = Me, Et, iPr, and Bn) rather than (S)-configuration sulfoxides under thermodynamic equilibrium due to the hydrogen-bonding interaction and the differences in the steric interference, and thus act as a highly efficient enantioreceptor for resolution of sulfoxide enatiomers. Treatment of Λ-[Ir(ppy)2(MeCN)2](PF6) with 2 equiv of rac-HLO-R offered (S)-HLO-R in yields of 46-47% with 97-99% enantiomeric excess (ee) values and Λ-[Ir(ppy)2{(S)-LO-R}] complex in yields of 89-93% with 98% diastereomeric excess (de). The (R)-HLO-R chiral sulfoxides were obtained by the acidolysis of Λ-[Ir(ppy)2{(S)-LO-R}] complexes with trifluoroacetic acid (TFA) in the presence of coordinated solvent MeCN in yields of 45-47% with 98-99% ee values. Moreover, the enantioreceptor Λ-[Ir(ppy)2(MeCN)2](PF6) can be recycled in a yield of 86-91% with complete retention of the configuration at metal center and can be reused in a next reaction cycle without loss of reaction activity and enantioselectivity. The absolute configurations at the metal centers and sulfur atoms were determined by X-ray crystallography.

Asymmetric Synthesis of Enantiomerically Pure Mono- and Binuclear Bis(cyclometalated) Iridium(III) Complexes.

Chiral precursors Λ-[Ir(ppy)2(l-pro)] (Λ-L, where ppy is 2-phenylpyridine; pro is proline), Λ-[Ir(ppy)2(MeCN)2](PF6) (Λ-1), Δ-[Ir(ppy)2(d-pro)] (Δ-D), and Δ-[Ir(ppy)2(MeCN)2](PF6) (Δ-1) were synthesized from rac-[(Ir(ppy)2)2Cl2] and l-pro or d-pro by means of the auxiliary ligand strategy with 99% de values. The enantiopure mono complexes Λ/Δ-[Ir(ppy)2(L)](PF6) (L is 2,2'-bipyridine, Λ/Δ-2; L is 2,2'-dipyrimidine (dpm), Λ/Δ-3; L is 2,2'-bibenzimidazole (H2bbim), Λ/Δ-4) with 99% ee values and binuclear complexes ΛΛ/ΔΔ-[(Ir(ppy)2)2(dpm)](PF6)2 (ΛΛ-5 and ΔΔ-5) and ΛΛ/ΔΔ-[(Ir(ppy)2)2(bbim)] (ΛΛ-6 and ΔΔ-6) with 99% de values were synthesized in one step using the corresponding chiral precursors. The absolute configurations at Ir(III) centers of precursor Δ-1, mononuclear Λ-3, and binuclear ΔΔ-6 were confirmed by single-crystal structural analysis and characterized by circular dichroism (CD) spectroscopy. The correlation between the absolute configuration at Ir(III) center and CD spectra was established. The configurations at Ir(III) centers are stable during the reactions, and the chiral precursors can be used for the asymmetric synthesis of enantiomerically pure mono- and polynuclear Ir(III) complexes. Moreover, meso ΛΔ-[(Ir(ppy)2)2(dpm)](PF6)2 (meso-5) and ΛΔ-[(Ir(ppy)2)2(bbim)] (meso-6) were also synthesized using these precursors.

Synthesis, characterization, photophysics, and anion binding properties of platinum(ii) acetylide complexes with urea group.

A new class of platinum(ii) acetylide complexes with urea group, [Pt((t)Bu3tpy)(C[triple bond, length as m-dash]CC6H4-4-NHC(O)NHC6H4-4-R)](OTf) ((t)Bu3tpy = 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine; R = H (), Cl (), CF3 (), and NO2 ()), has been synthesized and characterized. The crystal structures of , ·DMF·THF, ·CH3CN, and ·CH3CN have been determined by X-ray diffraction. Upon excitation at λ > 380 nm, the solid samples of complexes show orange light at 298 K. The anion binding properties of complexes have been studied by UV-vis titration experiments in CH3CN and DMSO. In general, the log K values of with the same anion in CH3CN depend on the substituent R on the acetylide ligand of and follow this order: R = NO2 () > CF3 () > Cl () > H (). For the same complex with different anions, the log K values are in the following order: F(-) > OAc(-) > Cl(-) > Br(-) ≈ HSO4(-) ≈ NO3(-) > I(-), which is in accordance with the decrease in the basicity of anions. Complex with NO2 group shows a dramatic colour change towards F(-) in DMSO, allowing the naked eye detection of F(-).

Enantioselective syntheses of sulfoxides in octahedral ruthenium(II) complexes via a chiral-at-metal strategy.

The preparation of chiral 2-(alkylsulfinyl)phenol compounds by enantioselective coordination-oxidation of the thioether ruthenium complexes with a chiral-at-metal strategy has been developed. The enantiomerically pure sulfoxide complexes Δ-[Ru(bpy)2{(R)-LO-R}](PF6) (bpy is 2,2'-bipyridine, HLO-R is 2-(alkylsulfinyl)phenol, R = Me (Δ-1a), Et (Δ-2a), iPr (Δ-3a), Bn (Δ-4a), and Nap (Δ-5a)) and Λ-[Ru(bpy)2{(S)-LO-R}](PF6) (R = Me (Λ-1a), Et (Λ-2a), iPr (Λ-3a), Bn (Λ-4a), and Nap (Λ-5a)) have been synthesized by the reaction of Δ-[Ru(bpy)2(py)2](2+) or Λ-[Ru(bpy)2(py)2](2+) with the prochiral thioether ligands 2-(alkylthio)phenol (HL-R), followed by enantioselective oxidation with m-CPBA as oxidant. The X-ray crystallography was used to verify the stereochemistry of ruthenium complexes and sulfur atoms. The configurations of the ruthenium complexes are stable during the coordination and oxidation reactions. Moreover, the chiral sulfoxide ligands are enantioselectively generated by controlling of the configuration of ruthenium centers in the course of oxidation reaction. That is, the Λ configuration at the ruthenium center generates the S sulfoxide ligand; on the contrary, the Δ configuration of the ruthenium complex originates the R sulfoxide ligand. Acidolysis of Λ-[Ru(bpy)2{(R)-LO-R}](PF6) and Δ-[Ru(bpy)2{(S)-LO-R}](PF6) complexes in the presence of TFA-MeCN afforded the chiral ligands (R)-HLO-R and (S)-HLO-R in 96-99% ee values, respectively. Importantly, the chiral ruthenium complexes can be recycled as Δ/Λ-[Ru(bpy)2(MeCN)2](PF6)2 and reused in a next reaction cycle with complete retention of the configurations at ruthenium centers.

In situ generation of sulfoxides with predetermined chirality via a structural template with a chiral-at-metal ruthenium complex.

The reaction of Δ/Λ-[Ru(bpy)2(py)2](2+) with a prochiral sulfide ligand, and then in situ oxidation, provide the corresponding Δ-[Ru(bpy)2{(R)-OSO-iPr}](+) and Λ-[Ru(bpy)2{(S)-OSO-iPr}](+) (OSO-iPr = 2-isopropylsulfonylbenzonate) enantiomers in a yield of 83% with 98% ee. The chiral sulfoxides were obtained by treatment of the sulfoxide complexes with TFA in a yield of 90% with 88-91% ee.

Visible-light-induced photooxidation of ruthenium(II) complex with 2,2'-biimidazole-like ligand by singlet oxygen.

Four new ruthenium(II) complexes [Ru(bpy)2(TMBiimH2)](ClO4)2 (Ru-5; bpy is 2,2'-bipyridine and TMBiimH2 is 4,5,4',5'-tetramethyl-2,2'-biimidazole), [Ru(bpy)2(L1H2)](ClO4)2·H2O (Ru-6; L1H2 is 4,5-dimethyl-2-(N,N-diacetyl)carboximidamide-1H-imidazole), [Ru(bpy)2(L2H2)](ClO4)2 (Ru-7; L2H2 is N(1),N(1),N(2),N(2)-tetrakis(acetyl)ethanediimidamide), and [Ru(phen)2(TMBiimH2)](ClO4)2 (Ru-8; phen is 1,10'-phenanthroline) have been synthesized and characterized. Their photophysical and electrochemical properties have been studied and compared to the previously reported [Ru(bpy)2(BiimH2)](PF6)2 (Ru-1), [Ru(bpy)2(BbimH2)](PF6)2 (Ru-2), [Ru(bpy)2(DMBbimH2)](PF6)2 (Ru-3), and [Ru(bpy)2(TMBbimH2)](PF6)2 (Ru-4). Under irradiation with either sunlight or household light in atmosphere, Ru-5 reacts with molecular oxygen to produce Ru-6 in an acetonitrile solution with a relatively high concentration and Ru-7 in a methanol or dilute acetonitrile solution, respectively. The mechanism studies show that singlet oxygen is the reactive oxygen species in the ring-opening reaction and the photooxidation reaction is solvent- and concentration-dependent. The photoreaction product Ru-6 is an intermediate, which has been isolated and structurally characterized by single-crystal X-ray diffraction. Ru-6 is stable in the solid state and an acetonitrile solution with a high concentration, but can be further oxidized to Ru-7 in a methanol or dilute acetonitrile solution.

Solvent-mediated crystal-to-crystal interconversion between discrete lanthanide complexes and one-dimensional coordination polymers and selective sensing for small molecules.

Two isostructural 1D coordination polymers {[Ln(OAc)2(H2O)(OBPT)]·3H2O}n (HOBPT = 4,6-bis(2-pyridyl)-1,3,5-triazin-2-ol, Ln = Eu(3+), 1; Tb(3+), 3) and two discrete complexes [Ln(OAc)2(DMF)2(OBPT)] (Ln = Eu(3+), 2; Tb(3+), 4) have been synthesized in H2O-MeOH or DMF solvents, respectively. Their structures were identified by powder X-ray diffraction. Single-crystal X-ray studies for complexes 1 and 2 revealed that the coordination geometries of the Eu(3+) ions are similar and can be described as a distorted tricapped trigonal prism with six oxygen atoms and three nitrogen atoms. The difference between them is that one aqua ligand and one oxygen atom from the OBPT ligand complete the coordination sphere in complex 1, whereas two DMF molecules complete the coordination sphere in complex 2. Interestingly, the solvent-mediated, reversible crystal-to-crystal transformation between them was achieved by immersing the crystalline samples in the corresponding solvent (H2O or DMF) or by exposing them to solvent vapor. Complex 1 shows a highly selective luminescence enhancement in response to DMF in comparison to that observed in response to other examined solvents such as acetone, ethyl acetate, ethanol, acetonitrile, methanol, and THF.

Selective recognition of cyanide anion via formation of multipoint NH and phenyl CH hydrogen bonding with acyclic ruthenium bipyridine imidazole receptors in water.

Five imidazole-based anion receptors A-E are designed for cyanide anion recognition via hydrogen bonding interaction in water. Only receptors A [Ru(bpy)(2)(mpipH)](ClO(4))(2) (bpy is bipyridine and mpipH is 2-(4-methylphenyl)-imidazo[4,5-f]-1,10-phenanthroline) and E [Ru(2)(bpy)(4)(mbpibH(2))](ClO(4))(4) (mbpibH(2) is 1,3-bis([1,10]-phenanthroline-[5,6-d]imidazol-2-yl)benzene) selectively recognize CN(-) from OAc(-), F(-), Cl(-), Br(-), I(-), NO(3)(-), HSO(4)(-), ClO(4)(-), H(2)PO(4)(-), HCO(3)(-), N(3)(-), and SCN(-) anions in water (without organic solvent) at physiological conditions via formation of multiple hydrogen bonding interaction with binding constants of K(A(H2O)) = 345 ± 21 and K(E(H2O)) = 878 ± 41, respectively. The detection limits of A and E toward CN(-) in water are 100 and 5 µM, respectively. Receptor E has an appropriate pK(a2)* value (8.75) of N-H proton and a C-shape cavity structure with three-point hydrogen bonding, consisting of two NH and one cooperative phenyl CH hydrogen bonds. Appropriate acidity of N-H proton and multipoint hydrogen bonding are both important in enhancing the selectivity and sensitivity toward CN(-) in water. The phenyl CH···CN(-) hydrogen bonding interaction is observed by the HMBC NMR technique for the first time, which provides an efficient approach to directly probe the binding site of the receptor toward CN(-). Moreover, CN(-) induced emission lifetime change of the receptor has been exploited in water for the first time. The energy-optimized structure of E-CN adduct is also proposed on the basis of theoretical calculations.

Interaction between biimidazole complexes of ruthenium and acetate: hydrogen bonding and proton transfer.

The hydrogen bonding and deprotonation processes between four ruthenium biimidazole complexes, namely [Ru(bpy)(2)(BiimH(2))](PF(6))(2) (1, bpy is bipyridine, BiimH(2) is 2,2'-biimidazole), [Ru(bpy)(2)-(BbimH(2))](PF(6))(2) (2, BbimH(2) is 2,2'-bibenzimidazole), and [Ru(bpy)(2)(DMBbimH(2))](PF(6))(2) (3, DMBbimH(2) is 7,7'-dimethyl-2,2'-bibenzimidazole) and [Ru(bpy)(2)(TMBbimH(2))](2+) (4, TMBbimH(2) is 5,6,5',6'-tetramethyl-2,2'-bibenzimidazole), and acetate are investigated. Their hydrogen bonded adducts are indeed trapped and observed by absorption spectra and electrochemical experiments in acetonitrile solution in the presence of an excess of acetic acid for the first time. The binding constants log K(B) for these adducts are 6.74 for 1·OAc, 7.11 for 2·OAc, 7.26 for 3·OAc, and 6.99 for 4·OAc. A new approach to calculate the deprotonation constant is also developed by establishing a set of circular equilibria. The equilibrium constants for the first deprotonation step of the complexes log K(A) are 2.74 for 1, 5.19 for 2, 4.54 for 3, and 3.78 for 4. The pK(a1) values of the complexes in acetonitrile solution are calculated by subtracting log K(A) from pK(a) (HOAc in acetonitrile), giving 19.6 for 1, 17.1 for 2, 17.8 for 3, and 18.5 for 4. The degree of proton transfer (D(PT)) can be quantified by the calculation of absorption spectral and redox data, which is 0.41 for 1·OAc, 0.53 for 2·OAc, 0.57 for 3·OAc, and 0.47 for 4·OAc. Interestingly, the binding constant log K(B) (7.26) and D(PT) value (0.57) both reach their maxima at a critical point, where pK(a1) for the complex is 17.8 and ΔpK(a) for the adduct is 4.5 (ΔpK(a) = pK(a)(HOAc) - pK(a1), in acetonitrile solution). Moreover, the binding constant log K(B) shows linear correlation with the degree of proton transfer D(PT).