Fluxional behavior of Al(Et)(q)2 (q=2-methyl-8-quinolinolato) studied by temperature dependent H NMR spectroscopy

Two α-CH₂ hydrogens of the Et group in Al(Et)(q^′)₂ (q^′=2-methyl-8-quinolinolato) show two ¹H NMR peaks at different positions with a separation of 0.19 ppm at 25 °C, due to the presence of a chiral center at Al. On raising the temperature, the two peaks collapsed, and coalesced above 100 °C. The ¹H NMR fluxional behavior is accounted for by simultaneous rotation of the q^′ ligands, and kinetic parameters of kJ mol⁻¹, kJ mol⁻¹, J K⁻¹ mol⁻¹ are evaluated.     

Reactivity of ZrCl4 and HfCl4 with silylamines and thermal decomposition of the compounds [MCl4{NH(R)(SiR′3)}] (M = Zr,Hf, R = tBu,R′ = Me; R = SiR′3 = SiMe3, SiMe2H)

The Lewis acid/base adducts [MCl₄{NH(R)(SiR′₃)}] (M = Zr, Hf; R = tBu, R′ = Me; R = SiR′₃ = SiMe₃, SiMe₂H) were synthesized by the 1:1 reaction of MCl₄ with NH(R)(SiR′₃) in dichloromethane solution at room temperature. The decomposition of [MCl₄{NH(R)(SiR′₃)}] proceeds with the elimination of R′₃SiCl, as shown by thermogravimetric analysis. Pyrolysis of the compounds at 620 °C under inert conditions (N₂, vacuum) afforded powders of composition [ClMN] or [Cl₂MNH]. Preliminary low pressure chemical vapour deposition experiments show that [MCl₄{NH(R)(SiR′₃)}] deposits thin films of metal nitride contaminated with metal oxide.     

Synthesis and characterization of metal diselenophosphates: M[Se2P(OR)2]2 (M = Pd,Pt; R = Et,Pr, Pr)

The first Pd(II) and Pt(II) complexes incorporating diselenophosphate (dsep) ligands are presented. Treatment of M(II) (M = Pd, Pt) salts with two equivalents of the dsep ligand in CH₂Cl₂ yielded square-planar compounds of the type M[Se₂P(OR)₂]₂ (M = Pd, Pt; R = Et, ⁱPr, ⁿPr) (1a–2c). These complexes were characterized by elemental analysis, multinuclear NMR spectroscopy and X-ray diffraction (1b and 2b). The dsep ligands coordinate to the metal in an approximately isobidentate fashion and form four-membered Se–P–Se–M chelate rings. Structural elucidations indicated that minute differences exist in the M–Se bond distances and these were observed from solution ³¹P NMR studies, which exhibited two sets of satellites arising from one-bond coupling to ⁷⁷Se nuclei. A packing diagram showed a chain-like motif which was composed of square-planar M[Se₂P(OR)₂]₂ units and occurred via non-covalent Se?Se secondary interactions.     

Alkaline earth metal poly(hydrogen fluorides) hexafluoroarsenates(V) and hexafluorophosphate(V): M2(H2F3)(HF2)2(AF6) (M = Ca, A = As; M = Sr, A = As, P)

New compounds of the type M₂(H₂F₃)(HF₂)₂(AF₆) with M = Ca, A = As and M = Sr, A = As, P) were isolated. Ca₂(H₂F₃)(HF₂)₂(AsF₆) was prepared from Ca(AsF₆)₂ with repeated additions of neutral anhydrous hydrogen fluoride (aHF). It crystallizes in a space group P4₃22 with a = 714.67(10) pm, c = 1754.8(3) pm, V = 0.8963(2) nm³ and Z = 4. Sr₂(H₂F₃)(HF₂)₂(AsF₆) was prepared at room temperature by dissolving SrF₂ in aHF acidified with AsF₅ in mole ratio SrF₂:AsF₅ = 2:1. It crystallizes in a space group P4₃22 with a = 746.00(12) pm, c = 1805.1(5) pm, V = 1.0046(4) nm³ and Z = 4. Sr₂(H₂F₃)(HF₂)₂(PF₆) was prepared from Sr(XeF₂)_n(PF₆)₂ in neutral aHF. It crystallizes in a space group P4₁22 with a = 737.0(3) pm, c = 1793.7(14) pm, V = 0.9744(9) nm³ and Z = 4. The compounds M₂(H₂F₃)(HF₂)₂(AF₆) gradually lose HF at room temperature in a dynamic vacuum or during being powdered for recording IR spectra or X-ray powder ray diffraction patterns. All compounds are isotypical with coordination of nine fluorine atoms around a metal center forming a distorted Archimedian antiprism with one face capped. This is the first example of the compounds in which H₂F₃⁻ and HF₂⁻ anions simultaneously bridge metal centers forming close packed three-dimensional network of polymeric compounds with low solubility in aHF. The HF₂⁻ anions are asymmetric with usual F?F distances of 227.3-228.5 pm. Vibrational frequency (ν₁) of HF₂⁻ is close to that in NaHF₂. The anion H₂F₃⁻ exhibits unusually small F?F?F angle of 95.1°-97.6° most probably as a consequence of close packed structure.     

Mixed ligand tris-chelate of copper(II) with N,N-donor ligands - Synthesis, structure and spectra of [Cu(en)(phen)2]X2·2phen·8H2O (X = Cl, NO3)

[Cu(en)(phen)₂]⁺ is crystallized along with two phenanthroline and eight lattice water molecules either as a chloride or a nitrate salt. The cation has almost identical structural and spectral properties which correspond to a tetragonally elongated octahedral geometry with the en ligand in the equatorial plane. EPR parameters reveal a slight rhombicity in the coordination polyhedron. Even though both compounds have the same composition (except for the anions), the hydrogen bond networks involving the lattice water molecules and anions are quite different in the two compounds. There are also extensive π-stacking interactions involving the phenanthroline molecules, both coordinated and non-coordinated. The non-bonding interactions have a major directing role in the crystallization of the tris-chelate cation. The analogous mixed ligand complex of 2,2-bipyridine could not be crystallized.     

Synthesis,characterization, DNA-binding and DNA-photocleavage studies of [Ru(bpy)2(BPIP)] and [Ru(phen)2(BPIP)] (BPIP = 2-(4′-biphenyl)imidazo[4,5-f][1,10]phenanthroline)

New ligand 2-(4′-biphenyl)imidazo[4,5-f][1,10]phenanthroline (BPIP) and its complexes [Ru(bpy)₂(BPIP)]²⁺ (1) (bpy = 2,2′-bipyridine) and [Ru(phen)₂(BPIP)]²⁺ (2) (phen = 1,10-phenanthroline) have been synthesized and characterized by mass spectroscopy, ¹H NMR and cyclic voltammetry. The interaction of two Ru(II) complexes with calf thymus DNA (CT-DNA) was investigated by spectroscopic and viscosity measurements. Results indicate that both complexes bind to DNA via an intercalative mode and the DNA-binding affinity of complex 2 is much greater than that of complex 1. Furthermore, when irradiated at 365 nm, both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA.     

Synthesis and structures of bimetallic silicon-containing imido alkylidene complexes of tungsten (R′O)2(ArN)WCH-SiR2-CHW(NAr)(OR′)2 (R = Me, Ph) and (R′O)2(ArN)WCH-SiMe2SiMe2-CHW(NAr)(OR′)2

Bimetallic alkylidene complexes of tungsten (R′O)₂(ArN)WCH-SiR₂-CHW(NAr)(OR′)₂ (R = Me (1), Ph (2)) and (R′O)₂(ArN)WCH-SiMe₂SiMe₂-CHW(NAr)(OR′)₂ (3) (Ar = ; R′ = CMe₂CF₃) have been prepared by the reactions of divinyl silicon reagents R₂Si(CHCH₂)₂ with known alkylidene compounds R′′-CHMo(NAr)(OR′)₂. (R′′ = Bu^t, PhMe₂C) Complexes 1-3 were structurally characterized. Ring opening metathesis polymerization (ROMP) of cyclooctene using compounds 1-3 as initiators led to the formation of high molecular weight polyoctenamers with predominant trans-units content in the case of 1 and 3 and predominant cis-units content in the case of 2.     

Group 15 ligand migration in the heteronuclear clusters RuOs3(μ-H)2(CO)12(EPh3) (E = P, As, Sb)

The monosubstituted clusters RuOs₃(μ-H)₂(CO)₁₂(EPh₃) (where E = P, As, Sb) exhibit isomers in which the group 15 ligand is on an Os or an Ru vertex. Evidence is presented for hydride fluxionality and EPh₃ ligand migration. These processes have been examined by variable temperature NMR studies, and the kinetic parameters estimated.     

Synthesis and crystal structures of the first germanium-containing alkylidene complexes of molybdenum R3Ge-CHMo(NAr)(OR′)2 (R = Me, Ph) with direct germanium-carbene carbon bond

The novel germanium-containing alkylidene complexes of molybdenum R₃Ge-CHMo(NAr)(OCMe₂CF₃)₂ (Ar = 2,6-i-Pr₂C₆H₃; R = Me, Ph) have been prepared by the reaction of organogermanium vinyl reagents R₃ GeCHCH₂ with known alkylidene compounds Alkyl-CHMo(NAr)(OCMe₂CF₃)₂ (Alkyl = Bu^t, PhMe₂C). The titled compounds were isolated as crystalline solids and characterized by elemental analysis, ¹H NMR, ¹³C NMR spectroscopy and X-ray diffraction studies. The geometry of the Mo atoms in the compounds can be described as a distorted tetrahedron.     

Syntheses, crystal structures and luminescent properties of two novel lanthanide/4-pya complexes: [Ln(4-pya)3(H2O)2]2 (Ln = Eu, La; 4-pya = trans-4-pyridylacrylate)

Reactions of Ln₂O₃ and trans-4-pyridylacrylic acid (4-Hpya) in EtOH/H₂O or MeOH/H₂O produced two new lanthanide/4-pya complexes [Ln(4-pya)₃(H₂O)₂]₂ (1: Ln = Eu; 2: Ln = La) in low yields. However, reactions of LnCl₃ · 6H₂O with 4-Hpya/aqueous ammonia in EtOH/H₂O or MeOH/H₂O gave rise to 1 or 2 in higher yields. Both compounds were structurally characterized by elemental analysis, IR spectroscopy and X-ray analysis. Compounds 1 · 2EtOH · 2H₂O and 2 · 2MeOH · 2H₂O were confirmed to possess one-dimensional polymeric chain structures. In the structure of 1, each Eu(III) adopts a monocapped square-antiprism coordination geometry and each dimer [Eu(4-pya)₃(H₂O)₂]₂ within the chain is interconnected by two pairs of different bridging 4-pya ligands. On the other hand, each La(III) of 2 takes a bicapped square-antiprism coordination geometry and each dimer [La(4-pya)₃(H₂O)₂]₂ within the chain is linked by two pairs of tridentate bridging 4-pya ligands. The luminescent properties of 1 and 2 in the solid state were investigated.     

2D hydrogen bond networks in the crystals of [(NH4 · H2O)2][(RO)(Fc)P(S)2]2 (R = 3-(BzO)-Bz, 4-(n-Bu)-Bz, Bz = benzyl)

Herein we report on the preparation of hydrated ammonium salts of the dithiophosphonic acids (RO)(Fc)P(S)(SH) (R = derivative of benzyl) featuring [(NH₄ · H₂O)₂]²⁺ cations formed by N-H?O hydrogen bonds. Interaction of these cations with the PS₂⁻ units gives rise to unprecedented 2D networks, formed solely by hydrogen bonds. These unique networks containing two- and three centered hydrogen bonds are valuable examples of the acceptor properties of sulfur atoms.     

Oxime-substituted NCN-pincer palladium and platinum halide polymers through non-covalent hydrogen bonding (NCN = [C6H2(CH2NMe2)2-2,6])

The oxime-substituted NCN-pincer molecules HONCH-1-C₆H₃(CH₂NMe₂)₂-3,5 (2a) and HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 (2b) were accessible by treatment of the benzaldehydes H(O)C-4-C₆H₃(CH₂NMe₂)₂-3,5 (1a) and H(O)C-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 (1b) with an excess of hydroxylamine. In the solid state both compounds are forming polymers with intermolecular O-H?N connectivities between the Me₂NCH₂ substituents and the oxime entity of further molecules of 2a and 2b, respectively. Characteristic for 2a and 2b is a helically arrangement involving a crystallographic 2₁ screw axis of the HONCH-1-C₆H₃(CH₂NMe₂)₂-3,5 and HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 building blocks.The reaction of 2b with equimolar amounts of [Pd₂(dba)₃ · CHCl₃] (3) (dba = dibenzylidene acetone) or [Pt(tol)₂(SEt₂)]₂ (4) (tol = 4-tolyl) gave by an oxidative addition of the C-Br unit to M coordination polymers with a [(HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6)MBr] repeating unit (5: M = Pd, 6: M = Pt). Complexes 5 and 6 are in the solid state linear hydrogen-bridged polymers with O-H?Br contacts between the oxime entities and the metal-bonded bromide.     

Reductive elimination of halogens assisted by phosphine ligands in Fe(CO)4X2 (X = I, Br) complexes

Fe(CO)₄X₂ complexes [X = I (1), Br(1′)] react with phosphine ligands L (L = PMe₃, PEt₃, PMe₂Ph, PMePh₂, PPh₃) via a two-step mechanism: in the first step fac-Fe(CO)₃LX₂ complexes are formed; in the second step two parallel pathways, a and b, are observed; in pathway a, reductive elimination with formation of equimolar amounts of Fe(CO)₃L₂ (5) and phosphonium salts [LX]⁺X⁻ is observed; in pathway b, disubstituted dihalide complexes cis,trans,cis-Fe(CO)₂L₂X₂ are formed. The relative weights of pathways a and b depend on the basicity, steric hindrance and concentration of ligand L, on the nature of the halogen and on temperature. A radical mechanism which accounts for most of the experimental results is proposed.     

Synthesis and characterization of Li(I)-M(II) (M = Co, Ni) heterometallic complexes as molecular precursors for LiMO2

Lithium-containing heterometallic complexes with cobalt (Li₂Co₂(Piv)₆(2,4-Lut)₂ (2, Piv is the pivalate anion) and Li₂Co₂(O₂CCH₂Bu^t)₆(2,4-Lut)₂ (3)) and with nickel (Li₂Ni₂(Piv)₆(DME)₂ (4) and Li₂Ni₂(Piv)₆(2,2′-bpy)₂ (5)) were synthesized. The structures of the complexes were established by X-ray diffraction. The magnetic properties of complexes 2 and 4 were studied. The thermal behavior of compounds 2, 3, and 5 was investigated. It was shown that the compounds under study can be used as molecular precursors for the synthesis of lithium cobaltate and nickelate.     

A DFT/TDDFT study on the structures, trend in DNA-binding and spectral properties of molecular “light switch” complexes [Ru(phen)2(L)](L = dppz, taptp, phehat)

Theoretical studies on a series of molecular “light switch” complexes [Ru(phen)₂L]²⁺ (phen = 1,10-phenanthroline; L: dppz = dipyrido [3,2-a:2′,3′-c]phenazine; taptp = 4,5,9,18-tetraazaphenanthreno-[9,10-b]triphenylene; phehat = 1,10-phenanthrolino[5,6-b]1,4,5,8,9,12-hexaazatriphenylene) 1-3 have been carried out applying DFT/TDDFT (density functional theory and time-dependent DFT) methods. The geometric and electric structure-characteristics of these complexes have been revealed, and the trend in their DNA-binding constants (K_b), i.e., K_b (2) < K_b (3) < K_b (1), which closely relates to the luminescence properties of the complexes in DNA, has been reasonably explained. The results show that simply increasing the planar area of intercalative ligand may be ineffective on improvement of DNA-binding of resulting complex because of going with the increase in the LUMO (and LUMO + x) energy, but introducing some heteroatoms (e.g., N atom) with stronger electronegativity into the ring skeleton of intercalative ligand should be effective because of the decrease in the LUMO (and LUMO + x) energy to a certain extent. In addition, the spectra of this series of complexes in vacuo are also computed, simulated, and minutely discussed by the DFT/TDDFT methods, and it is interesting to find that the symmetries of the excited and accepting orbitals of the transition with the largest f value are the same.     

Synthesis,spectroscopic investigation,structural characterization and DFT calculation of the complexes [ReX2(N2COPh)(4-PhPyr)(PPh3)2] (X = Cl, Br)

The reactions of [ReX₂(η²-N₂COPh-N′,O)(PPh₃)₂] with 4-phenylpyrimidine have been performed. As a result, the two complexes [ReX₂(N₂COPh)(4-PhPyr)(PPh₃)₂] (X = Cl, Br) (4-PhPyr = 4-phenylpyrimidine), isostructural in the solid state, have been obtained. The crystal and molecular structures of ([ReCl₂(N₂COPh)(4-PhPyr)(PPh₃)₂])₂·CHCl₃ (1) and ([ReBr₂(N₂COPh)(4-PhPyr)(PPh₃)₂])₂·CHCl₃ (2) have been determined. The electronic structure of [ReCl₂(N₂COPh)(4-PhPyr)(PPh₃)₂] has been examined using the density functional theory (DFT) method. The spin-allowed electronic transitions of 1 have been calculated with the time-dependent DFT method, and the UV–Vis spectrum of [ReCl₂(N₂COPh)(4-PhPyr)(PPh₃)₂] has been discussed on this basis.