Nitridorhenium(V) Complexes with 1,3,4‐Triphenyl‐1,2,4‐triazol‐5‐ylidene

[ReNCl₂(PPh₃)₂] and [ReNCl₂(PMe₂Ph)₃] react with the N‐heterocyclic carbene (NHC) 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (HL^Ph) under formation of the stable rhenium(V) nitrido complex [ReNCl(HL^Ph)(L^Ph)], which contains one of the two NHC ligands with an additional orthometallation. The rhenium atom in the product is five‐coordinate with a distorted square‐pyramidal coordination sphere. The position trans to the nitrido ligand is blocked by one phenyl ring of the monodentate HL^Ph ligand. The Re–C(carbene) bond lengths of 2.072(6) and 2.074(6) Å are comparably long and indicate mainly σ‐bonding between the NHC ligand and the electron deficient d² metal atom. The chloro ligand in [ReNCl(HL^Ph)(L^Ph)] is labile and can be replaced by ligands such as pseudohalides or monoanionic thiolates such as diphenyldithiophosphinate (Ph₂PS₂^?) or pyridine‐2‐thiolate (pyS^?). X‐ray structure analyses of [ReN(CN)(HL^Ph)(L^Ph)] and [ReN(pyS)(HL^Ph)(L^Ph)] show that the bonding situation of the NHC ligands (Re–C(carbene) distances between 2.086(3) and 2.130(3) Å) in the product is not significantly influenced by the ligand exchange. The potentially bidentate pyS^? ligand is solely coordinated via its thiolato functionality. Hydrogen atoms of each one of the phenyl rings come close to the unoccupied sixth coordination positions of the rhenium atoms in the solid state structures of all complexes. Re–H distances between 2.620 and 2.712Å do not allow to discuss bonding, but with respect to the strong trans labilising influence of “N^3?”, weak interactions are indicated.     

Novel aluminium compounds derived from Schiff bases: Synthesis,characterization and catalytic performance in hydroboration

Seven novel aluminium complexes supported by Schiff base ligands derived from o‐diaminobenzene or o‐aminothiophenol were synthesized and characterized. The reactions of AlMe₃ with L¹ (N,N′‐bis(benzylidine)‐o‐phenylenediamine) and L² (N,N′‐bis(2‐thienylmethylene)‐o‐phenylenediamine) gave the complexes L¹AlMe₃ ( 1 ) and L²AlMe₂ ( 2 ), respectively, which involved two types of reaction mechanisms: one was proton transfer and ring closure, and the other was alkyl transfer. Complexes L³AlMe₂ (HL³ = 4‐chlorobenzylidene‐o‐aminothiophenol) ( 3 ), L⁴AlMe₂ (HL⁴ = 2‐thiophenecarboxaldehyde‐o‐aminothiophenol) ( 4 ), L³AlH(NMe₃) ( 5 ), L⁴AlH(NMe₃) ( 6 ) and L⁵AlH(NMe₃) (HL⁵ = 4‐methylbenzylidene‐o‐aminothiophenol) ( 7 ) were prepared by reacting HL^3–5 with equimolar AlMe₃ or H₃Al?NMe₃, respectively. Compounds 3 – 7 feature an organic–inorganic hybrid containing CNAlSC five‐membered ring. All complexes were characterized using ¹H NMR and ¹³C NMR spectroscopy, X‐ray crystal structure analysis and elemental analysis. The efficient catalytic performances of 1 – 7 for the hydroboration of carbonyl groups were investigated, with compound 4 exhibiting the highest catalytic activity among all the complexes.     

Synthesis and Crystal Structures of an Unexpected Tetranuclear Zinc(II) Complex and a Benzoquinone Compound Derived from ZnII‐ and CdII‐Promoted Reactivity of Schiff Base Ligands

An unexpected polyhydroxyl‐bridged tetranuclear Zn^II complex and a benzoquinone compound derived from metal‐ion promoted reactivity of Schiff base ligands were synthesized and characterized. The reaction of zinc(II) acetate dihydrate with oxime‐type Schiff base ligand HL¹ [HL¹ = 1‐(3‐((3,5‐dibromosalicylaldehyde)amino)phenyl)ethan‐1‐one O‐benzyl oxime] in methanol, acetone, and acetonitrile resulted in the chemoselective cleavage of the C=N bond of the Schiff base HL¹, and then the further addition of acetone to two salicylaldehyde molecules derived from cleavage of the C=N bond in situ α,α double aldol reaction promoted by Zn^II ions. The newly formed ligands H₄L² coordinate to four Zn^II ions forming a defect‐dicubane core structure [Zn^II₄(H₂L²)₂(μ₃‐OCH₃)₂(μ‐OCH₃)₂(CH₃OH)₂] ( 1 ) bridged exclusively by oxygen‐based ligands. The similar ligand HL³ [HL³ = 1‐(3‐((3,5‐dichlorosalicylaldehyde)amino)phenyl)ethan‐1‐one O‐benzyl oxime)] was employed to react with Cd^II acetate dihydrate under the same reaction conditions. No aldol addition occurred but a unexpected benzoquinone compound 2,5‐bis(((3‐(1‐((benzyloxy)imino)ethyl)phenyl)imino)methyl)‐1,4‐benzoquinone ( 2 ) formed. The results provided interesting insights into one‐pot routes involving in situ reactions act as a strategy for obtaining a variety of polymeric/polynuclear complexes which are inconvenient to obtain from directly presynthesizing the ligands.     

Cationic Heterocycles as Ligands: Synthesis and Reactivity with Anionic Nucleophiles of Cationic Triruthenium Clusters Containing C‐Metalated N‐Methylquinoxalinium or N‐Methylpyrazinium Ligands

The cationic cluster complexes [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐L¹Me)]⁺ ( 3 ⁺; HL¹=quinoxaline) and [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐L²Me)]⁺ ( 5 ⁺; HL²=pyrazine) have been prepared as triflate salts by treatment of their neutral precursors [Ru₃(CO)₁₀(μ‐H)(μ‐κ²N,C‐Lⁿ)] with methyl triflate. The cationic character of their heterocyclic ligands is responsible for their enhanced tendency to react with anionic nucleophiles relative to that of hydrido triruthenium carbonyl clusters that have neutral N‐heterocyclic ligands. These clusters react instantaneously with methyl lithium and potassium tris‐sec‐butylborohydride (K‐selectride) to give neutral products that contain novel nonaromatic N‐heterocyclic ligands. The following are the products that have been isolated: [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L¹Me₂)] ( 6 ; from 3 ⁺ and methyl lithium), [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L¹HMe)] ( 7 ; from 3 ⁺ and K‐selectride), [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L²Me₂)] ( 8 ; from 5 ⁺ and methyl lithium), and [Ru₃(CO)₉(μ‐H)(μ₃‐κ²N,C‐L²HMe)] ( 11 ; from 5 ⁺ and K‐selectride). Whereas the reactions of 3 ⁺ lead to products that arise from the attack of the corresponding nucleophile at the C atom of the only CH group adjacent to the N‐methyl group, the reactions of 5 ⁺ give mixtures of two products that arise from the attack of the nucleophile at one of the C atoms located on either side of the N‐methyl group. The LUMOs and the atomic charges of 3 ⁺ and 5 ⁺ confirm that the reactions of these clusters with anionic nucleophiles are orbital‐controlled rather than charge‐controlled processes. The N‐heterocyclic ligands of all of these neutral products are attached to the metal atoms in nonconventional face‐capping modes. Those of compounds 6 – 8 have the atoms of a ligand C?N fragment σ‐bonded to two Ru atoms and π‐bonded to the other Ru atom, whereas the ligand of compound 11 has a C? N fragment attached to a Ru atom through the N atom and to the remaining two Ru atoms through the C atom. A variable‐temperature ¹H NMR spectroscopic study showed that the ligand of compound 7 is involved in a fluxional process at temperatures above ?93 °C, the mechanism of which has been satisfactorily modeled with the help of DFT calculations and involves the interconversion of the two enantiomers of this cluster through a conformational change of the ligand CH₂ group, which moves from one side of the plane of the heterocyclic ligand to the other, and a 180° rotation of the entire organic ligand over a face of the metal triangle.     

Platinum(II) Mixed Ligand Complexes with Thiourea Derivatives,Dimethyl Sulphoxide and Chloride: Syntheses,Molecular Structures,and ESCA Data

The platinum(II) mixed ligand complexes [PtCl(L^1‐6)(dmso)] with six differently substituted thiourea derivatives HL, R₂NC(S)NHC(O)R′ (R = Et, R′ = p‐O₂N‐Ph: HL¹; R = Ph, R′ = p‐O₂N‐Ph: HL²; R = R′ = Ph: HL³; R = Et, R′ = o‐Cl‐Ph: HL⁴; R₂N = EtOC(O)N(CH₂CH₂)₂N, R′ = Ph: HL⁵) and Et₂NC(S)N=CNH‐1‐Naph (HL⁶), as well as the bis(benzoylthioureato‐κO, κS)‐platinum(II) complexes [Pt(L^{1, 2})₂] have been synthesized and characterized by elemental analysis, IR, FAB(+)‐MS, ¹H‐NMR, ¹³C‐NMR, as well as X‐ray structure analysis ([PtCl(L¹)(dmso)] and [PtCl(L^{3, 4})(dmso)]) and ESCA ([PtCl(L^{1, 2})(dmso)] and [Pt(L^{1, 2})₂]). The mixed ligand complexes [PtCl(L)(dmso)] have a nearly square‐planar coordination at the platinum atoms. After deprotonation, the thiourea derivatives coordinate bidentately via O and S, DMSO bonds monodentately to the Pt^II atom via S atom in a cis arrangement with respect to the thiocarbonyl sulphur atom. The Pt—S‐bonds to the DMSO are significant shorter than those to the thiocarbonyl‐S atom. In comparison with the unsubstituted case, electron withdrawing substituents at the phenyl group of the benzoyl moiety of the thioureate (p‐NO₂, o‐Cl) cause a significant elongation of the Pt—S(dmso)‐bond trans arranged to the benzoyl‐O—Pt‐bond. The ESCA data confirm the found coordination and bonding conditions. The Pt 4f_7/2 electron binding energies of the complexes [PtCl(L^{1, 2})(dmso)] are higher than those of the bis(benzoylthioureato)‐complexes [Pt(L^{1, 2})₂]. This may indicate a withdrawal of electron density from platinum(II) caused by the DMSO ligands.     

Delocalization and Valence Tautomerism in Vanadium Tris(iminosemiquinone) Complexes

To survey the noninnocence of bis(arylimino) acenaphthene (BIAN) ligands (L) in complexes with early metals, the homoleptic vanadium complex, [V(L)₃] ( 1 ), and its monocation, [V(L)₃]PF₆ ( 2 ), were synthesized. These complexes were found to have a very rich electronic behavior, whereby 1 displays strong electronic delocalization and 2 can be observed in unprecedented valence tautomeric forms. The oxidation states of the metal and ligand components in these complexes were assigned by using spectroscopic, crystallographic, and magnetic analyses. Complex 1 was identified as [V^IV(L^red)(L^.)₂] (L^red=N,N′‐bis(3,5‐dimethylphenylamido)acenaphthylene; L^.=N,N′‐bis(3,5‐dimethylphenylimino)acenaphthenesemiquinonate). Complex 2 was determined to be [V^V(L^red)(L^.)₂]⁺ at T<150 K and [V^IV(L^.)₃]⁺ at T>150 K. Cyclic voltammetry experiments reveal six quasi‐reversible processes, thus indicating the potential of this metal–ligand combination in catalysis or materials applications.     

Synthesis,Structure and Magnitic Properties of a Diphenoxobridged Binuclear Copper（Ⅲ） Complex

A mixed-ligand copper(Ⅱ） complex[Cu2(phen)2(HL^1)2]-(ClO4)2(1) was synthesized.X-ray analyses reveal that 1 has a bis(μ2-phenoxo)-bridged dicopper(Ⅱ） structure.2D hydrogen-bonded network is formed utilizing the N-H,O-H and C-H groups of the (HL^1) ligands (H2L^1=N-(2-hydroxybenzyl)ethanolamine),the C-H groups of the phenanthrolines and the perchlorate anions.Variable temperature magnetic properties of 1 have shown comparatively weak antiferromagnetic interactions with respect to the bridge angles, which have been ascribed to the unfavorable overlaps of the magnetic orbitals fo the highly distorted copper coordination polyhedra and the pyramidal distortions at the phenoxo oxygen atoms.     

Dioxouranium Complexes with Acetylpyridine Benzoylhydrazones and Related Ligands

Acetylpyridine benzoylhydrazone and related ligands react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu₄]₂[UO₂Cl₄] to form air‐stable complexes. Reactions with 2, 6‐diacetylpyridinebis(benzoylhydrazone) (H₂L^1a) or 2, 6‐diacetylpyridinebis(salicylhydrazone) (H₂L^1b) give yellow products of the composition [UO₂(L¹)]. The neutral compounds contain doubly deprotonated ligands and possess a distorted pentagonal‐bipyramidal structure. The hydroxo groups of the salicylhydrazonato ligand do not contribute to the complexation of the metal. The equatorial coordination spheres of the complexes can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting deep‐red complexes have hexagonal‐bipyramidal coordination environments with the oxo ligands in axial positions. The sterical strains inside the hexagonal plane can be reduced when two tridentate benzoylhydrazonato ligands are used instead of the pentadentate 2, 6‐diacetylpyridine derivatives. Acetylpyridine benzoylhydrazone (HL²) and bis(2‐pyridyl)ketone benzoylhydrazone (HL³) deprotonate and form neutral, red [UO₂(L)₂] complexes. The equatorial coordination spheres of these complexes are puckered hexagons. X‐ray diffraction studies on [UO₂(L^1a)(pyridine)], [UO₂(L^1b)(DMSO)], [UO₂(L²)₂] and [UO₂(L³)₂] show relatively short U—O bonds to the benzoylic oxygen atoms between 2.328(6) and 2.389(8) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U—N bond lengths: 2.588(7)—2.701(6) Å ).     

Imines in the Titanium Coordination Sphere – Transformation of Imidoyl Chlorides to Nitrilium Ions

In the reaction of TiCl₄ in benzene as solvent with the imidoyl chloride p‐Tolyl(Cl)C=NPh ( 1 ) the abstraction of the chloride substituent is observed, leading to the nitrilium salt [p‐Tolyl–C≡N–Ph]⁺[Ti₂Cl₉]^– ( 2 ) in quantitative yield. The highly electrophilic salt 2 is characterized by IR‐ and NMR spectroscopy. The observed band for the C≡N stretching mode of 2 clearly indicates the formation of a nitrilium ion. Especially a characteristic line broadening of the ¹³C{¹H}‐NMR signals related to carbon atoms next to the nitrogen is observed. By ¹⁵N,¹H‐HMBC NMR experiments it is shown that the nitrogen signal of 2 is significantly shifted to high‐field in relation to nitriles and imines. The molecular structure of 2 was confirmed by single‐crystal X‐ray diffraction. The C≡N bond length and the linearity of the C–C≡N–C unit in 2 confirm the triple bond character of this bond.     

Cerium(IV) Hexanuclear Clusters from Cerium(III) Precursors: Molecular Models for Oxidative Growth of Ceria Nanoparticles

Reactions of cerium(III) nitrate, Ce(NO₃)₃?6 H₂O, with different carboxylic acids, such as pivalic acid, benzoic acid, and 4‐methoxybenzoic acid, in the presence of a tridentate N,N,N‐donor ligand, diethylenetriamine (L¹), under aerobic conditions yielded the corresponding cerium hexamers Ce₆O₈(O₂CtBu)₈(L¹)₄ ( 1 ), Ce₆O₈(O₂CC₆H₅)₈(L¹)₄ ( 2 ), and Ce₆O₈(O₂CC₆H₄‐4‐OCH₃)₈(L¹)₄ ( 3 ). Hexamers 1 , 2 , and 3 contain the same octahedral Ce^IV₆O₈ core, in which all interstitial oxygen atoms are connected by μ₃‐oxo bridging ligands. In contrast, treatment of the Ce^IV precursor (NH₄)₂Ce(NO₃)₆ (CAN) with pivalic acid and the ligand L¹ under the same conditions afforded Ce₆O₄(OH)₄(O₂CtBu)₁₂(L¹)₂ ( 4 ), exhibiting a deformed octahedral Ce^IV₆O₄(OH)₄ core containing μ₃‐oxo and μ₃‐hydroxo moieties in defined positions. In contrast to the formation of 1 – 3 , the use of N‐methyldiethanolamine (L) in the reaction with Ce(NO₃)₃?6 H₂O and pivalic acid afforded a previously reported Ce^III dinuclear cluster, Ce₂(O₂CtBu)₆L₂, even in the presence of dioxygen. ESI‐MS analysis of the reaction mixture clearly indicated the importance of the ligand L¹ in promoting oxidation of the Ce^III aggregates, [Ce_n(O₂CtBu)_3n(L¹)₂], which is necessary for the formation of Ce^IV hexamers.     

Pyrrole‐2‐carbaldehyde Thiosemicarbazonates of Nickel(II) and Palladium(II): Synthesis,Structure, and Spectroscopy

Complexes of pyrrole‐2‐carbaldehyde thiosemicarbazones, [(C₄H₄N⁴)(H)C²=N³–N²(H)–C¹(=S)–N¹HR; R = Ph, H₂L¹; Me, H₂L²; H, H₂L³] with nickel(II) and palladium(II) are described. The reaction of nickel(II) acetate with H₂L¹ in methanol in 1:1 molar ratio yielded a complex of composition, [Ni(κ²‐N³,S‐HL¹)₂] ( 1 ). Likewise reaction of NiCl₂ with H₂L² in 1:1 molar ratio in acetonitrile in the presence of triethylamine base followed by the addition of pyridine did not yield the anticipated [Ni(κ³‐N⁴,N³,S‐L²)(py)] complex, moreover a bis‐square‐planar complex, [Ni(κ²‐N³,S‐HL²)₂] ( 2 ) was formed. However, in the presence of bipyridine (bipy), it yielded the addition product, [Ni(κ²‐N³,S‐HL²)₂(κ²‐N, N‐bipy)] ( 3 ). Reaction of PdCl₂(κ²‐P, P–PPh₂–CH₂–PPh₂) with H₂L³ in toluene in the presence of triethylamine has yielded a complex of stoichiometry, [Pd(κ³‐N⁴,N³,S–L³)(κ¹‐P–PPh₂–CH₂–P(O)Ph₂] ( 4 ). The ligands (HL¹)^– and (HL²)^– are chelating to Ni^II metal atom as anions binding through N³,S‐donor atoms with pendant pyrrole groups, and (L³)^2– is chelating to the Pd^II metal atom as dianion through N⁴,N³,S‐donor atoms (pyrrole is N⁴‐bonded). Fourth site in 4 is bonded to one P‐donor atom of PPh₂–CH₂–P(O)Ph₂, whose pendant –PPh₂ group involves auto oxidation to –P(O)PPh₂ during reaction. These complexes were characterized using analytical data, IR, NMR (¹H, ³¹P) spectroscopy and X‐ray crystallography. Complexes 1 , 2 , and 4 have square‐planar arrangement, whereas complex 3 is octahedral.     

Reductive Dimerization of Triruthenium Clusters Containing Cationic Aromatic N‐Heterocyclic Ligands

The cationic cluster complexes [Ru₃(μ‐H)(μ‐κ²N,C‐L¹ Me)(CO)₁₀]⁺ ( 1 ⁺; HL¹ Me=N‐methylpyrazinium), [Ru₃(μ‐H)(μ‐κ²N,C‐L² Me)(CO)₁₀]⁺ ( 2 ⁺; HL² Me=N‐methylquinoxalinium), and [Ru₃(μ‐H)(μ‐κ²‐N,C‐L³ Me)(CO)₁₀]⁺ ( 3 ⁺; HL³ Me=N‐methyl‐1,5‐naphthyridinium), which contain cationic N‐heterocyclic ligands, undergo one‐electron reduction processes to become short lived, ligand‐centered, trinuclear, radical species ( 1 – 3 ) that end in the formation of an intermolecular C? C bond between the ligands of two such radicals, thus leading to neutral hexanuclear derivatives. These dimerization processes are selective, in the sense that they only occur through the exo face of the bridging ligands of trinuclear enantiomers of the same configuration, as they only afford hexanuclear dimers with rac structures (C₂ symmetry). The following are the dimeric products that have been isolated by using cobaltocene as reducing agent: [Ru₆(μ‐H)₂{μ₆‐κ⁴N₂,C₂‐(L¹ Me)₂}(CO)₁₈] ( 5 ; from 1 ⁺), [Ru₆(μ‐H)₂{μ₆‐κ⁴N₂,C₂‐(L² Me)₂}(CO)₁₈] ( 6 ; from 2 ⁺), and [Ru₆(μ‐H)₂{μ₄‐κ⁸N₂,C₆‐(L³ Me)₂}(CO)₁₈] ( 7 ; from 3 ⁺). The structures of the final hexanuclear products depend on the N‐heterocyclic ligand attached to the starting materials. Thus, although both trinuclear subunits of 5 and 6 are face‐capped by their bridging ligands, the coordination mode of the ligand of 5 is different from that of the ligand of 6 . The trinuclear subunits of 7 are edge‐bridged by its bridging ligand. In the presence of moisture, the reduction of 3 ⁺ with cobaltocene also affords a trinuclear derivative, [Ru₃(μ‐H)(μ‐κ²N,C‐L^3′ Me)(CO)₁₀] ( 8 ), whose bridging ligand (L^3′ Me) results from the formal substitution of an oxygen atom for the hydrogen atom (as a proton) that in 3 ⁺ is attached to the C⁶ carbon atom of its heterocyclic ligand. The results have been rationalized with the help of electrochemical measurements and DFT calculations, which have also shed light on the nature of the odd‐electron species, 1 – 3 , and on the regioselectivity of their dimerization processes. It seems that the sort of coupling reactions described herein requires cationic complexes with ligand‐based LUMOs.     

Ligand Bridged and Bis-ligand Coordinated Titanium Complexes： Synthesis, Structure and Relevance to Phenylacetylene Hydroanilination Catalysis

Two ligand bridged binuclear titanium complexes Ti2（bppda）3（NMe2）2·3THF （1） and Ti2（bppda）3（NEt2）2·3THF （2） and one bis-ligand coordinated mononuclear complex Ti（bppda）2 （3） （ligand- HEbppda=N,N＇-Bis（2-pyrrylmeth- ylidene）-1,2-phenylenediamine） were synthesized by adjusting the ratio of the starting materials and the reaction speed. The complexes were fully characterized with NMR, elemental analysis and X-ray crystal diffraction. The catalytic activity of the complex 1 to phenylacetylene hydroanilination reaction was also investigated.     

Kinetics and mechanism of reaction between zirconium‐lactate and pentane‐2,4‐dione in excess lactate

The kinetics of the reaction of pentane‐2,4‐dione (HA) with Zr^IV has been studied at 25.0°C in an excess lactate (L^?) media. The equilibrium reaction was found to be: Zr₂L₆+HA?HL+Zr₂AL₅. The equilibrium was approached from either direction and a plausible mechanism has been proposed with kinetic constants, but individual reactivities of the keto and the enol tautomers of pentane‐2,4‐dione could not be apportioned. However, it was found that both the uncatalyzed and acid‐catalyzed paths contribute to the reverse reaction. But 2‐thenoyltrifluoroacetone (HT) forms a stronger chelate with Zr^IV, so its reaction with less reactive Zr₂L₅(OH₂) could not be detected; reactivity of the more reactive Zr₂L₅(OH₂)(OH) could be found. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 725–729, 2011     

An oxo‐bridged centrosymmetric tetranuclear titanium compound

The title compound, octa‐tert‐butoxybis­[μ₃‐2,2′‐(N‐methyl­imino)­diethanolato]­di‐μ‐oxo‐tetratitanium(IV), [Ti₂O{(OCH₂CH₂)₂(NCH₃)}{(CH₃)₃CO}₄]₂ or [Ti₄(C₅H₁₁NO₂)₂(C₄H₉O)₈O₂], lies about an inversion centre, and displays the less usual zigzag configuration. One O atom of the N‐methyl­diethoxo­amine ligand bridges the symmetry‐related Ti atoms, while the other bridges the two independent Ti atoms, with the N atom binding to give a facial configuration. Four ^tBuO⁻ ligands and a bridging oxide complete the respective five‐ and sixfold coordination of the two Ti atoms. The Ti—O bond lengths range in a self‐consistent fashion from 1.7624 (17) to 2.0878 (18) Å, while the Ti—N bond length is 2.374 (2) Å.     

Methanol[1‐(methoxymethanimidoyl)‐2‐(pyridin‐2‐ylmethyl)guanidine]bis(perchlorato)copper(II)

The title complex, [Cu(ClO₄)₂(C₉H₁₃N₅O)(CH₃OH)], was synthesized from a methanolysis reaction of N‐(methylpyridin‐2‐yl)cyanoguanidine (L³) and copper(II) perchlorate hexahydrate in a 1:1 molar ratio. The Cu^II ion is six‐coordinated by an N₃O₃ donor set which confers a highly distorted and asymmetric octahedral geometry. Three N‐donor atoms from the chelating 1‐(methoxymethanimidoyl)‐2‐(pyridin‐2‐ylmethyl)guanidine (L^3m) ligand and one O atom from the methanol molecule define the equatorial plane, with two perchlorate O atoms in the apical sites, one of which has a long Cu—O bond of 2.9074 (19) Å. The dihedral angle between the five‐ and six‐membered chelate rings is 8.21 (8)°. Two molecules are associated into a dimeric unit by intermolecular N—H...O(perchlorate) hydrogen bonds. Additionally, the weakly coordinated perchlorate anions also link adjacent [Cu(ClO₄)₂(L^3m)(CH₃OH)] dimers by hydrogen‐bonding interactions, resulting in a two‐dimensional layer in the (100) plane. Further C—H...O hydrogen bonds link the two‐dimensional layers along [100] to generate a three‐dimensional network.     

Co(III) complexes with optically active bis(menthane), pinano-para-menthane, carano-para-menthane, and bis(carane) propylenediaminodioximes

Novel optical ligands bis(menthane) (H₂L¹), pinano-para-menthane (H₂L²), and carano-para-menthane (H₂L³) propylenediaminodioximes are obtained. Diamagentic Co(III) complexes of the composition Co(HL¹)Cl₂ (I), Co(HL²)Cl₂ (II), Co(HL³)Cl₂ (III), and Co(HL⁴)Cl₂ · H₂O(IV) are synthesized by reactions of CoCl₂ with H₂L¹, H₂L², H₂L³ and bis(carane) propylenediaminodioxime (H₂L⁴) in ethanol in air. The crystal and molecular structures of compound I is determined by X-ray diffraction analysis. The crystals are monoclinic with the unit cell parameters a = 7.8385(3) Å, b = 11.4074(6) Å, c = 14.9509(6) Å, β = 104.278(2)°, V = 1295.57(10) ų, Z = 2, ρ(calcd) = 1.367 g/cm³, F(000) = 564, M = 533.41, space group P2₁. The crystal structure of complex I consists of individual mononuclear molecules. The Co³⁺ ion coordinates four N atoms of tetradentate cycle-forming anionic ligand and two Cl atoms. The coordination polyhedron of Cl₂N₄ is a distorted octahedron. The ¹³C and ¹H NMR spectra of the complexes synthesized confirm coordination of four N atoms of a ligand.     

Oxorhenium(V) Complexes with 1,3,4‐Triphenyl‐1,2,4‐triazol‐5‐ylidene

Reactions of the oxorhenium(V) complexes [ReOX₃(PPh₃)₂] (X = Cl, Br) with the N‐heterocyclic carbene (NHC) 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (L^Ph) under mild conditions and in the presence of MeOH or water give [ReOX₂(Y)(PPh₃)(L^Ph)] complexes (X = Cl, Br; Y = OMe, OH). Attempted reactions of the carbene precursor 5‐methoxy‐1,3,4‐triphenyl‐4,5‐dihydro‐1H‐1,2,4‐triazole ( 1 ) with [ReOCl₃(PPh₃)₂] or [NBu₄][ReOCl₄] in boiling xylene resulted in protonation of the intermediately formed carbene and decomposition products such as [HL^Ph][ReOCl₄(OPPh₃)], [HL^Ph][ReOCl₄(OH₂)] or [HL^Ph][ReO₄] were isolated. The neutral [ReOX₂(Y)(PPh₃)(HL^Ph)] complexes are purple, airstable solids. The bulky NHC ligands coordinate monodentate and in cis‐position to PPh₃. The relatively long Re–C bond lengths of approximate 2.1Å indicate metal‐carbon single bonds.     

Reactivity of an N,N‐Chelated Germylene Toward Substituted Alkynes,Alkenes, and Allenes

Treatment of N,N‐chelated germylene [(iPr)₂NB(N‐2,6‐Me₂C₆H₃)₂]Ge ( 1 ) with ferrocenyl alkynes containing carbonyl functionalities, FcC≡CC(O)R, resulted in [2+2+2] cyclization and formation of the respective ferrocenylated 3‐Fc‐4‐C(O)R‐1,2‐digermacyclobut‐3‐enes 2 – 4 [R = Me ( 2 ), OEt ( 3 ) and NMe₂ ( 4 )] bearing intact carbonyl substituents. In contrast, the reaction between 1 and PhC(O)C≡CC(O)Ph led to activation of both C≡C and C=O bonds producing bicyclic compound containing two five‐membered 1‐germa‐2‐oxacyclopent‐3‐ene rings sharing one C–C bond, 4,8‐diphenyl‐3,7‐dioxa‐2,6‐digermabicyclo[3.3.0]octa‐4,8‐diene ( 5 ). With N‐methylmaleimide containing an analogous C(O)CH=CHC(O) fragment, germylene 1 reacted under [2+2+2] cyclization involving the C=C double bond, producing 1,2‐digermacyclobutane 6 with unchanged carbonyl moieties. Finally, 1 selectively added to the terminal double bond in allenes CH₂=C=CRR′ giving rise to 3‐(=CRR′)‐1,2‐digermacyclobutanes [R/R′ = Me/Me ( 7 ), H/OMe ( 8 )] bearing an exo‐C=C double bond. All compounds were characterized by ¹H, ¹³C{¹H} NMR, IR and Raman spectroscopy and the molecular structures of 3 , 4 , 5 , and 8 were established by single‐crystal X‐ray diffraction analysis. The redox behavior of ferrocenylated derivatives 2 – 4 was studied by cyclic voltammetry.     

Tweaking the affinity of aryl‐substituted diazosalicylato‐ and pyridine ligands towards Zn (II) and its neighbors in the periodic system of the elements,Cu (II) and Cd (II), and their antimicrobial activity

A series of six new Zn (II) compounds, viz., [Zn(HL^ASA)₂(Py)₂] ( 1 ), [Zn(HL^MASA)₂(Py)₂] ( 2 ), [Zn(HL^MASA)₂(4‐MePy)₂] ( 3 ), [Zn(HL^CASA)₂(4‐MePy)₂] ( 4 ), [Zn(HL^BASA)₂(Py)₂] ( 5 ), [Zn(HL^BASA)₂(4‐MePy)₂] ( 6 ) and representative Cu (II) and Cd (II) complexes, viz., [Cu(HL^ASA)₂(Py)₂(H₂O)] ( 7 ) and [Cd(HL^BASA)₂(Py)₃] ( 8 ) [(HL^XASA)^? = para‐substituted 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoate with X = H (ASA), Me (MASA), Cl (CASA) or Br (BASA); Py = pyridine; 4‐MePy = 4‐methylpyridine] have been synthesized and characterized by spectroscopic techniques and single‐crystal X‐ray diffraction analysis. The structural characterization of the compounds revealed distorted tetrahedral ( 1 – 6 ), square‐pyramidal ( 7 ) and pentagonal‐bipyramidal ( 8 ) coordination geometries around the metal atom, in which the aryl‐substituted diazosalicylate ligands are coordinated only through the oxygen atoms of carboxylate groups, either in an anisobidentate or isobidentate mode; meanwhile, the 2‐hydroxy groups of the monoanionic ligand (HL^XASA)^? are involved only in intramolecular O‐H···O hydrogen bonds with the carboxylate function. In the crystal structures of 1 – 8 , the complex molecules are assembled by π‐stacking interactions giving mostly infinite 1D strands. The intermolecular binding in the solid state structures is accomplished by diverse additional non‐covalent contacts including C‐H···O, C‐H···N, C‐H···π, C‐H···Br, O···Br, Br···π and van der Waals contacts. Although the primary and secondary ligands in the Zn (II) complex series 1 – 6 carry different substituents at the periphery (X = H, Me, Cl, Br for (HL^XASA)^? and R = H, Me for 4‐Py‐R), five of the crystal structures were isostructural. Additionally, the antimicrobial activity of the pro‐ligands H₂L^XASA and their Zn (II), Cu (II) and Cd (II) compounds were studied in a comparative manner, showing high sensitivity (IZD ≥ 20) against Bacillus subtilis.