Networks based on hydrogen-bonds containing phosphorus anions and tris(3,5-dimethylpyrazolyl)borate nickel(II) moieties

Five structural kinds of nickel hydrogen-bonded networks containing hydrotris(3,5-dimethylpyrazolyl)borate ligands (Tp^∗) have been elucidated by X-ray diffraction, [Tp^∗Ni(OH₂)₃][(p-NO₂C₆H₄O)₂PO₂] (4), [Tp^∗Ni(OH₂)₃][Me₂PO₂]·Me₂P(O)OH (5), [Tp^∗Ni(OH₂)₃][(nBuO)₂PO₂]·0.5H₂O (6), [(Hpz)Tp^∗Ni(OH₂)₂][(Ph)PO₂OH] (7) and [Tp^∗Ni(OH₂)₂(Me₂PO₂)] (8). The most relevant supramolecular feature of complexes 4-8 is all of them form coordination networks based on hydrogen bonds between water molecules and phosphate, phosphonate or phosphinate anions. These hydrogen bonds are formed within the monomer units in addition to connect monomers along the chains. Their behaviors in solution were investigated by one- and two-dimensional ¹H NMR techniques.     

Expanding the Ligand Classes Used for Mn(II) Complexation: Oxa-aza Macrocycles Make the Difference

We report two macrocyclic ligands based on a 1,7-diaza-12-crown-4 platform functionalized with acetate (tO2DO2A²⁻) or piperidineacetamide (tO2DO2AM^Pip) pendant arms and a detailed characterization of the corresponding Mn(II) complexes. The X−ray structure of [Mn(tO2DO2A)(H₂O)]·2H₂O shows that the metal ion is coordinated by six donor atoms of the macrocyclic ligand and one water molecule, to result in seven-coordination. The Cu(II) analogue presents a distorted octahedral coordination environment. The protonation constants of the ligands and the stability constants of the complexes formed with Mn(II) and other biologically relevant metal ions (Mg(II), Ca(II), Cu(II) and Zn(II)) were determined using potentiometric titrations (I = 0.15 M NaCl, T = 25 °C). The conditional stabilities of Mn(II) complexes at pH 7.4 are comparable to those reported for the cyclen-based tDO2A²⁻ ligand. The dissociation of the Mn(II) chelates were investigated by evaluating the rate constants of metal exchange reactions with Cu(II) under acidic conditions (I = 0.15 M NaCl, T = 25 °C). Dissociation of the [Mn(tO2DO2A)(H₂O)] complex occurs through both proton− and metal−assisted pathways, while the [Mn(tO2DO2AM^Pip)(H₂O)] analogue dissociates through spontaneous and proton-assisted mechanisms. The Mn(II) complex of tO2DO2A²⁻ is remarkably inert with respect to its dissociation, while the amide analogue is significantly more labile. The presence of a water molecule coordinated to Mn(II) imparts relatively high relaxivities to the complexes. The parameters determining this key property were investigated using ¹⁷O NMR (Nuclear Magnetic Resonance) transverse relaxation rates and ¹H nuclear magnetic relaxation dispersion (NMRD) profiles.     

Copper(II)-Mediated Iodination of 1-Nitroso-2-naphthol

The 3-Iodo-1-nitrosonaphthalene-2-ol (I-NON) was obtained by the copper(II)-mediated iodination of 1-nitroso-2-naphthol (NON). The suitable reactants and optimized reaction conditions, providing 94% NMR yield of I-NON, included the usage of Cu(OAc)₂·H₂O and 1:2:8 Cu^II/NON/I₂ molar ratio between the reactants. The obtained I-NON was characterized by elemental analyses (C, H, N), high-resolution ESI⁺-MS, ¹H and ¹³C{¹H} NMR, FTIR, UV-vis spectroscopy, TGA, and X-ray crystallography (XRD). The copper(II) complexes bearing deprotonated I-NON were prepared as follows: cis-[Cu(I-NON–H)(I-NON)](I₃) (1) was obtained by the reaction between Cu(NON-H)₂ and I₂ in CHCl₃/MeOH, while trans-[Cu(I-NON–H)₂] (2) was synthesized from I-NON and Cu(OAc)₂ in MeOH. Crystals of trans-[Cu(I-NON–H)₂(THF)₂] (3) and trans-[Cu(I-NON–H)₂(Py)₂] (4) were precipitated from solutions of 2 in CHCl₃/THF and Py/CHCl₃/MeOH mixtures, respectively. The structures of 1 and 3–4 were additionally verified by X-ray crystallography. The characteristic feature of the structures of 1 and 3 is the presence of intermolecular halogen bonds with the involvement of the iodine center of the metal-bound deprotonated I-NON. The nature of the I···I and I···O contacts in the structures of 1 and 3, correspondingly, were studied theoretically at the DFT (PBE0-D3BJ) level using the QTAIM, ESP, ELF, NBO, and IGM methods.     

Tuning Photophysical Properties by p-Functional Groups in Zn(II) and Cd(II) Complexes with Piperonylic Acid

Aggregation between discrete molecules is an essential factor to prevent aggregation-caused quenching (ACQ). Indeed, functional groups capable of generating strong hydrogen bonds are likely to assemble and cause ACQ and photoinduced electron transfer processes. Thus, it is possible to compare absorption and emission properties by incorporating two ligands with a different bias toward intra- and intermolecular interactions that can induce a specific structural arrangement. In parallel, the π electron-donor or electron-withdrawing character of the functional groups could modify the Highest Ocuppied Molecular Orbital (HOMO)–Lowest Unocuppied Molecular Orbital (LUMO) energy gap. Reactions of M(OAc)₂·2H₂O (M = Zn(II) and Cd(II); OAc = acetate) with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) and 4-acetylpyridine (4-Acpy) or isonicotinamide (Isn) resulted in the formation of four complexes. The elucidation of their crystal structure showed the formation of one paddle-wheel [Zn(μ-Pip)₂(4-Acpy)]₂ (1); a mixture of one dimer and two monomers [Zn(µ-Pip)(Pip)(Isn)₂]₂·2[Zn(Pip)₂(HPip)(Isn)]·2MeOH (2); and two dimers [Cd(μ-Pip)(Pip)(4-Acpy)₂]₂ (3) and [Cd(μ-Pip)(Pip)(Isn)₂]₂·MeOH (4). They exhibit bridged (1, µ₂-η¹:η¹), bridged, chelated and monodentated (2, µ₂-η¹:η¹, µ₁-η¹:η¹ and µ₁-η¹), or simultaneously bridged and chelated (3 and 4, µ₂-η²:η¹) coordination modes. Zn(II) centers accommodate coordination numbers 5 and 6, whereas Cd(II) presents coordination number 7. We have related their photophysical properties and fluorescence quantum yields with their geometric variations and interactions supported by TD-DFT calculations.     

A Molecular Barium Hydrido Complex Stabilized by a Super‐Bulky Hydrotris(pyrazolyl)borate Ligand

Hydrogenolysis of the scorpionate‐supported barium alkyl complex (Tp^Ad,iPr)Ba[CH(SiMe₃)₂](THF) (Tp^Ad,iPr=hydrotris(3‐adamantyl‐5‐isopropyl‐pyrazolyl)borate) afforded the dinuclear barium hydrido complex [(Tp^Ad,iPr)Ba(μ‐H)]₂ ( 2 ), which was characterized by NMR spectroscopy and single‐crystal X‐ray analysis. Exposure of 2 with 1 atm of CO resulted in a reductive coupling process to form the cis‐ethendiolate dianion ( 3 ). Reaction of 2 with one equivalent of PhC≡C−C≡CPh gave barium 1,4‐diphenyl‐2‐butyne‐1,4‐diyl complex {[(Tp^Ad,iPr)Ba]₂(PhCH−C≡C−CHPh) ( 4 ).     

Photoelectron spectra of potassium salts of hydrotris(pyrazol-1-yl)borates: electronic structure of the electron withdrawing scorpionates Tp(CF3)2, Tp*Cl and comparison to Tp* and Tp

The electronic structures of the potassium salts of the homoscorpionates hydrotris(3,5-dimethylpyrazol-1-yl)borate (Tp*, 1), hydrotris(4-chloro-3,5-dimethylpyrazol-1-yl)borate (Tp*^Cl, 2) and hydrotris(3,5-bis(trifluoromethyl)pyrazol-1-yl)borate (Tp^(CF₃)₂, 3) are compared using gas-phase photoelectron spectroscopy and density functional theory (DFT). DFT calculations also are reported for the generic scorpionate potassium (hydrotris(pyrazol-1-yl)borate) (KTp). This is the first such experimental probe of the electronic structure of halogen containing scorpionate ligands and subtle differences in the ionizations from the frontier orbitals in the photoelectron spectra of 1 and 3 are observed that give insight into the influence of substituents upon metal–scorpionate bonding. Distinct assignments of the ionizations from the nitrogen σ-donor orbitals (σ_N) and σ_BH molecular orbitals are possible experimentally by the use of variable (He I and He II) excitation energies. The experimentally observed first ionization energy of 3 is stabilized by ∼2.0 eV relative to 1 due to the strong electron withdrawing effect of the trifluoromethyl groups. The photoelectron spectroscopic studies of NaTp^(CF₃)₂ further confirm the assignments of ionizations from σ_N orbitals for 3 associated with the a and e sets in C₃ symmetry. The X-ray crystal structure of 2 as the (μ-aqua)₃(potassium hydrotris(4-chloro-3,5-dimethylpyrazol-1-yl)borate)₂ dimer is also reported.     

Mono- and Binuclear Copper(II) and Nickel(II) Complexes with the 3,6-Bis(picolylamino)-1,2,4,5-Tetrazine Ligand

Four new compounds of formulas [Cu(hfac)₂(L)] (1), [Ni(hfac)₂(L)] (2), [{Cu(hfac)₂}₂(µ-L)]·2CH₃OH (3) and [{Ni(hfac)₂}₂(µ-L)]·2CH₃CN (4) [Hhfac = hexafluoroacetylacetone and L = 3,6-bis(picolylamino)-1,2,4,5-tetrazine] have been prepared and their structures determined by X-ray diffraction on single crystals. Compounds 1 and 2 are isostructural mononuclear complexes where the metal ions [copper(II) (1) and nickel(II) (2)] are six-coordinated in distorted octahedral MN₂O₄ surroundings which are built by two bidentate hfac ligands plus another bidentate L molecule. This last ligand coordinates to the metal ions through the nitrogen atoms of the picolylamine fragment. Compounds 3 and 4 are centrosymmetric homodinuclear compounds where two bidentate hfac units are the bidentate capping ligands at each metal center and a bis-bidentate L molecule acts as a bridge. The values of the intramolecular metal···metal separation are 7.97 (3) and 7.82 Å (4). Static (dc) magnetic susceptibility measurements were carried out for polycrystalline samples 1–4 in the temperature range 1.9–300 K. Curie law behaviors were observed for 1 and 2, the downturn of χ_MT in the low temperature region for 2 being due to the zero-field splitting of the nickel(II) ion. Very weak [J = −0.247(2) cm⁻¹] and relatively weak intramolecular antiferromagnetic interactions [J = −4.86(2) cm⁻¹] occurred in 3 and 4, respectively (the spin Hamiltonian being defined as H = −JS₁·S₂). Simple symmetry considerations about the overlap between the magnetic orbitals across the extended bis-bidentate L bridge in 3 and 4 account for their magnetic properties.     

Stabilization of a Discrete Lanthanide(II) Hydrido Complex by a Bulky Hydrotris(pyrazolyl)borate Ligand

Divalent and solvent-free : the ytterbium hydrido complex 1 was obtained by the hydrogenolysis of [(Tp^tBu,Me)Yb(CH₂SiMe₃)(thf)]. The steric demand of the bulky hydrotris(3-tert-butyl-5-methylpyrazolyl)borate ligand, Tp^tBu,Me, is sufficient to stabilize the dimer, yet facile room-temperature reactions with amines, alkynes, diynes, and CO indicate a rich chemistry of 1 .     

Synthesis and Structural Characterization of a Silver(I) Pyrazolato Coordination Polymer

Coinage metal(I)···metal(I) interactions are widely of interest in fields such as supramolecular assembly and unique luminescent properties, etc. Only two types of polynuclear silver(I) pyrazolato complexes have been reported, however, and no detailed spectroscopic characterizations have been reported. An unexpected synthetic method yielded a polynuclear silver(I) complex [Ag(μ-L1Clpz)]_n (L1Clpz⁻ = 4-chloride-3,5-diisopropyl-1-pyrazolate anion) by the reaction of {[Ag(μ-L1Clpz)]₃}₂ with (ⁿBu₄N)[Ag(CN)₂]. The obtained structure was compared with the known hexanuclear silver(I) complex {[Ag(μ-L1Clpz)]₃}₂. The Ag···Ag distances in [Ag(μ-L1Clpz)]_n are slightly shorter than twice Bondi’s van der Waals radius, indicating some Ag···Ag argentophilic interactions. Two Ag–N distances in [Ag(μ-L1Clpz)]_n were found: 2.0760(13) and 2.0716(13) Å, and their N–Ag–N bond angles of 180.00(7)° and 179.83(5)° indicate that each silver(I) ion is coordinated by two pyrazolyl nitrogen atoms with an almost linear coordination. Every five pyrazoles point in the same direction to form a 1-D zig-zag structure. Some spectroscopic properties of [Ag(μ-L1Clpz)]_n in the solid-state are different from those of {[Ag(μ-L1Clpz)]₃}₂ (especially in the absorption and emission spectra), presumably attributable to this zig-zag structure having longer but differently arranged intramolecular Ag···Ag interactions of 3.39171(17) Å. This result clearly demonstrates the different physicochemical properties in the solid-state between 1-D coordination polymer and metalacyclic trinuclear (hexanuclear) or tetranuclear silver(I) pyrazolate complexes.     

A family of four-coordinate iron(II) complexes bearing the sterically hindered tris(pyrazolyl)borato ligand Tp(tBu,Me)

A new family of 14‐electron, four‐coordinate iron(II) complexes of the general formula [Tp^tBu,MeFeX] (Tp^tBu,Me is the sterically hindered hydrotris(3‐tert‐butyl‐5‐methyl‐pyrazolyl) borate ligand and X=Cl ( 1 ), Br, I) were synthesized by salt metathesis of FeX₂ with Tp^tBu,MeK. The related fluoride complex was prepared by reaction of 1 with AgBF₄. Chloride 1 proved to be a good precursor for ligand substitution reactions, generating a series of four‐coordinate iron(II) complexes with carbon, oxygen, and sulphur ligands. All of these complexes were fully characterized by conventional spectroscopic methods and most were characterized by single‐crystal X‐ray crystallographic analysis. Magnetic measurements for all complexes agreed with a high‐spin (d⁶, S=2) electronic configuration. The halide series enabled the estimation of the covalent radius of iron in these complexes as 1.24 Å.     

A contribution to 1-azapentadienylmetal chemistry: Si, Sn(II), Fe(II) and Co(II) complexes

Complexes of three related 1-azapentadienyl ligands [N(SiMe₂R¹)C(Bu^t)(CH)₃SiMe₂R]⁻, abbreviated as L (R = Bu^t, R¹ = Me), L′ (R = Me = R¹), and L″ (R = Bu^t = R¹), are described. The crystalline compounds Sn(L)₂ (1), Sn(L′)₂ (2), [Sn(L′)(μ-Cl)]₂ (3) and [Sn(L″)(μ-Cl)]₂ (4) were prepared from SnCl₂ and 2 K(L), 2 K(L′), K(L′) and K(L″), respectively, in thf. Treatment of the appropriate lithium 1-azapentadienyl with Si(Cl)Me₃ yielded the yellow crystalline Me₃Si(L) (5) and the volatile liquid Me₃Si(L′) (6) and Me₃Si(L″) (7), each being an N,N,C-trisilyldieneamine. The red, crystalline Fe(L)₂ (8) and Co(L′)₂ (9) were obtained from thf solutions of FeCl₂ with 2 Li(L)(tmeda) and CoCl₂ with 2 K(L′), respectively. Each of 1-9 gave satisfactory C, H, N analyses; 6 and 7 (GC-MS) and 1, 2, 8 and 9 (MS) showed molecular cations and appropriate fragments (also 3 and 4). The ¹H, ¹³C and ¹¹⁹Sn NMR (1-4) and IR spectra support the assignment of 1-4 as containing Sn-N(SiMe₂R¹)-C(Bu^t)(CH)₃SiMe₂R moieties and 5-7 as N(SiMe₃)(SiMe₂R¹)C(Bu^t)(CH)₃SiMe₂R molecules; for 1-4 this is confirmed by their X-ray structures. The magnetic moments for 8 (5.56 μ_B) and 9 (2.75 μ_B) are remarkably close to the appropriate Fe and Co complex [M{η³-N(SiMe₃)C(Bu^t)C(H)SiMe₃}₂]; hence it is proposed that 8 and 9 have similar metal-centred, centrosymmetric, distorted octahedral structures.     

Co(II), Ni(II), and Cu(II) Complexation with Isatin Aminoguanisone and Nitroaminoguanisone

New complexes of bivalent Co, Ni, and Cu with isatin aminoguanisone (HL) and nitroaminoguanisone (HL¹) of the composition ([Co(HL)₂]Cl₂ (I), [Ni(HL)₂]Cl₂ (II), [Cu(L)Cl] (III), [Co(L¹)₂] (IV), [Ni(L¹)₂] (V), and [Cu(L¹)₂] (VI) are synthesized. Their molecular conductivities and effective magnetic moments are measured and thermal stabilities are studied. The type of the ligand coordination in I–VI is proposed on the basis of IR data. The summary of physicochemical data for I–VI and the energy calculations for their molecules by the molecular mechanics method made it possible to establish stoichiometry of the coordination polyhedra of the complexes.     

Syntheses and structures of lanthanide(III) complexes with some bis(pyrazolyl)borate and tris(pyrazolyl)borate podand ligands

Two new poly(pyrazolyl)borate ligands have been prepared: potassium tris[3-{(4-^tbutyl)-pyrid-2-yl}-pyrazol-1-yl]hydroborate (KTp^BuPy) which has three bidentate arms and is therefore hexadentate; and potassium bis[3-(2-pyridyl)-5-(methoxymethyl)pyrazol-1-yl]-dihydroborate (KBp^(COC)Py) which has two bidentate arms and is therefore tetradentate. The crystal structures of their lanthanide complexes [La(Tp^BuPy)(NO₃)₂] and [La(Bp^(COC)Py)₂X] (X=nitrate or triflate) have been determined. In [La(Tp^BuPy)(NO₃)₂] the metal ion is ten-coordinate, from the hexadentate N-donor podand ligand and two bidentate nitrates. [La(Bp^(COC)Py)₂(NO₃)] is also ten-coordinate, from two tetradentate ligands and a bidentate nitrate, but in [La(Bp^(COC)Py)₂(CF₃SO₃)] the metal ion is nine-coordinate because the triflate anion is monodentate. Two unexpected new complexes which arose from partial decomposition of the poly(pyrazolyl)borate ligands have also been characterised structurally. In [La(^BuPypzH)₃(O₃SCF₃)₃] the metal ion is nine-coordinate from three bidentate pyrazolyl-pyridine arms (liberated by decomposition of KTp^BuPy) and three triflate anions; there is extensive NH· · · O hydrogen-bonding between the pyrazolyl and triflate ligands. [Nd(Tp^Py)(Bp^Py)][Nd(PypzH)(NO₃)₄] was isolated from the reaction of hexadentate tris[3-(2-pyridyl)-pyrazol-1-yl]hydroborate (Tp^Py) with Nd(NO₃)₃. One of the Tp^Py ligands has lost one bidentate pyrazolyl-pyridine ‘arm’ (PypzH) to leave tetradentate tris[3-(2-pyridyl)-pyrazol-1-yl]dihydroborate (Bp^Py). In this structure, the cation [Nd(Tp^Py)(Bp^Py)]⁺ is ten-coordinate from inter-leaved hexadentate and tetradentate ligands, and the anion [Nd(PypzH)(NO₃)₄]⁻ is also ten-coordinate from the bidentate N-donor ligand PypzH and four bidentate nitrates.     

Interaction of the Negishi reagent Cp2ZrBun 2 with 1,4-bis(tert-butyl)butadiyne

The interaction of the Negishi reagent Cp₂ZrBuⁿ ₂ with 1,4-bis(tert-butyl)butadiyne Bu^tC≡C-C≡CBu^t leads to four products: a five-membered zirconacyclocumulene complex Cp₂Zr(η⁴-Bu^tC₄Bu^t) (2) synthesized earlier by another method, the previously unknown seven-membered zirconacyclocumulene Cp₂Zr[η⁴-Bu^tC₄(Bu^t)-C(C₂Bu^t)=CBu^t] (3) as well as small amounts of the zirconocene binuclear butatrienyl complex Cp₂(Buⁿ)Zr(Bu^tC₄Bu^t)Zr(Buⁿ)Cp₂ (4), and the dimeric acetylide [Cp₂ZrC≡CBu^t]₂ (5). The structure of complexes 2–5 was established by X-ray diffraction studies.     

t-Butyl isocyanide complexes of rhenium(I), chromium(O), tungsten(O,I) and platinum(II); X-ray crystal structures of bis(t-butylisocyanide)- tris(trimethylphosphine)chlororhenium(I) and tris(t-butylisocyanide)bis(trimethyl- phosphine)chlororhenium(I)

The reduction of ReCl₄(THF)₂ in the presence of excess t-butylisocyanide by sodium amalgam produces pentakis(t-butylisocyanide)chlororhenium(I), which has been converted to the corresponding methyl and ethyl derivatives. The reaction of pentakis(trimethylphosphine)chlororhenium(I) with Bu^tNC gives partially substituted complexes, ReCl(CNBu^t)₂(PMe₃)3 and ReCl(CNBu^t)₃(PMe₃)₂. The structures of both compounds have been determined by X-ray methods. Octahedral ReCl(CNBu^t)₂(PMe₃)₃ has trans isocyanide groups with one linear [C---N---C = 175(1)°] and one slightly bent [C---N---C = 159(1)°]. The Re---C bond lengths are equal within experimental error [2.004(7), 2.003(7)Å]. In the octahedral ReCl(CNBu^t)₃(PMe₃)₂, for which the structure is not well defined, due to disorder, the unique isocyanide trans to chlorine is considerably bent at the nitrogen atom [C--- ---C = 141(6)°] and appears to show the shortest Re---C bond length, 1.94(5) vs 2.02(5)Å for the other two isocyanides which are mutually trans. Protonation of these two isocyanide complexes with fluoroboric acid gives, respectively, the salts [ReCl(CNBu^t)CNHBu^t(PMe₃)₃]BF₄ and [ReCl(CNBu^t)₂CNHBu^t(PMe₃)₂]BF₄, whose configurations have been determined by NMR spectroscopy. The reduction by sodium amalgam of Cr₂(CO₂Me)₄ in tetrahydrofuran in presence of Bu^tNC gives a high yield of Cr(CNBu^t)₆ while similar reduction of the dimeric tungsten(II) complex of the anion (mhp) of 2-methyl-6- hydroxypyridine gives W(CNBu^t)₆. Interaction of W₂(mhp)₄ in methanol-ether with Bu^tNC gives a tungsten(I) complex W₂(η-mhp)₂(Bu^tNC)₄, which may be an intermediate in the reductive cleavage reaction. Interaction of cis-PtMe₂(PMe₃)₂ with Bu^tNC leads only to replacement of one PMe₃ group to give the complex cis-PtMe₂(PMe₃)(CNBu^t).     

Synthesis and evaluation of substituted pyrazoles palladium(II) complexes as ethylene polymerization catalysts

The substituted pyrazole palladium complexes, (3,5-^tBu₂pz)₂PdCl₂ (1) (3,5-Me₂pz)₂PdCl₂ (2), (3-Mepz)₂PdCl₂ (3) and (pz)₂PdCl₂ (4) (pzH=pyrazole), can be prepared from the reaction of (COD)PdCl₂ with the appropriate pyrazole. The chloromethyl derivative, (3,5-^tBu₂pz)₂PdCl(Me) (5), was prepared from (COD)PdClMe and ^tBu₂pzH. X-ray crystal structure determination of 1 and 5 established their structures in the solid state to be the trans-isomer. After activation of 1-4 and 5 with methylaluminoxane (MAO) the resulting palladium complexes were used as catalysts in ethylene polymerization, yielding linear high-density polyethylene (HDPE). The highest activity was observed for (3,5-^tBu₂pz)PdClMe.     

Selective Formation of Unsymmetric Multidentate Azine-Based Ligands in Nickel(II) Complexes

A mixture of 2-pyridine carboxaldehyde, 4-formylimidazole (or 2-methyl-4-formylimidazole), and NiCl₂·6H₂O in a molar ratio of 2:2:1 was reacted with two equivalents of hydrazine monohydrate in methanol, followed by the addition of aqueous NH₄PF₆ solution, afforded a Ni^II complex with two unsymmetric azine-based ligands, [Ni(HL^H)₂](PF₆)₂ (1) or [Ni(HL^Me)₂](PF₆)₂ (2), in a high yield, where HL^H denotes 2-pyridylmethylidenehydrazono-(4-imidazolyl)methane and HL^Me is its 2-methyl-4-imidazolyl derivative. The spectroscopic measurements and elemental analysis confirmed the phase purity of the bulk products, and the single-crystal X-ray analysis revealed the molecular and crystal structures of the Ni^II complexes bearing an unsymmetric HL^H or HL^Me azines in a tridentate κ³ N, N’, N” coordination mode. The HL^H complex with a methanol solvent, 1·MeOH, crystallizes in the orthorhombic non-centrosymmetric space group P2₁2₁2₁ with Z = 4, affording conglomerate crystals, while the HL^Me complex, 2·H₂O·Et₂O, crystallizes in the monoclinic and centrosymmetric space group P2₁/n with Z = 4. In the crystal of 2·H₂O·Et₂O, there is intermolecular hydrogen-bonding interaction between the imidazole N–H and the neighboring uncoordinated azine-N atom, forming a one-dimensional polymeric structure, but there is no obvious magnetic interaction among the intra- and interchain paramagnetic Ni^II ions.     

Cu(II) and Pd(II) complexes of N-(2-hydroxybenzyl)aminopyridines

N-(2-Hydroxybenzyl)aminopyridines (Lⁱ) react with Cu(II) and Pd(II) ions to form complexes in the compositions Cu(Lⁱ)₂(CH₃COO)₂ · nH₂O (n = 0, 2, 4), Pd(Lⁱ)₂Cl₂ · nC₂H₅OH (n = 0, 2) and Pd(L²)₂Cl₂ · 2H₂O. In the complexes, the ligands are neutral and monodentate which coordinate through pyridinic nitrogen. Crystal data of the complexes obtained from 2-amino pyridine derivative have pointed such a coordinating route and comparison of the spectral data suggests the validity of similar complexation modes of other analog ligands. Cu(II) complex of N-(2-hydroxybenzyl)-2-aminopyridine (L¹), [Cu(L¹)₂(CH₃COO)₂] has slightly distorted square planar cis-mononuclear structure which is built by two oxygen atoms of two monodentate carboxylic groups disposed in cis-position and two nitrogen atoms of two pyridine rings. The remaining two oxygen atoms of two carboxylic groups form two Cu and H bridges containing cycles which joint at same four coordinated copper(II) ion. IR and electronic spectral data and the magnetic moments as well as the thermogravimetric analyses also specify on mononuclear octahedric structure of complexes [Cu(L²)₂(CH₃COO)₂ · 2H₂O] and [Cu(L³)₂(CH₃COO)₂ · 4H₂O] where L² and L³ are N-(2-hydroxybenzyl)-2- or 3-aminopyridines, respectively.     

Syntheses and structures of doubly tucked-in titanocene complexes with tetramethyl(aryl)cyclopentadienyl ligands

Titanocene–bis(trimethylsilyl)ethyne complexes [Ti(η⁵-C₅Me₄R)₂(η²-Me₃SiCCSiMe₃)], where R=benzyl (Bz, 1a), phenyl (Ph, 1b) and p-fluorophenyl (FPh, 1c), thermolyse at 150–160°C to give products of double C---H activation [Ti(η⁵-C₅Me₄Bz){η³:η⁴-C₅Me₃(CH₂)(CHPh)}] (2a), [Ti(η⁵-C₅Me₄Bz){η³:η⁴-C₅Me₂Bz(CH₂)₂}] (2a′), [Ti(η⁵-C₅Me₄Ph){η³:η⁴-C₅Me₂Ph(CH₂)₂}] (2b), and [Ti(η⁵-C₅Me₄FPh){η³:η⁴-C₅Me₂FPh(CH₂)₂}] (2c). In the presence of 2,2,7,7-tetramethylocta-3,5-diyne (TMOD) the thermolysis affords analogous doubly tucked-in compounds bearing one η³:η⁴-allyldiene and one η⁵-C₅Me₄R ligand having TMOD attached by its C-3 and C-6 carbon atoms to the vicinal methylene groups adjacent to the substituent R (R=Bz (3a), Ph (3b), and FPh (3c)). Compound 3a is smoothly converted into air-stable titanocene dichloride [TiCl₂{η⁵-C₅Me₂Bz(CH₂CH(t-Bu)CH=CHCH(t-Bu)CH₂)}(η⁵-C₅Me₄Bz)] (4a) by a reaction with hydrogen chloride. Yields in both series of doubly tucked-in complexes decrease in the order of substituents: BzPh>FPh. Crystal structures of 1c, 2a, 2b, and 3b have been determined.     

Magnesium–halobenzene bonding: mapping the halogen sigma-hole with a Lewis-acidic complex

Complexes of the Lewis base-free cations (^MeBDI)Mg⁺ and (^tBuBDI)Mg⁺ with Ph–X ligands (X = F, Cl, Br, I) have been studied (^MeBDI = HC[C(Me)N-DIPP]₂ and ^tBuBDI = HC[C(tBu)N-DIPP]₂; DIPP = 2,6-diisopropylphenyl). For the smaller β-diketiminate ligand (^MeBDI) only complexes with PhF could be isolated. Heavier Ph–X ligands could not compete with bonding of Mg to the weakly coordinating anion B(C₆F₅)₄⁻. For the cations with the bulkier ^tBuBDI ligand, the full series of halobenzene complexes was structurally characterized. Crystal structures show that the Mg⋯X–Ph angle strongly decreases with the size of X: F 139.1°, Cl 101.4°, Br 97.7°, I 95.1°. This trend, which is supported by DFT calculations, can be explained with the σ-hole which increases from F to I. Charge calculation and Atoms-In-Molecules analyses show that Mg⋯F–Ph bonding originates from electrostatic attraction between Mg²⁺ and the very polar C^δ+–F^δ− bond. For the heavier halobenzenes, polarization of the halogen atom becomes increasingly important (Cl < Br < I). Complexation with Mg leads in all cases to significant Ph–X bond activation and elongation. This unusual coordination of halogenated species to early main group metals is therefore relevant to C–X bond breaking.

Complexes of a highly Lewis acidic Mg cation and the full series of Ph–X (X = F, Cl, Br, I) have been structurally characterized. The Mg⋯X–Ph angle decreases with halogen size on account of the growing halogen σ-hole.