Structural studies of metal complexes containing amide ligands

Complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Pd(II) with di-N-phenyl pyromellitic diimide (PhPMDI) and di-N-pyridyl pyromellitic diimide (PyPMDI) were prepared and characterized based on analytical, molar conductance, magnetic, IR, PMR, electronic and ESR data. Based on analytical and molar conductance, the complexes have been formulated as [M(PhPMDA)(H₂O)₂]_n (M = Mn, Fe, Co, Ni), [Cu(PhPMDA)]_n [Pd₂(PhPMDA)Cl₂(H₂O)₂], [M(PyPMDA)]_n (M = Mn, Fe, Co, Ni and Cu) and [Pd₂(PyPMDA)Cl₂] In all these complexes PhPMDA acts as a mononegative bidentate ligand whereas PyPMDA acts as a mononegative tridentate one in the form of amide rather than imide. The geometries of the complexes have been proposed based on the electronic spectra. The various bonding parameters have been calculated from the ESR spectra of Cu(II) complexes.     

Structural studies on iminophosphine ligands and their palladium complexes

The crystal and molecular structures of the iminophosphine o-(Ph₂P)C₆H₄CH=NC₆H₄OMe-4 (1) and its palladium complexes [Pd(³-C₃H₅){o-(Ph₂P)C₆H₄CH=NC₆H₄OMe-p}]BF₄ (2) and [Pd(²-fn){o-(Ph₂P)C₆H₄CH=NC₆H₄OMe-4}] [fn=fumaronitrile, (3)] have been determined by X-ray analysis. In the free ligand (1), the planar imino group of E configuration is oriented, relative to the PPh₂ unit, so that the CH=N hydrogen atom points towards phosphorus, with the nitrogen atom on the opposite side. In (2) and (3) the iminophosphine behaves as a P,N-chelate ligand, this coordination mode being achieved by the imino group rotation of 169.3° and 145.3°, respectively, around its bond with the ortho disubstituted phenyl ring. Complex (2) shows a structural disorder with two different orientations of the allyl ligand. The trigonal planar coordination around the central metal in complex (3) involves the P- and N-donor atoms of (1) and the ²-bound olefin, with a marked lengthening of the olefinic carbon-carbon bond. In both the complexes, the chelate six-membered ring of the iminophosphine with palladium is not coplanar with the N-Pd-P coordination plane, the imino carbon atom and the ortho disubstituted phenyl group lying on the same side out of the N-Pd-P plane, whereas the N-substituent and one of the PPh₂ groups are on the opposite side. The ¹H-n.m.r. spectra at low temperatures of (2) and (3), and of [Pd(²-tmetc){o-(Ph₂P)C₆H₄CH=NCMe₃}] [tmetc=tetramethyl ethylenetetracarboxylate, (4)] are interpreted on the basis of a non-rigid conformation of the chelate iminophosphine, which undergoes a fast dynamic process whereby the N- and P-substituents move above and below the coordination plane.     

Synthesis and spectral studies of copper(II) complexes with amide group ligands

Complexes of copper(II) with 2-(acetylamino)benzoic acid, 2-(benzoylamino) benzoic acid, 2-(aminocarbonyl)benzoic acid, 2-[(phenylamino)carbonyl]benzoic acid, 2-[(1-naphthalenylamino)carbonyl]benzoic acid, 2-[(2-aminophenylamino)carbonyl]benzoic acid, 2-aminobenzanilide, 2(aminobenzoyl)benzoic acid, maleanilic acid and malea-1-naphthalanilic acid have been prepared and characterized by chemical analyses, molar conductivity, magnetic susceptibility measurements, thermal data, IR, electronic and ESR spectra. The visible and ESR spectral studies of these complexes (except those of maleanilic acid and malea-1-naphthalanilic acid) indicate that they are monomeric having either square planar or distorted octahedral geometry around Cu(II). The Cu(II) complexes of maleanilic acid and malea-1-naphthalanilic acid have been tentatively assigned dimeric structures. From the ESR spectra of Cu(II) complexes various parameters have been calculated.     

Structural and catalytic studies of zinc complexes containing amido-oxazolinate ligands

Several zinc complexes bearing amido-oxazolinate ligands are described. Reactions of ligand precursors, HNC(2)(E)Oxa (HNC(2)(E)Oxa = HNC(2)(Me)Oxa, HNC(2)(OMe)Oxa, HNC(2)(StBu)Oxa and HNC(2)(NMe2)Oxa) or HNPh(SMe)Oxa, with half or one molar equivalent of ZnEt(2) afford bis(chelate) zinc complexes, (NC(2)(E)Oxa)(2)Zn [C(2)(E) = propyl, (1); C(2)(E) = 2-methoxyethyl, (2); C(2)(E) = 2-N,N'-dimethylethyl, (3)] or zinc ethyl complexes, (NC(2)(StBu)Oxa)ZnEt(4) and (NPh(SMe)Oxa)ZnEt(5), using tetrahydrofuran or hexane as solvents. The zinc benzyl oxide complexes, [(NC(2)(E)Oxa)Zn(μ-OBn)](2) [C(2)(E) = propyl, (6); C(2)(E) = 2-methoxyethyl, (7); C(2)(E) = 2-tert-butylthioethyl, (8)], are obtained from the reactions of ligand precursors, HNC(2)(E)Oxa, with one molar equivalent of ZnEt(OBn) (generated in situ on 1:1 ratio of ZnEt(2) and BnOH) in tetrahydrofuran. The molecular structures are reported for compounds 1, 3, 5, 6 and 7. All eight compounds were assessed as efficient catalyst precursors towards the ring-opening polymerization of L-lactide and ε-caprolactone.     

Luminescent palladium complexes containing thioamide-based SCS pincer ligands

Thioamide-based tridentate ligands, 1,3-benzenedicarbothioamides (1a-c), were used to afford pincer palladium(II) complexes (Pd(1-H)Cl, 2a-c) with η³-S,C,S type coordination. The complexes exhibit strong emission in a glassy frozen state as well as in the solid state. The decay lifetime of the emission from the complexes is in a range of 8-9 × 10⁻⁵ s, which is indicative of phosphorescent emission.     

Crystallographic and spectroscopic studies on palladium(II) complexes containing pyrazole and thiocyanate ligands

Mononuclear palladium(II) complexes containing both pyrazole-type ligands and thiocyanate, of general formula [Pd(SCN)₂(L)₂] {L = pyrazole (HPz) and 1-phenyl-3-methylpyrazole (phmPz)} have been prepared and characterized by elemental analysis, i.r. and n.m.r. spectroscopy and by single crystal X-ray diffraction methods. The Pd atom in these structures lies on the crystallographic inversion center; in a square-planar coordination geometry made by two sulfur and two nitrogen atoms of the ligands, both in trans positions.     

Synthesis and antimicrobial studies of half-sandwich arene platinum group complexes containing pyridylpyrazolyl ligands

The reaction of [(arene)MCl₂]₂ with pyridylpyrazolyl ligands (L1 and L2) in the presence of ammonium hexafluorophosphate leads to formation of cationic complexes having the general formula [(arene)M(L)Cl]PF₆ {M?=?Ru, arene = p-cymene (1, 4); Cp*, M?=?Rh (2, 5); Cp*, M?=?Ir (3, 6); L?=?2-(1H-pyrazol-1-yl)pyridine (L1), 2-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine (L2)}. Similarly the reaction of [CpRu(PPh₃)₂Cl] and [(ind)Ru(PPh₃)₂Cl] (ind?=?η⁵-C₉H₇) with L1 and L2 yielded cationic complexes which have been formulated as [(Cp/ind)Ru(L)PPh₃]PF₆ (7–10). All these complexes were characterized by analytical and spectroscopic techniques. The pyridylpyrazolyl ligands coordinated metal through pyridyl and pyrazolyl nitrogens forming a six-membered metallacycle. The ligands as well as the complexes were evaluated for their in vitro antibacterial activity by agar well diffusion method against two Gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and two Gram positive bacteria (Staphylococcus aureus and Bacillus thuriengiensis). Results show that the ligands and the complexes have significant antibacterial activity against Gram negative bacteria.     

From mononuclear to multinuclear complexes of palladium containing unsaturated hydrocarbon ligands

This review summarizes the author’s contributions to the field of chemistry of group 10 metal complexes containing unsaturated hydrocarbon ligands, with a brief introduction showing how his research subject has shifted from mononuclear type to multinuclear type complexes. New structure and reactivity trends in the multipalladium complexes with bridging allyl and allenyl/propargyl ligands, as well as bridging conjugated polyene molecules are discussed in terms of some unique bonding features of these complexes.     

Anionic carbonyl complexes of the group VI transition metals with sulfur containing ligands

Anionic complexes of the type [M(CO)₄(dpet)]^? (where M is Cr, Mo or W and dpet is the anion of 2-(diphenylphosphino)ethanthiol) are readily prepared by the reaction of the Tl(dpet) and [M(CO)₅X]^? anions (X = halogen). These complex anions appear to have the normal octahedral geometry with the dpet ligand coordinated through both the P and S atoms. When treated with methyl or allyl halides, neutral complexes of the type M(CO)₄(dpet—R) are formed (where R is an allyl or methyl group now bound to the sulfur atom). By treating Tl^I salts of o-aminothiophenol (atp), o-methylmercaptophenol (nmp) and methylxanthic acid (mxt), with [M(CO)₅]^? anions, the respective complexes [M(CO)₄(atp)]^?, [M(CO)₄(mmp)]^? and [M(CO)₅(mxt)]^? are formed.     

Synthesis and spectral studies of platinum complexes with amide-group containing ligands

Summary Complexes of platinum(II) with 2-(acetylamino)benzoic acid, 2-(benzoylamino)benzoic acid, maleanilic acid, malea-1-naphthanilic acid, 2-(phenylamino)benzoic acid, 2-[(2-aminophenylamino)carbonyl]benzoic acid, 2-(aminobenzoyl)benzoic acid, 2-[1-naphthalenylamino)-carbonyl]benzoic acid, 2-(2-aminobenzoylamino)-benzoic acid have been prepared and characterized by elemental analysis, molar conductivity measurements, thermal data and i.r., electronic and n.m.r. spectra.     

Solution studies of some technetium complexes containing sulfur ligands

Interactions between technetium and the following series of sulfur ligands are described: 2,5-dimercapto-1,3,4-thiadiazole, 1-methylimidazol-2-thiol, 6,6-dithiodinicotinic acid, 2-amino-6-mercaptopurine and DL--amino-2-thiopheneacetic acid. The complexation reactions have been investigated (species formed,e, stoichiometry, etc.) and the results obtained have been comparatively evaluated with the aim to find relations between structure of the ligands and its complexing activity.     

Structural and electrochemical studies on trithia macrocyclic complexes of palladium

The single crystal X-ray structure of [Pd(1)₂](PF₆)₂ (1 = 1,4,7-trithiacyclononane) shows a crystallographically centrosymmetric cation with a distorted octahedral stereochemistry about the Pd^II centre with PdS_eq 2.332(3) and 2.311(3) Å for the equatorial thia donors, and PdS_ax 2.952(4) Å for the two apically coordinated donors. The crystals have space group C2/C, with a 17.879(8), b 15.627(13), c 11.476(8) Å, β 125.92(4)° and Z = 4. Least squares refinement gave R = 0.0565 for 1153 unique observed reflections measured by counter diffracometry using Mo-K_α radiation. This green complex undergoes a chemically reversible, one-electron oxidation in CH₃CN, E_pa = +0.65V, E_pc = +0.56 V vs. Fc/Fc⁺, ΔE_p = 84 mV. Oxidation of [Pd(1)₂](PF₆)₂ by controlled potential electrolysis at +0.7 V affords an orange, ESR active product which may be tentatively assigned to the corresponding palladium(III) species. These results are contrasted with data for the related homoleptic thia complexes [Pd(L)]²⁺ (L = 1,4,8,11-tetrathiacyclotetradecane (2), 1,4,7,10,13,16-hexathiacyclooctadecane (3)). The syntheses of the complexes cis-[Pd(1)Cl₂], cis-[Pt(1)Cl₂], cis-[Pd(1)(PPh₃)₂](PF₆)₂ and cis-[Pt(1)(PPh₃)₂](PF₆)₂ are also described.     

Thermal studies on some group VIII complexes with biologically active ligands

The mode of decomposition of complexes involving biologically important ligands such as thiouracil and xanthine coordinated to some group VIII metals has been studies by thermogravimetry. The results show that the complex tris-(dithiouracil) trichlororhodium(III) is monomeric and not polymeric as suggested previously. The decomposition behavior of the complex indicates that after the initial loss of a ligand molecule to form a four-coordinate complex, further ligand removal takes place in one sharp step. In the case of the complexes bis-(3-methylxanthine) diammineplatinum(II) and bis-(9-methylxanthine) diamminepalladium(II), ammonia comes off first, followed by rapid loss of the remaining xanthine ligands. Moreover, the activation energy determined for the main decomposition step suggests that the breakdown of the xanthine ligand involves the initial cleavage of the pyrimidine moiety, followed closely by loss of the remaining imidazole portion.

---

Zusammenfassung Die Art der Zersetzung von Komplexen einiger Metalle der VIII. Gruppe mit biologisch wichtigen Liganden, wie Thiouracil and Xanthin, wurde thermogravimetrisch untersucht. Die Ergebnisse zeigen, daß der Komplex Tris-(dithiouracil) trichlororhodium(III) monomer und nicht — wie früher vermutet — polymer ist. Das Zersetzungsverhalten des Komplexes zeigt, daß nach dem zu einem tetrakoordinierten Komplex führenden Verlust eines Ligandmoleküls die Abgabe eines weiteren Liganden in einem scharfen Schritt erfolgt. Im Falle der Komplexe Bis-(3-methylxanthin) diamminplatin(II) und Bis-(9-methylxanthin) diamminpalladium(II) erfolgt zunächst eine Abspaltung von Ammoniak, der ein schneller Verlust der verbleibenden Xanthinliganden folgt. Die für die Hauptzersetzungsreaktion bestimmte Aktivierungsenergie läßt vermuten, daß der Abbau der Xanthinliganden über eine Spaltung des Pyrimidinteils verläuft, der schnell die Abgabe des verbleibenden Imidazolteils folgt.

---

, , VIII . , -() (III) , , . - , . - (3-) (II) -(9 -) - (II) -(II) , . , , , , .

     

Aggregation studies of complexes containing a chiral lithium amide and n-Butyllithium

A system consisting of a chiral lithium amide and n-BuLi in tol-d(8) solution was investigated with (1)H and (13)C INEPT DOSY, (6)Li and (15)N NMR, and other 2D NMR techniques. A mixed 2:1 trimeric complex was identified as the major species as the stoichiometry approached 1.5 equiv of n-BuLi to 1 equiv of amine compound. (1)H and (13)C INEPT DOSY spectra confirmed this lithium aggregate in the solution. The formula weight of the aggregate, correlated with diffusion coefficients of internal references, indicated the aggregation number of this complex. Plots of log D(rel) vs log FW are linear (r > 0.9900). (6)Li and (15)N NMR titration experiments also corroborated these results. These NMR experiments indicate that this mixed aggregate is the species that is responsible for asymmetric addition of n-BuLi to aldehydes.     

Structural analysis of chiral complexes of palladium(0) with 15-membered triolefinic macrocyclic ligands

The complete structural analysis of the palladium complexes of the triolefinic macrocycles (E,E,E)-1,6,11-tris(arylsulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-trienes, which featured from three identical to three different aryl groups, was achieved by performing X-ray diffraction studies, NMR spectroscopy, and other calculations. The stereochemical complexity is determined by the different isomers formed through complexation of the metal to one or other face of each of the three olefins involved. The palladacyclopropane formulation of the palladium-olefin interaction offers a clear picture of the stereogenicity of the olefin carbon atoms that are complexed to the metal. The energetically favorable isomers were identified in the solid-state and in solution by performing X-ray diffraction and NMR spectroscopic analysis, respectively.     

Spectroscopic,structure and DFT studies of palladium(II) complexes with pyridine-type ligands

Five palladium(II) complexes with pyridine derivative ligands have been synthesized. The molecular structures of the complexes were determined by X-ray crystallography, and their spectroscopic properties were studied. Based on the crystal structures, computational investigations were carried out in order to determine the electronic structures of the complexes. The electronic spectra were calculated with the use of time-dependent DFT methods, and the electronic spectra of the transitions were correlated with the molecular orbitals of the complexes. The emission properties of the complexes have been examined.     

New palladium(II) complexes with pyrazole ligands

The pyrazole ligand 3,5-dimethyl-4-iodopyrazole (HdmIPz) has been used to obtain a series of palladium(II) complexes (1–4) of the type [PdX₂(HdmIPz)₂] {X = Cl⁻ (1); Br⁻ (2); I⁻ (3); SCN⁻ (4)}. All compounds have been isolated, purified, and characterized by means of elemental analysis, IR spectroscopy, ¹H and ¹³C{¹H}-NMR experiments, differential thermal analysis (DTA), and thermogravimetry (TG). The TG/DTA curves showed that the compounds released ligands in the temperature range 137–605 °C, yielding metallic palladium as final residue. The complexes and the ligand together with cisplatin have been tested in vitro by MTT assay for their cytotoxicity against two murine cancer cell lines: mammary adenocarcinoma (LM3) and lung adenocarcinoma (LP07).     

Diastereoselective cyclocarbonylation of isopulegol by palladium(II) complexes containing no chiral ligands

The cyclocarbonylation of isopulegol catalyzed by palladium(II) complexes containing no chiral ligands produces the two compounds (1R,5R or 5S,6S,9R)-5,9-dimethyl-2-oxabicyclo[4.4.0]decan-3-one with a diastereoisomeric excess up to 60%. X-Ray diffraction of the 5S stereoisomer, ¹H and ¹³C NMR, and NOE measurements have allowed complete characterization of the two diastereoisomers. These results gave more details about the mechanism of cyclocarbonylation, and particularly the role of the OH group in the substrate.