NN Ligand Research Articles

Evaluation of cellular uptake, cytotoxicity and cellular ultrastructural effects of heteroleptic oxidovanadium(IV) complexes of salicylaldimines and polypyridyl ligands

Searching for prospective vanadium-based drugs for cancer treatment, a new series of structurally related [VIVO(L−2H)(NN)] compounds (1–8) was developed. They include a double deprotonated salicylaldimine Schiff base ligand (L-2H) and different NN-polypyridyl co-ligands having DNA intercalating capacity. Compounds were characterized in solid state and in solution. EPR spectroscopy suggests that the NN ligands act as bidentate and bind through both nitrogen donor atoms in an axial-equatorial mode. The cytotoxicity was evaluated in human tumoral cells (ovarian A2780, breast MCF7, prostate PC3). The cytotoxic activity was dependent on type of cell and incubation time. At 24h PC3 cells presented low sensitivity, but at 72h all complexes showed high cytotoxic activity in all cells. Human kidney HEK293 and ovarian cisplatin resistant A2780cisR cells were also included to evaluate selectivity towards cancer cells and potency to overcome cisplatin resistance, respectively. Most complexes showed no detectable interaction with plasmid DNA, except 2 and 7 which depicted low ability to induce single strand breaks in supercoiled DNA. Based on the overall cytotoxic profile, complexes with 2,2´-bipyridine and 1,10-phenanthroline ligands (1 and 2) were selected for further studies, which consisted on cellular distribution and ultrastructural analyses. In the A2780 cells both depicted different distribution profiles; the former accumulates mostly at the membrane and the latter in the cytoskeleton. Morphology of treated cells showed nuclear atypia and membrane alterations, more severe for 1. Complexes induce different cell death pathways, predominantly necrosis for 1 and apoptosis for 2. Complexes alternative mode of cell death motivates the possibility for further developments.

Facile preparation of a three-coordinate copper(I) complex: Steric hindrance, supramolecular structure, optical property and TD-DFT study

GRAPHICAL ABSTRACT

Synthesis, Structure, and Photophysical Properties of Mo2(NN)4 and Mo2(NN)2(T(i)PB)2, Where NN = N,N'-Diphenylphenylpropiolamidinate and T(i)PB = 2,4,6-Triisopropylbenzoate.

Two dimolybdenum compounds featuring amidinate ligands with a C≡C bond, Mo2(NN)4 (I), where NN = N,N'-diphenylphenylpropiolamidinate, and trans-Mo2(NN)2(T(i)PB)2 (II), where T(i)PB = 2,4,6-triisopropylbenzoate, have been prepared and structurally characterized by single-crystal X-ray crystallography. Together with Mo2(DAniF)4 (III), where DAniF = N,N'-bis(p-anisyl)formamidinate, all three compounds have been studied with steady-state UV-vis, IR, and time-resolved spectroscopy methods. I and II display intense metal to ligand charge transfer (MLCT). Singlet state (S1) lifetimes of I-III are determined to be 0.7, 19.1, and 2.0 ps, respectively. All three compounds have long-lived triplet state (T1) lifetimes around 100 μs. In femtosecond time-resolved infrared (fs-TRIR) experiments, one ν(C≡C) band is observed at the S1 state for I but two for II, which indicate different patterns of charge distribution. The electron would have to be localized on one NN ligand in I and partially delocalized over two NN ligands in II to account for the observations. The result is a standard showcase of excited-state mixed valence in coordination compounds.

Synthesis, characterization and catalytic reactivity of pentacoordinate iron dicarbonyl as a model of the [Fe]-hydrogenase active site

Two mono iron complexes Fe(CO)2PR3(NN) (R = Cy (3), Ph (4), NN = o-phenylenediamine dianion ligand, N2H2Ph2–) derived from the ligand substitution of Fe(CO)3I2PR3 by the NN ligand were isolated and structurally characterized by single crystal X-ray diffraction. They have a similar first coordination sphere and oxidation state of the iron center as the [Fe]-hydrogenase active site, and can be a model of it. IR demonstrated that the effect of the NN ligand on the coordinated CO stretching frequencies was due to its excellent electron donating ability. The reversible protonation/deprotonation of the NN ligand was identified by infrared spectroscopy and density functional theory computation. The NN ligand is an effective proton acceptor as the internal base of the cysteine thiolate ligand in [Fe]-hydrogenase. The electrochemical properties of complexes 3, 4 were investigated by cyclic voltammograms. Complex 3 catalyzed the transfer hydrogenation of benzoquinone to hydroquinone effectively under mild conditions.

Influence of a Naphthaldiimide Substituent at the Diimine Ligand on the Photophysics and Reverse Saturable Absorption of PtII Diimine Complexes and Cationic IrIII Complexes

AbstractTwo PtII complexes containing benzothiazolylfluorenyl (BTF) acetylide ligands and different diimine (NN) ligands [NN = 1,10‐phenanthroline (1), 5‐naphthaldiimide–1,10‐phenanthroline (2)] and two heteroleptic cationic IrIII complexes containing the 5‐naphthaldiimide–1,10‐phenanthroline ligand and different phenylpyridine (CN) ligands [CN = 2‐phenylpyridine (3), 2‐{3‐[7‐(benzothiazol‐2‐yl)fluoren‐2‐yl]phenyl}pyridine (4)] were synthesized and characterized. The influence of naphthaldiimide (NDI) attached to the NN ligands and benzothiazolylfluorene attached to the CN ligands on the photophysical properties of these PtII/IrIII complexes has been investigated spectroscopically and theoretically. All complexes exhibit ligand‐localized 1π,π* transitions below 400 nm, and broad and structureless metal‐to‐ligand/ligand‐to‐ligand charge transfer (1MLCT/1LLCT) transitions between 400 and 550 nm. Complexes 1 and 4 show red phosphorescence in toluene solutions at room temperature, where the emitting state is assigned predominantly to the 3π,π* state for complex 1 and 3LLCT/3MLCT states for complex 4. Incorporation of the NDI substituent to the NN ligand completely or partially quenches the emission of complexes 2–4. Complexes 1–4 all possess broad singlet transient absorption from 400 to 800 nm, which is ascribed to 1π,π*/1MLCT/1LLCT states for complex 1, and to 1NDI–· for complexes 2–4. The ns transient absorption study reveals that complex 1 exhibits a broad triplet excited‐state absorption from the 3π,π*/3MLCT states, while complexes 2–4 give moderately strong triplet excited‐state absorption from 3NDI–·. Nonlinear transmission experiments at 532 nm using nanosecond laser pulses demonstrate that these complexes all exhibit strong reverse saturable absorption (RSA) at 532 nm for ns laser pulses. Introduction of the NDI substituent to the NN ligand causes charge transfer to the NDI component, which in turn increases the RSA of the PtII complex 2 in comparison with that of the PtII complex 1; while attaching the BTF component to the CN ligands enhances the RSA of the IrIII complex 4 in comparison with that of complex 3.

New Rh2(II,II) Architecture for the Catalytic Reduction of H+

Formamidinate-bridged Rh2(II,II) complexes containing diimine ligands of the formula cis-[Rh2(II,II)(μ-DTolF)2(NN)2](2+) (Rh2-NN2), where DTolF = p-ditolylformamidinate and NN = dppn (benzo[i]dipyrido[3,2-a:2',3'-h]quinoxaline), dppz (dipyrido[3,2-a:2',3'-c]phenazine), and phen (1,10-phenanthroline), electrocatalytically reduce H(+) to H2 in DMF solutions containing CH3COOH at a glassy carbon electrode. Cathodic scans in the absence of acid display a Rh(III,II/II,II) reduction at -0.90 V vs Fc(+)/Fc followed by NN(0/-) reduction at -1.13, -1.36, and -1.65 V for Rh2-dppn2, Rh2-dppz2, and Rh2-phen2, respectively. Upon the addition of acid, Rh2-dppn2 and Rh2-dppz2 undergo reduction-protonation-reduction at each pyrazine-containing NN ligand prior to the Rh2(II,II/II,I) reduction. The Rh2(II,I) species is then protonated at one of the metal centers, resulting in the formation of the corresponding Rh2(II,III)-hydride. In the case of Rh2-phen2, the reduction of the phen ligand is followed by intramolecular electron transfer to the Rh2(II,II) core in the presence of protons to form a Rh2(II,III)-hydride species. Further reduction and protonation at the Rh2 core for all three complexes rapidly catalyzes H2 formation with varied calculated turnover frequencies (TOF) and overpotential values (η): 2.6 × 10(4) s(-1) and 0.56 V for Rh2-dppn, 2.8 × 10(4) s(-1) and 0.50 V for Rh2-dppz2, and 5.9 × 10(4) s(-1) and 0.64 V for Rh2-phen2. Bulk electrolysis confirmed H2 formation, and further CH3COOH addition regenerates H2 production, attesting to the robust nature of the architecture. The cis-[Rh2(II,II)(μ-DTolF)2(NN)2](2+) architecture benefits by combining electron-rich formamidinate bridges, a redox-active Rh2(II,II) core, and electron-accepting NN diimine ligands to allow for the electrocatalysis of H(+) substrate to H2 fuel.

Expanding the family of heteroleptic oxidovanadium(IV) compounds with salicylaldehyde semicarbazones and polypyridyl ligands showing anti-Trypanosoma cruzi activity

Searching for prospective vanadium-based drugs for the treatment of Chagas disease, a new series of heteroleptic [VIVO(L-2H)(NN)] compounds was developed by including the lipophilic 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp) NN ligand and seven tridentate salicylaldehyde semicarbazone derivatives (L1–L7). The compounds were characterized in the solid state and in solution. EPR spectroscopy suggests that the NN ligand is bidentate bound through both nitrogen donor atoms in an axial–equatorial mode. The EPR and 51V-NMR spectra of aerated solutions at room temperature indicate that the compounds are stable to hydrolysis and that no significant oxidation of VIV to VV takes place at least in 24h. The complexes are more active in vitro against Trypanosoma cruzi, the parasite responsible for Chagas disease, than the reference drug Nifurtimox and most of them are more active than previously reported [VIVO(L-2H)(NN)] complexes of other NN co-ligands. Selectivity towards the parasite was analyzed using J-774 murine macrophages as mammalian cell model. Due to both, high activity and high selectivity, L2, L4, L5 and L7 complexes could be considered new hits for further drug development. Lipophilicity probably plays a relevant role in the bioactivity of the new compounds. The [VIVO(L-2H)(NN)] compounds were designed aiming DNA as potential molecular target. Therefore, the novel L1–L7 tmp complexes were screened by computational modeling, comparing their DNA-binding features with those of previously reported [VIVO(L-2H)(NN)] compounds with different NN co-ligands. Whereas all the complexes interact well with DNA, with binding modes and strength tuned in different extents by the NN and semicarbazone co-ligands, molecular docking suggests that the observed anti-T. cruzi activity cannot be explained upon DNA intercalation as the sole mechanism of action.

Heteroleptic Silver(I) Complexes Prepared from Phenanthroline and Bis-phosphine Ligands

The heteroleptic coordination scenario of silver(I) with various phenanthroline ligands (NN) and different bis-phosphine (PP) derivatives has been investigated. In addition to the X-ray crystal structural characterization of the resulting mixed ligand Ag(I) complexes, detailed NMR studies have been performed to disclose the behavior of the prepared silver(I) complexes in solution. The results obtained with silver(I) have been also systematically related to the one obtained for copper(I) with the same combination of PP and NN ligands. Starting from an equimolar mixture of AgBF4, bis[(2-diphenylphosphino)phenyl] ether (POP), and 1,10-phenanthroline (phen), the mononuclear complex [Ag(POP)(phen)](+) has been obtained as the tetrafluoroborate salt. By following the same experimental procedure starting from bis(diphenylphosphino)methane (dppm) or 1,3-bis(diphenylphosphino)propane (dppp) as the PP ligand, dinuclear complexes with two bridging PP ligands, i.e., [Ag2(NN)2(μ-dppm)2](2+) and [Ag2(NN)2(μ-dppp)2](2+) with NN = phen or Bphen (bathophenanthroline), have been isolated as the tetrafluoroborate salts. Surprisingly, by using an equimolar ratio of AgBF4, phen or Bphen, and 1,2-bis(diphenyl-phosphino)ethane (dppe), the corresponding monobridged diphosphine dinuclear complexes [Ag2(NN)2(μ-dppe)](2+) have been obtained as the tetrafluoroborate salts. These compounds have been also prepared in excellent yield by using a more appropriate 2:1:2 (phen:dppe:Ag) stoichiometry. These results prompted us to also perform the reactions with dppm and dppp using a 1:2:2 (PP:NN:Ag) stoichiometry. Under these conditions, [Ag2(NN)2(μ-dppm)](BF4)2 (NN = phen or Bphen) and [Ag2(NN)2(μ-dppp)](BF4)2 (NN = phen or Bphen) have been obtained upon crystallization. When compared to their copper(I) analogues, the complexation scenario becomes more complex with silver(I) as the system tolerates also coordinatively frustrated metal ligand assemblies, i.e., with a trigonal coordination geometry. Depending on the stoichiometry or on the nature of the PP partner, silver(I) shows an adaptive capability leading to various complexes with different coordination geometries and composition. However, as in the case of copper(I), their solution behavior is highly dependent on the relative thermodynamic stability of the various possible complexes. In most of the cases, a single Ag(I) complex is observed in solution and the NMR data are in a perfect agreement with their solid state structures. The dppp-containing complexes are the only notable exception; both [Ag2(NN)2(μ-dppp)2](BF4)2 and [Ag2(NN)2(μ-dppp)](BF4)2 are stable in the solid state but a dynamic mixture is observed as soon as these compounds are dissolved. Finally, whereas both dppe and dppp are chelating ligands for copper(I), it is not the case anymore with silver(I) for which a destabilization of species with chelating dppe and dppp ligands is clearly suggested by our results.

Secondary Kinetic Isotope Effects in Oxidative Addition of Benzyl Bromide to Dimethylplatinum(II) Complexes

The secondary α-deuterium kinetic isotope effects (KIEs), (kH/kD)α, have been determined, at different temperatures and in solvents having different polarities, for reaction of PhCH2Br/PhCD2Br with the dimethylplatinum(II) complexes [PtMe2(NN)], in which the bidentate NN ligand is bpy (=2,2′-bipyridine) or bu2bpy (=4,4′-di-tert-butyl-2,2′-bipyridine). The values obtained for the secondary α-deuterium KIEs in acetone solution are close to 1 and may be normal or inverse, but much larger values are found for the reactions in benzene. An explanation is presented on the basis of solvent dependence of the degree of looseness of the transition state in the SN2 mechanism.

Functional models of α-keto acid dependent nonheme iron oxygenases: synthesis and reactivity of biomimetic iron(II) benzoylformate complexes supported by a 2,9-dimethyl-1,10-phenanthroline ligand

Two biomimetic iron(II) benzoylformate complexes, [LFe(II)(BF)(2)] (2) and [LFe(II)(NO(3))(BF)] (3) (L is 2,9-dimethyl-1,10-phenanthroline and BF is monoanionic benzoylformate), have been synthesized from an iron(II)-dichloro complex [LFe(II)Cl(2)] (1). All the iron(II) complexes have been structurally and spectroscopically characterized. The iron(II) center in 2 is coordinated by a bidentate NN ligand (2,9-dimethyl-1,10-phenanthroline) and two monoanionic benzoylformates to form a distorted octahedral coordination geometry. One of the benzoylformates binds to the iron in 2 via both carboxylate oxygens but the other one binds in a chelating bidentate fashion via one carboxylate oxygen and the keto oxygen. On the other hand, the iron(II) center in 3 is ligated by one NN ligand, one bidentate nitrate, and one monoanionic chelating benzoylformate. Both iron(II) benzoylformate complexes exhibit the facial NNO donor environment in their solid-state structures. Complexes 2 and 3 are stable in noncoordinating solvents under an inert atmosphere, but react with dioxygen under ambient conditions to undergo oxidative decarboxylation of benzoylformate to benzoate in high yields. Evidence for the formation of an iron(IV)-oxo intermediate upon oxidative decarboxylation of benzoylformate was obtained by interception and labeling experiments. The iron(II) benzoylformate complexes represent the functional models of α-keto acid dependent oxygenases.

A Bis(terpyridine)ruthenium Complex with Three Redox-Active Amine Sites: Electrochemical, Optical, and Computational Studies

Two ruthenium complexes, [Ru(NN)(ttpy)](2+) and [Ru(NN)(daatpy)](2+), have been designed and prepared, where NN is bis(amine) ligand 4'-tolyl-5,5"-bis(di-p-anisylamino)-2,2':6',2"-terpyridine, ttpy is 4'-tolyl-2,2':6',2"-terpyridine, and daatpy is 4'-di-p-anisylamino-2,2':6',2"-terpyridine. Complex [Ru(NN)(daatpy)](2+) contains three redox-active amine groups and has been characterized by single-crystal X-ray analysis. These two complexes display much-enhanced light absorption capabilities with respect to the prototype compound [Ru(tpy)(2)](2+) (tpy = 2,2':6',2"-terpyridine), which has been rationalized on the basis of time-dependent density functional theory calculations. Electrochemical and optical studies showed that there was little electronic coupling between two amine sites in complex [Ru(NN)(ttpy)](2+). On the other hand, a ligand-to-ligand (N → N'(•+)) charge-transfer band has been observed at 1430 nm for singly and doubly oxidized forms of [Ru(NN)(daatpy)](2+), and an electronic coupling parameter of 1000 cm(-1) was derived using the Hush formula. This band is interpreted as a charge transfer from the neutral amine of the daatpy ligand to oxidized aminium units in the NN ligand.

Correction to Blue-Light Emission of Cu(I) Complexes and Singlet Harvesting

Page 8293. The emission decay time of Cu(pop)(pz₂Bph₂) at ambient temperature is erroneously given as 13 s instead of 13 μs. This short decay time represents an essential and characteristic property of the discussed Cu(I) complex. Therefore, the corrected Abstract is reproduced again. Strongly luminescent neutral copper(I) complexes of the type Cu(pop)(NN), with pop = bis(2-(diphenylphosphanyl)-phenyl)ether and NN = bis(pyrazol-1-yl)borohydrate (pz₂BH₂), tetrakis(pyrazol-1-yl)borate (pz₄B), or bis(pyrazol-1-yl)-biphenylborate (pz₂Bph₂), are readily accessible in reactions of Cu(acetonitrile)⁴⁺ with equimolar amounts of the pop and NN ligands at ambient temperature. All products were charcterized by means of single crystal X-ray diffractometry. The compounds exhibit very strong blue/white luminescence with emission quantum yields of up to 90%. Investigations of spectroscopic properties and the emission decay behavior in the temperature range between 1.6 K and ambient temperature allow us to assign the emitting electronic states. Below 100 K, the emission decay times are in the order of many hundreds of microseconds. Therefore, it is concluded that the emission stems from the lowest triplet state. This state is assigned to a metal-to-ligand charge-transfer state (³MLCT) involving Cu-3d and pop-π* orbitals. With temperature increase, the emission decay time is drastically reduced, e.g. to 13 μs (Cu(pop)-(pz₂Bph₂)), at ambient temperature. At this temperature, the complexes exhibit high emission quantum yields, as neat material or doped into poly(methyl methacrylate) (PMMA). This behavior is assigned to an efficient thermal population of a singlet state (being classified as ¹MLCT), which lies only 800 to 1300 cm⁻¹ above the triplet state, depending on the individual complex. Thus, the resulting emission at ambient temperature largely represents a fluorescence. For applications in OLEDs and LEECs, for example, this type of thermally activated delayed fluorescence (TADF) creates a new mechanism allowing for harvesting both singlet and triplet excitations in the lowest singlet state. This effect of singlet harvesting leads to drastically higher radiative rates than obtainable for emissions from triplet states of Cu(I) complexes.

Synthesis and Self-Association of Organoplatinum(IV) Boronic Acids

Oxidative addition of ortho,meta, and para isomers of BrCH2C6H4B(OH)2 to dimethylplatinum(II) complexes gave the corresponding organoplatinum(IV) boronic acids [PtBrMe2{CH2C6H4B(OH)2}(NN)], with the bidentate ligand NN = 4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine or 2,5-bis(2-pyridyl)-1,3,4-oxadiazole. The complexes undergo self-assembly in the solid state through hydrogen bonding to give dimers, polymers, or sheet structures.

Blue-Light Emission of Cu(I) Complexes and Singlet Harvesting

Strongly luminescent neutral copper(I) complexes of the type Cu(pop)(NN), with pop = bis(2-(diphenylphosphanyl)phenyl)ether and NN = bis(pyrazol-1-yl)borohydrate (pz(2)BH(2)), tetrakis(pyrazol-1-yl)borate (pz(4)B), or bis(pyrazol-1-yl)-biphenyl-borate (pz(2)Bph(2)), are readily accessible in reactions of Cu(acetonitrile)(4)(+) with equimolar amounts of the pop and NN ligands at ambient temperature. All products were characterized by means of single crystal X-ray diffractometry. The compounds exhibit very strong blue/white luminescence with emission quantum yields of up to 90%. Investigations of spectroscopic properties and the emission decay behavior in the temperature range between 1.6 K and ambient temperature allow us to assign the emitting electronic states. Below 100 K, the emission decay times are in the order of many hundreds of microseconds. Therefore, it is concluded that the emission stems from the lowest triplet state. This state is assigned to a metal-to-ligand charge-transfer state (3MLCT) involving Cu-3dand pop-π* orbitals. With temperature increase, the emission decay time is drastically reduced, e.g. to 13 μs [corrected] (Cu(pop)-(pz(2)Bph(2))), at ambient temperature. At this temperature, the complexes exhibit high emission quantum yields, as neat material or doped into poly(methyl methacrylate) (PMMA). This behavior is assigned to an efficient thermal population of a singlet state (being classified as (1)MLCT), which lies only 800 to 1300 cm(-1) above the triplet state, depending on the individual complex. Thus, the resulting emission at ambient temperature largely represents a fluorescence. For applications in OLEDs and LEECs, for example, this type of thermally activated delayed fluorescence (TADF) creates a new mechanism that allows to harvest both singlet and triplet excitons (excitations) in the lowest singlet state. This effect of singlet harvesting leads to drastically higher radiative rates than obtainable for emissions from triplet states of Cu(I) complexes.

A Structure–Activity Study of Ni-Catalyzed Alkyl–Alkyl Kumada Coupling. Improved Catalysts for Coupling of Secondary Alkyl Halides

A structure-activity study was carried out for Ni catalyzed alkyl-alkyl Kumada-type cross coupling reactions. A series of new nickel(II) complexes including those with tridentate pincer bis(amino)amide ligands ((R)N(2)N) and those with bidentate mixed amino-amide ligands ((R)NN) were synthesized and structurally characterized. The coordination geometries of these complexes range from square planar, tetrahedral, to square pyramidal. The complexes had been examined as precatalysts for cross coupling of nonactivated alkyl halides, particularly secondary alkyl iodides, with alkyl Grignard reagents. Comparison was made to the results obtained with the previously reported Ni pincer complex [((Me)N(2)N)NiCl]. A transmetalation site in the precatalysts is necessary for the catalysis. The coordination geometries and spin-states of the precatalysts have a small or no influence. The work led to the discovery of several well-defined Ni catalysts that are significantly more active and efficient than the pincer complex [((Me)N(2)N)NiCl] for the coupling of secondary alkyl halides. The best two catalysts are [((H)NN)Ni(PPh(3))Cl] and [((H)NN)Ni(2,4-lutidine)Cl]. The improved activity and efficiency was attributed to the fact that phosphine and lutidine ligands in these complexes can dissociate from the Ni center during catalysis. The activation of alkyl halides was shown to proceed via a radical mechanism.

Dynamic ring-opening polymerization of silver(i) complexes with bis(amidopyridine) ligands

The factors which influence the formation of chelate, macrocycle or polymer in the reaction of silver(i) salts with bis(pyridine) ligands have been probed by studying structures in the solid state and cold spray ionization mass spectra in solution, with the ligands C(6)H(4)-1,3-[CONR(CH(2))(n)-3-C(5)H(4)N](2), 1 (R = Me, n = 0) or (R = H, n = 1) or 5-t-Bu-C(6)H(3)-1,3-[CONR(CH(2))(n)-4-C(5)H(4)N](2), 2 (R = Me, n = 0) or 4 (R = H, n = 1). In both the solid state and solution, the complex [Ag12)]BF(4) exists as a chelate complex 5. The ligands NN = 2-4 form complexes in the solid state with either macrocyclic structures [Ag(2)(mu-NN)(2)]X(2) [6, NN =2, X = BF(4); 9, NN = 3, X = NO(3)] or polymeric structures [7, NN = 2, X = NO(3); 8, NN = 3, X = CF(3)CO(2); 10, NN = 4, X = CF(3)CO(2)]. The ligands 2 and 3 gave both macrocyclic and polymeric complexes, depending on the anion. In solution, these complexes existed as mixtures of macrocycles and ring-opened oligomers. In the crystalline state, the complexes 6-10 underwent supramolecular association through combinations of hydrogen bonding, secondary bonding of the type Ag...X to anions, or argentophilic bonding of the type Ag...Ag.

Tetrapodal pentadentate ligands: Single site reactivity and bond activation in iron(II) complexes

Tetrapodal pentadentate ligands occupy five coordination positions in a coordination octahedron, thereby providing the metal ion with a square-pyramidal "coordination cap": In such complexes, all reactivity is focused on a single coordination site. The review highlights recent advances in the coordination chemistry of iron. With a variety of NN(4) ligands, the concept is being used to model non-heme active sites in biomolecules. Tetraphosphane ligands (donor set: NP(4)) undergo, depending on the solvent, remarkably specific P-C bond activation reactions, which may be reversed under suitable conditions.

Synthesis and Photophysical Properties of Copper(I) Complexes Obtained from 1,10‐Phenanthroline Ligands with Increasingly Bulky 2,9‐Substituents

AbstractIn this paper, we describe the synthesis and the electronic properties of a series of [Cu(NN)2]+ systems. The NN ligands investigated are 2,9‐bis[(tert‐butyldimethylsilyloxy)methyl]‐1,10‐phenanthroline (1), 2,9‐bis[(triisopropylsilyloxy)methyl]‐1,10‐phenanthroline (2), 2,9‐bis[(tert‐butyldiphenylsilylmoxy)ethyl]‐1,10‐phenanthroline (3), 2,9‐bis[2,6‐bis(benzyloxy)phenethyl]‐1,10‐phenanthroline (4) and 2‐(1,3‐diphenylpropan‐2‐yl)‐9‐phenethyl‐1,10‐phenanthroline (5). The electrochemical properties and the ground state electronic absorption spectra of Cu(1)2–Cu(5)2 are in line with the classical behaviour of such [Cu(NN)2]+ derivatives. Whereas all the compounds exhibit MLCT luminescence centered around 630–650 nm, the emission quantum yields and the lifetimes are dramatically different as a function of stereoelectronic effects and/or the possibility of internal exciplex quenching when oxygen‐containing functional groups are attached to the phenanthroline ligands.

Steric and Solvent Effects on the Secondary Kinetic α-Deuterium Isotope Effects in the Reaction of Methyl Iodide with Organoplatinum(II) Complexes: Application of a Second-Order Technique in Measuring the Rates of Rapid Processes

The kinetic isotope effects (KIEs), kH/kD, have been determined for reaction of CH3I/CD3I with several organoplatinum(II) complexes [PtR2(NN)], in which the bidentate NN ligand is bpy = 2,2′-bipyridine, tBu2bpy = 4,4′-bis(tert-butyl)-2,2′-bipyridine, phen = 1,10-phenanthroline, or Me2phen = 2,9-dimethyl-1,10-phenanthroline, at different temperatures and in solvents having different polarities. The values obtained for the secondary α-deuterium KIEs are close to 1 and are dependent on the solvent; values of up to 7−10% larger are obtained for the reactions in the polar solvent acetone as compared to those obtained in the nonpolar solvent benzene. The data also indicate that the steric crowding around the square-planar coordination sphere of the platinum(II) complexes with the ligand Me2phen results in higher KIEs. The reactions involving dimethylplatinum(II) complexes, [PtMe2(NN)], were fast, and a 1:1 molar ratio (of complex and reagent) technique was successfully used to measure the rate constants accurately by conventional UV−visible spectroscopy. It is shown that there are significant advantages to measuring the reaction rates under second-order condition, as compared to the usual pseudo-first-order method.

Nickel Complexes of a Pincer Amidobis(amine) Ligand: Synthesis, Structure, and Activity in Stoichiometric and Catalytic CC Bond‐Forming Reactions of Alkyl Halides

The synthesis, properties, and reactivity of nickel(II) complexes of a newly developed pincer amidobis(amine) ligand ((Me)NN(2)) are described. Neutral or cationic complexes [((Me)NN(2))NiX] (X = OTf (6), OC(O)CH(3) (7), CH(3)CN (8), OMe (9)) were prepared by salt metathesis or chloride abstraction from the previously reported [((Me)NN(2))NiCl] (1). The Lewis acidity of the {((Me)NN(2))Ni} fragment was measured by the (1)H NMR chemical shift of the coordinated CH(3)CN molecule in 8. Electrochemical measurements on 1 and 8 indicate that the electron-donating properties of NN(2) are similar to those of the analogous amidobis(phosphine) (pnp) ligands. The solid-state structures of 6-8 were determined and compared to those of 1 and [((Me)NN(2))NiEt] (3). In all complexes, the (Me)NN(2) ligand coordinates to the Ni(II) ion in a mer fashion, and the square-planar coordination sphere of the metal is completed by an additional donor. The coordination chemistry of (Me)NN(2) thus resembles that of other three-dentate pincer ligands, for example, pnp and arylbis(amine) (ncn). Reactions of 2 with alkyl monohalides, dichlorides, and trichlorides were investigated. Selective C-C bond formation was observed in many cases. Based on these reactions, efficient Kumada-Corriu-Tamao coupling of unactivated alkyl halides and alkyl Grignard reagents with 1 as the precatalyst was developed. Good yields were obtained for the coupling of primary and secondary iodides and bromides. Double C-C coupling of CH(2)Cl(2) with alkyl Grignard reagents by 1 was also realized. The scope and limitations of these transformations were studied. Evidence was found for a radical pathway in Ni-catalyzed C-C cross-coupling reactions, which involves Ni(II) alkyl intermediates.