Influence of the bridging azine ligand on the rate of ligand substitution in a series of dinuclear platinum(II) complexes

A series of azine‐bridged dinuclear platinum(II) complexes of the type [{trans‐Pt(NH₃)₂(OH₂)}₂(μ‐azn)](ClO₄)₄ (where azn = pyrazine (pzn, Pt1 ), 2,3‐dimethylpyrazine (2,3‐pzn, Pt2 ), and 2,5‐dimethylpyrazine (2,5‐pzn, Pt3 )) were synthesized to investigate the influence of the bridging azine ligand on the reactivity of the platinum(II) centers. The pK_a values of the complexes were determined via acid–base titration, and the rate of substitution of the aqua moiety by a series of neutral nucleophiles, viz. thiourea (TU), 1,3‐dimethyl‐2‐thiourea (DMTU), and 1,1,3,3‐tetramethyl‐2‐thiourea (TMTU), was determined under pseudo‐first‐order conditions as a function of concentration and temperature using standard spectrophotometric techniques. The introduction of the methyl groups to the bridging azine linker in Pt2 and Pt3 leads to a moderate increase in the pK_a values obtained for the first and second deprotonation steps, respectively, as a result of the increased σ‐donor capacity of the bridging azine ligand trans to the aqua moiety. A comparison of the rate constants, k₁ and k₂, at 298 K, obtained for the substitution of the aqua moieties from Pt1 , Pt2 , and Pt3 by TU, shows that the introduction of the σ‐donating methyl groups on the bridging azine ligand in Pt2 and Pt3 results in a corresponding decrease in the reactivity, by ca. five times for the first substitution step and ca. 10 times for the second substitution step. Density functional theory calculations at the B3LYP/LACVP** level of theory for the complexes demonstrate that the introduction of electron‐donating methyl groups results in (i) increased steric hindrance over the metal centers and (ii) decreased the positive charge on the metal center and increases energy separation of the frontier molecular orbitals (E_HOMO – E_LUMO) of the ground‐state platinum(II) complexes, leading to a less‐reactive metal center. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 161–174, 2011     

Role of bridging diamine linkers on the rate of ligand substitution in a series of dinuclear PtII complexes

A series of dinuclear platinum^II complexes of the type [{trans‐Pt(H₂O)(NH₃)₂}₂‐NH₂(CH₂)_nH₂N]⁴⁺ (where n = 2, 3, 4, and 6) were synthesized to investigate the influence of the bridging diamine linker on the reactivity of the platinum centers. The pK_a values were determined, and the rates of substitution of the aqua moieties by a series of neutral nucleophiles viz. thiourea, 1,3‐dimethyl‐2‐thiourea, and 1,1,3,3‐tetramethyl‐2‐thiourea were studied as a function of concentration and temperature. All reactions studied gave excellent fits to a single exponential and obeyed the simple rate law, k_obs=k₂[Nu]. Negative activation entropies support an associative mode of substitution. The results obtained suggest that the rate of substitution is definitely influenced by the length of the diamine chain, with the rate of substitution decreasing as the length of the diamine chain increases. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 202–210, 2006     

Platinum(II) Mixed Ligand Complexes with Thiourea Derivatives,Dimethyl Sulphoxide and Chloride: Syntheses,Molecular Structures,and ESCA Data

The platinum(II) mixed ligand complexes [PtCl(L^1‐6)(dmso)] with six differently substituted thiourea derivatives HL, R₂NC(S)NHC(O)R′ (R = Et, R′ = p‐O₂N‐Ph: HL¹; R = Ph, R′ = p‐O₂N‐Ph: HL²; R = R′ = Ph: HL³; R = Et, R′ = o‐Cl‐Ph: HL⁴; R₂N = EtOC(O)N(CH₂CH₂)₂N, R′ = Ph: HL⁵) and Et₂NC(S)N=CNH‐1‐Naph (HL⁶), as well as the bis(benzoylthioureato‐κO, κS)‐platinum(II) complexes [Pt(L^{1, 2})₂] have been synthesized and characterized by elemental analysis, IR, FAB(+)‐MS, ¹H‐NMR, ¹³C‐NMR, as well as X‐ray structure analysis ([PtCl(L¹)(dmso)] and [PtCl(L^{3, 4})(dmso)]) and ESCA ([PtCl(L^{1, 2})(dmso)] and [Pt(L^{1, 2})₂]). The mixed ligand complexes [PtCl(L)(dmso)] have a nearly square‐planar coordination at the platinum atoms. After deprotonation, the thiourea derivatives coordinate bidentately via O and S, DMSO bonds monodentately to the Pt^II atom via S atom in a cis arrangement with respect to the thiocarbonyl sulphur atom. The Pt—S‐bonds to the DMSO are significant shorter than those to the thiocarbonyl‐S atom. In comparison with the unsubstituted case, electron withdrawing substituents at the phenyl group of the benzoyl moiety of the thioureate (p‐NO₂, o‐Cl) cause a significant elongation of the Pt—S(dmso)‐bond trans arranged to the benzoyl‐O—Pt‐bond. The ESCA data confirm the found coordination and bonding conditions. The Pt 4f_7/2 electron binding energies of the complexes [PtCl(L^{1, 2})(dmso)] are higher than those of the bis(benzoylthioureato)‐complexes [Pt(L^{1, 2})₂]. This may indicate a withdrawal of electron density from platinum(II) caused by the DMSO ligands.     

Platinum and Palladium Complexes Bearing New (1R,2R)‐(–)‐1,2‐Diaminocyclohexane (DACH)‐Based Nitrogen Ligands: Evaluation of the Complexes Against L1210 Leukemia

The reaction of (1R,2R)‐(–)‐1,2‐diaminocyclohexane ( 1 ) [DACH] with the aldehyde (1R)‐(–)‐myrtenal ( 2 ) in MeOH afforded the bidentate diimine ligand, (1R,2R)‐(–)‐N¹,N²‐bis{(1R)‐(–)myrtenylidene}‐1,2‐diaminocyclohexane ( 3 ) in a high yield. Reduction of 3 using LiAlH₄ led to the formation of the desired ligand ( 4 ) (1R,2R)‐(–)‐N¹,N²‐bis{(1R)‐(–)myrtenyl}‐1,2‐diaminocyclohexane. Treatment of compound 4 with K₂PtCl₄ or K₂PdCl₄ yielded the corresponding platinum(II) and palladium(II) complexes, Pt‐5 and Pd‐6 , respectively. The reaction of compound 3 with K₂PtCl₄ gave the diimine complex Pt‐7 . The cytotoxic activity of the complexes Pt‐5 , Pd‐6 and Pt‐7 was tested and compared to the approved drugs, cisplatin ( Cis ‐Pt ) and oxaliplatin ( Ox‐Pt ). The complexes ( Pt‐5 , Pd‐6 and Pt‐7 ) inhibit L1210 cell line proliferation with an IC₅₀ of 0.6, 4.2, and 0.7 μL, respectively as evidenced by measuring thymidine incorporation.     

Enhanced Anion Binding from Unusual Coordination Modes of Bis(thiourea) Ligands in Platinum Group Metal Complexes

Treatment of a range of bis(thiourea) ligands with inert organometallic transition‐metal ions gives a number of novel complexes that exhibit unusual ligand binding modes and significantly enhanced anion binding ability. The ruthenium(II) complex [Ru(η⁶‐p‐cymene)(κS,S′,N‐ L³ ?H)]⁺ ( 2 b ) possesses juxtaposed four‐ and seven‐membered chelate rings and binds anions as both 1:1 and 2:1 host guest complexes. The pyridyl bis(thiourea) complex [Ru(η⁶‐p‐cymeme)(κS,S′,N_py‐ L⁴ )]²⁺ ( 4 ) binds anions in both 1:1 and 1:2 species, whereas the free ligand is ineffective because of intramolecular NH???N hydrogen bonding. Novel palladium(II) complexes with nine‐ and ten‐membered chelate rings are also reported.     

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.     

2,3‐Di(2‐pyridyl)‐5‐phenylpyrazine: A NN‐CNN‐Type Bridging Ligand for Dinuclear Transition‐Metal Complexes

A new bridging ligand, 2,3‐di(2‐pyridyl)‐5‐phenylpyrazine (dpppzH), has been synthesized. This ligand was designed so that it could bind two metals through a NN‐CNN‐type coordination mode. The reaction of dpppzH with cis‐[(bpy)₂RuCl₂] (bpy=2,2′‐bipyridine) affords monoruthenium complex [(bpy)₂Ru(dpppzH)]²⁺ ( 12+ ) in 64 % yield, in which dpppzH behaves as a NN bidentate ligand. The asymmetric biruthenium complex [(bpy)₂Ru(dpppz)Ru(Mebip)]³⁺ ( 23+ ) was prepared from complex 12+ and [(Mebip)RuCl₃] (Mebip=bis(N‐methylbenzimidazolyl)pyridine), in which one hydrogen atom on the phenyl ring of dpppzH is lost and the bridging ligand binds to the second ruthenium atom in a CNN tridentate fashion. In addition, the RuPt heterobimetallic complex [(bpy)₂Ru(dpppz)Pt(C?CPh)]²⁺ ( 42+ ) has been prepared from complex 12+ , in which the bridging ligand binds to the platinum atom through a CNN binding mode. The electronic properties of these complexes have been probed by using electrochemical and spectroscopic techniques and studied by theoretical calculations. Complex 12+ is emissive at room temperature, with an emission λ_max=695 nm. No emission was detected for complex 23+ at room temperature in MeCN, whereas complex 42+ displayed an emission at about 750 nm. The emission properties of these complexes are compared to those of previously reported Ru and RuPt bimetallic complexes with a related ligand, 2,3‐di(2‐pyridyl)‐5,6‐diphenylpyrazine.     

The Controlled Formation and Cleavage of an Intramolecular d8–d8 Pt–Pt Interaction in a Dinuclear Cycloplatinated Molecular “Pivot‐Hinge”

The bis(diphenylphosphino)methane (dppm)‐bridged dinuclear cycloplatinated complex {[Pt(L)]₂(μ‐dppm)}²⁺ (Pt₂ ? dppm; HL: 2‐phenyl‐6‐(1H‐pyrazol‐3‐yl)‐pyridine) demonstrates interesting reversible “pivot‐hinge”‐like intramolecular motions in response to the protonation/deprotonation of L. In its protonated “closed” configuration, the two platinum(II) centers are held in position by intramolecular d⁸–d⁸ Pt–Pt interaction. In its deprotonated “open” configuration, such Pt–Pt interaction is cleaved. To further understand the mechanism behind this hingelike motion, an analogous dinuclear cycloplatinated complex, {[Pt(L)]₂(μ‐dchpm)}²⁺ (Pt₂ ? dchpm) with bis(dicyclohexylphosphino)methane (dchpm) as the bridging ligand, was synthesized. From its protonation/deprotonation responses, it was revealed that aromatic π–π interactions between the phenyl moieties of the μ‐dppm and the deprotonated pyrazolyl rings of L was essential to the reversible cleavage of the intramolecular Pt–Pt interaction in Pt₂ ? dppm. In the case of Pt₂ ? dchpm, spectroscopic and spectrofluorometric titrations as well as X‐ray crystallography indicated that the distance between the two platinum(II) centers shrank upon deprotonation, thus causing a redshift in its room‐temperature triplet metal–metal‐to‐ligand charge‐transfer emission from 614 to 625 nm. Ab initio calculations revealed the presence of intramolecular hydrogen bonding between the deprotonated and negatively charged 1‐pyrazolyl‐N moiety and the methylene CH and phenyl C–H of the μ‐dppm. The “open” configuration of the deprotonated Pt₂ ? dppm was estimated to be 19 kcal mol^?1 more stable than its alternative “closed” configuration. On the other hand, the open configuration of the deprotonated Pt₂ ? dchpm was 6 kcal mol^?1 less stable than its alternative closed configuration.     

A new double‐cube nitride complex containing titanium and potassium

The reaction of the imide–nitride complex [{Ti(η⁵‐C₅Me₅)(μ‐NH)}₃(μ₃‐N)] with potassium iodide in pyridine at room temperature affords the adduct di‐μ‐iodido‐1:1′κ⁴I‐bis{tri‐μ₃‐imido‐1:2:3κ³N;1:2:4κ³N;1:3:4κ³N‐μ₃‐nitrido‐2:3:4κ³N‐tris[2,3,4(η⁵)‐pentamethylcyclopentadienyl](pyridine‐1κN)‐tetrahedro‐potassiumtrititanium(IV)}, [K₂Ti₆(C₁₀H₁₅)₆I₂N₂(NH)₆(C₅H₅N)₂] or [(C₅H₅N)(μ‐I)K{(μ₃‐NH)₃Ti₃(η⁵‐C₅Me₅)₃(μ₃‐N)}]₂. The crystal structure contains two [KTi₃N₄] cube‐type units held together by two bridging I atoms. There is a centre of inversion located in the middle of this unprecedented discrete K₂I₂ unit. The geometry around K is best described as distorted trigonal prismatic, with three imide groups, two bridging I atoms and one pyridine ligand.     

A one‐dimensional zinc(II) coordination polymer incorporating [1,1′‐biphenyl]‐4,4′‐dicarboxylate and N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide ligands

In the title compound, catena‐poly[[[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]chloridozinc(II)]‐μ‐[1,1′‐biphenyl]‐4,4′‐dicarboxylato‐[[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]chloridozinc(II)]‐μ‐[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]], [Zn₂(C₁₄H₈O₄)Cl₂(C₂₆H₂₂N₄O₂)₃]_n, the Zn^II centre is four‐coordinate and approximately tetrahedral, bonding to one carboxylate O atom from a bidentate bridging dianionic [1,1′‐biphenyl]‐4,4′‐dicarboxylate ligand, to two pyridine N atoms from two N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide ligands and to one chloride ligand. The pyridyl ligands exhibit bidentate bridging and monodentate terminal coordination modes. The bidentate bridging pyridyl ligand and the bridging [1,1′‐biphenyl]‐4,4′‐dicarboxylate ligand both lie on special positions, with inversion centres at the mid‐points of their central C—C bonds. These bridging groups link the Zn^II centres into a one‐dimensional tape structure that propagates along the crystallographic b direction. The tapes are interlinked into a two‐dimensional layer in the ab plane through N—H...O hydrogen bonds between the monodentate ligands. In addition, the thermal stability and solid‐state photoluminescence properties of the title compound are reported.     

COMPLEXES OF BINUCLEATING LIGANDS. X. SOME COPPER(II), NICKEL(II), PALLADIUM(II), AND PLATINUM(II) COMPLEXES OF SULPHUR-CONTAINING LIGANDS

Abstract

Copper(II) and nickel(II) complexes of the trianionic binucleating ligand (R^3-) derived from 4-hydroxy-bis-3,5-[N-(S-methyl-dithiocarbamate) formimidoyl]toluene have the general form RM₂(Z) where Z represents a range of monoanionic bridging species. Palladium(II) and platinum(II) complexes formed by R^3- and the related trianionic ligands derived from 2-hydroxy-5-methylisophthalaldehyde di-2′-mercaptoanil and 2-hydroxy-5-methylisophthalaldehyde dithiosemicarbazone have the 2:1 formulation [(ligand)M₂(Z)] only when the bridging species, Z, coordinates strongly enough to give the binucleating ligand substantial assistance in maintaining the binuclear structure. In the absence of a ‘good’ bridging group and in the presence of pyridine, 3:2 complexes of the form [(ligand)₂ M₃ (pyridine)₂] (where M = Pd, Pt) are produced in which the binucleating ligand fails to bind the two metals in close proximity.     

A Dissociative Route to C?H Bond Activation: Ligand Cyclometalation in cis‐Dimethyl[(sulfinyl‐κS)bis[methane]][tris(2‐methylphenyl)phosphine]platinum(2+)

The dialkyl compound cis‐dimethyl[(sulfinyl‐κS)bis[methane]][tris(2‐methylphenyl)phosphine]platinum(2+) (cis‐[Pt(Me)₂(dmso)(P(o‐tol)₃]; 1 ) has been isolated from the reaction of cis‐dimethylbis[(sulfinyl‐κS)bis[methane]]platinum(2+) (cis‐[Pt(Me)₂(dmso)₂]) with tris(2‐methylphenyl)phosphane (P(o‐tol)₃). Restricted rotation around the P? C_ipso bonds of the phosphane ligand generates two different conformers, 1a and 1b , in rapid exchange in non‐polar solvents at low temperature. Strong through‐space contacts between the ortho‐Me substituent groups on the ligand and the cis‐Me groups in the coordination plane were determined, which proved useful for identifying the atropisomers formed. At room temperature, ¹H‐NMR spectra of 1 maintain a ‘static’ pattern upon onset of easy and rapid ortho‐platination, leading to [[2‐[bis(2‐methylphenyl)phosphino‐κP]phenyl]methyl‐κC]methyl[(sulfinyl‐κS)bis[methane]]platinum(2+) ( 2 ), a new C,P‐cyclometalated compound of platinum(II), with liberation of methane. The process has been studied by ¹H‐ and ³¹P{¹H}‐NMR in CDCl₃, and kinetics experiments were performed by conventional spectrophotometric techniques. The first‐order rate constants k_c decrease with the addition of dimethyl sulfoxide until the process is blocked by the presence of a sufficient excess of sulfoxide. This behavior reveals a mechanism initiated by ligand dissociation and formation of a three‐coordinate species. The value of the rate constant for dimethyl sulfoxide dissociation k₁ has been measured independently over a wide temperature range by both ¹H‐NMR ligand exchange (isotopic labeling experiments) and ligand substitution (stopped‐flow pyridine for dimethyl sulfoxide substitution). The rates of the two processes are in reasonable agreement at the same temperature, and a single Eyring plot can be constructed with the two sets of kinetics data. However, the value of the derived dissociation constant at 308 K (k₁=6.5±0.3 s^?1) is at least two orders of magnitude higher than that of cyclometalation (k_c=0.0098±0.0009 s^?1 at 308 K). Clearly, the dissociation step is not rate‐determining for cyclometalation. A multistep mechanism consistent with mass‐law retardation is derived, which involves a pre‐equilibrium that controls the concentration of an unsaturated three‐coordinate, 14‐electron T‐shaped cis‐[PtMe₂{P(o‐tol)₃}] intermediate. Cyclometalation is initiated in this latter by an agostic interaction with the σ(C? H) orbital of a methyl group. Oxidative addition of the C? H bond follows, yielding a cyclometalated‐hydrido 16‐electron Pt(IV) five‐coordinate intermediate. Finally, reductive elimination and re‐entry of dimethyl sulfoxide with liberation of methane should yield the cyclometalated species 2 .     

First‐row transition metal–pyridine (py)–sulfate [(py)xM](SO4) complexes (M = Ni,Cu and Zn): crystal field theory in action

The crystal structures of three first‐row transition metal–pyridine–sulfate complexes, namely catena‐poly[[tetrakis(pyridine‐κN)nickel(II)]‐μ‐sulfato‐κ²O:O′], [Ni(SO₄)(C₅H₅N)₄]_n, (1), di‐μ‐sulfato‐κ⁴O:O‐bis[tris(pyridine‐κN)copper(II)], [Cu₂(SO₄)₂(C₅H₅N)₆], (2), and catena‐poly[[tetrakis(pyridine‐κN)zinc(II)]‐μ‐sulfato‐κ²O:O′‐[bis(pyridine‐κN)zinc(II)]‐μ‐sulfato‐κ²O:O′], [Zn₂(SO₄)₂(C₅H₅N)₆]_n, (3), are reported. Ni compound (1) displays a polymeric crystal structure, with infinite chains of Ni^II atoms adopting an octahedral N₄O₂ coordination environment that involves four pyridine ligands and two bridging sulfate ligands. Cu compound (2) features a dimeric molecular structure, with the Cu^II atoms possessing square‐pyramidal N₃O₂ coordination environments that contain three pyridine ligands and two bridging sulfate ligands. Zn compound (3) exhibits a polymeric crystal structure of infinite chains, with two alternating zinc coordination environments, i.e. octahedral N₄O₂ coordination involving four pyridine ligands and two bridging sulfate ligands, and tetrahedral N₂O₂ coordination containing two pyridine ligands and two bridging sulfate ligands. The observed coordination environments are consistent with those predicted by crystal field theory.     

Asymmetric structure of cis‐[N‐(9‐anthracenylmethyl)‐1,2‐ethanediamine]dipyridineplatinum(II) dinitrate

Platinum antitumour agents, containing aromatic rings, which are used for targeting DNA in effective therapies for the treatment of cancer. We have synthesized the title metallocomplex with an aromatic ligand and determined its crystal structure. In many cases, complexes of platinum and other metals have a symmetrical structure. In contrast, the platinum(II) complex with pyridine and N‐(9‐anthracenylmethyl)‐1,2‐ethanediamine as ligands (systematic name: cis‐{N‐[(anthracen‐9‐yl)methyl]ethane‐1,2‐diamine‐κ²N ,N ′}bis(pyridine‐κN )platinum(II) dinitrate), [Pt(C₅H₅N)₂(C₁₇H₁₈N₂)](NO₃)₂, is asymmetric. Of the two pyridine ligands, only one is π‐stacked with anthracene, resulting in an asymmetric structure. Moreover, the angle of orientation of each pyridine ligand is variable. Further examination of the packing motif confirms an intermolecular edge‐to‐face interaction.     

Kinetics of substitution of aqua ligands from cis‐diaqua (ethylenediamine)platinum(II) perchlorate by L‐asparagine in aqueous medium

The kinetics of the interaction of L ‐asparagine with [Pt(ethylenediamine)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(ethylenediamine)(H₂O)₂²⁺], [L ‐asparagine], and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species and L ‐asparagine as the zwitterion. The substitution reaction shows two consecutive steps: the first step is the ligand‐assisted anation and the second one is the chelation step. Activation parameters for both the steps have been calculated using Eyring equation. The low ΔH₁^≠ (43.59 ± 0.96 kJ mol^?1) and large negative values of ΔS₁^≠ (?116.98 ± 2.9 J K^?1 mol^?1) as well as ΔH₂^≠ (33.78 ± 0.51 kJ mol^?1) and ΔS₂^≠ (?221.43 ± 1.57 J K^?1 mol^?1) indicate an associative mode of activation for both the aqua ligand substitution processes. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 252–259, 2003     

Neutral and cationic half‐sandwich arene d6 metal complexes containing pyridyl and pyrimidyl thiourea ligands with interesting bonding modes: Synthesis,structural and anti‐cancer studies

The reaction of [(p‐cymene)RuCl₂]₂ and [Cp*MCl₂]₂ (M = Rh/Ir) with benzoyl (2‐pyrimidyl) thiourea (L1) and benzoyl (4‐picolyl) thiourea (L2) led to the formation of cationic complexes bearing formula [(arene) M (L1)к² _(N,S) Cl]⁺ and [(arene) M (L2)к²_(N,S)Cl]⁺ [(arene) = p‐cymene, M = Ru, ( 1 , 4 ); Cp*, M = Rh ( 2 , 5 ) and Ir ( 3 , 6 )]. Precursor compounds reacted with benzoyl (6‐picolyl) thiourea (L3) affording neutral complexes having formula [(arene) M (L3)к¹_(S)Cl₂] [arene = p‐cymene, M = Ru, ( 7 ); Cp*, M = Rh ( 8 ), Ir ( 9 )]. X‐ray studies revealed that the methyl substituent attached to the pyridine ring in ligands L2 and L3 affects its coordination mode. When methyl group is at the para position of the pyridine ring (L2), the ligand coordinated metal in a bidentate chelating N, S‐ mode whereas methyl group at ortho position (L3), it coordinated in a monodentate mode. Further the anti‐cancer studies of the thiourea derivatives and its complexes carried out against HCT‐116, HT‐29 (human colorectal cancer), Mia‐PaCa‐2 (human pancreatic cancer) and ARPE‐19 (non‐cancer retinal epithelium) cell lines showed that the thiourea ligands are inactive but upon complexation, the metal compounds displayed potent and selective activity against cancer cells in vitro. Iridium complexes were found to be more potent as compared to ruthenium and rhodium complexes.     

Luminescent Amphiphilic 2,6‐Bis(1,2,3‐triazol‐4‐yl)pyridine?Platinum(II) Complexes: Synthesis,Characterization, Electrochemical,Photophysical, and Langmuir–Blodgett Film‐Formation Studies

A new series of platinum(II) complexes with tridentate ligands 2,6‐bis(1‐alkyl‐1,2,3‐triazol‐4‐yl)pyridine and 2,6‐bis(1‐aryl‐1,2,3‐triazol‐4‐yl)pyridine (N7R), [Pt(N7R)Cl]X ( 1 – 7 ) and [Pt(N7R)(C?CR′)]X ( 8 – 17 ; R=n‐C₄H₉, n‐C₈H₁₇, n‐C₁₂H₂₅, n‐C₁₄H₂₉, n‐C₁₈H₃₇, C₆H₅, and CH₂‐C₆H₅; R′=C₆H₅, C₆H₄‐CH₃‐p_, C₆H₄‐CF₃‐p, C₆H₄‐N(CH₃)₂‐p, and cholesteryl 2‐propyn‐1‐yl carbonate; X=OTf^?, PF₆^?, and Cl^?), has been synthesized and characterized. Their electrochemical and photophysical properties have also been studied. Two amphiphilic platinum(II)? 2,6‐bis(1‐dodecyl‐1,2,3‐triazol‐4‐yl)pyridine complexes ( 3‐Cl and 8 ) were found to form stable and reproducible Langmuir–Blodgett (LB) films at the air/water interface. These LB films were characterized by the study of their surface‐pressure–molecular‐area (π–A) isotherms, XRD, and IR and polarized‐IR spectroscopy.     

Polymorphism of mer‐μ‐oxalato‐bis[chloridotripyridinecobalt(II)] pyridine disolvate

Single crystals of a triclinic polymorphic form of mer‐μ‐oxalato‐bis[chloridotripyridinecobalt(II)] pyridine disolvate, [Co₂(C₂O₄)Cl₂(C₅H₅N)₆]·2C₅H₅N, have been prepared by solvothermal methods. The structure and geometric parameters strongly resemble those of the previously reported monoclinic polymorph [Bolte (2006). Acta Cryst. E 62 , m597–m598]. In both polymorphic forms, the dinuclear complex molecules are located on a crystallographic centre of inversion, with the Co^II cations in a distorted octahedral environment consisting of a chloride ligand, three pyridine ligands and a chelating bis‐bidentate oxalate ligand. This last serves as a bridging ligand between two Co^II cations. The polymorphs differ in the mutual orientation of their pyridine ligands in the dinuclear molecules and in their intermolecular connectivity. In the triclinic polymorph, C—H...O, C—H...Cl, C—H...π and π–π interactions link the dinuclear molecules into a three‐dimensional structure. Pyridine solvent molecules are attached to this structure via weak interactions.     

Kinetics and mechanism of the interaction of adenosine with cis‐diaqua(cis‐1,2‐diaminocyclohexane)platinum(II) perchlorate in aqueous medium

The kinetics of the interaction of adenosine with cis‐[Pt(cis‐dach)(OH₂)₂]²⁺ (dach = diaminocyclohexane) was studied spectrophotometrically as a function of [cis‐[Pt(cis‐dach)(OH₂)₂]²⁺], [adenosine], and temperature at a particular pH (4.0), where the substrate complex exists predominantly as the diaqua species and the ligand adenosine exists as a neutral molecule. The substitution reaction shows two consecutive steps: the first is the ligand‐assisted anation followed by a chelation step. The activation parameters for both the steps have been evaluated using Eyring equation. The low negative value of ΔH^≠₁ (43.1 ± 1.3 kJ mol^?1) and the large negative value of ΔS^≠₁ (?177 ± 4 J K^?1 mol^?1) along with ΔH^≠₂ (47.9 ± 1.8 kJ mol^?1) and ΔS^≠₂ (?181 ± 6 J K^?1 mol^?1) indicate an associative mode of activation for both the aqua ligand substitution processes. The kinetic study was substantiated by infrared and electrospray ionization mass spectroscopic analysis. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 219–229, 2011