Expanding the Arsenal of PtIV Anticancer Agents: Multi‐action PtIV Anticancer Agents with Bioactive Ligands Possessing a Hydroxy Functional Group

Most multi‐action Pt^IV prodrugs have bioactive ligands containing carboxylates. This is probably due to the ease of carboxylating the OH axial ligands and because following reduction, the active drug is released. A major challenge is to expand the arsenal of bioactive ligands to include those without carboxylates. We describe a general approach for synthesis of Pt^IV prodrugs that release drugs with OH groups. We linked the OH groups of gemcitabine (Gem), paclitaxel (Tax), and estramustine (EM) to the Pt^IV derivative of cisplatin by a carbonate bridge. Following reduction, the axial ligands lost CO₂, rapidly generating the active drugs. In contrast, succinate‐linked drugs did not readily release the free drugs. The carbonate‐bridged ctc‐[Pt(NH₃)₂(PhB)(Gem‐Carb)Cl₂] was significantly more cytotoxic than the succinate‐bridged ctc‐[Pt(NH₃)₂(PhB)(Gem‐Suc)Cl₂], and more potent and less toxic than gemcitabine, cisplatin, and co‐administration of cisplatin and gemcitabine.     

First example of ruthenium nitroso monoammine complex. Crystal structure of [Ru(NO)(NH3)3(H2O)Cl] × [Ru(no)(NH3)3(OH)Cl][Ru(NO)(NH3)Cl4]2Cl·2H2O

The structure of the interaction products of (NH₄)₂[Ru(NO)Cl₅] solution with ammonium acetate on heating is studied. The crystal structure of the [Ru(NO)(NH₃)₃(H₂O)Cl][Ru(NO)(NH₃)₃(OH)Cl] × [Ru(NO)(NH₃)Cl₄]₂Cl-2H₂O compound (compound I) containing a previously unknown anion of the nitrosomonoammine series is determined: Cc space group; a = 33.530(7) ?, b = 8.202(2) ?, c = 11.844(2) ?; β= 101.54(3)°.     

Immobilization of Platinum(II) and Platinum(IV) Complexes on Oxidized Nanoporous Carbon Material and Evaluation of the Enthalpy of Adsorption

Physicochemical study of cis-[Pt(NH3)2Cl2] and cis-[Pt(NH₃)₂Cl₂(OH)₂] is carried out, and immobilization of platinum complexes on the nanoporous carbon substrate is investigated. The solubility of cis-[Pt(NH₃)₂Cl₂] in 1 M HCl solution is determined, and the average enthalpy of dissolution is calculated: Δ_solH° = 27.3 ± 0.9 kJ/mol. The batch capacity is determined experimentally for cis-[Pt(NH3)2Cl2] and cis- [Pt(NH₃)₂Cl₂(OH)₂] to be 32.9 mg/g (0.17 mg-equiv/g) and 47.6 mg/g (0.24 mg-equiv/g), respectively. Immobilization of platinum complexes on the oxidized carbon surface is found to take place due to interaction between carboxy groups and ammine groups of platinum complexes. The resulting heat capacity curves are used to calculate the enthalpies of adsorption for cis-[Pt(NH₃)₂Cl₂] and cis-[Pt(NH₃)₂Cl₂(OH)₂] on the oxidized carbon surface, equal to 24.46 and 27.46 kJ/mol, respectively.     

Prediction of 195Pt NMR chemical shifts of dissolution products of H2[Pt(OH)6] in nitric acid solutions by DFT methods: how important are the counter‐ion effects?

¹⁹⁵Pt NMR chemical shifts of octahedral Pt(IV) complexes with general formula [Pt(NO₃)_n(OH)_{6 ? n}]^2?, [Pt(NO₃)_n(OH₂)_{6 ? n}]^{4 ? n} (n = 1–6), and [Pt(NO₃)_{6 ? n ? m}(OH)_m(OH₂)_n]^{?2 + n ? m} formed by dissolution of platinic acid, H₂[Pt(OH)₆], in aqueous nitric acid solutions are calculated employing density functional theory methods. Particularly, the gauge‐including atomic orbitals (GIAO)‐PBE0/segmented all‐electron relativistically contracted–zeroth‐order regular approximation (SARC–ZORA)(Pt) ∪ 6–31G(d,p)(E)/Polarizable Continuum Model computational protocol performs the best. Excellent second‐order polynomial plots of δ_calcd(¹⁹⁵Pt) versus δ_exptl(¹⁹⁵Pt) chemical shifts and δ_calcd(¹⁹⁵Pt) versus the natural atomic charge Q_Pt are obtained. Despite of neglecting relativistic and spin orbit effects the good agreement of the calculated δ ¹⁹⁵Pt chemical shifts with experimental values is probably because of the fact that the contribution of relativistic and spin orbit effects to computed σ^{iso 195}Pt magnetic shielding of Pt(IV) coordination compounds is effectively cancelled in the computed δ ¹⁹⁵Pt chemical shifts, because the relativistic corrections are expected to be similar in the complexes and the proper reference standard used. To probe the counter‐ion effects on the ¹⁹⁵Pt NMR chemical shifts of the anionic [Pt(NO₃)_n(OH)_{6 ? n}]^2? and cationic [Pt(NO₃)_n(OH₂)_{6 ? n}]^{4 ? n} (n = 0–3) complexes we calculated the ¹⁹⁵Pt NMR chemical shifts of the neutral (PyH)₂[Pt(NO₃)_n(OH)_{6 ? n}] (n = 1–6; PyH = pyridinium cation, C₅H₅NH⁺) and [Pt(NO₃)_n(H₂O)_{6 ? n}](NO₃)_{4 ? n} (n = 0–3) complexes. Counter‐anion effects are very important for the accurate prediction of the ¹⁹⁵Pt NMR chemical shifts of the cationic [Pt(NO₃)_n(OH₂)_{6 ? n}]^{4 ? n} complexes, while counter‐cation effects are less important for the anionic [Pt(NO₃)_n(OH)_{6 ? n}]^2? complexes. The simple computational protocol is easily implemented even by synthetic chemists in platinum coordination chemistry that dispose limited software availability, or locally existing routines and knowhow. Copyright © 2016 John Wiley & Sons, Ltd.     

Reactions of Beryllium Halides in Liquid Ammonia: The Tetraammineberyllium Cation [Be(NH3)4]2+, its Hydrolysis Products,and the Action of Be2+ as a Fluoride‐Ion Acceptor

The first structural characterization of the text‐book tetraammineberyllium(II) cation [Be(NH₃)₄]²⁺, obtained in the compounds [Be(NH₃)₄]₂Cl₄ ? 17NH₃ and [Be(NH₃)₄]Cl₂, is reported. Through NMR spectroscopic and quantum chemical studies, its hydrolysis products in liquid ammonia were identified. These are the dinuclear [Be₂(μ‐OH)(NH₃)₆]³⁺ and the cyclic [Be₂(μ‐OH)₂(NH₃)₄]²⁺ and [Be₃(μ‐OH)₃(NH₃)₆]³⁺ cations. The latter species was isolated as the compound [Be₃(μ‐OH)₃(NH₃)₆]Cl₃ ? 7NH₃. NMR analysis of solutions of BeF₂ in liquid ammonia showed that the [BeF₂(NH₃)₂] molecule was the only dissolved species. It acts as a strong fluoride‐ion acceptor and forms the [BeF₃(NH₃)]^? anion in the compound [N₂H₇][BeF₃(NH₃)]. The compounds presented herein were characterized by single‐crystal X‐ray structure analysis, ⁹Be, ¹⁷O, and ¹⁹F NMR, IR, and Raman spectroscopy, deuteration studies, and quantum chemical calculations. The extension of beryllium chemistry to the ammine system shows similarities but also decisive differences to the aquo system.     

Fluorination Reactions at a Platinum Carbene Complex: Reaction Routes to SF3, S(=O)F and Fluorido Complexes

The electron-rich Pt complex [Pt(IMes)₂] (IMes: [1,3-bis(2,4,6-trimethylphenyl)-2-imidazolinylidine]) can be used as precursor for the syntheses of a variety of fluorido ligand containing compounds. The sulfur fluoride SF₄ undergoes a rapid oxidative addition at Pt⁰ to yield trans-[Pt(F)(SF₃)(IMes)₂]. A photolytic reaction of SF₆ at [Pt(IMes)₂] in the presence of IMes gave the fluorido complexes trans-[Pt(F)₂(IMes)₂] and trans-[Pt(F)(SF₃)(IMes)₂] along with trans-[Pt(F)(SOF)(IMes)₂] and trans-[Pt(F)(IMes’)(IMes)] (IMes’: cyclometalated IMes ligand), the latter being products produced by reaction with adventitious water. trans-[Pt(F)(SOF)(IMes)₂] and trans-[Pt(F)₂(IMes)₂] were synthesized independently by treatment of [Pt(IMes)₂] with SOF₂ or XeF₂. A reaction of [Pt(IMes)₂] with a HF source gave trans-[Pt(H)(F)(IMes)₂], and an intermediate bifluorido complex trans-[Pt(H)(FHF)(IMes)₂] was identified. Compound trans-[Pt(H)(F)(IMes)₂] converts in the presence of CsF into trans-[Pt(F)(IMes’)(IMes)].     

Syntheses,structures and catecholase activities of homo‐ and hetero‐trinuclear cobalt(II) complexes constructed from an acyclic naphthalenediol‐based bis(Salamo)‐type ligand

A series of homo‐ and hetero‐trinuclear cobalt(II) complexes [Co₃(L)(OAc)₂(CH₃CH₂OH)(H₂O)] ( 1 ), [Co₂Ba(L)(OAc)₂] ( 2 ) and [Co₂Ca(L)(OAc)₂]·CHCl₃ ( 3 ), containing an acyclic naphthalenediol‐based ligand H₄L were synthesized. All the three complexes were characterized by elemental analyses, IR, UV – vis spectra and single crystal X‐ray diffraction analyses. Comparative studies of the structures and spectroscopic properties are carried out on these complexes. All of the complexes show catechol oxidase activities in MeCN. Using UV – vis spectroscopy, we monitored the aerial oxidation of 3,5‐di‐tert ‐butylcatechol (3,5‐DTBCH₂) to 3,5‐di‐tert ‐butylquinone (3,5‐DTBQ), which confirms the essential role of these complexes in enhancing the catalytic reaction.     

4′-(2-Methylphenyl)-2,2′:6′,2″-terpyridine: coordination chemistry with Ni(II), Cu(II), Zn(II) and Ag(I)

The synthesis of 4′-(2-methylphenyl)-2,2′:6′,2″-terpyridine (L) has been improved. The coordination chemistry of the ligand was explored using Ni(II), Cu(II), Zn(II), and Ag(I) ions. X-ray crystallography, elemental analysis, NMR, and mass spectrometry were used to characterize the 13 new compounds that have been synthesized. Under different reaction conditions, Ni(II), Cu(II), and Zn(II) produced discrete complexes, sometimes containing more than one metal ion, while Ag(I) furnished a polymeric spiral complex in which the central pyridine nitrogen of each terpyridine ligand bridges two Ag(I) ions. Crystallographically characterized complexes are [Ni(L)₂]Cl₂, [Ni₂Cl₄(L)₂], [Ni(L)(OH₂)₃]Cl₂, [Ni(L)₂]Br₂, [Cu(L)(OH₂)(OSO₃)], [Cu₃Cl₆(L)₂], [Cu(L)(OH)(OH₂)₂]PF₆, [Cu(L)₂](OTf)₂, [Cu(L)(OAc)₂], [Zn(L)(OAc)₂], [Zn(L)Cl₂], [Zn(L)₂](NO₃)₂, [{Ag₂(μ-L)₂(μ-NO₃)}_n](NO₃)_n.     

Influence of the chloride counterion on the redox reactivity of tetraammineplatinum(II) cation with octacyanotungstate(V) anion: Crystal structure of [Pt(NH3)4]2[W(CN)8]

The redox reaction between [Pt(NH₃)₄]²⁺ and [W(CN)₈]³⁻ in the presence of Cl⁻ anions in aqueous solution affords single crystals of [Pt^II(NH₃)₄]₂[W^IV(CN)₈] and [Pt^IV(NH₃)₄Cl₂]Cl₂. Trapped cyano ligands of [W(CN)₈]⁴⁻ rectangular antiprisms of D₂ point symmetry between parallel Pt(II) square planes show that the inner-sphere redox pathway is prohibited. The presence of Cl⁻ counterions enables the formation of [Pt(NH₃)₄Cl₂]Cl₂ as the product of the rare outer-sphere pathway of the oxidation of Pt(II) by [W(CN)₈]³⁻.     

Ab Initio Calculations of Hydroxoplatinum Compounds: II. Binuclear Platinum(IV) Superoxo Complexes

The structural and spectral data have been obtained by ab initio methods for the [(OH)₄Pt(μ-O₂)(μ- OH)Pt(OH)₄]^2?, [(OH)₄Pt(μ-O₂)(μ-OH)Pt(OH)₄(OH)]^3?, [(OH)₅Pt(μ-O₂)Pt(OH)₅]^3?, and [(H₂O)(OH)₄Pt(μ- O₂)Pt(OH)₄(H₂O)]- clusters, corresponding to binuclear platinum(IV) superoxo complexes with one and two bridges. The data obtained are in good agreement with experimental data and make it possible to judge the structure of available complexes.     

Analogues of Cis‐ and Transplatin with a Rich Solution Chemistry: cis‐[PtCl2(NH3)(1‐MeC‐N3)] and trans‐[PtI2(NH3)(1‐MeC‐N3)]

Mono(nucleobase) complexes of the general composition cis‐[PtCl₂(NH₃)L] with L=1‐methylcytosine, 1‐MeC ( 1 a ) and L=1‐ethyl‐5‐methylcytosine, as well as trans‐[PtX₂(NH₃)(1‐MeC)] with X=I ( 5 a ) and X=Br ( 5 b ) have been isolated and were characterized by X‐ray crystallography. The Pt coordination occurs through the N3 atom of the cytosine in all cases. The diaqua complexes of compounds 1 a and 5 a , cis‐[Pt(H₂O)₂(NH₃)(1‐MeC)]²⁺ and trans‐[Pt(H₂O)₂(NH₃)(1‐MeC)]²⁺, display a rich chemistry in aqueous solution, which is dominated by extensive condensation reactions leading to μ‐OH‐ and μ‐(1‐MeC^?‐N3,N4)‐bridged species and ready oxidation of Pt to mixed‐valence state complexes as well as diplatinum(III) compounds, one of which was characterized by X‐ray crystallography: h,t‐[{Pt(NH₃)₂(OH)(1‐MeC^?‐N3,N4)}₂](NO₃)₂ ? 2 [NH₄](NO₃) ? 2 H₂O. A combination of ¹H NMR spectroscopy and ESI mass spectrometry was applied to identify some of the various species present in solution and the gas phase, respectively. As it turned out, mass spectrometry did not permit an unambiguous assignment of the structures of +1 cations due to the possibilities of realizing multiple bridging patterns in isomeric species, the occurrence of different tautomers, and uncertainties regarding the Pt oxidation states. Additionally, compound 1 a was found to have selective and moderate antiproliferative activity for a human cervix cancer line (SISO) compared to six other human cancer cell lines.     

New method for the synthesis of trans-hydroxotetraamminenitrosoruthenium(II) dichloride and its characterization

A procedure for the synthesis of mpa h c-[Ru(NO)(NH₃)₄(OH)]Cl₂ in a nearly quantitative yield (～95%) comprising treatment of a solution of (NH₄)₂[Ru(NO)Cl₅] with ammonium carbonate at t ～80°C was developed. It was found that [Ru(NO)(NH₃)₄(H₂O)]Cl₃·H₂O and trans-[Ru(NO)(NH₃)₄Cl]Cl₂ formed in the reaction of [Ru(NO)(NH₃)₄(OH)]Cl₂ with hydrochloric acid at various temperatures most often contain some initial hydroxy complex. The former compound is unstable, even at room temperature, it slowly eliminates water and HCl. A procedure for preparing the latter compound in a pure state in 85–90% yield was proposed. The acidity constant of the complex trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺ at room temperature (K _a = (4 ± 1) × 10^?2) was estimated by ¹⁴N NMR spectroscopy.     

On the Heterogeneous Nature of Cisplatin-1-Methyluracil Complexes: Coexistence of Different Aggregation Modes and Partial Loss of NH3 Ligands as Likely Explanation

The conversion of the 1 : 1-complex of Cisplatin with 1-methyluracil (1MeUH), cis-[Pt(NH₃)₂(1MeU-N3)Cl] ( 1 a ) to the aqua species cis-[Pt(NH₃)₂(1MeU-N3)(OH₂)]⁺ ( 1 b ), achieved by reaction of 1 a with AgNO₃ in water, affords a mixture of compounds, the composition of which strongly depends on sample history. The complexity stems from variations in condensation patterns and partial loss of NH₃ ligands. In dilute aqueous solution, 1 a , and dinuclear compounds cis-[(NH₃)₂(1MeU-N3)Pt(μ-OH)Pt(1MeU-N3)(NH₃)₂]⁺( 3 ) as well as head-tail cis-[Pt₂(NH₃)₄(μ-1MeU-N3,O4)₂]²⁺ ( 4 ) represent the major components. In addition, there are numerous other species present in minor quantities, which differ in metal nuclearity, stoichiometry, stereoisomerism, and Pt oxidation state, as revealed by a combination of ¹H NMR and ESI-MS spectroscopy. Their composition appears not to be the consequence of a unique and repeating coordination pattern of the 1MeU ligand in oligomers but rather the coexistence of distinctly different condensation patterns, which include μ-OH, μ-1MeU, and μ-NH₂ bridging and combinations thereof. Consequently, the products obtained should, in total, be defined as a heterogeneous mixture rather than a mixture of oligomers of different sizes. In addition, a N₂ complex, [Pt(NH₃)(1MeU)(N₂)]⁺ appears to be formed in gas phase during the ESI-MS experiment. In the presence of Na⁺ ions, multimers n of 1 a with n=2, 3, 4 are formed that represent analogues of non-metalated uracil quartets found in tetrastranded RNA.     

Vinyliden-Übergangsmetallkomplexe XXVI. Synthese und struktur kationischer Carbonyl-, Alken-, Vinyliden-, Alkinyl- und Alkin-Rhodiumkomplexe mit der Baueinheit trans-[Rh(PPr3)2]

The complex trans-[Rh(CO)(NH₃)(PiPr₃)₂]PF₆ (2) was prepared from [(η³-C₃H₅)Rh(PⁱPr₃)₂] (1), NH₄PF₆ and CO or from 1 and NH₄PF₆ in presence of an excess of methanol. With an excess of CO, the dicarbonyl and tricarbonyl compounds trans-[Rh(CO)₂(PⁱPr₃)₂]PF₆ (3) and [Rh(CO)₃(PⁱPr₃)₂]PF₆ (4) were obtained. Displacement of one CO ligand in 3 by pyridine and acetone led to the formation of trans-[Rh(CO)(py)PⁱPr₃)₂]PF₆ (5a) and trans-[Rh(CO) (O=CMe₂(PⁱPr₃)₂]PF₆ (6), respectively. Treatment of 1 with [pyH]BF₄ and pyridine gave trans-[Rh(py)₂(PⁱPr₃)₂]BF₄ (7); in presence of H₂ the dihydrido complex [RhH₂(py)₂(PⁱPr₃)₂]BF₄ (8) was formed. The reaction of 1 with NH₄PF₆ and ethylene produced trans [Rh(C₂H₄(NH₃(PⁱPr₃)₂]PF₆(9) whereas with methylvinylketone and acetophenone the octahedral hydridorhodium(III) complexes [RhH(η²-CH=CHC(=O)CH₃ (NH₃(PⁱPr₃)₂]PF₆(11) and [RhH(η2-C₆H₄C(=O)CH₃(NH₃(Pⁱpr₃)₂]PF₆ (13) were obtained. The synthesis of the cationic vinylidenerhodium(I) compounds trans-[Rh(=C=CHR)(py)(PⁱPr₃)₂]BF₄ (14–16) and trans-[Rh(=C=CHR)(NH₃)(PⁱPr₃) ₂]PF6 (17–19) was achieved either on treatment of 1 with [pyH]BF₄ or NH₄PF₆ in presence of 1-alkynes or by ethylene displacement from 9 by HCCR. With tert-butylacetylene as substrate, the alkinyl(hydrido)rhodium(III) complex [RhH(CC^tBu)(NH₃)(O=CMe₂)(PⁱPr₃) ₂]PF₆ (20) was isolated which in CH₂Cl₂ solution smoothly reacted to give 19 (R =^tBu). The cationic but-2-yne compound trans-[Rh(MeCCMe)(NH₃)(Pⁱ Pr₃)₂]PF₆ (21) was prepared from 1, NH₄PF₆ and C₂Me₂. The molecular structures of 3 and 14 were determined by X-ray crystallography; in both cases the square-planar coordination around the metal and the trans disposition of the phosphine ligands was confirmed.

Abstract

Der Komplex trans-[Rh(CO)(NH₃)(PⁱPr₃)₂]PF₆ (2) wurde aus [(η³-C₃H₅)Rh(PⁱPr₃)₂] (1), NH₄PF₆ und CO oder aus 1, NH₄PF₆ und Methanol hergestellt. In Gegenwart von überschüssigem CO wurden die Dicarbonyl- und Tricarbonyl-Verbindungen trans-[Rh(CO)₂(PⁱPr₃)₂]PF₆ (3) und [Rh(CO)₃(PⁱPr₃)₂]PF₆ (4) erhalten. Die Verdrängung eines CO-Liganden in 3 durch Pyridin oder Aceton führte zur Bildung von trans-[Rh(CO)(py)(PⁱPr₃)₂]PF₆ (5a) bzw. trans-[Rh(CO)(O=CMe₂)(PⁱPr₃)₂]PF₆ (6). Bei Einwirkung von [pyH]BF₄ und Pyridin auf 1 entstand trans-[Rh(py)₂(PⁱPr₃)₂]BF₄ (7); in Gegenwart von H₂ bildete sich der Dihydrido-Komplex [RhH₂(py)₂(PⁱPr₃) ₂]BF₄ (8). Die Reaktion von 1 mit NH₄PF₆ und Ethen lieferte trans-[Rh(C₂H₄)(NH₃)(PⁱPr₃)₂] PF₆ (9) während mit Methylvinylketon und Acetophenon die oktaedrischen Hydridorhodium(III)-Komplexe [RhH(η²-CH=CHC(=O)CH₃ (NH₃)-(PⁱPr₃)₂]PF₆ (11) und [RhH(η-²-C₆H₄C(=O)CH₃(NH₃)(PⁱPr₃)₂)₂]PF₆ (13) erhalten wurden. Die Synthese der kationischen Vinyli-denrhodium(I)-Verbindungen trans-[Rh(=C=CHR(py)(PⁱPr₃)₂]BF₄ (14–16) und trans-[Rh(=C=CHR)(NH₃)(PⁱPr₃)₂]PF₆ (17–19) gelang durch Einwirkung von [pyH]BF₄ bzw. NH₄PF₆ auf 1 in Gegenwart von 1-Alkinen oder durch Ethen-Verdrängung aus 9 mit HCCR. Mit tert-Butylacetylen als Reaktionspartner wurde der Alkinyl(hydrido)rhodium(III)-Komplex [RhH(CC^tBu)(NH₃(O=CMe₂)(PⁱPr₃)₂]PF₆ (20) isoliert, der in CH₂Cl₂-Lösung sofort zu 19 (R =^tBu) reagiert. Die kationische 2-Butin-Verbindung trans -[Rh(MeCCMe)(NH₃)PⁱPr₃)₂]PF₆ (21) wurde aus 1, NH₄PF₆ und C₂Me₂ hergestellt. Die Strukturen von 3 und 14 wurden kristallographisch bestimmt; in beiden Fa len ließ sich die quadratisch-planare Koordination des Metalls und die trans-Anordnung der Phosphanliganden bestätigen.     

Synthesis,Spectra and Electrochemistry of Isomeric DichloroBis-[1-Alkyl-2-(Naphthyl-(α/β)-Azo)Imidazole]Osmium(II): Single Crystal X-Ray Structure of Blue-Violet DichloroBis-[1-Ethyl-2-(Naphthyl-α-Azo) Imidazole]Osmium(II)

1-Alkyl-2-(naphthyl-(α/β)-azo)imidazoles (α/β-NaiR; R = Me, Et and CH₂Ph) react with (NH₄)₂[OsCl₆] and complexes OsCl₂(NaiR)₂ are isolated in two isomeric forms: blue-violet (3, 4) and red-violet (5, 6). The ligand is a bidentate N (N(imidazole)), N' (N(azo)) donor type. With reference to the pairs of Cl, Cl; N, N and N', N' atoms the blue-violet and red-violet isomers are assigned to cis-trans-cis (ctc) and cis-cis-cis (ccc) configurations respectively. IR spectra of the complexes show two v(Os-Cl) bands and support the cis-OsCl₂ configuration. ¹H NMR spectra also support the ctc and ccc-configuration. The structure of the blue-violet complex OsCl₂(α-NaiEt)₂ has been determined by X-ray crystallography and the ctc configuration has been confirmed. The structure shows an unusually long N=N bond length, 1.331(4) Å, which is elongated by 0.07 Å compared to the free ligand value.     

Novel Platinum(II) Complexes with Dipyridyl Containing Chelating Ligands and their Products with the Model Nucleobases 1‐Methylthymine and 1‐Methyluracil

The reactions of [Pt(dpma)(H₂O)₂]²⁺ (dpma = 2,2′‐dipyridylmethylamine) and [Pt(dpk)(H₂O)₂]²⁺ (dpk = 2,2′‐dipyridylketone) with the model nucleobases 1‐methylthymine (1‐MeT) and 1‐methyluracil (1‐MeU) were studied. Reaction products were characterized by ¹⁹⁵Pt NMR spectroscopy and by X‐ray structure analysis. The symmetric dpma and dpk diaqua complexes form dinuclear complexes with 1‐methylthymine, acting as secondary bridging ligand via its N3 and O4 donor atoms. [Pt₂(dpma)₂(1‐MeT)₂](ClO₄)₂ · H₂O ( 5 ) and [Pt₂(dpk)(dpk · H₂O)(1‐MeT)₂](PF₆)₂ · 4 H₂O ( 6 ) both show a head‐to‐head arrangement. Biological tests show a significant in vitro antitumor activity of [Pt(dpk)Cl₂] against the human glioma cell line U 87.     

PtII Coordination to N1 of 9‐Methylguanine: Why it Facilitates Binding of Additional Metal Ions to the Purine Ring

The preparation and X‐ray crystal structure analysis of {trans‐[Pt(MeNH₂)₂(9‐MeG‐N1)₂]} ? {3 K₂[Pt(CN)₄]} ? 6 H₂O ( 3 a ) (with 9‐MeG being the anion of 9‐methylguanine, 9‐MeGH) are reported. The title compound was obtained by treating [Pt(dien)(9‐MeGH‐N7)]²⁺ ( 1 ; dien=diethylenetriamine) with trans‐[Pt(MeNH₂)₂(H₂O)₂]²⁺ at pH 9.6, 60 °C, and subsequent removal of the [(dien)Pt^II] entities by treatment with an excess amount of KCN, which converts the latter to [Pt(CN)₄]^2?. Cocrystallization of K₂[Pt(CN)₄] with trans‐[Pt(MeNH₂)₂(9‐MeG‐N1)₂] is a consequence of the increase in basicity of the guanine ligand following its deprotonation and Pt coordination at N1. This increase in basicity is reflected in the pK_a values of trans‐[Pt(MeNH₂)₂(9‐MeGH‐N1)₂]²⁺ (4.4±0.1 and 3.3±0.4). The crystal structure of 3 a reveals rare (N7,O6 chelate) and unconventional (N2,C2,N3) binding patterns of K⁺ to the guaninato ligands. DFT calculations confirm that K⁺ binding to the sugar edge of guanine for a N1‐platinated guanine anion is a realistic option, thus ruling against a simple packing effect in the solid‐state structure of 3 a . The linkage isomer of 3 a , trans‐[Pt(MeNH₂)₂(9‐MeG‐N7)₂] ( 6 a ) has likewise been isolated, and its acid–base properties determined. Compound 6 a is more basic than 3 a by more than 4 log units. Binding of metal entities to the N7 positions of 9‐MeG in 3 a has been studied in detail for [(NH₃)₃Pt^II], trans‐[(NH₃)₂Pt^II], and [(en)Pd^II] (en=ethylenediamine) by using ¹H NMR spectroscopy. Without exception, binding of the second metal takes place at N7, but formation of a molecular guanine square with trans‐[(Me₂NH₂)Pt^II] cross‐linking N1 positions and trans‐[(NH₃)₂Pt^II] cross‐linking N7 positions could not be confirmed unambiguously, despite the fact that calculations are fully consistent with its existence.     

Azoimidazole Complexes of Manganese(II)-thiocyanate. X-ray Structures of 2-(p-tolylazo)imidazole and Bis-[1-methyl-2-(p-tolylazo)imidazole]- Di-thiocyanato-manganese(II)

The reaction of Mn(OAc)₂ · 4H₂O and 1-alkyl-2-(arylazo)imidazole [RaaiR′ where R = H (a), Me (b); R′ = Me (1/3/), Et (2/4/)] and NH₄NCS in MeOH in a 1:2:2 mole ratio afforded [Mn(RaaiR′)₂(NCS)₂] (3) and (4) complexes. They were characterized by different physicochemical methods and the structure has been confirmed by single crystal X-ray diffraction study for title compound. One of the primary ligands was also characterised by an X-ray diffraction study.     

Über einige ein‐ und zweikernige Hydroxoiridium(I)‐Komplexe

Some mono‐ and dinuclear Hydroxoiridium(I) Complexes The chloro‐bridged iridium(I) compound [Ir₂(μ‐Cl)₂(C₈H₁₄)₄] ( 1 ) reacts in the biphasic system benzene/water with KOH in the presence of [NEt₃(CH₂Ph)]Cl (TEBA) to give the corresponding dinuclear complex [Ir₂(μ‐OH)₂(C₈H₁₄)₄] ( 2 ). Stepwise substitution of the cyclooctene ligands by PiPr₃ and ethene affords via the intermediate [Ir₂(μ‐OH)₂(C₈H₁₄)₂(PiPr₃)₂] (isolated as a mixture of isomers 3 a , b ) the product [Ir₂(μ‐OH)₂(C₂H₄)₂(PiPr₃)₂] ( 4 ) in excellent yield. Reaction of 4 with PiPr₃in the molar ratio of 1:2 leads to the formation of the mononuclear compound trans‐[Ir(OH)(C₂H₄)(PiPr₃)₂] ( 5 ), the ethene ligand of which cannot be replaced by CPh₂ upon treatment with Ph₂CN₂.     

Synthese und dynamisches Verhalten von [Rh2(μ-H)3H2(PiPr3)4]+. Beiträge zur Reaktivität des Tetrahydridodirhodium-Komplexes [Rh2H4(PiPr3)4]

Synthesis and Dynamic Behaviour of [Rh₂(μ-H)₃H₂(PiPr₃)₄]⁺. Contributions to the Reactivity of the Tetrahydridodirhodium Complex [Rh₂H₄(PiPr₃)₄] An improved synthesis of [Rh₂H₄(PiPr₃)₄] ( 2 ) from [Rh(η³-C₃H₅)(PiPr₃)₂] ( 1 ) or [Rh(η³-CH₂C₆H₅)(PiPr₃)₂] ( 3 ) and H₂ is described. Compound 2 reacts with CO or CH₃OH to give trans-[RhH(CO)(PiPr₃)₂] ( 4 ) and with ethene/acetone to yield a mixture of 4 and trans-[RhCH₃(CO)(PiPr₃)₂] ( 5 ). The carbonyl(methyl) complex 5 has also been prepared from trans-[RhCl(CO)(PiPr₃)₂] ( 6 ) and CH₃MgI. Whereas the reaction of 2 with two parts of CF₃CO₂H leads to [RhH₂(η²-O₂CCF₃) · (PiPr₃)₂] ( 8 ), treatment of 2 with one equivalent of CF₃CO₂H in presence of NH₄PF₆ gives the dinuclear compound [Rh₂H₅(PiPr₃)₄]PF₆ ( 9a ). The reactions of 2 with HBF₄ and [NO]BF₄ afford the complexes [Rh₂H₅(PiPr₃)₄]BF₄ ( 9b ) and trans-[RhF(NO)(PiPr₃)₂]BF₄ ( 11 ), respectively. In solution, the cation [Rh₂(μ-H)₃H₂(PiPr₃)₄]⁺ of the compounds 9a and 9b undergoes an intramolecular rearrangement in which the bridging hydrido and the phosphane ligands are involved.