Oxidative addition of MeI to some cyclometalated organoplatinum(II) complexes: Kinetics and mechanism

New cyclometalated platinum(II) complexes [PtMe(C^N)L], 1, in which C^N = deprotonated 2-phenylpyridine (ppy), benzo[h]quinoline (bhq) or 2-(p-tolyl)pyridine (tpy) and L = PPh₃ or PMePh₂, were synthesized by the reaction of [PtMe(C^N)(SMe₂)] with 1 equiv of L. The reaction of complexes 1 with MeI gave the cyclometalated Pt(IV) complexes [PtMe₂I(C^N)L], 3. On the basis of kinetic studies, using Uv–visible spectroscopy, it was suggested that the latter oxidative addition reactions were proceeded by an S_N2 mechanism. The rates of the reactions at different temperatures were measured and consistent with the proposed mechanism, large negative ΔS³ values were found for each reaction. Besides, rate of reactions (in CHCl₃) involving the PPh₃ complexes [PtMe(C^N)(PPh₃)], were almost 3–5 times slower than those involving the PMePh₂ complexes [PtMe(C^N)(PMePh₂)]. This was attributed to the electronic and steric effects of PPh₃ ligand as compared with that of PMePh₂ ligand which was further confirmed using density functional theory (DFT) calculations through finding approximate structures for the described complexes.     

Exploring Excited‐State Tunability in Luminescent Tris‐cyclometalated Platinum(IV) Complexes: Synthesis of Heteroleptic Derivatives and Computational Calculations

The synthesis, structure, electrochemistry, and photophysical properties of a series of heteroleptic tris‐ cyclometalated Pt^IV complexes are reported. The complexes mer‐[Pt(C^N)₂(C′^N′)]OTf, with C^N=C‐deprotonated 2‐(2,4‐difluorophenyl)pyridine (dfppy) or 2‐phenylpyridine (ppy), and C′^N′=C‐deprotonated 2‐(2‐thienyl)pyridine (thpy) or 1‐phenylisoquinoline (piq), were obtained by reacting bis‐ cyclometalated precursors [Pt(C^N)₂Cl₂] with AgOTf (2 equiv) and an excess of the N′^C′H pro‐ligand. The complex mer‐[Pt(dfppy)₂(ppy)]OTf was obtained analogously and photoisomerized to its fac counterpart. The new complexes display long‐lived luminescence at room temperature in the blue to orange color range. The emitting states involve electronic transitions almost exclusively localized on the ligand with the lowest π–π* energy gap and have very little metal character. DFT and time‐dependent DFT (TD‐DFT) calculations on mer‐[Pt(ppy)₂(C′^N′)]⁺ (C′^N′=thpy, piq) and mer/fac‐[Pt(ppy)₃]⁺ support this assignment and provide a basis for the understanding of the luminescence of tris‐cyclometalated Pt^IV complexes. Excited states of LMCT character may become thermally accessible from the emitting state in the mer isomers containing dfppy or ppy as chromophoric ligands, leading to strong nonradiative deactivation. This effect does not operate in the fac isomers or the mer complexes containing thpy or piq, for which nonradiative deactivation originates mainly from vibrational coupling to the ground state.     

Binuclear cyclometalated organoplatinum complexes containing 1,1'-bis(diphenylphosphino)ferrocene as spacer ligand: kinetics and mechanism of MeI oxidative addition

The binuclear complex [Pt2Me2(ppy)2(mu-dppf)], 1, in which ppy = deprotonated 2-phenylpyridyl and dppf = 1,1'-bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe2)(ppy)] with 0.5 equiv of dppf at room temperature. In this reaction when 1 equiv of dppf was used, the dppf chelating complex 2, [PtMe(dppf)(ppy-kappa1C)], was obtained. The reaction of Pt(II)-Pt(II) complex 1 with excess MeI gave the Pt(IV)-Pt(IV) complex [Pt2I2Me4(ppy)2(mu-dppf)], 3. When the reaction was performed with 1 equiv of MeI, a mixture containing unreacted complex 1, a mixed-valence Pt(II)-Pt(IV) complex [PtMe(ppy)(mu-dppf)PtIMe2(ppy)], 4, and complex 3 was obtained. In a comparative study, the reaction of [PtMe(SMe2)(ppy)] with 1 equiv of monodentate phosphine PPh3 gave [PtMe(ppy)(PPh3)], A. MeI was reacted with A to give the platinum(IV) complex [PtMe2I(ppy)(PPh3)], C. All the complexes were fully characterized using multinuclear (1H, 31P, 13C, and 195Pt) NMR spectroscopy, and complex 2 was further identified by single crystal X-ray structure determination. The reaction of binuclear Pt(II)-Pt(II) complex 1 with excess MeI was monitored by low temperature 31P NMR spectroscopy and further by 1H NMR spectroscopy, and the kinetics of the reaction was studied by UV-vis spectroscopy. On the basis of the data, a mechanism has been suggested for the reaction which overall involved stepwise oxidative addition of MeI to the two Pt(II) centers. In this suggested mechanism, the reaction proceeded through a number of Pt(II)-Pt(IV) and Pt(IV)-Pt(IV) intermediates. Although MeI in each step was trans oxidatively added to one of the Pt(II) centers, further trans to cis isomerizations of Me and I groups were also identified. A comparative kinetic study of the reaction of monomeric platinum(II) complex A with MeI was also performed. The rate of reaction of MeI with complex 1 was some 3.5 times faster than that with complex A, indicating that dppf in the complex 1, as compared with PPh 3 in the complex A, has significantly enhanced the electron richness of the platinum centers.     

Strong red emissions induced by Pt–Pt interactions in binuclear cycloplatinated(II) complexes containing bridging diphosphines

A series of dinuclear cycloplatinated(II) complexes with general closed formula of [Pt₂Me₂(C^N)₂(μ‐P^P)] (C^N = 2‐vinylpyridine (Vpy), 2,2′‐bipyridine N‐oxide (O‐bpy), 2‐(2,4‐difluorophenyl)pyridine (dfppy); P^P = 1,1‐bis(diphenylphosphino)methane (dppm), N,N‐bis(diphenylphosphino)amine (dppa)) are reported. The complexes were characterized by means of NMR spectroscopy. Due to the presence of dppm and dppa with short backbones as bridging ligands, two platinum centres are located in front of each other in these complexes so a Pt…Pt interaction is established. Because of this Pt…Pt interaction, the complexes have bright orange colour under ambient light and are able to strongly emit red light under UV light exposure. These strong red emissions originate from a ³MMLCT (metal–metal‐to‐ligand charge transfer) electronic transition. In most of these complexes, the emissions have unstructured bell‐shaped bands, confirming the presence of large amount of ³MMLCT character in the emissive state. Only the complexes bearing dfppy and dppa ligands reveal dual luminescence: a high‐energy structured emission originating from ³ILCT/³MLCT (intra‐ligand charge transfer/metal‐to‐ligand charge transfer) and an unstructured low‐energy band associated with ³MMLCT. In order to describe the nature of the electronic transitions, density functional theory calculations were performed for all the complexes.     

A cyclometalated diplatinum complex containing 1,1′-bis(diphenylphosphino)ferrocene as spacer ligand: Antitumor study

Cyclometalated platinum(II) complex [Pt(C^N)Cl(dmso)], 1, in which C^N = N(1),C(2′)-chelated deprotonated 2-phenylpyridine and dmso = dimethylsulfoxide, was reacted with 1 equiv of 1,1′-bis(diphenylphosphino)ferrocene, dppf, to give the cyclometalated diplatinum(II) complex [Pt₂(C^N)₂Cl₂(μ-dppf)], 2, along with 0.5 equiv of unreacted dppf. However, the related reaction with 0.5 equiv of dppf produced complex 2 in pure form. Complex 2 in solution was fully characterized by using multinuclear NMR spectroscopy (¹H, ¹³C, ³¹P, and ¹⁹⁵Pt) and a number of 2D NMR experiments. The structure of complex 2 in solid state was determined by X-ray crystallography showing that the bridging dppf ligand is arranged close to “antiperiplanar staggered” conformation. Cytotoxicity of the complex 2 was studied in three human cancer cell lines derived from ovarian carcinoma(CH1), lung carcinoma(A549), and colon carcinoma (SW480) by means of the MTT assay (MTT = 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide).     

Design of Luminescent,Heteroleptic, Cyclometalated PtII and PtIV Complexes: Photophysics and Effects of the Cyclometalated Ligands

Neutral pentafluorophenyl benzoquinolinyl Pt^II [Pt(bzq)(HC^N−κN)(C₆F₅)] ( 1 a – g ) complexes, bearing nonmetalated N-heterocyclic HC^N ligands [HC^N=2,5-diphenyl-1,3,4-oxadiazole (Hoxd) a , 2-(2,4-difluorophenyl)pyridine (dfppy) b , 2-phenylbenzo[d]thiazole (pbt) c , 2-(4-bromophenyl)benzo[d]thiazole (Br-pbt) d , 2-phenylquinoline (pq) e , 2-thienylpyridine (thpy) f , 1-(2-pyridyl)pyrene (pypy) g ], and heteroleptic bis(cyclometalated) Pt^IV fac-[Pt(bzq)(C^N)(C₆F₅)Cl] ( 2 b – g , bzq: benzo[h]quinolinyl) derivatives, generated by oxidation of 1 b – g with PhICl₂, are reported. The oxidation reaction of 1 a evolved with formation of the bimetallic Pt^IV complex syn-[Pt(bzq)(C₆F₅)Cl(μ-OH)]₂ 3 . The crystal structures of 1 a,d,f , 2 b,d,e and 3 were corroborated by X-ray crystallography. A comparative study of the absorption and photoluminescence properties of the two series of complexes Pt^II ( 1 ) and Pt^IV ( 2 ), supported by time-dependent DFT calculations (TD-DFT), is presented. The low-lying transitions (absorption and emission) of Pt^II complexes 1 a – e [solution and polystyrene (PS) films] were assigned to the IL/MLCT mixture located on the cyclometalated Pt(bzq) unit, with minor IL′/ML′CT/LL′CT contributions involving the non-metalated ligand. Complex 1 g , bearing the more delocalized pyridyl pyrene (Hpypy) as an ancillary ligand, shows dual ¹ππ* and ³ππ* (Hpypy) emission in fluid CH₂Cl₂ and dual ³IL/³MLCT [Pt(bzq)] and [³ππ*, Hpypy] phosphorescence at 77 K. Upon oxidation, Pt^IV complexes 2 b – f display (solution, PS) ligand-based phosphorescence that arises from the bzq in 2 b (³LC) or from the second C^N ligand in 2 c – f (³L′C) with some ³LL′CT in 2 f . Despite metalation of the pyrenyl group, 2 g exhibits dual emission ¹ππ*/³ππ* located on the pypy chromophore.     

Luminescent mononuclear and dinuclear cycloplatinated (II) complexes comprising azide and phosphine ancillary ligands

A new series of cycloplatinated (II) complexes with general formulas of [Pt (bhq)(N₃)(P)] [bhq = deprotonated 7,8‐benzo[h]quinoline, P = triphenyl phosphine (PPh₃) and methyldiphenyl phosphine], [Pt (bhq)(P^P)]N₃ [P^P = 1,1‐bis (diphenylphosphino)methane (dppm) and 1,2‐bis (diphenylphosphino)ethane] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂] [P^P = dppm and 1,2‐bis (diphenylphosphino)acetylene] is reported in this investigation. A combination of azide (N₃^?) and phosphine (monodentate and bidentate) was used as ancillary ligands to study their influences on the chromophoric cyclometalated ligand. All complexes were characterized by nuclear magnetic resonance spectroscopy. To confirm the presence of the N₃^? ligand directly connected to the platinum center, complex [Pt (bhq)(N₃)(PPh₃)] was further characterized by single‐crystal X‐ray crystallography. The photophysical properties of the new products were studied by UV–Vis spectroscopy in CH₂Cl₂ and photoluminescence spectroscopy in solid state (298 or 77 K) and in solution (77 K). Using density functional theory calculations, it was proved that, in addition to intraligand charge‐transfer (ILCT) and metal‐to‐ligand charge‐transfer (MLCT) transitions, the L′LCT (L′ = N₃, L = C^N) electronic transition has a remarkable contribution in low energy bands of the absorption spectra (for complexes [Pt (bhq)(N₃)(P)] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂]). It is indicative of the determining role of the N₃^? ligand in electronic transitions of these complexes, specifically in the low energy region. In this regard, the photoluminescence studies indicated that the emissions in such complexes originate from a mixed ³ILCT/³MLCT (intramolecular) and also from aggregations (intermolecular).     

trans-[Pt(BCat')Me(PCy3)2]: an experimental case study of reductive elimination processes in Pt-Boryls through associative mechanisms

A stable trans‐(alkyl)(boryl) platinum complex trans‐[Pt(BCat′)Me(PCy₃)₂] (Cat′=Cat‐4‐tBu; Cy=cyclohexyl=C₆H₁₁) was synthesised by salt metathesis reaction of trans‐[Pt(BCat′)Br(PCy₃)₂] with LiMe and was fully characterised. Investigation of the reactivity of the title compound showed complete reductive elimination of Cat′BMe at 80 °C within four weeks. This process may be accelerated by the addition of a variety of alkynes, thereby leading to the formation of the corresponding η²‐alkyne platinum complexes, of which [Pt(η²‐MeCCMe)(PCy₃)₂] was characterised by X‐ray crystallography. Conversion of the trans‐configured title compound to a cis derivative remained unsuccessful due to an instantaneous reductive elimination process during the reaction with chelating phosphines. Treatment of trans‐[Pt(BCat′)Me(PCy₃)₂] with Cat₂B₂ led to the formation of CatBMe and Cat′BMe. In the course of further investigations into this reaction, indications for two indistinguishable reaction mechanisms were found: 1) associative formation of a six‐coordinate platinum centre prior to reductive elimination and 2) σ‐bond metathesis of B? B and C? Pt bonds. Mechanism 1 provides a straightforward explanation for the formation of both methylboranes. Scrambling of diboranes(4) Cat₂B₂ and Cat′₂B₂ in the presence of [Pt(PCy₃)₂], fully reductive elimination of CatBMe or Cat′BMe from trans‐[Pt(BCat′)Me(PCy₃)₂] in the presence of sub‐stoichiometric amounts of Cat₂B₂, and evidence for the reversibility of the oxidative addition of Cat₂B₂ to [Pt(PCy₃)₂] all support mechanism 2, which consists of sequential equilibria reactions. Furthermore, the solid‐state molecular structure of cis‐[Pt(BCat)₂(PCy₃)₂] and cis‐[Pt(BCat′)₂(PCy₃)₂] were investigated. The remarkably short B? B separations in both bis(boryl) complexes suggest that the two boryl ligands in each case are more loosely bound to the Pt^II centre than in related bis(boryl) species.     

Syntheses and Structures of Terminal Arylalumylene Complexes

Terminal arylalumylene complexes of platinum [Ar‐Al‐Pt(PCy₃)₂] (Ar=2,6‐[CH(SiMe₃)₂]₂C₆H₃ (Bbp) or 2,6‐[CH(SiMe₃)₂]₂‐4‐(tBu)C₆H₂ (Tbb)) have been synthesized either by the reaction of a dialumene–benzene adduct with [Pt(PCy₃)₂], or by the reduction of 1,2‐dibromodialumanes Ar(Br)Al‐Al(Br)Ar in the presence of [Pt(PCy₃)₂]. X‐Ray crystallographic analysis reveals that the Al? Pt bond lengths of these arylalumylene complexes are shorter than the previously reported shortest Al? Pt distance. DFT calculations suggest that the Al? Pt bonds in the arylalumylene complexes have a significantly high electrostatic character.     

2-苯基吡啶铱(Ⅲ)配合物及其衍生物光谱性质的理论研究

采用密度泛函理论B3PW91和UB3PW91方法, 分别对4种Ir(Ⅲ)配合物(ppy)₂Ir(acac)(1, ppy=2-苯基吡啶, acac=乙酰丙酮)、(npy)₂Ir(acac)(2, npy=2-萘-1-基吡啶)、(pq)₂Ir(acac)(3, pq=2-苯基喹啉)和(bzq)₂Ir(acac)(4, bzq=苯并喹啉)进行了基态和激发态的几何优化, 在此基础上用TD-DFT方法计算了吸收和发射光谱. 结果表明, 随着ppy配体上并苯环位置的变化, 参与最大吸收和发射的分子轨道能隙降低程度不同, 从而使配合物2, 3, 4的最大吸收和发射光谱都比配合物1发生红移, 其中在吡啶环上增加苯环对吸收光谱的影响最大. 这4个分子最大吸收波长的顺序为1<2<4<3, 而最大发射波长顺序则是1<4<3<2. 由于配合物2的两个苯环上H的强排斥作用降低了其共轭程度, 使分子发生很大程度的扭曲, 导致其斯托克位移最大.     

Stable trans isomer as the kinetic and theromodynamic product for the oxidative addition of MeI to cycloplatinated(II) complexes comprising isocyanide ligands

The present investigation introduces a new series of cycloplatinated(II) complexes, with the general formula Pt(O‐bpy)(Me)(CN‐R)] (R = benzyl, 2‐naphtyl and tert‐butyl), which are able to generate the stable trans‐Pt(IV) product in the solution after the reaction with iodomethane. In fact, the trans product is both the kinetic and thermodynamic product of the reaction; this observation was supported by DFT calculations. These Pt(II) complexes are supported by 2,2'‐bipyridine N‐oxide (O‐bpy) and one of several isocyanides as the cyclometalated and ancillary ligands, respectively. These new Pt(II) complexes undergo oxidative addition with MeI to give the corresponding trans‐Pt(IV) complexes. All the complexes were identified employing the multi‐nuclear NMR spectroscopy and single crystal X‐ray crystallography. The kinetic investigations were also performed for the oxidative addition reactions in order to measure the reaction rates; the reaction was followed by UV‐Vis spectroscopy. The rates obtained follow the trend CN‐^tBu > CN‐Bz > CN‐2 Np for the CN‐R ligands in the Pt(II) complexes. The order can be related to the degree of electron‐donation of the R group (tert‐butyl > benzyl > 2‐naphtyl).     

Luminescent Benzoquinolate‐Isocyanide Platinum(II) Complexes: Effect of Pt⋅⋅⋅Pt and π⋅⋅⋅π Interactions on their Photophysical Properties

The neutral compounds [Pt(bzq)(CN)(CNR)] (R=tBu ( 1 ), Xyl ( 2 ), 2‐Np ( 3 ); bzq= benzoquinolate, Xyl=2,6‐dimethylphenyl, 2‐Np=2‐napthyl) were isolated as the pure isomers with a trans‐C_bzq,CNR configuration, as confirmed by ¹³C{¹H} NMR spectroscopy in the isotopically marked [Pt(bzq)(¹³CN)(CNR)] (R=tBu ( 1′ ), Xyl ( 2′ ), 2‐Np ( 3′ )) derivatives (δ¹³C_CN≈110 ppm; ¹J(Pt,¹³C)≈1425 Hz]. By contrast, complex [Pt(bzq)(C≡CPh)(CNXyl)] ( 4 ) with a trans‐N_bzq,CNR configuration, has been selectively isolated from [Pt(bzq)Cl(CNXyl)] (trans‐N_bzq,CNR) using Sonogashira conditions. X‐ray diffraction studies reveal that while 1 adopts a columnar‐stacked chain structure with Pt–Pt distances of 3.371(1) Å and significant π???π interactions (3.262 Å), complex 2 forms dimers supported only by short Pt???Pt (3.370(1) Å) interactions. In complex 4 the packing is directed by weak bzq???Xyl and bzq???C≡E (C, N) interactions. In solid state at room temperature, compounds 1 and 2 both show a bright red emission (?=42.1 % 1 , 57.6 % 2 ). Luminescence properties in the solid state at 77 K and concentration‐dependent emission studies in CH₂Cl₂ at 298 K and at 77 K are also reported for 1 , 1·CHCl3 , 2 , 2' , 2·CHCl3 , 3 , 4 .     

Cyclometalated platinum(II) complexes containing monodentate phosphines: antiproliferative study

Reaction of cyclometalated platinum(II) precursor [Pt(C^N)Cl(dmso)], 1, C^N = N(1), C(2′)-chelated deprotonated 2-phenylpyridine and dmso = dimethylsulfoxide, with 1 equivalent of triphenyl phosphine, PPh₃, or 1,3,5-triaza-7-phosphaadamantane, PTA, gave the complex [Pt(C^N)Cl(PPh₃)], 2, or [Pt(C^N)Cl(PTA)], 3, respectively. On the basis of careful multinuclear NMR spectroscopy, supported by a number of 2D NMR experiments, structures of the complexes 2 and 3 in solution were determined to be neutral four coordinate. The X-ray crystallography indicated that the solid-state structure of complex 3 comprised a common square-planar geometry around platinum(II). Cytotoxicity of the complexes 2 and 3 was studied in three human cancer cell lines derived from ovarian carcinoma (CH1), lung carcinoma (A549), and colon carcinoma (SW480).     

Water‐Soluble Luminescent Cyclometalated Gold(III) Complexes with cis‐Chelating Bis(N‐Heterocyclic Carbene) Ligands: Synthesis and Photophysical Properties

A new class of cyclometalated Au^III complexes containing various bidentate C‐deprotonated C^N and cis‐chelating bis(N‐heterocyclic carbene) (bis‐NHC) ligands has been synthesized and characterized. These are the first examples of Au^III complexes supported by cis‐chelating bis‐NHC ligands. [Au(C^N)(bis‐NHC)] complexes display emission in solutions under degassed condition at room temperature with emission maxima (λ_max) at 498–633 nm and emission quantum yields of up to 10.1 %. The emissions are assigned to triplet intraligand (IL) π→π* transitions of C^N ligands. The Au^III complex containing a C^N (C‐deprotonated naphthalene‐substituted quinoline) ligand with extended π‐conjugation exhibits prompt fluorescence and phosphorescence of comparable intensity with λ_max at 454 and 611 nm respectively. With sulfonate‐functionalized bis‐NHC ligand, four water‐soluble luminescent Au^III complexes, including those displaying both fluorescence and phosphorescence, were prepared. They show similar photophysical properties in water when compared with their counterparts in acetonitrile. The long phosphorescence lifetime of the water‐soluble AuIII complex with C‐deprotonated naphthalene‐substituted quinoline ligand renders it to function as ratiometric sensor for oxygen. Inhibitory activity of one of these water‐soluble Au^III complexes towards deubiquitinase (DUB) UCHL3 has been investigated; this complex also displayed a significant inhibitory activity with IC₅₀ value of 0.15 μM .     

Density functional studies of influences of Ni triad metals and solvents on oxidative addition of MeI to [M(CH3)2(NH3)2] complexes and C-C reductive elimination from [M(CH3)3(NH3)2I] complexes

Three metal square planar complexes of the type [M(CH₃)₂(NH₃)₂] (M = Ni, Pd, Pt), with a systematic variation in the metals, are chosen to investigating their S_N2-type oxidative addition reactions with methyl iodide by using the B3LYP levels of theory. The oxidative addition was found to take place via a transition state with a nearly linear arrangement of the I-CH₃-M moiety. Solvation effects in these oxidative addition reactions were also investigated. Considering the nature of the metal centre and solvation effects, the following conclusions emerge: (i) addition of MeI is exothermic for all three metals, and Pt is predicted to react with a much lower barrier than either Pd or Ni. The results describe that the MeI addition would be expected to be more favourable with the complex bearing the third-row metal (platinum) as compared to the other triad metals, nickel or palladium, in which case a more strongly bound MeI adduct is formed with a lower activation barriers and the reaction being more exothermic; (ii) the reaction is very difficult to occur in low polar solvents, such as benzene, due to the high barrier which is induced by dissociation of iodide anion from methyl group, but the reaction easily occurs in polar solvents, such as acetonitrile; this is attributed to the ability of polar solvents to solvate and therefore stabilize the related polar intermediate ion pair. Ethane reductive elimination from the M(VI) complexes fac-[M(CH₃)₃(NH₃)₂I] were also studied, indicating that the Ni(IV) and Pd(IV) complexes are very prone to undergo the reductive elimination while the Pt(IV) analogous is less reactive towards the reductive elimination. The results indicate that in contrast to the Me-Me reductive elimination, the S_N2 oxidative addition reaction of MeI to M(II) is much less sensitive to the nature of the metal centre, suggesting that the nucleophilicity of M(II) in [M(CH₃)₂(NH₃)₂] does not change significantly as one moves from M = Ni to Pt.     

New water soluble and luminescent platinum(II) compounds, vapochromic behavior of [K(H2O)][Pt(bzq)(CN)2], new examples of the influence of the counterion on the photophysical properties of d8 square-planar complexes

This work describes the synthesis of compounds [Pt(C=N)(NCMe) 2]ClO 4 (C=N = 7,8-benzoquinolinato (bzq), 2-phenylpyridinato (ppy)) and their use as precursors for the preparation of the cyanido complexes [Pt(C=N)(CN) 2] (-), which were isolated as the potassium, [K(H 2O)][Pt(C=N)(CN) 2] [C=N = bzq ( 3a), ppy ( 4a)], and the tetrabutylammonium, NBu 4[Pt(C=N)(CN) 2] [C=N = bzq ( 5), ppy ( 6)], salts. The difference in the cation has an influence on the solubility, color, and emission properties of these compounds. Compounds 5 and 6 are yellow and soluble in organic solvents, while the potassium salts are also soluble in water and exhibit two forms: the water-containing [K(H 2O)][Pt(C=N)(CN) 2] [C=N = bzq ( 3a), ppy ( 4a)] complexes and the anhydrous ones K[Pt(C=N)(CN) 2] [C=N = bzq ( 3b), ppy ( 4b)], the former being strongly colored [red ( 3a) or purple ( 4a)] and the latter being yellow. Compounds 3a and 4a transform reversibly into the yellow, 3b and 4b, compounds upon desorption/ reabsorption of water molecules from the environment. The red solid, 3a, also exhibits vapochromic behavior when it is exposed to volatile organic compounds, the shortest response times being those observed for methanol and ethanol. UV-vis and emission spectra of all compounds were recorded both in solution and in the solid state. In methanol solution, the difference in the cation causes no differences in the absorption nor in the emission spectra, which is as expected for the monomer species. However, in the solid state, the differences are notable. For both the red ( 3a) and purple ( 4a) compounds, a prominent absorption, which has maxima at about 550 nm and is responsible for their intense colors, as well as a structureless emission at lambda > 700 nm that suffers a significant red-shift upon cooling, are due to (1,3)MMLCT (= metal-metal-to-ligand charge transfer) [dsigma*(Pt) --> pi*(C=N)] transitions characteristic of linear-chain platinum complexes with short Pt...Pt contacts. Time-dependent density-functional theory calculations on complex 5 and the X-ray diffraction study on compound [K(OCMe 2) 2][Pt(ppy)(CN) 2] ( 4c) are also included.     

Activation of SF6 at Platinum Complexes: Formation of SF3 Derivatives and Their Application in Deoxyfluorination Reactions

The activation of SF₆ at [Pt(PR₃)₂] R=Cy, i Pr complexes in the presence of PR₃ led selectively and in an unprecedented reaction route to the generation of the SF₃ complexes trans ‐[Pt(F)(SF₃)(PR₃)₂]. These can also be synthesized from SF₄ and the SF₂ derivative trans ‐[Pt(F)(SF₂)(PCy₃)₂][BF₄] was characterized by X‐ray crystallography. trans ‐[Pt(F)(SF₃)(PR₃)₂] complexes are useful tools for deoxyfluorination reactions and novel fluorido complexes bearing a SOF ligand are formed. Based on these studies a process for the deoxyfluorination of ketones was developed with SF₆ as fluorinating agent.     

Oxovanadium(IV) and ruthenium(II) carbonyl complexes of ONS‐donor ligands derived from dehydroacetic acid and dithiocarbazate: Synthesis,characterization, antioxidant activity,DNA binding and in vitro cytotoxicity

A series of new complexes of oxovanadium(IV) [VO(L)(B)] and ruthenium(II) [Ru(CO)(PPh₃)₂(L)] ( 1.1- 1.3,  2.1–2.3 ) (H₂L = dehydroacetic acid Schiff base of S‐methyldithiocarbazate, H₂smdha ( 1 ) or S‐benzyldithiocarbazate, H₂sbdha ( 2 ); B = 2,2′‐bipyridine (bpy) or 1,10‐phenanthroline (phen)) have been synthesized. The structure of these complexes was authenticated using elemental analyses and spectroscopic techniques, and their magnetic properties and electrochemical behaviour were studied. The molecular structures of oxovanadium(IV) complexes [VO(smdha)(bpy)]?CH₂Cl₂ ( 1.1 ) and [VO(sbdha)(phen)]?2H₂O ( 2.2 ) were confirmed using single‐crystal X‐ray crystallography. Analytical data showed that the ligands 1 and 2 are chelated to the metal centres in a bi‐negative tridentate fashion through azomethine N, thiol S and deprotonated hydroxyl group. The antioxidant activity of the synthesized compounds was tested against 2,2‐diphenyl‐1‐picrylhydrazyl) radical, which showed that the complexes demonstrate a better scavenging activity than their corresponding ligands. The cupric ion reducing antioxidant capacity method was also employed and the total equivalent antioxidant capacity values were found to be higher for the oxovandium(IV) complexes. DNA binding affinity of the compounds was determined using UV–visible and fluorescence spectra, revealing an intercalation binding mode. Higher cytotoxicity for the complexes compared to their ligands was found against human liver hepatocellular carcinoma (HepG2) and breast adenocarcinoma (MCF7) cell lines using MTT assay.     

Synthesis,antimicrobial activity and molecular docking of di‐ and triorganotin (IV) complexes with thiosemicarbazide derivatives

Six organotin (IV) complexes with two ligands derived from 2,3‐butanedione and thiosemicarbazide have been synthesized and fully characterized by several spectroscopic techniques, including ¹¹⁹Sn NMR and single crystal X‐ray diffraction. Reactions of the ligand diacetyl‐2‐(thiosemicarbazone)‐3‐(3‐hydroxy‐2‐naphthohydrazone), L¹H₂, with SnR₂Cl₂ (R = Me, Bu, Ph) lead to the obtaining of complexes 1 – 3 with general formula [SnR₂L¹] (R = Me 1 , R = Bu 2 , R = Ph 3 ), in which the ligand is doubly deprotonated and behaves as a N₂SO donor, whereas from the reactions of diacetyl‐2‐thiosemicarbazone, HATs, with the same organotin precursors any complex could be isolated. By contrast, reaction of HATs with SnR₃Cl induces the ligand cyclization to form a 1,2,4‐triazine‐3‐thione that binds to the metal as a monoanionic donor in a mono or bidentate manner to form compounds 4 – 6 with formula [SnR₃L²] (R = Me 4 , R = Bu 5 , R = Ph 6 ). The antimicrobial activity of the ligands and the six complexes was tested towards bacteria and fungi, including clinical isolated strains. The results show that the ligands are devoid of activity, except HATs that displays activity against Bacillus subtilis. Conversely, the complexes exhibit good antimicrobial properties against Gram positive and negative bacteria, yeasts and moulds. The best results are obtained for complexes [SnBu₃L²] 5 and [SnPh₃L²] 6 , indicating that their more lipophilic nature could play an important role in the ease of microbial cell penetration. In some cases, these complexes display similar or higher activity than that of ampicillin and miconazole, used as antibacterial and antifungal positive controls, respectively. Docking study with DHPS protein (S. aureus) has shown that out of six drugs, the compound 6 has the best binding affinity (?8.5 Kcal/mol).     

Manipulation of Phosphorescence Efficiency of Cyclometalated Iridium Complexes by Substituted o‐Carboranes

A series of [(C^N)₂Ir(acac)] complexes [{5‐(2‐R‐CB)ppy}₂Ir(acac)] ( 3 a – 3 g ; acac=acetylacetonate, CB=o‐carboran‐1‐yl, ppy=2‐phenylpyridine; R=H ( 3 a ), Me ( 3 b ), iPr ( 3 c ), iBu ( 3 d ), Ph ( 3 e ), CF₃C₆H₄ ( 3 f ), C₆F₅ ( 3 g )) with various 2‐R‐substituted o‐carboranes at the 5‐position in the phenyl ring of the ppy ligand were prepared. X‐ray diffraction studies revealed that the carboranyl C?C bond length increases with increasing steric and electron‐withdrawing effects from the 2‐R substituents. Although the absorption and emission wavelengths of the complexes are almost invariant to the change of 2‐R group, the phosphorescence quantum efficiency varies from highly emissive (Φ_PL≈0.80 for R=H, alkyl) to poorly emissive (R=aryl) depending on the 2‐R group and the polarity of the medium. Theoretical studies suggest that 1) the almost nonemissive nature of the 2‐aryl‐substituted complexes is mainly attributable to the large contribution to the LUMO in the S₁ excited state from an o‐carborane unit and 2) the variation in the C?C bond length between the S₀ and T₁ state structures increases with increasing steric (2‐alkyl) and electronic effects (2‐aryl) of the 2‐R substituent and the polarity of the solvent. The solution‐processed electroluminescence (EL) devices that incorporated 3 b and 3 d as emitters displayed higher performance than the device based on the parent [(ppy)₂Ir(acac)] complex. Along with the high phosphorescence efficiency, the bulkiness of the 2‐R‐o‐carborane unit is shown to play an important role in improving device performance.