Dinuclear palladium-azido complexes containing thiophene derivatives: reactivity toward organic isocyanides and isothiocyanates

Cyclopalladated tetranuclear Pd(II) complexes, [Pd2(micro-Cl)2(Y)]2 (Y = L1 or L2; H2L1 = di(2-pyridyl)-2,2'-bithiophene; H2L2 = 5,5'-di(2-pyridyl)-2,2':5',2'-terthiophene), containing two pyridyl-alpha, alpha'-disubstituted derivatives of thiophene were prepared. Treating these products with PR3 and subsequently with NaN3 produced the dinuclear Pd-azido complexes [(PR3)2(N3)Pd-Y-Pd(N3)(PR3)2] (Y = L1 or L2) or a cyclometallated complex [(PR3)(N3)Pd-Y'-Pd(N3)(PR3)] (Y' = C,N-L2). Reactions of these Pd-azido complexes with CN-Ar (Ar = 2,6-Me(2)C(6)H(3), 2,6-i-Pr(2)C(6)H(3)) or R-NCS (R = i-Pr, Et, allyl) led to the complexes containing end-on carbodiimido groups [(PMe3)2(N[double bond]C[double bond]N-Ar)Pd-Y-Pd(N[double bond]C[double bond]N-Ar)(PMe3)2] or S-coordinated tetrazole-thiolato groups {(PMe3)2[CN4(R)]S-Pd-Y-Pd-S[CN4)(R)](PMe3)2}. Interestingly, when treated with elemental sulfur, the carbodiimido complexes transformed into the cyclometallated derivatives, [(PMe3)(N[double bond]C[double bond]N-Ar)Pd-Y'-Pd(N[double bond]C[double bond]N-Ar)(PMe3)] (Y' = C,N-L1, C,N-L2). We also report the preparation of linear, thienylene-bridged dinuclear Pd complexes [L2(N3)Pd-X(or X')-Pd(N3)L2] (L = PMe3 or PMe2Ph; H2X = 2,2'-bithiophene or H2X' = 2,2':5',2'-terthiophene) and their reactivity toward organic isocyanide and isothiocyanates.     

Bis(isothiocyanato)bis(phosphine) complexes of group 10 metals: reactivity toward organic isocyanides

Treatment of Ni(NCS)2(PMe2Ph)2 with organic isocyanides CN-R gave five-coordinate isocyanide Ni(II) complexes, Ni(CN-R)(NCS)2(PMe2Ph)2 (R = C6H3-2,6-Me2 (1), t-Bu (2)). Interestingly, the corresponding reaction of Ni(NCS)2(P(n-Pr)3)2 with 2 equiv. of CN-t-Bu gave an unusual compound, which exists as an ion pair of the trigonal bipyramidal cation [Ni(P(n-Pr)3)2(CN-t-Bu)3]2+ (3) and the dinuclear NCS-bridged anion [Ni(1,3-micro-NCS)(NCS)3]2(2-) (4). In contrast, Pd(NCS)2(P(n-Pr)3)2 underwent substitution with 2 equiv. of CN-t-Bu to give the four-coordinate mono(isocyanide) Pd(II) complex Pd(NCS)(SCN)(CN-t-Bu)(P(n-Pr)3) (5) via phosphine dissociation. Reactions of M(NCS)2L2 (M = Pd, Pt; L = PMe3, PEt3, PMePh2, P(n-Pr)3) with two equiv. of CN-R (R = t-Bu, i-Pr, C6H3-2,6-Me2) gave the corresponding bis(isocyanide) complexes [M(CN-R)2(PR3)2](SCN)2 (7-13), except for Pd(NCS)2(PEt3)2 that reacted with CN-R' (R' = i-Pr, C6H3-2,6-Me2) and produced the mono(isocyanide) Pd(II) complexes [Pd(CN-R')(SCN)(PEt3)2](SCN) (14 and 15). Finally, treatment of M(NCS)2(PMe3)2 (M = Ni, Pd, Pt) with sterically bulky isocyanide CN-C6H3-2,6-i-Pr2 gave various products, (16-18) depending on the identity of the metal.     

Cyclometallated Pt(II) and Pd(II) complexes with a trithiacrown ligand

We report the synthesis and full characterization for a series of cyclometallated complexes of Pt(II) and Pd(II) incorporating the fluxional trithiacrown ligand 1,4,7-trithiacyclononane ([9]aneS3). Reaction of [M(C insertion mark N)(micro-Cl)]2 (M = Pt(II), Pd(II); C insertion mark N = 2-phenylpyridinate (ppy) or 7,8-benzoquinolinate (bzq)) with [9]aneS3 followed by metathesis with NH4PF6 yields [M(C insertion mark N)([9]aneS3)](PF6). The complexes [M(C insertion mark P)([9]aneS3)](PF6) (M = Pt(II), Pd(II); Cinsertion markP = [CH2C6H4P(o-tolyl)2-C,P]-) were synthesized from their respective [Pt(C insertion mark P)(micro-Cl)]2 or [Pd(C insertion mark P)(micro-O2CCH3)]2 (C insertion mark P) starting materials. All five new complexes have been fully characterized by multinuclear NMR, IR and UV-Vis spectroscopies in addition to elemental analysis, cyclic voltammetry, and single-crystal structural determinations. As expected, the coordinated [9]aneS3 ligand shows fluxional behavior in its NMR spectra, resulting in a single 13C NMR resonance despite the asymmetric coordination environment of the cyclometallating ligand. Electrochemical studies reveal irreversible one-electron metal-centered oxidations for all Pt(II) complexes, but unusual two-electron reversible oxidations for the Pd(II) complexes of ppy and bzq. The X-ray crystal structures of each complex indicate an axial M-S interaction formed by the endodentate conformation of the [9]aneS3 ligand. The structure of [Pd(bzq)([9]aneS3)](PF6) exhibits disorder in the [9]aneS3 conformation indicating a rare exodentate conformation as the major contributor in the solid-state structure. DFT calculations on [Pt([9]aneS3)(ppy)](PF6) and [Pd([9]aneS3)(ppy)](PF6) indicate the HOMO for both complexes is primarily dz2 in character with a significant contribution from the phenyl ring of the ppy ligand and p orbital of the axial sulfur donor. In contrast, the calculated LUMO is primarily ppy pi* in character for [Pt([9]aneS3)(ppy)](PF6), but dx2-y2 in character for [Pd([9]aneS3)(ppy)](PF6).     

Cyclometallated derivatives of palladium(II) and platinum(II) derived from 6-t-butyl-2,2′-bipyridine

The synthesis of the cyclometallated derivatives [PdLCl] and [PtLCl](HL = 6-t-butyl-2,2′-bipyridine) is reported. The deprotonated bipyridine is terdentate through the two nitrogen atoms and a carbon atom of the t-butyl substituent. The new complexes were characterized by ¹H and ¹³C NMR and FAB-MS spectra.     

Controlling the helicity of 2,2'-bipyridyl ruthenium(II) and zinc(II) hemicage complexes

Two enantiomers of a new 4,5-pineno-2,2'-bipyridine ligand were synthesized and subsequently incorporated into hemicage ligands through a phenyl linker to yield ligands (+)-L1 and (-)-L1 or through a mesityl linker to yield ligands (+)-L2 and (-)-L2. Complexation of these ligands to Ru(II) afforded diastereomerically pure Delta and Lambda isomers, as verified through circular dichroism and circularly polarized luminescence spectroscopy. Ligands (+)-L2 and (-)-L2 were further coordinated to Zn(II) to form a complex with intriguing photophysical properties. Whereas Zn(bpy)32+ was shown to be a fluorescent emitter outside the visible spectrum, the caging process provided an unprecedented enhancement of intersystem crossing and subsequent switching to the phosphorescent emission of blue light. Additionally, the chiroptical properties of the Zn(II) complexes were also studied.     

Pd(II) and Pt(II) complexes of 2-(2'-pyridyl)-4,6-diphenylphosphinine: synthesis, structure, and reactivity

The coordination chemistry of the bidentate P,N hybrid ligand 2-(2'-pyridyl)-4,6-diphenylphosphinine (1) towards Pd(II) and Pt(II) has been investigated. The molecular structures of the complexes [PdCl(2)(1)] and [PtCl(2)(1)] were determined by X-ray diffraction, representing the first crystallographically characterized λ(3)-phosphinine-Pd(II) and -Pt(II) complexes. Both complexes reacted with methanol at the P=C double bond at an elevated temperature, leading to the corresponding products [MCl(2)(1H·OCH(3))]. The molecular structure of [PdCl(2)(1H·OCH(3))] was determined crystallographically and revealed that the reaction with methanol proceeds selectively by syn addition and exclusively to one of the P=C double bonds. Strikingly, the reaction of [PdCl(2)(1H·OCH(3))] with the chelating diphosphine DPEphos at room temperature in CH(2)Cl(2) led quantitatively to [PdCl(2)(DPEphos)] and phosphinine 1 by elimination of CH(3)OH and rearomatization of the phosphorus heterocycle.     

Electrochemical studies on mixed-ligand iron(II) complexes containing isocyanides and phosphines

Voltammetry at a stationary platinum electrode and polarography were carried out in dichloromethane (0.1 mol dm^?3 tetrabutylammonium perchlorate as supporting electrolyte) for complexes of the type [FeX(CNR)₂L₃][ClO₄] [X = Cl, Br or I; L = PPh(OEt)₂; R = phenyl, 4-methylphenyl, 4-methoxyphenyl, 2-methylphenyl or 2,6-dimethylphenyl] and for [Fe(CNR)₃L₃][ClO₄]₂ [L = PPh(OEt)₂; R = cyclohexyl]. A mechanism of the redox process for both oxidation and reduction is postulated. A simple redox change without any complication from chemical reaction occurs in the case of oxidation at a platinum elec$\text{t}$rode, whereas the reduction is complicated by a subsequent chemical reaction.     

Complexes of Cu(II) with 2,2'-bipyridyl and maleic or phthalic acid

The stability constants of ternary copper(II) complexes with 2,2'-bipyridyl and a dicarboxylic acid (maleic and phthalic) have been determined by means of pH-titrations at 25 +/- 0.1 degrees and an ionic strength of 0.1M (Na,H)ClO(4). The stabilities of ternary complexes are compared with those of similar complexes and related to the size of the chelate rings and the nature of the dicarboxylic ligands.     

Luminescent cyclometalated alkynylgold(III) complexes with 6-phenyl-2,2'-bipyridine derivatives: synthesis, characterization, electrochemistry, photophysics, and computational studies

A novel class of luminescent gold(III) complexes containing various tridentate cyclometalating ligands derived from 6-phenyl-2,2'-bipyridine and alkynyl ligands, [Au(RC^N^N)(C≡C-R')]PF(6), has been successfully synthesized and characterized. One of the complexes has also been determined by X-ray crystallography. Electrochemical studies show a ligand-centered reduction originated from the cyclometalating RC^N^N ligands as well as an alkynyl-centered oxidation. The electronic absorption and photoluminescence properties of the complexes have also been investigated. In acetonitrile at room temperature, the complexes show intense absorption at higher energy region with wavelength shorter than 320 nm, and a moderately intense broad absorption band at 374-406 nm, assigned as the metal-perturbed intraligand π-π* transition of the cyclometalating RC(∧)N(∧)N ligand, with some charge transfer character from the aryl ring to the bipyridine moiety. Most of the complexes have been observed to show vibronic-structured emission bands at 469-550 nm in butyronitile glass at 77 K, assigned to an intraligand excited state of the RC^N^N ligand, with some charge transfer character from the aryl to the bipyridyine moiety. Insights into the origin of the absorption and emission have also been provided by density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations.     

A quantum chemical study on the mechanism of S-coordinated tetrazole-thiolato formation by the reaction of organic isothiocyanates with metal azido complexes of Pt(II), Pd(II), and Sn

The mechanism of the reaction of isothiocyanates with metal-azido complexes of Pt(II), Pd(II), and Sn as well as hydrazoic acid is studied using the density functional theory method. The relative stability between two possible product isomers (S-coordinated tetrazole-thiolato and N-coordinated tetrazolato complexes) does not directly relate to the experimentally synthesized product. The overall reaction proceeds via three steps. The first step is the approach of the S-atom of the organic isothiocyanate to the central metal atom followed by the nucleophilic attack of the coordinated N-atom of the azido group to the C-atom of the isothiocyanate. The activation barrier of this step is 22-24 kcal mol⁻¹, and the resulting intermediate has the imidoyl azide form. In the second reaction step, electrophilic attack of the terminal N-atom of the azido group to the N-atom of the isothiocyanate transforms the intermediate to the S-coordinated tetrazole-thiolato product with a barrier of about 11 kcal mol⁻¹. The N-coordinated tetrazole could be made from the S-coordinated tetrazole-thiolato complex only after the third step, in which the metal coordination migrates from the S- to the N-atom.     

(2,2':6',2' '-Terpyridine)platinum(II) complexes containing (thioalkyl)dicarba-closo-dodecaborane(12) ligands

A series of novel platinum(II)-2,2':6',2' '-terpyridine (trpy) complexes containing (thioalkyl)dicarba-closo-dodecaborane(12) (closo-carborane) derivatives were prepared by treatment of the labile precursor species [Pt(MeCN)(trpy)](OTf)2 with R(CH2)nSH (R = closo-1,2-carborane, n = 0-3; R = closo-1,7-carborane, n = 1; R = closo-1,12-carborane, n = 1) in the presence of NEt3 to afford brightly colored complexes of the type [PtS(CH2)nR(trpy)]OTf. All products were characterized by means of multinuclear (1H, 13C, 11B, and 195Pt) 1D- and 2D-NMR spectroscopy, ESI-MS, and, for the 1,7-carborane derivative, X-ray crystallography. Preliminary in vitro cytotoxicity studies of selected complexes against human ovarian carcinoma cells are also reported.     

Cyclometallated Ni(II) and Pd(II) Complexes of the Azomethine Compounds: Synthesis and Structures

Russian Journal of Coordination Chemistry - New Ni(II) and Pd(II) complexes (Ia and Ib) are synthesized on the basis of the azomethine compound...     

Luminescent mononuclear and binuclear cyclometalated palladium(II) complexes of 6-phenyl-2,2 bipyridines: spectroscopic and structural comparisons with platinum(II) analogues

The mononuclear cyclometalated Pd(II) complexes [Pd(L1)X] (HL1 = 6-phenyl-2,2'-bipyridine; X = Cl, la; Br, 1b; I, 1c), [Pd(L1)PPh3]+ (1d), [Pd(L2-5)Cl] [2a-5a, HL2-5 = 4-(aryl)-6-phenyl-2,2'-bipyridine; aryl = phenyl (2), 4-chlorophenyl (3), 4-tolyl (4), 4-methoxyphenyl (5)] and the binuclear derivatives [Pd2(L1-5)2(mu-dppm)]2+ (1e-5e, dppm = bis(diphenylphosphino)methane) and [Pd2(L1)2(mu-dppCs)]2+, (1f, dppC5 = 1,5-bis(diphenylphosphino)pentane) were prepared. The crystal structures of 1d(ClO4), 1e(ClO4)2 x DMF, and 2e(ClO4)2 have been determined by X-ray crystallography. The magnitude of the Pd-Pd distances in le and 2e (3.230(1) and 3.320(2) A, respectively) suggest minimal metal-metal interaction, although pi-stacking of the aromatic ligands (interplanar separations 3.34 and 3.35 A, respectively) is evident. All complexes display low-energy UV absorptions at lambda approximately 390 nm, which are tentatively assigned to 1MLCT transitions; red shifts resulting from Pd-Pd interactions in the binuclear species are not apparent. The complexes in this work are non-emissive at 298 K, but the cationic derivatives exhibit intense luminescence at 77 K. The structured emissions of 1d and 1f in MeOH/EtOH glass (lambdamax 467-586 nm) and all cationic species in the solid state (lambdamax 493-578 nm) are assigned to intraligand excited states. Complexes le-5e display dual emissions in MeOH/EtOH glass at 77 K, and the broad structureless bands at lambdamax 626-658 nm are attributed to pi-pi excimeric IL transitions. A comparison between the photophysical properties of Pd(II) and Pt(II) congeners is presented.     

Palladium(II) and platinum(II) dichloro complexes containing diamine-estrone derivatives

The preparation ofcis-dichloro Pt(II) andcis-dichloro Pd(II) complexes ofN-[3-hydroxyestra 1:3:5 (10)trien-17β]ethylendiamine,N-[3-hydroxyestra 1:3:5 (10)trien-17β]1,3-propylendiamine, andN-[3-hydroxyestra 1:3:5 (10)trien-17β]2-aminomethylpyridine is reported. The complexes have been characterized by chemical analysis, infrared spectroscopy and molar conductivity.     

Pd(II) and Au(III) complexes of some 4-glycopyranosylamino-5-nitroso-6-oxo-pyrimidine derivatives

Six Pd(II) and Au(III) complexes of 4-glycopyranosylamino-5-nitroso-6-oxo-pyrimidine derivatives were prepared. On the basis of their¹H-NMR and IR spectra, it has been found that the coordination sites are the 5-nitroso and the 6-oxo substituents. Likewise, the thermal behaviour of the complexes has also been studied.

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Komplexe des Pd(II) und Au(III) mit einigen Derivaten des 4-Glycopyranosylamino-5-nitroso-6-oxo-pyrimidins

Zusammenfassung Sechs Pd(II)- und Au(III)-Komplexe mit 4-Glycopyranosylamino-5-nitroso-6-oxo-pyrimidin-Derivaten wurden hergestellt. Auf der Basis ihrer¹H-NMR und IR-Spektren wurde herausgefunden, daß die Substituenten 5-nitroso und 6-oxo die Koordinationsstellen sind. Das thermische Verhalten der Komplexe wurde ebenfalls untersucht.

     

Mixed complexes of Ni(2+) or Zn(2+) and citric acid with 2,2'-bipyridyl in aqueous solution

The stability constants of ternary Ni(2+) or Zn(2+) complexes with 2,2'-bipyridyl and citric acid have been determined by means of pH-titrations at 25.0 +/- 0.2 degrees and an ionic strength of 0.1M (KNO(3)). The stability constants of ternary complexes have been compared with those of similar ternary species.     

Substituent effects in homoleptic iron(II) and ruthenium(II) complexes of 4′-hydrazone derivatives of 2,2′:6′,2″-terpyridine

The synthesis and characterization of eight homoleptic iron(II) and ruthenium(II) complexes containing 4′-hydrazone-substituted 2,2′:6′,2″-terpyridine ligands are described. ¹H NMR spectroscopic data illustrate that the coordinated ligands undergo facile rotation about the C_pyridine–N_hydrazone bond when the N atom is methylated, and hindered bond rotation when the hydrazone NH unit is available for hydrogen bonding to solvent molecules. Detailed structural studies illustrate how the flexibility of the backbone of the complexes leads to significant variation in packing. Throughout the series of solid structures, the packing is dictated by a combination of face-to-face aromatic π-stacking, edge-to-face aromatic interactions and classical and non-classical hydrogen bonding.     

New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties

The reaction of AMTT (AMTT = 4-amino-3-methyl-1,2,4-triazol-5-thione, HL1) with palladium(II) chloride and triphenylphosphane as a co-ligand in acetonitrile afforded the mononuclear Pd^II-complex [(PPh₃)Pd(HL1)Cl]Cl·2CH₃CN (1). The complex [(PPh₃)Pd(HL1)I]Cl·1/2H₂O (2) was prepared via halogen exchange between 1 and sodium iodide in methanol/acetonitrile. The first binuclear palladium(II) complex containing singly deprotonated HL1, [(PPh₃)₂ClPd(L1)Pd(PPh₃)Cl]Cl·1/3H₂O·CH₃OH (3), was prepared by the reaction of HL1 with palladium(II) chloride and triphenylphosphane in the presence of sodium acetate in methanol.     

Thermal studies on Ni(II), Cu(II) and Pd(II) complexes of 6-amino-5-formyluracil and its N-methyl derivatives

The thermal behaviour of 6-amino-5-formyluracil (HFU), 6-amino-1-methyl-5-formyluracil (1-MFU), 6-amino-3-methyl-5-formyluracil (3-HFU) and 6-amino-1,3-dimethyl-5-formyluracil (HDFU) is described. Only HDFU is shown to contain crystallization water. Dehydration and fusion enthalpy values have been calculated from the DSC curves. Likewise, the thermal behaviour of new complexes obtained by reaction between the above pyrimidine derivatives and Ni(II), Cu(II) and Pd(II) ions is reported.