Novel carboplatin analogs containing flexible and potentially intercalating ligands: preparation and X-ray crystal structures of di-2-pyridyl ketone cyclobutanedicarboxylate platinum(II) and of 2,3-bis(2-pyridyl)pyrazine cyclobutane dicarboxylate platinum(II)

Palladium(II) and Platinum(II) Mononuclear Complexes and Tendency to Undergo Dehydrogenation of the Multiple N-Donor Ligand Di-(2-pyridyl)dihydropyrazine

The already known di(2-pyridyl)dihydropyrazine (dhdpp) was prepared and isolated also in the form of a bis-hydrated species, i.e., dhdpp·2H₂O. As established by X-ray work, a small amount of single crystals of di(2-pyridyl)-pyrazine (dpp) was also obtained from the mother liquors, this testifying the possibility of a dehydrogenation process dhdpp → dpp in the absence of a catalyst. Using dhdpp as a ligand, mononuclear metal derivatives of formula [(dhdpp)MCl₂]·xH₂O (M = Pd^II, Pt^II) were obtained as stable-to-air solids, studied by X-ray powder, IR, UV-visible, and ¹H NMR spectra, and proved to exhibit a N₂MCl₂ coordination site involving one pyridine and one pyrazine N atom ("py-pyz" coordination). An interesting relationship has been established in terms of the observed types of coordination with the analogs of di(2-pyridyl)-pyrazine (dpp) formulated as [(dpp)MCl₂]·3H₂O, proved also by ¹H NMR spectra to exhibit the "py-pyz" mode of coordination. Attempts to isolate from the reaction of dhdpp with Pd(OAc)₂ the corresponding mononuclear derivatives were shown to lead, as definitely supported by ¹H NMR spectral data and crystallographic work, to the exclusive formation of the corresponding dpp complex [(dpp)Pd(OAc)₂]·5H₂O ("py-pyz" coordination site), this proving the tendency of dhdpp to generate dpp under different reaction conditions. The promoted conversion of dhdpp into dpp in the complex was examined by sequential NMR analysis and established to be determined by Pd(OAc)₂ which plays the role of catalyst. The new salt-like species [(CH₃)(dhdpp)PdI₂](I)·7H₂O, prepared starting from [(dhdpp)PdCl₂] in its reaction with CH₃I, allowed the separation from the mother liquors of small brown crystals identified on the basis of X-ray analysis as the already known complex of formula [(dpp)PdI₂] ("py-py" coordination), this result once again outlining the tendency of dhdpp to be dehydrogenated to dpp.

Oxidation of dimethylplatinum(II) complexes with malonyl peroxide derivatives

The reaction of the cyclic peroxides cyclobutane malonoyl peroxide and cyclopentane malonoyl peroxide to dimethylplatinum(II) complexes with the bidentate nitrogen donor ligand 4,4′-di-t-butyl-2,2′-bipyridine (bubpy) gave a mixture of the products of cis and trans oxidative addition, [PtMe2{(O2C)2C(C3H6)}(bubpy)] and [PtMe2{(O2C)2C(C4H8)}(bubpy)], respectively. The cis isomers exist with a chelating dicarboxylate ligand, forming a six-membered ring, while the trans isomers are thought to exist as oligomers, which may react with water or solvent to give complexes containing a monodentate dicarboxylate ligand. Equilibration of the product of cis oxidative addition, cis-[PtMe2{(O2C)2C(C3H6)}(bubpy)], with oxalic or phthalic acid to give equilibria with the oxalate cis-[PtMe2(O4C2)(bubpy)] or phthalate cis-[PtMe2{(O2C)2C6H4}(bubpy)] derivative, respectively, indicated the expected sequence of chelate stability oxalate > cyclobutane malonate > phthalate.

(Cyclobutane-1,1-dicarboxylato-κ2O,O′)(1,10-phenanthroline-κ2N,N′)platinum(II) dihydrate

The title compound, [Pt(C₆H₆O₄)(C₁₂H₈N₂)]·2H₂O, which crystallizes as two independent formula units, has the metal atom in a square-planar geometry defined by two O atoms of the chelating cyclo­butane-1,1-di­carboxyl­ate dianion and two N atoms of the chelating 1,10-phenanthroline mol­ecule (r.m.s. deviations of the PtO₂N₂ units = 0.026 and 0.026 Å). Adjacent complex and water mol­ecules are connected through inter­molecular O—H⋯O hydrogen bonds and C—H⋯O, C⋯O [shortest C⋯O distance = 3.140 (5) Å], π–π [shortest C⋯C distances = 3.234 (6) and 3.347 (6) Å] and Pt⋯π [shortest Pt⋯C distance = 3.358 (4) Å] inter­actions into a three-dimensional network.

Crystal structures and cytotoxicity of isopropylamine Pt(II) complexes: A trinuclear squarato-bridged [Pt3(μ2-C4O4)3(H2NPri)6]·3H2O and a mononuclear cis-[Pt(NO3)2(H2NPri)2]

Crystals of a novel platinum(II) complex with squarato ligand, [Pt(3)(mu(2)-C(4)O(4))(3)(H(2)NPr(i))(6)].3H(2)O (1) (H(2)NPr(i)=ipa), have been isolated from the aqueous solution of cis-[Pt(H(2)O)(2)(H(2)NPr(i))(2)]SO(4) and barium squarate. Slow evaporation of methanol solution of cis-[Pt(NO(3))(2)(H(2)NPr(i))(2)] (2) resulted in crystallization of nitrato complex. The single crystal X-ray diffraction method was used to determine structures of 1 and 2. Complex 1 crystallizes in a triclinic space group P1 with a=11.17380(10)A, b=14.4535(2)A, c=14.8010(2)A, alpha=86.0901(10) degrees , beta=78.4343(11) degrees , gamma=69.1915(5) degrees , and complex 2 in a monoclinic space group P2(1)/n, with a=10.1161(2)A, b=9.9188(2)A, c=13.3766(2)A, beta=102.7360(7) degrees . The X-ray structure analysis revealed that three platinum atoms in 1 are connected with three squarates which adopt bis(unidentate) binding modes. The squarato ligands span relatively long intramolecular Ptcdots, three dots, centeredPt distances (4.8842(3)-5.2699(3)A). A pair of cis positioned isopropylamine ligands completes a square planar coordination sphere of each Pt(II) ion. The square-planar coordination of complex 2 consists of two cis positioned isopropylamine ligands and two nitrato ligands. The results of cytotoxicity assay of trimer 1, monomer 2 and cis-diamminedichloroplatinum(II) (cisplatin) performed on human bladder tumor cell line T24 provide evidence that complex 2 is less cytotoxic compared to cisplatin and that the survival of tumor cells after exposure to 1 was minimally reduced.

Dipyridylketone binding and subsequent C-C bond insertion reactions at cyclopentadienylrhodium

UV irradiation of a solution of (eta5-C5H5)bis(ethene)rhodium in the presence of 2,2'-dipyridylketone yields (eta5-C5H5)Rh(kappa2-N,O-2,2'-dipyridylketone) which inserts ethene to yield a bicyclic oxametallacyclopentane.

Dicubane-like tetrameric cobalt(II)-pseudohalide ferromagnetic clusters

Three tetrameric cobalt(II)-pseudohalide complexes have been structurally and magnetically characterized. Compounds 1 and 2 are isomorphous and exhibit the general formula [Co2(dpk-OH)(dpk-CH3O)(L)(H2O)]2A2-4H2O where dpk = di-2-pyridyl ketone, L = N3(-) and A = BF4(-) for 1, and L = NCO(-) and A = ClO4(-) for 2. The ligands dpk-OH(-) and dpk-CH3O(-) result from solvolysis and ulterior deprotonation of dpk in water and methanol, respectively. Both compounds exhibit cationic tetramers consisting of a dicubane-like core with two missing vertexes where the Co(II) ions are connected through end-on pseudohalide and oxo-bridges. A similar tetranuclear core has been found for 3 whose formula is [Co2(dpk-OH)(dpk-CH3O)(NCO)2]2. In this case, the tetramers are neutral and exhibit a terminal cyanate in place of the coordinated molecule of water for 1 and 2. The tetrameric units for 2 and 3 represent the first examples of any kind of cubanes exhibiting cyanate bridges as well as the first Co(II) compounds exhibiting intermetallic bridges through these pseudohalide groups. Measurements of the magnetic susceptibility indicated the presence of ferromagnetic Co(II)-Co(II) interactions in the three compounds.

Synthesis, structures and antitumor activity of the first crown ester-linked bipyridyl platinum complexes

Three new crown ester-linked bipyridine homologs with three, four or five ethylene glycol units, which are bulky and soluble in both hydrophilic and lipophilic media, were synthesized. The reaction of the appropriate macrocycles with K2PtCl4 in water gave yellow cisplatin analogs in good yield. These complexes were converted to carboplatin analogs by exchange of the leaving group. All the compounds were characterized by elemental analysis and various spectroscopic methods. Carboplatin analogs showed good solubility in both hydrophilic and lipophilic media. The crystal structure of 2c, the carboplatin analog with macrocycles containing five ethylene glycol units, was determined by X-ray diffraction: space group P1, a = 9.798(1), b = 12.580(3), c = 13.945(2) A, alpha = 108.61(2), beta = 94.59(1), gamma = 97.42(2) degrees, Z = 2, R = 0.0618. Some of platinum complexes showed a moderate cytotoxic effect on both murine leukemia L1210 and P388 even though they do not have any NH proton.