Synthesis and characterization of ruthenium(II) complexes based on diphenyl-2-pyridylphosphine and their applications in transfer hydrogenation of ketones

Synthesis and characterization of the ruthenium complexes [RuH(CO)Cl(κ¹-P-PPh₂Py)₂(PPh₃)] (1) and [Ru(CO)Cl₂(κ¹-P-PPh₂Py)(κ²-P-N-PPh₂Py)] (2) containing diphenyl-2-pyridylphosphine (PPh₂Py) are described. Spectral and structural data suggested linkage of the PPh₂Py in κ¹-P bonding mode in 1 and both the κ¹-P and κ²-P-N bonding modes in 2. The complex 1 reacted with N,N-donor bases viz., ethylenediamine (en), N,N′-dimethyl-(ethylenediamine) (dimen), 1,3-diaminopropane (diap), 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) and di-2-pyridylaminomethylbenzene (dpa) to afford cationic complexes of formulation [RuH(CO)(κ¹-P-PPh₂Py)₂(N-N)]⁺ (3-8) [N-N = en, 3; dimen, 4; diap, 5; bipy, 6; phen, 7; and dpa, 8], which have been isolated as their tetrafluoroborate salts. The complexes under investigation have been characterized by elemental analyses, spectroscopic and electrochemical studies. Molecular structures of 2, 3, 6, and 8 have been determined by single crystal X-ray diffraction analyses. Further, the complexes 1-8 act as effective precursor catalyst in transfer hydrogenation of acetophenone/ketones in basic 2-propanol.     

A systematic study on the thermal decomposition reactions of coordination polymers based on metal(II) selenocyanates and 4,4′-bipyridine: Directed synthesis of a μ-1,3 bridging selenocyanate

Reaction of manganese(II), iron(II), cobalt(II) and nickel(II) selenocyanate with 4,4′-bipyridine (bipy) in water at room temperature leads to the formation of the ligand-rich 1:2 hydrates [{M(bipy)(NCSe)₂(H₂O)₂}·bipy]_n (bipy = 4,4′-bipyridine) with M = Mn (1-Mn), Fe (1-Fe), Co (1-Co) and Ni (1-Ni). In their crystal structures, the metal cations are coordinated by two terminally N-bonded selenocyanato anions, two water molecules, and two bridging bipy ligands in an octahedral coordination mode. These building blocks are connected into linear M-bipy-M chains, which are further linked by hydrogen bonds between the water molecules and non-coordinated bipy ligands into layers. On heating these precursor compounds, they decompose into ligand-rich 1:2 anhydrates [M(NCSe)₂(bipy)₂]_n with M = Mn (2-Mn), Fe (2-Fe), Co (2-Co) and Ni (2-Ni). After water removal the coordination spheres of the metal cations are completed by N-coordination of the bipy ligand which formerly was involved in OH···N hydrogen bonding. On further heating, the manganese(II) compound loses half of its bipy ligands leading to a new ligand-deficient 1:1 intermediate [Mn(NCSe)₂(bipy)]_n (3-Mn) with μ-1,3-bridging selenocyanato anions. In contrast, all other compounds decompose without the formation of ligand-deficient intermediates. These structural changes are accompanied with a dramatic change in their magnetic properties: Whereas all ligand-rich 1:2 compounds 1-M and 2-M (M = metal) show only Curie-Weiss paramagnetism, in the ligand-deficient 1:1 intermediate 3-Mn an antiferromagnetic long-range ordering at T_N = 10.5 K is found. The thermal and magnetic properties are qualitatively compared with those of the related ligand-rich and ligand-deficient selenocyanato and thiocyanato compounds based on bipy, pyrazine and pyrimidine as ligand.     

Neighbouring metal induced oxidative addition at the iron centre amongst the iron-arylpyridylphosphine complexes

Complexes of the type (η⁴-BuC₅H₅)Fe(CO)₂(P) (P = PPh₂Py 3, PPhPy₂4, PPy₃5; Py = 2-pyridyl) were satisfactorily prepared. Upon treatment of 3 with M(CO)₃(EtCN)₃ (M = Mo, 6a; W, 6b), the pyridyl N-atom could be coordinated to the metal M, which then eliminates a CO ligand from the Fe-centre and induced an oxidative addition of the endo-C-H of (η⁴-BuC₅H₅). This results in a bridged hydrido heterodimetallic complex [(η⁵-BuC₅H₄)Fe(CO)(μ-P,N-PPh₂Py)(μ-H)M(CO)₄] (M = Mo, 7a, 81%; W, 7b, 76%). The reaction of 4 or 5 with 6a,b did not give the induced oxidative addition, although these complexes contain more than one pyridyl N-atom. The reaction of 4 with M(CO)₄(EtCN)₂ (M = Mo, 9a; W, 9b) produced heterodimetallic complexes [(η⁴-BuC₅H₅)Fe(CO)₂(μ-P:N,N′-PPhPy₂)M(CO)₄] (M = Mo, 10a, 81%; W, 10b, 83%). Treatment of 5 with 6a,b gave [(η⁴-BuC₅H₅)Fe(CO)₂(μ-P:N,N′,N″-PPy₃)M(CO)₃] (M = Mo, 12a, 96%; W, 12b, 78%).     

Luminescence properties of cyclopalladated complexes with Schiff base ligands

Direct reaction between the hydroxo-complexes [{Pd(μ-OH)(C^N)}₂] (C^N = 2-(2-pyridyl)phenyl (Phpy) I; C^N = 7,8-benzoquinolyl (Bzq) II) and N-naphtylsalycilaldimine (N-naphsal) 1 yields new mononuclear cyclometallated palladium(II) complexes [Pd(N-naphsal)(C^N)] (I1, II1). Photophysical properties were investigated together with those of complexes with related ligands N-phenylsalycilaldiminate (N-Phsal) 2, N-p-chlorophenylsalycilaldiminate (N-pClPhsal) 3. All the compounds absorb intensely below 300 nm via¹LC transitions located in Bzq or Phpy ligands, and display additional low energy absorptions of mixed ¹MLCT-¹LC character. The complexes under study are quite unusual in terms of luminescence behavior, since some of them are emissive in solution at room temperature and all display intense emissions in frozen CHCl₃ solution, but also in solid state at 298 and 77 K. Structural characterization by X-ray diffraction of complexes I2, I3 and II2 confirmed the proposed formulae.     

New insight in coordination of vic-dioximes: Bis- and tris(E,E-dioximato)Ni(II) complexes

N,N′-Bis[allylamino]glyoxime, N,N′-bis[anilino]glyoxime, and N,N′-bis[1,2,3,4-tetrahydro-5-naphthalenamino]glyoxime have been prepared from corresponding amines and (E,E)-dichloroglyoxime. These ligands gave orange-red compound with NiCl₂ in less acidic medium (pH ∼ 5) that are bis(E,E-dioximato)nickel(II) complexes {[(E,E)-Ni(HL)₂]} (1a-3a) and green compounds in acidic medium (pH ∼ 2) that are tris(E,E-dioximato)nickel(II) dichloride complexes {[(E,E)-Ni(LH₂)₃]Cl₂} (1b-3b). The crystal structures of all complexes have been determined by X-ray diffraction on a single crystal. The study of absorption spectra of these two types of complexes shows that they may be converted to each other by addition of acids (1a-3a) or bases (1b-3b) and there is no way for the amphi form.     

Functional mimics of catechol oxidase by mononuclear copper complexes of sterically demanding [NNO] ligands

Several mononuclear copper complexes 1(a-b) and 2(a-b) supported over sterically demanding [NNO] ligands namely, N-(aryl)-2-[(pyridin-2-ylmethyl)amino]acetamide [aryl = 2,6-diethylphenyl (1) and mesityl (2)], exhibit catecholase-like activity in performing the aerial oxidation of 3,5-di-t-butylcatehol (3,5-DTBC) to 3,5-di-t-butyl-catequinone (3,5-DTBQ) under ambient conditions. The 1(a-b) and 2(a-b) complexes were directly synthesized from the reaction of the respective ligands 1-2 with CuX₂·nH₂O (X = Cl, NO₃, n = 2, 3) in 55-85% yield. Mechanistic insights on the catalytic cycle as obtained by density functional theory studies for a representative complex 1a suggest that an intramolecular hydrogen transfer, from a catechol-OH moiety to a copper bound superoxo moiety, form the rate-determining step of the oxidation process, displaying an activation barrier of 18.3 kcal/mol (ΔG^‡) [6.9 kcal/mol in Δ(PE + ZPE)^‡ scale].     

Different coordination modes of 5,5-diethylbarbiturate in the copper(II) complexes with some aliphatic amines: Synthesis, spectroscopic, thermal and structural studies

Three new copper(II) complexes of 5,5-diethlybarbiturate (barb), [Cu(barb)₂(dmen)]·0.5H₂O (dmen = N,N-dimethylethylenediamine) 1, [Cu(barb)₂(bapa)] (bapa = bis(3-aminopropyl)amine) 2, and [Cu(barb)(apen)](barb)·2H₂O (apen = N,N′-bis(3-aminopropyl)ethylenediamine) 3, have been synthesized and characterized by chemical, spectroscopic and thermal methods. Single crystal X-ray diffraction studies revealed that all complexes are mononuclear. The copper(II) ion exhibits a square-pyramidal coordination geometry in 1 and 3, but a trigonal-bipyramidal geometry in 2. The barb ligand shows different coordination modes. 1 presents the unequal coordination of the barb ligands: one is monodentate (N) and the other one is bidentate (N, O). In 2, both barb ligands are N-coordinated, whereas in 3, one barb ligand is N-coordinated, while the second barb ligand behaves as a counter-ion. The dmen, bapa and apen ligands act as bi-, tri- and tetradentate ligands, respectively. All complexes display a hydrogen-bonded network structure. The IR spectroscopic analysis shows that the ν(CO) stretching frequencies do not correlate predictably with the coordination mode of the barb ligand in 1. Thermal analysis data for 1-3 are in agreement with the crystal structures.     

Syntheses, structures and magnetic properties of three 1-D chain metal-nitroxide coordination polymers bridged by e,e-trans-1,4-cyclohexanedicarboxylate

Three new one-dimensional (1-D) chain metal-nitroxide complexes of the formula [M(NIT4Py)₂(e,e-trans-1,4-chdc)(H₂O)₂]_n (M = Co(II) 1, Ni(II) 2 and Zn(II) 3; NIT4Py = 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and 1,4-chdc = 1,4-cyclohexanedicarboxylate dianion) have been synthesized and characterized structurally as well as magnetically. The X-ray crystal structure analyses of complexes 1, 2 and 3 reveal that they are isostructural. Three complexes all crystallize in neutral 1-D chains where metal-nitroxide units [M(NIT4Py)₂(H₂O)₂] are linked by the linear 1,4-cyclohexanedicarboxylate dianion. The 1,4-chdc completes the segregation and only possesses the e,e-trans-conformation, although there are both cis- and trans-isomers in the raw material. The magnetic measurements show that complexes 1 and 2 both exhibit weak antiferromagnetic interactions between the metal ions and the nitroxides.     

Synthesis, characterization and magnetic properties of new homotrinuclear copper(II) complexes

Two new mononuclear bis(oxamato) complexes with the formula [nBu₄N]₂[M(nabo)] M = Ni (4), Cu (5), with nabo = 2,3-naphthalene-bis(oxamato) have been synthesized as precursors for trinuclear oxamato-bridged transition metal complexes. Starting from 5 the homo-trinuclear complex [Cu₃(nabo)(pmdta)₂(BF₄)](BF₄) · MeCN · Et₂O (7), with pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, has been prepared. The central N,N′-2,3-naphthalene bridge of 7 is so far the most extended π-conjugated bridge of trinuclear bis(oxamato) type transition metal complexes. The goal of this work was to verify the N,N′-2,3-naphthalene bridge of 7 on its magnetic properties in comparison to the N,N′-o-phenylene bridge of the related homo-trinuclear complex [Cu₃(opba)(pmdta)₂(NO₃)](NO₃) · 2MeCN (6) (opba = o-phenylene-bis(oxamato)). The crystal structures of 4-7 were solved. The magnetic properties of 6 and 7 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, values of −89 cm⁻¹ (6) and −113 cm⁻¹ (7) were obtained. The different J values are discussed based on the crystal structures of 6 and 7.     

X-ray powder and single crystal structures of two unprecedented families of bpca-based 1-D magnetic chains (Hbpca = bis(2-pyridylcarbonyl)amine)

Two unprecedented families of bpca-based mono-dimensional complexes Cu(bpca)(X) (X = CN, 1; N₃, 2) and [Cu_1 − xFe_x(bpca)](ClO₄) (x = 0, 3; 0.23, 4) were synthesised. The structure of 1 was solved ab initio from X-ray powder diffraction data and refined by Rietveld methods. The complexes 3-4 were characterised by X-ray single crystal diffraction. In 1 the cyano ligand coordinates the metal centres, the Cu centres forming a zigzag 1-D chain along the (0 0 1) direction, while in 3-4, the bpca ligand itself acts as the link towards the metal ions which are arranged in a linear 1-D chain running parallel to the (0 0 1) direction. An infrared spectroscopy study confirmed these coordination modes. The magnetic properties of both chain families were studied. 1-2 do not show significant magnetic interactions, whereas the magnetic behaviour for 3-4 suggests dominant antiferromagnetic interactions between the metal ions within the chains. The magnetic behaviour of 3 was analysed using the Padé approximation of the Bonner-Fisher model for S = 1/2 antiferromagnetic chains. The J value was estimated as 10 K.     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

Fine-tuning the luminescent properties of metal-chelating 8-hydroxyquinolines through amido substituents in 5-position

New series of 5-substituted-8-hydroxyquinolines HL_n (1-6) bearing aliphatic or aromatic amido groups were synthesised. The chelating ability of these ligands toward the zinc(II) ion was tested and the photophysical characterisation of the resulting complexes (ZnL_n)₂ · 2H₂O (7-12) is reported and compared to those of the uncomplexed ligands. The photophysical data of 1-6 revealed interesting differences between aliphatic (1-3) and aromatic (4-6) amido-substituted species which, however, are no longer evident upon metal complexation. In fact while the ligands 1-3 showed a very high quantum yield (2, λ_em=470 nm; Φ=0.22) higher than that of the unsubstituted HQ compound, the ligands 4-6 displayed low quantum yield, similar to that of the complexes 7-12, which was in turn lower than that of ZnQ₂·2H₂O. The behaviour of these compounds is discussed with particular reference to the possibility of controlling the photophysical properties of such compounds through selective modification of the amido substituents.     

New amino-dithiaphospholanes and phosphoramidodithioites and their rhodium and iridium complexes

New sulfur derivatives of phosphoramidite ligands were synthesized and the impact of the sulfur unit on the spectroscopic properties of their rhodium and iridium complexes was investigated. The new ligands Bn₂NPSCH₂CH₂S^a(P-S^a) (Bn = benzyl, 4), Bn₂NPSCHCHS^a(CH₂)₃C^aH₂(P-S^a)(C^a-S^a) (6) and Bn₂NP(4-XC₆H₄OMe)₂ (X = S, 7a; X = O, 7b) were converted to the rhodium and iridium complexes trans-[Rh(CO)Cl(L)₂] (L = 4, 6, 7), [RhCl(COD)(L)] (L = 4, 6, 7), [IrCl(COD)(7a)] and [IrCl₂Cp∗(6)]. For comparison, some phosphoramidite complexes of these formulations also were synthesized. The new metal complexes were spectroscopically analyzed. For the carbonyl complexes, the ν_CO IR stretching frequencies were lower than for the corresponding phosphite and phosphoramidite ligands. The ¹J_PRh coupling constants for the rhodium complexes with the new ligands were also smaller than for the respective phosphoramidite and phosphite complexes. Finally, the ¹J_PSe coupling constants of the selenides of the new ligands were lower than those of the phosphoramidite ligands but higher than for PPh₃. The spectroscopic data reveal that the new thio ligands 4, 6 and 7a are more electron donating than phosphites and phosphoramidites but less electron donating than PPh₃.     

Diamidato-bis(diphenylphosphino) platinum(II) complexes: Synthesis, characterization, and reactivity in the presence of acid

The reaction of Pt(COD)Cl₂, where COD is 1,5-cyclooctadiene, with one equivalent of a diamidato-bis(phosphino) Trost ligand ((R,R)-2 = N,N′-bis(2-diphenylphosphino-1-benzoyl)-(1R,2R)-1,2-diaminocyclohexane, (R,R)-3 = N,N′-bis(2-diphenylphosphino-1-naphthoyl)-(1R,2R)-1,2-diaminocyclohexane, or (±)-4 = N,N′-bis(2-diphenylphosphino-1-benzoyl)-1,2-bis(aminobenzene)) in the presence of base afforded square planar diamidato-bis(phosphino) platinum(II) complexes (R,R)-2-Pt, (R,R)-3-Pt, (±)-4-Pt. Characterization of all complexes included the solution and solid state structure determination of each complex based on multinuclear NMR and X-ray analyses, respectively. Stability of the complexes in acid was examined on addition of HCl to (R,R)-2-Pt in chloroform and compared to the unreactive nature of the similar diamidato-bis(phosphino) complex 1-Pt (1 = 1,2-bis-N-[2′-(diphenylphosphino)benzoyl]diamino-benzene) in the presence of acid. Protonation of the bound amidato nitrogen atoms of (R,R)-2-Pt was observed along with decoordination of the nitrogen atoms from the platinum(II) center producing (R,R)-2-PtCl₂ in quantitative yield by NMR analysis. Confirmation of the product was made on comparison of the NMR spectra to that of authentic (R,R)-2-PtCl₂ prepared on reaction of Pt(COD)Cl₂ with (R,R)-2 in CH₂Cl₂ and characterized by single-crystal X-ray diffraction analysis and NMR spectroscopy. Results add to the knowledge of rich coordination chemistry of bis(phosphino) ligands with late transition metals, metal-amidato chemistry, and has implications in catalysis.     

Towards absolute asymmetric synthesis. Synthesis and crystal structure of stereochemically labile MCl2 (M = Co, Ni, Cu, Zn) complexes with diamine ligands

In search for new conglomerates, seven stereochemically labile complexes between MCl₂ (M = Co, Cu, Ni, Zn) and bidentate ligands, the commercially available N,N,N′-trimethylethane-1,2-diamine (trimeda) and the somewhat bulkier N-isopropyl-N,N′,N′-trimethylethane-1,2-diamine (itmeda), have been synthesized and characterized using single crystal X-ray diffraction. The trimeda and itmeda ligands exhibit chirogenic nitrogen centers and may form chiral metal complexes that are candidates for total spontaneous resolution. Copper(II) chloride forms the dimeric meso complexes [{CuCl₂(trimeda)}₂] (1) and [{CuCl₂(itmeda)}₂] (2), while [CoCl₂(trimeda)₂] (3) and [NiCl₂(trimeda)₂] (4) exhibit six-coordinate but chiral (R,R)- and (S,S)-complexes. Three examples of the chiral target complex, comprising four-coordinate stereochemically labile monomers, was successfully prepared, viz. [NiCl₂(itmeda)] (5), [ZnCl₂(itmeda)] (6), and [CoCl₂(itmeda)] (7).In all seven complexes, the λ-conformation of the five-membered trimeda-metal chelate ring corresponds to the (S)-configuration at nitrogen, and vice versa. Supramolecular interactions in 3 and 4 form hydrogen-bonded heterochiral ribbons. However, crystals of 5-7 display homochiral interactions resulting in polar phases. Weak CH-Cl interactions in 5 and 6 form homochiral layers. In 7, interactions form homochiral helices along the a-axis.     

Synthesis, characterisation and crystal structures of a few coordination complexes of nickel(II), cobalt(III) and zinc(II) with N′-[(2-pyridyl)methylene]salicyloylhydrazone Schiff base

Four new coordination complexes, Ni^II(L)₂ (1), [Co^III(L)₂]ClO₄ (2), [Zn(HL)(L)]ClO₄ · H₂O (3) and [Zn(L)₂][Zn(L)(HL)]ClO₄ · 7H₂O (4) (where L is a monoanion of a Schiff base ligand, N′-[(2-pyridyl)methylene]salicyloylhydrazone (HL) with NNO tridentate donor set), have been synthesised and systematically characterised by elemental analysis, spectroscopic studies and room temperature magnetic susceptibility measurements. Single crystal X-ray diffraction analysis reveals that 1 is a neutral complex, while 2-4 are cationic complexes. Among them, 4 is a rare type of cationic complex with two molecules in the asymmetric unit. The ligand chelates the metal centre with two nitrogen atoms from the pyridine and imino moieties and one oxygen atom coming from its enolic counterpart. All the reported complexes show distorted octahedral geometry around the metal centres, with the two metal-N (imino) bonds being significantly shorter than the two metal-N (Py) bonds.     

An investigation of Cu(II) and Ni(II)-catalysed hydrolysis of (di)imines

The reactions of six diimine ligands with Cu(II) and Ni(II) halide salts have been investigated. The diimine ligands were Ph₂CN(CH₂)_nNCPh₂ (n = 2 (Bz₂en, 1a), 3 (Bz₂pn, 1b), 4 (Bz₂bn, 1c)), N,N′-bis-(2-tert-butylthio-1-ylmethylenebenzene)-2,2′diamino-biphenyl (2), N,N′-bis-(2-chloro-1-ylmethylenebenzene)-1,3-diaminobenzene (3) and N,N′-bis-(2-chloro-1-ylmethylenebenzene)-1,2-ethanediamine (4). Reactions of 1a-c, 2-4 with CuCl₂·2H₂O in dry ethanol at ambient temperature led to complete or partial hydrolysis of the diimine ligands to ultimately form copper diamine complexes. The non-hydrolyzed complexes of 1b and 1c, [Cu(L)Cl₂] (L = 1b, 1c), could be isolated when the reactions were carried out at low temperatures, and the half-hydrolyzed complex [Cu(Bzpn)Cl₂] could also be identified via X-ray crystallography. Similarly, reactions of 1a or 1b with NiCl₂·6H₂O or [NiBr₂(dme)] led to rapid hydrolysis of the imines and Ni complexes containing half-hydrolyzed 1a (Bzen; [trans-[Ni(Bzen)₂Br₂]) and 1b (Bzpn; [Ni(Bzpn)Br₂] could be isolated and identified via single crystal X-ray analysis. Kinetic studies were made of the hydrolyses of 1a, 1b in THF and 2 in acetone, in the presence of Cu(II), and of 1a in acetonitrile, in the presence of Ni(II). Activation parameters were determined for the latter reaction and for the copper-catalyzed hydrolysis of 2; the relatively large negative activation entropies clearly indicate rate-determining steps of an associative nature.     

Extended structures of three new coordination polymers based on 1,10-phenanthroline derivatives and 1,4-benzenedicarboxylate mixed ligands: Preparation, structural characterization and properties

Three coordination polymers, namely, [Cd(HOIP)₂(1,4-bdc)] (1), [Cu(HOIP)(1,4-bdc)] (2) and [Cu(PDIP)(1,4-bdc)] (3) (HOIP = 2-(4-hydroxylbenzene) imidazo[4,5-f]1,10-phenanthroline, PDIP = 2-(3-pyridine) imidazo[4,5-f]1,10-phenanthroline, and 1,4-bdc = 1,4-benzenedicarboxylate), have been synthesized under the hydrothermal conditions. All complexes have been characterized by elemental analyses, IR and single-crystal X-ray diffraction. Structural analyses reveal that complex 1 possesses infinite one-dimensional (1D) chain bridged by 1,4-bdc ligands, complexes 2 and 3 both exhibit two-dimensional (2D) (4,4) network structures based on dinuclear [Cu₂O₂] units. However, the weak interactions are different in complexes 1-3. Moreover, the thermal properties of all complexes, fluorescence property of 1, and the electrochemical behavior of 3 are also reported in this paper.     

Synthesis and electrochemical studies of octahedral nickel β-diketonate complexes

The reaction of [Ni(tmhd)₂] and [Ni(dbm)₂] with N-donor chelating ligands in dichloromethane and acetone, respectively, yields the complexes [Ni(tmhd)₂(L-L)] (L-L = 2,2′-bpy 1, phen 2 and dmae 3) and [Ni(dbm)₂(L-L)] (L-L = 2,2′-bpy 4, phen 5, dmae 6). UV-Vis spectroscopy shows very strong bands in the UV region consistent with ligand centred π → π^∗ transitions. The electrochemical studies of 1-6 reveal oxidation to Ni(III). The [Ni(tmhd)₂(L-L)] 1-3 are more easily oxidized by ca. 300 mV and are quasi-reversible whereas for the [Ni(dbm)₂(L-L)] series only complex 6 shows significant reversibility. X-ray crystallographic studies have been conducted in the case of [Ni(dbm)₂(phen)] 5 and [Ni(dbm)₂(dmae)] 6. The structures both show that the nickel metal centre is octahedral with an O₄N₂ coordination environment. In the structures the β-diketonate ligands exhibit a cis-arrangement, with the metal displaced out of the planar chelate ring.     

Synthesis, structure, and catalytic activity of chiral Cu(II) and Ag(I) complexes with (S,S)-1,2-diaminocyclohexane-based N4-donor ligands

Condensation of (S,S)-1,2-cyclohexanediamine with 2 equiv. of 2-pyridine carboxaldehyde in toluene in the presence of molecular sieves at 70 °C gives N,N′-bis(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine (S,S-1) in 95% yield. Reduction of 1 with an excess of NaBH₄ in MeOH at 50 °C gives N,N′-bis(pyridin-2-ylmethyl)-(S,S)-1,2-cyclohexanediamine (S,S-2) in 90% yield. Reaction of 1 or 2 with 1 equiv. of CuCl₂ · 2H₂O in methanol gives complexes [N-(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine]CuCl₂ (3) and [Cu(S,S-2)(H₂O)]Cl₂ · H₂O (4), respectively, in good yields. Complex 4 can further react with 1 equiv. of CuCl₂ · 2H₂O in methanol to give [Cu(S,S-2)][CuCl₄] (5) in 75% yield. The rigidity of the ligand coupled with the steric effect of the free anion plays an important role in the formation of the helicates. Treatment of ligand S,S-1 with AgNO₃ induces a polymer helicate {[Ag(S,S-1)][NO₃]}_n (6), while reaction of ligand 2 with AgPF₆ or AgNO₃ in methanol affords a mononuclear single helicate [Ag(S,S-2)][PF₆] (7) or a dinuclear double helicate [Ag₂(S,S-2)₂][NO₃]₂ · 2CH₃OH (8) in good yields, respectively. All compounds have been characterized by various spectroscopic data and elemental analyses. Compounds 1, 3-5, 7 and 8 have been further subjected to single-crystal X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do show catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.