Nadezhda A. Bokach

Alkenylation of Arenes and Heteroarenes with Alkynes

This review is focused on the analysis of current data on new methods of alkenylation of arenes and heteroarenes with alkynes by transition metal catalyzed reactions, Bronsted/Lewis acid promoted transformations, and others. The synthetic potential, scope, limitations, and mechanistic problems of the alkenylation reactions are discussed. The insertion of an alkenyl group into aromatic and heteroaromatic rings by inter- or intramolecular ways provides a synthetic route to derivatives of styrene, stilbene, chalcone, cinnamic acid, various fused carbo- and heterocycles, etc.

A new family of luminescent compounds: platinum(II) imidoylamidinates exhibiting pH-dependent room temperature luminescence

The imidoylamidinate platinum(II) compounds [Pt{NH=C(R)NC(Ph)NPh}2] (R = CH2Ph 2, p-ClC6H43, Ph 4) were prepared by the reaction of the appropriate trans-[PtCl2(RCN)2] with 4 equiv of the amidine PhC(NH)NHPh giving 2-4 and 2 equivs of the salt PhC(=NH)NHPh.HCl. We also synthesized, by the double alkylation of 4 with MeOSO2CF3, complex [Pt{NH=C(Ph)N(Me)C(Ph)=NPh}2][CF3SO3]2 (5) which models the bis-protonated form of 4. The complexes were characterized by 1H, 13C NMR, and IR spectroscopies, FAB-MS and by C, H, N elemental analysis. The X-ray crystallography of 4.2CH2Cl2 enables the confirmation of the square planar coordination geometry of the metal center with almost planar imidoylamidine ligands, while in 5.2CHCl3 the planarity of the metallacycles is lost and and the central N atom is sp3-hybridized. The imidoylamidinate complexes represent a new family of Pt(II)-based luminescent complexes and they are emissive at room temperature both in solution and in the solid state, with an emission quantum yield ranging from 3.7 x 10(-4) to 6.2 x 10(-2) in methanol solution; the emission intensity is pH-dependent, being quenched at low pH. UV-visible and luminescence spectroscopies indicate that the lowest excited state of these compounds is 3MLCT or 3IL with significant MLCT character, with emission lifetimes of a few micros. A blue shift of both the absorption and emission with increasing solvent polarity and with decreasing pi-electron withdrawing properties of the ligand substituent was observed.

Different Routes for Amination of Platinum(II)-Bound Cyanoguanidine

The consecutive addition of AgSO(3)CF(3) (1 or 2 equiv) and cyanoguanidine (1 or 2 equiv, respectively) to the platinum(II) precursor [PtI(2)(tmeda)] leads to the cis-[PtI(tmeda){NCN=C(NH(2))(2)}](SO(3)CF(3)) (1.(SO(3)CF(3))) or cis-[Pt(tmeda){NCN=C(NH(2))(2)}(2)](SO(3)CF(3))(2) (2.(SO(3)CF(3))(2)) complexes. The reaction between 1.(SO(3)CF(3)) or 2.(SO(3)CF(3))(2) and the excess of R(2)NH (R = H, R(2) = C(5)H(10)) in EtOH gives the triazapentadiene compounds cis-[Pt(tmeda){NHC(NR(2))NC(NH(2))NH}](SO(3)CF(3)) (3.(SO(3)CF(3)) and 4.(SO(3)CF(3)), correspondingly). Protonation of these species results in cis-[Pt(tmeda){NHC(NR(2))NHC(NH(2))NH}](SO(3)CF(3))(2) ([3.H](SO(3)CF(3))(2) and [4.H](SO(3)CF(3))(2), respectively). The interaction of solid 2.(SO(3)CF(3))(2) and the gaseous RNH(2) (R = H, Me) leads to cis-[Pt(tmeda){NHC(NHR)NHC(NH(2))NH}(2)](SO(3)CF(3))(2) (5.(SO(3)CF(3))(2) and 6.(SO(3)CF(3))(2), respectively). Treatment of an acetone solution of 2.(SO(3)CF(3))(2) with an aqueous NH(3) or the reaction of 5.(SO(3)CF(3))(2) with Me(2)CO produces the triazine complex cis-{Pt(tmeda){NH=CNHC(Me)(2)}NHC(NH)(2)N}(2)(SO(3)CF(3))(2) (7.(SO(3)CF(3))(2)). The reaction of 5.(SO(3)CF(3))(2) with Me(2)CO also leads to 7.(SO(3)CF(3))(2). All new complexes were characterized by elemental analyses (C, H, N), electrospray ionization mass spectrometry, IR, and (1)H and (13)C NMR spectroscopies. The structures of 1.(SO(3)CF(3)), 2.(SO(3)CF(3))(2), 3.(SO(3)CF(3)), [4.H](SO(3)CF(3))(2), 5.(SO(3)CF(3))(2), and 7.(SO(3)CF(3))(2) were determined by single-crystal X-ray diffraction.

The first example of ligand-mediated dehydration of aldoximes

Abstract The nitrile complex trans -[PtCl 4 (EtCN) 2 ] reacts with the aldoximes HONC(H)R [R=C(Ph)(O), Me, Ph] in CH 2 Cl 2 to afford products of the addition of the aldoxime HON group across the nitrile CN triple bond, i.e. trans -[PtCl 4 {NHC(Et)ONC(H)R} 2 ] ( 1 – 3 ). These compounds were characterized by elemental analyses, FAB MS, IR and 1 H and 13 C{ 1 H} spectroscopies and X-ray structure determination has been performed for 1 . In CHCl 3 solution, 1 – 3 undergo the spontaneous imine ligand splitting to achieve the carboxamide complex trans -[PtCl 4 {NHC(Et)OH} 2 ] and RCN thus giving the first example of a ligand-mediated dehydration of aldoximes. The carboxamide and RCN products are also formed upon treatment of trans -[PtCl 4 (EtCN) 2 ] with 2 equiv. of HONC(H)R in CH 2 Cl 2 .

Platinum(IV)-mediated coupling of dione monoximes and nitriles: a novel reactivity pattern of the classic oxime-based chelating ligands

The reaction between dione monoximes and platinum(IV) nitrile complexes leads, instead of the conventional substitution, to metal-mediated coupling, giving iminoacylated species which, on being liberated, undergo disintegration to the nitrile and the oxime.

Guanidine platinum(II) complexes: synthesis, in vitro antitumor activity, and DNA interactions.

The novel guanidine compounds trans-[Pt(NH2Me)2{NH=C(NHMe)NR}2](Cl)2 (R = NEt2 [7], NC5H10 [8]) (trans-7,8) were synthesized by the nucleophilic addition of methylamine to dialkylcyanamide ligands of the push–pull nitrile complexes trans-[PtCl2(RCN)2] (R = NEt2, NC5H10). In vitro cytotoxicity tests conducted for the entire series of the guanidine complexes, i.e. trans-7,8, the neutral cis- or trans-[PtCl2{NH=C(NH2)R}2] (cis-1–3 and trans-1–3) and the cationic cis- or trans-[Pt(NH3)2{NH=C(NH2)R}2](Cl)2 (cis-4–6 and trans-4–6) (R = NMe2 [1,4], NEt2 [2,5], NC5H10 [3,6]) in two human cancer cell lines, CH1 (ovarian carcinoma) and SW480 (colon cancer), confirmed that the cytotoxicity of several trans-configured (trans-3,6) complexes is higher than that of cis-congeners (cis-3,6). Cellular platinum levels were analyzed by inductively coupled plasma mass spectrometry upon treatment of SW480 cells, revealing a dependence of cellular accumulation on the geometrical isomerism and the steric hindrance of the variable substituent R on the guanidine ligand. DNA interactions of selected guanidine complexes were studied in order to find hints for the possible reasons for their different activities. Changes induced to the electrophoretic mobility of a dsDNA plasmid confirmed the potency of the guanidine complexes (e.g. trans-1,3,5,6 and cis-1,3,4) to significantly alter DNA secondary structure, indicating DNA as a possible critical target of these compounds.

1,3-dipolar cycloaddition of nitrones to free and coordinated nitriles: Routes to control the synthesis of 2,3-dihydro-1,2,4-oxadiazoles

Data on 1,3-dipolar cycloaddition of nitrones to free and coordinated nitriles producing 2,3-dihydro-1,2,4-oxadiazoles (or Δ4-1,2,4-oxadiazolines) are summarized. The latter compounds belong to the virtually unknown class of heterocyclic systems. The main factors responsible for the cycloaddition reactions are discussed. Particular attention is given to the role of metal centers in controlling the synthesis of 2,3-dihydro-1,2,4-oxadiazoles.

Metal-Involving Synthesis and Reactions of Oximes

This review classifies and summarizes the past 10-15 years of advancements in the field of metal-involving (i.e., metal-mediated and metal-catalyzed) reactions of oximes. These reactions are diverse in nature and have been employed for syntheses of oxime-based metal complexes and cage-compounds, oxime functionalizations, and the preparation of new classes of organic species, in particular, a wide variety of heterocyclic systems spanning small 3-membered ring systems to macroheterocycles. This consideration gives a general outlook of reaction routes, mechanisms, and driving forces and underlines the potential of metal-involving conversions of oxime species for application in various fields of chemistry and draws attention to the emerging putative targets.

Trinuclear (aminonitrone)ZnII complexes as key intermediates in zinc(ii)-mediated generation of 1,2,4-oxadiazoles from amidoximes and nitriles

Aliphatic and aromatic amidoximes RC(NH2)NOH (R = Et, tBu, Ph, o-ClC6H4) react with Zn(OAc)2·2H2O in Me2CO giving [Zn(OAc)2{RC(NH2)NOH}2] complexes bearing N-bound amidoximes, which are involved in a moderate strength (7.3–11.9 kcal mol−1 by the DFT calculations) intramolecular resonance-assisted hydrogen bonding between the oxime HO group and the oxo group of the acetate ligand. The complexes [Zn(OAc)2{RC(NH2)NOH}2] react with excess Zn(OTf)2 in acetone accomplishing trinuclear species [Zn3(μ2-OAc)2{μ2-RC(NH2)N(H)O}4(H2O)6](OTf)4 featuring both O-ligated amidoximes—stabilized in the aminonitrone tautomeric form—and bridging acetate ligands. The aminonitrone trinuclear species were also prepared directly via the reaction of the amidoximes with Zn(OTf)2 in EtOAc; ethyl acetate in this reaction plays the role of the acetate donor and OAc− is generated in situ via ZnII-mediated hydrolysis of EtOAc. Although [Zn(OAc)2{RC(NH2)NOH}2] are inactive toward dimethylcyanamide, the [Zn3(μ2-OAc)2{μ2-RC(NH2)N(H)O}4(H2O)6](OTf)4 complexes readily react with Me2NCN giving, as a result of ZnII-mediated amidoxime–cyanamide coupling, the O-carbamidine amidoxime complexes [Zn(OTf)2{RC(NH2)NOC(NMe2)NH}2]. All synthesized compounds were characterized by HRESI-MS, FTIR, 1H-, CP-MAS TOSS 13C{1H}-, and 13C{1H} NMR, and additionally by single-crystal X-ray diffraction for eight species. Different types of non-covalent interactions in the obtained solid-state structures were studied by DFT calculations (M06-2X/6-311+G(d,p) level of theory) and topological analysis of the electron density distribution within the formalism of Baders theory (QTAIM method).

Metal-mediated generation of triazapentadienate-terminated di- and trinuclear μ2-pyrazolate NiII species and control of their nuclearity

1,3,5-Triazapentadienate-terminated di- and trinuclear nickel(II) complexes featuring bridging azolate ligands, [Ni2(μ2-azolate)2(TAP)2] (TAP = HC(OMe)NC(OMe)H; azole = 3,5-Me2pyrazole 2, 3,5-Ph2pyrazole 3) and [Ni3(μ2-azolate)4(TAP)2] (azole = 3,5-Me2pyrazole 4, indazole 5), were obtained from systems Ni2+/NCNR2/azole systems in MeOH. The terminal TAP ligands in the [Ni2(μ2-azolate)2(TAP)2] and [Ni3(μ2-azolate)4(TAP)2] species originate from the previously unreported cascade NiII-mediated and chelation-driven reaction between cyanamides and methanol. The oligomeric species and also [Ni(TAP)2] (1) are subject to interconversions that depend on the reactants involved and the reaction conditions. The control of the nuclearity of the complexes can be achieved by changing the amount of azoles or by their protonation, alteration of the steric hindrance of the substituents in the heterocycles, and by changing the reaction temperature. Complexes 1–4 were characterized using elemental (C, H, N) analyses, 1H, 13C{1H} NMR, FTIR, HRESI-MS, TG-DTA, X-ray crystallography, and 5 was characterized using HRESI-MS and X-ray crystallography. Unconventional metallophilic contacts NiII⋯NiII were observed in dimer 3 in the solid state (the distance for Ni⋯Ni is 2.99 A, whereas the double Bondis vdW radius for Ni is 3.26 A) and the reality of these interactions was confirmed theoretically by the topological analysis of the electron density distribution (AIM method). The estimated energy for these non-covalent Ni⋯Ni interactions (ca. 4 kcal mol−1) fills the gap in the reported energies of the metal⋯metal interactions in a series comprising of NiII⋯NiII (this work), PdII⋯PdII (4.3–6.0 kcal mol−1), and PtII⋯PtII (3.9–11.7 kcal mol−1).