A fluorene-based diphosphinite ligand, its Ni, Pd, Pt, Fe, Co and Zn complexes and the first structurally characterized diphosphinate metal chelates

The diphosphinite ligand 9,9-(Ph₂POCH₂)₂-fluorene (1) was reacted with group 10 metal dichlorides to form chelate complexes of formula [MCl₂(1)] (MNi, 2; MPd, 3; MPt, 4) showing 8-membered metallocycles. Chloride abstraction from 3 with AgOTf afforded the dinuclear complex [M(μ-Cl)Pd(1)]₂(OTf)₂ (5), in which the ligand adopts a different conformation with respect of 3. In 5, the fluorene moiety and the phenyl groups display stabilizing interactions with the anion which is located close to the metal centre. With Fe(II), Co(II) and Zn(II) chlorides, the non-isolated intermediates [MCl₂(1)] readily undergo oxidation to [MCl₂(1_ox)] (MFe, 6; MCo, 7; MZn, 8; 1_ox = 9,9-(Ph₂P(O)OCH₂)₂-fluorene) in which the diphosphinate ligand and the metal centre form 10-membered metallocycles. Complexes 6-8 are the first examples of structurally characterized diphosphinate metal chelates. The Zn(II) diphosphinite complex [ZnCl₂(1)] (9) could be observed by NMR spectroscopy, along with the mixed phosphinite-phosphinate, mono-oxidized complex which is an intermediate in the formation of 8. Complex [ZnCl₂(9.9-fluorene-dimethanol)(Ph₂P(O)H)] (10) was also observed as hydrolysis product of 9. The X-ray molecular structures of 2, 3, 5.2OTf, 6, 7, 8 and 10 are reported.     

Reactivity of alkynyl Pd(II) azido complexes toward organic isocyanides, isothiocyanates, and nitriles

Alkynyl Pd(II) azido complexes of the type [Pd(N₃)(CCR)L₂] (1-3) were obtained by reactions of aqueous NaN₃ with [Pd(Cl)(CCR)L₂] (R = Ph or C(O)OMe). Treating compounds 1-3 with organic isocyanides (R-NC) afforded novel complexes, trans-[Pd(CCPh)(NCNR)(PMe₃)₂] (R = 2,6-Me₂C₆H₃ (4) or 2,6-Et₂C₆H₃ (5)) and trans-[Pd(CCR)(CN₄-t-Bu)L₂] (6: L = PMe₃, R = Ph; 7: L = PEt₃, R = C(O)OMe; 8: L = PMe₃, R = C(O)OMe), which contain either a carbodiimido or a C-coordinated tetrazolato group. Reactions of compounds 1 and 2 with R-NCS (R = 2,6-Me₂C₆H₃ or CH₂CH₃) and 1,4-phenylene diisothiocyanate (C₆H₄(NCS)₂) smoothly proceeded to give tetrazole-thiolato complexes, trans-[Pd(CCPh)(SCN₄-R)L₂] (L = PMe₃, R = Et (9) or 2,6-Me₂C₆H₃ (10); L = PEt₃, R = 2,6-Me₂C₆H₃ (11)), and a phenylene-bridged dinuclear Pd(II) tetrazole-thiolato complex, [(PEt₃)₂(CCPh)Pd(SCN₄-(μ-C₆H₄)-SCN₄)Pd(CCPh)(PEt₃)₂] (12), respectively. Complexes 9-12 contain the Pd-S bond that is formed by the dipolar cycloaddition of the organic isothiocyanate to the Pd-azido bond. In contrast, the corresponding reactions of compounds 1and 2 with C₆F₅CN and Me₃SiCN (organic nitriles, R-CN) gave an N-coordinated Pd(II)-tetrazolato compound {trans-[Pd(CCPh)(N₄C-C₆F₅)(PMe₃)₂] (13)} and a mixture of Pd(II)-cyano complexes {trans-[Pd(CCPh)(CN)(PEt₃)₂] (14) and [Pd(CN)₂(PEt₃)₂] (15)}, respectively. Bis(phosphine) bis(cyano) complexes of Pd and Ni, [M(CN)₂L₂] (L = PEt₃, PMe₃; L₂ = DEPE), could be obtained independently by the reactions of [M(N₃)₂L₂] with excess Me₃SiCN in organic solvents.     

Synthesis and structural diversity of 2-pyridylmethylideneamine complexes of zinc(II) chloride

The addition reactions of zinc(II) chloride to N-substituted pyridine-2-carbaldimines [Py-CHNR, R = Me (1a), Ph (1b), Bz (1c), allyl (1d)] lead to different complexes dependent on the N-bound substituent R. The 1:1 complexes show molecular structures of the type [(Py-CHNR)ZnCl₂] for R = methyl (2a), phenyl (2b), and allyl (2d) with a distorted tetrahedral environment for the zinc atom. The zinc complex with the N-methylated pyridine-2-carbaldimine also forms a dimer of the type [(Py-CHNR)ZnCl₂]₂ (2a)₂ with a square pyramidal coordination sphere of zinc. A 3:2 stoichiometry is observed for R = benzyl and an ion pair of the type [Zn(Py-CHNR)₃]²⁺ [ZnCl₄]²⁻ (2c) is found in the solid state.     

Modification of aminoallenylidene complexes of chromium via exchange of the C3-bound amino group

The aminoallenylidene(pentacarbonyl)chromium complexes [(CO)₅CrCCC(NR¹R²)Ph] (1a-c) react with dimethylamine by addition of the amine to the C1C2 bond of the allenylidene ligand to give alkenyl(amino)carbene complexes [(CO)₅CrC(NMe₂)CHC(NR¹R²)Ph] (2a-c) (R¹ = Me: R² = Me (a), Ph (b); R¹ = Et: R² = Ph (c)). In contrast, addition of a large excess (usually 20 equivalents) of ammonia or primary amines, H₂NR, to solutions of [(CO)₅CrCCC(NMe₂)Ph] (1a) affords the aminoallenylidene complexes [(CO)₅CrCCC(NHR)Ph] (1d-w) in which the dimethylamino group is replaced by NH₂ or NHR, respectively. In addition to simple amines such as methylamine, butylamine, and aniline, amines carrying a functional group (allylamine, propargylamine) and amino acid esters as well as amino terpenes and amino sugars can be used to displace the NMe₂ substituent. Usually the Z isomer (with respect to the partial C3-N double bond) is formed exclusively. Products derived from addition of H₂NR to the C1C2 bond of 1a are not observed. The amino group in 1d-w is rapidly deprotonated by excess of amine to form iminium alkynyl chromates [1d-w]⁻, thus protecting 1d-w from addition of free amine to either C3 or across the C1C2 bond. The iminium alkynyl chromates are readily reprotonated by acids or by chromatography on wet SiO₂ to reform 1d-w.     

Novel stable five-coordinate diorgano cobalt(III) complexes: Formation, structure, and reaction with carbon monoxide

A series of new five-coordinate acyl vinyl cobalt(III) complexes Co{η¹-C(CCPh)CHPh}[C(O)CCO] L₂(L = PMe₃) (6-10) were prepared via formal insertion of diphenylbutadiyne into Co-H function of mer-octahedral hydrido-acyl(phenolato)-cobalt(III) complexes. The complexes are diamagnetic. One square pyramidal structure of complex 6 was confirmed by X-ray diffraction analysis. These complexes are stable in solid state. In solution, six-coordinate acyl vinyl carbonyl cobalt(III) complex 11 is approved through the reaction of complex 7 with CO and the structure of complex 11 was determined by X-ray method.     

Cu(II) and Ni(II) complexes based on monofunctional and dendrimeric pyrrole-imine ligands: Applications in catalytic liquid phase hydroxylation of phenol

New bis(pyrrolide-imine) copper(II) and Ni(II) complexes C1 and C2 [{ (C₃H₇)-NCH (C₄H₃N)}₂Cu], [{(C₃H₇)-NCH-(C₄H₃N)}₂Ni] as well as the bimetallic dendrimeric (pyrrolide-imine) copper(II) and nickel(II) complexes C3 and C4, [DAB-{(NCH-C₄H₃N)₄}Cu₂], [DAB-{(NCH-C₄H₃N)₄}Ni₂] (DAB = G1-polypropyleneimine dendrimer with a diaminobutane core) were prepared in good yields. The structure and composition of the complexes were confirmed by a combination of analytical techniques. These complexes were investigated as catalysts in the hydroxylation of phenol in aqueous media in the pH range of 2-6 for the mononuclear complexes, C1 and C2 while the bimetallic systems, C3 and C4 were studied over the pH range 2-8. H₂O₂ was used as the oxidant under an oxygen atmosphere. The copper systems generally showed higher activity as compared to their nickel analogues. Catechol was the predominant product followed by hydroquinone with small amounts of para-benzoquinone. The nickel complexes showed better selectivity for catechol. The pH of the reaction medium also plays a role in both activity and selectivity with pH 3 being optimal for activity and pH 6 for selectivity to catechol.     

Platinum(II) and palladium(II) complexes with (N,N') and (C,N,N')- ligands derived from pyrazole as anticancer and antimalarial agents: synthesis, characterization and in vitro activities

The study of the reactivity of three 1-(2-dimethylaminoethyl)-1H-pyrazole derivatives of general formula [1-(CH₂)₂NMe₂}-3,5-R₂-pzol] {where pzol represents pyrazole and RH (1a), Me (1b) or Ph (1c)} with [MCl₂(DMSO)₂] (MPt or Pd) under different experimental conditions allowed us to isolate and characterize cis-[M{κ²-N,N′-{[1-(CH₂)₂NMe₂}-3,5-R₂-pzol])}Cl₂] {MMPtPt (2a-2c) or Pd (3a-3c)} and two cyclometallated complexes [M{κ³-C,N,N′-{[1-(CH₂)₂NMe₂}-3-(C₅H₄)-5-Ph-pzol])}Cl] {MPt(II) (4c) or Pd(II) (5c)}. Compounds 4c and 5c arise from the orthometallation of the 3-phenyl ring of ligand 1c. Complex 2a has been further characterized by X-ray crystallography. Ligands and complexes were evaluated for their in vitro antimalarial against Plasmodium falciparum and cytotoxic activities against lung (A549) and breast (MDA MB231 and MCF7) cancer cellular lines. Complexes 2a-2c and 5c exhibited only moderate antimalarial activities against two P. falciparum strains (3D7 and W2). Interestingly, cytotoxicity assays revealed that the platinacycle 4c exhibits a higher toxicity than cisplatin in the three human cell lines and that the complex 2a presents a remarkable cytotoxicity and selectivity in lung (IC₅₀ = 3 μM) versus breast cancer cell lines (IC₅₀ > 20 μM). Thus, complexes 2c and 4c appear to be promising leads, creating a novel family of anticancer agents. Electrophoretic DNA migration studies in presence of the synthesized compounds have been performed, in order to get further insights into their mechanism of action.     

Synthesis and characterization of triphenylphosphine stabilized silver α,β-unsaturated carboxylate: Crystal structure of [Ag(O2CCHC(CH3)2)(PPh3)2]

A series of triphenylphosphine coordinated silver α,β-unsaturated carboxylates of type [Ag(O₂CR)(PPh₃)_n: n = 1, R = CH₃CHCH (2a), (CH₃)₂CCH (2b), CH₃CH₂CHCH (2c), CH₃CH₂CH₂CHCH (2d), PhCHCH (2e), CH₂CH (2f); n = 2, CH₃CHCH (3a), (CH₃)₂CCH (3b), CH₃CH₂CHCH (3c), CH₃CH₂CH₂CHCH (3d)] were prepared by reaction of relative silver carboxylates (1a-1f) with triphenylphosphine in chloroform. These complexes were obtained in high yields and characterized by elemental analysis, ¹H NMR, ¹³C NMR, ³¹P NMR and IR spectroscopy. Thermal stability of the complexes has been determined by TG analysis. The molecular structure of [Ag((O₂CCHC(CH₃)₂))(PPh₃)₂] (3b) shows that the senecioato ligand is chelated with silver atom and generate, a distorted tetrahedron.     

Preparation, structure and decomposition of gold(I) and gold(III) acetylide complexes

1-Alkynyl-dimethyl(triorganophosphine)gold(III) complexes of the type cis-Me₂(Ph₃P)Au-CC-R with R = H, Me, Ph (1-3) have been prepared from the cis-Me₂(Ph₃P)AuX (X = Cl, I) complexes and lithium alkynyls. The crystal structures of 1 and 2 have been determined together with those of the reference compounds cis-Me₂(Ph₃P)AuX (X = Cl, I) and cis-Me₂(Me₃P)AuI. The molecules have a standard square planar geometry and are not associated into oligomers. Due to the different hybridization of the carbon orbitals, the Au-C(CR) bonds are found significantly shorter than the Au-CH₃ bonds. Compounds 1-3 are stable colourless, crystalline solids at 20 °C but decompose on heating with selective (cis) reductive elimination of ethane and formation of the gold(I) alkynyls (Ph₃P)Au-CC-R thus retaining the stronger gold-alkynyl bonds. Two complexes of this type have also been prepared by conventional routes from (R₃P)AuX complexes and the crystal structures of (Me₃P)Au-CC-Ph and [(p-Tol)₃P]Au-CC-H have been determined. The former with the small Me₃P ligand is associated into two different trimers via aurophilic bonding and further aggregated into chains via weak inter-trimer contacts, while the latter is a monomer owing to the steric bulk of the (p-Tol)₃P ligand.     

A new cumulene diiron complex related to the active site of Fe-only hydrogenases and its phosphine substituted derivatives: synthesis, electrochemistry and structural characterization

A new cumulene diiron complex related to the Fe-only hydrogenase active site [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₆] (1) was obtained by treatment of (μ-LiS)₂Fe₂(CO)₆ with excess 1,4-dichloro-2-butyne. By controllable CO displacement of 1 with PPh₃ and bis(diphenylphosphino)methane (dppm), mono- and di-substituted complexes, namely [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₅L] (2: L = PPh₃; 3: L = dppm) and [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₄L₂] (4: L = PPh₃; 5: L = dppm) could be prepared in moderate yields. Treatment of 1 with bis(diphenylphosphino)ethane (dppe) afforded a double butterfly complex [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₅]₂(μ-dppe) (7). With dppm in refluxing toluene, a dppm-bridged complex [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₄(μ-dppm)] (6) was obtained. These model complexes were characterized by IR, ¹H, ³¹P NMR spectra and the molecular structures of 1, 2 and 5-7 were determined by single crystal X-ray analyses. The electrochemistry of 1-3 was studied and the electrocatalytic property of 1 was investigated for proton reduction in the presence of HOAc.     

Reactivity of the N-heterocyclic carbene complexes [Ru(IMes)2(CO)HX] (X = OH, Cl) with alkynes

Treatment of the 16-electron hydroxy hydride complex [Ru(IMes)₂(CO)H(OH)] (1, IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene) with HCCR affords the alkynyl species [Ru(IMes)₂(CO)H(CCR)] (R = Ph 3, SiMe₃, 4) and [Ru(IMes)₂(CO)(CCR)₂] (R = Ph, 5). Deuterium labelling studies show that the mono-alkynyl complexes are formed via hydrogen transfer from a coordinated alkyne ligand to Ru-OH, while bis-alkynyl formation is proposed to take place through hydrogen transfer to Ru-H. Both 3 and 5 readily coordinate CO to give the corresponding dicarbonyl species 6 and 7. Addition of HCCPh to the hydride chloride precursor [Ru(IMes)₂(CO)HCl] (2) results in a different reaction pathway involving alkyne insertion into the Ru-H bond to yield the alkenyl chloride complex [Ru(IMes)₂(CO)(CHCHPh)Cl] 8. Complexes 3-8 have been structurally characterised by X-ray crystallography.     

Synthesis and structures of copper and gold complexes of the P,N ligands RNC(Bu)C(H)RPPh2 (R = SiMe3, H)

The reaction of the chelating P,N ligand RNC(Bu^t)CH(R)PPh₂ (R = SiMe₃) (1) with CuCl and CuCl₂ (probably by way of reduction to Cu(I) by the phosphine ligand) or Cu(NCCH₃)₄ClO₄ yielded the dimeric 1:1 complex [Cu{PPh₂CH(R)C(Bu^t)NR}Cl]₂ (2) or the monomeric 2:1 complex [Cu{PPh₂CH(R)C(Bu^t)NR}₂]ClO₄ (3), respectively. The presence of trace amounts of water during the reaction resulted in the successive cleavage of the two trimethylsilyl groups of the ligand and the formation of the monomeric chelate complexes [Cu{PPh₂CH(R)C(Bu^t)NH}₂]ClO₄ (4) and [Cu{PPh₂CH₂C(Bu^t)NH}₂]ClO₄ (5). Oxidation of 5 by atmospheric oxygen led to small quantities of the blue Cu(II) complex [Cu{(O)PPh₂CH₂C(Bu^t)NH}₂](ClO₄)₂ (6). The dimeric gold complexes [Au{PPh₂CH₂C(Bu^t)NH}]₂X₂ (X = BF₄, ClO₄) (7) were similarly obtained from the previously described Au{PPh₂CH(R)C(Bu^t)NR}Cl by replacing the covalently bound chlorine with the weakly coordinating anions in the presence of small quantities of water. The solution and solid state structures (except 5) of all complexes were determined by NMR spectroscopy and X-ray crystallography.     

Synthesis and non-linear optical properties of (η-pentaphenylcyclopentadienyl)dicarbonylruthenium(II) σ-alkenyl complexes

The complexes [Ru{(Z)-HCCHPh}(CO)₂(η⁵-C₅Ph₅)] (1) and [Ru{(Z)-HCCHC₆H₄NO₂}(CO)₂(η⁵-C₅Ph₅)] (2) have been synthesized and their identity confirmed by single-crystal X-ray diffraction studies. Reaction of 2 with PMe₂Ph and Me₃NO in tetrahydrofuran afforded [Ru{(Z)-HCCHC₆H₄NO₂}(CO)(PMe₂Ph)(η⁵-C₅Ph₅)] (3). Cyclic voltammetry confirms the expected increase in ease of oxidation on proceeding from 2 to 1 and from 2 to 3. Hyper-Rayleigh scattering studies at 1064 nm reveal a dramatic increase in quadratic non-linearity on co-ligand replacement of CO by PMe₂Ph, in proceeding from 2 to 3. Z-scan studies at 800 nm are consistent with significant contribution from two-photon states, and with an increase in γ_real on co-ligand replacement of CO by PMe₂Ph in proceeding from 2 to 3.     

Bis(diphenylphosphino)acetonitrile oxides, -sulfides and -imines: Their formation and structural features, and the remarkable structures of two lithiated derivatives

Oxidation of bis(diphenylphosphino)acetonitrile (dppmCN, 8) yields the corresponding bis-phosphinoxide system (9). Analogously, treatment of dppmCN with sulfur gave bis(diphenylphosphinsulfido)acetonitrile (10). Both compounds show very similar structures in the solid state, featuring strongly distorted U-shaped conformations. The Staudinger reaction of dppmCN with phenylazide gives rise to the formation of the bis(diphenylphosphinimino)acetonitrile product that was obtained in its ylidic P-NH tautomer form in solution and in the crystalline state. Deprotonation of the bis(diphenylphosphinchalcogenido)acetonitriles 9 and 10 gave the corresponding [NC-(Ph₂PX)₂]⁻ anions (X = O, S). Their lithio compounds show a remarkable structural diversity in dependence of the chalcogene element used. The oxygen-containing compound (13) forms an oxygen-coordinated Li⁺-bridged 12-membered heteromacrocyclic structure, whereas Li⁺ avoids sulfur coordination in 14 and exhibits a THF-stabilized Li⁺-NC-R adduct structure in the crystal.     

Synthesis and coordination of the bifunctionalized ylides Ph2P(CH2)n(Ph)2PCHCOOMe (n = 1, 2) and ketenylidene Ph2P(CH2)2(Ph)2PCCO to Pd and Pt complexes

In this paper it is reported the synthesis of the phosphonium salts [Ph₂P(CH₂)_n(Ph)₂PCH₂COOMe]Br (n = 1 (1), 2 (2)) and [Ph₂P(CH₂COOMe)(CH₂)_n(Ph)₂PCH₂COOMe]Br₂ (n = 3 (3)) derived from the reactions of the diphosphines dppm, dppe and dppp with methyl bromoacetate. By reaction of the monophosphonium salt of dppm and dppe with the strong base Na[N(SiMe₃)₂] the corresponding carbonyl stabilized ylides Ph₂P(CH₂)_n(Ph)₂PCHCOOMe (n = 1 (4), 2 (5)) were obtained. The Ph₂P(CH₂)₂(Ph)₂PCHCOOMe (5) ylide was reacted with Pd(II) and Pt(II) substrates. From these reactions were isolated exclusively complexes in which the ylide was chelated to the metal through the free phosphine group and the ylidic carbon atom. A further reaction of the Ph₂P(CH₂)₂(Ph)₂PCHCOOMe (5) ylide with 1.5 equiv. of Na[N(SiMe₃)₂] gives the bifunctionalized ketenylidene Ph₂P(CH₂)₂(Ph)₂PCCO (6) system. This cumulenic ylide reacts with Pt(II) complexes to form a chelated derivative in which IR and NMR spectra suggest the breaking of the CC bond of the -CCO group.     

Synthesis and characterization of [H2NC(S)NP(S)(OiPr)2] complexes of Co(II), Ni(II), Zn(II) and Cd(II)

Reaction of the potassium salt of the N-thiophosphorylthiourea H₂NC(S)NHP(S)(OiPr)₂ (HL) with Co(II), Ni(II), Zn(II) and Cd(II) cations in aqueous EtOH leads to the chelate complexes [ML₂] all showing a 1,5-S,S′-coordination formed by the CS and PS sulfur atoms of two deprotonated ligands L⁻. The structures of the resulting compounds were studied by IR, UV-Vis, ¹H, ³¹P{¹H} NMR spectroscopy and microanalysis. The metal center is found in a tetrahedral environment in [CoL₂], [ZnL₂] and [CdL₂]. According to NMR and UV-Vis spectroscopy the metal cation of [NiL₂] exhibits square planar coordination geometry in CH₂Cl₂, CHCl₃ and C₆H₆, while tetrahedral geometry is observed in acetone, DMSO and DMF. Regardless of the solvent used for the crystallization of [NiL₂], the molecular structure in the solid is always square planar as was confirmed by XRD of single crystals and magnetic measurements of the polycrystalline material. The magnetic and photoluminescent properties of all complexes are also reported.     

Platinum(II) halide complexes of PPh2(CFCF2) and PPh2(CClCF2). The synthesis and crystal structure of [PtI(μ-I){PPh2(CXCF2)}]2, (X = F, Cl); the first crystallographically characterised iodide-bridged platinum(II) phosphine dimers

The reactions of the fluorovinyl-substituted phosphines PPh₂(CFCF₂) and PPh₂(CClCF₂), with K₂PtX₄ (X = Br, I) have been investigated. The resulting complexes have been characterized by a combination of ¹⁹F and ³¹P{¹H} NMR, IR and Raman spectroscopy. The reactions of these phosphines with K₂PtBr₄ yield the monomeric complexes cis-[PtBr₂{PPh₂(CFCF₂)}₂] (1) and trans-[PtBr₂{PPh₂(CClCF₂)}₂] (2), respectively, whilst the reactions with K₂PtI₄ yield both the monomeric species trans-[PtI₂{PPh₂(CXCF₂)}₂], {X = F (3), Cl (4)}, and the dimeric species [PtI(μ-I){PPh₂(CXCF₂)}]₂, {X = F (5), Cl (6)}. The dimers 5 and 6 represent the first crystallographically characterised platinum(II) iodide-bridged phosphine complexes, and both adopt the symmetric-trans structure.     

New bis(macrocyclic) dinickel(II) complexes obtained by oxidation of bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,7-dien-6-yl)dinickel(II) perchlorate

New bis(macrocyclic) dinickel(II) complexes with bis(Me₂[14]-4,7-dien-6-ylidene), 2a and 2b, were synthesized by oxidation of a dinickel(II) complex with an unsaturated bis(macrocyclic) ligand containing four CN bonds, bis(Me₂[14]-4,7-dien-6-yl) (1). Complex 2a was found to undergo intramolecular cyclization between the methyl group of one macrocycle and the carbon atom of the CN group of the other macrocycle to produce a bis(macrocyclic) dinickel(II) complex bridged by a fivemembered ring (3). The structures of 2b and 3 were determined by X-ray crystallography. The nonsymmetrical bis(macrocyclic) structure of the dinickel(II) complex 3 was reflected in its cyclic voltammogram and ¹H and ¹³C NMR spectra. The catalytic capabilities of these bis(macrocyclic) nickel(II) complexes in the reductive debromination of 1-bromo-4-tert-butylbenzene were also investigated.     

Organometallic π-tweezers incorporating pyrazine- and pyridine-based bridging units

Pyrazine- and pyridine-based π-conjugated σ-donor molecules, such as 4,4′-bipyridine, 1,2-di(4-pyridyl)ethylene, 3,5-dipyridyl-1,2,4-triazole, N,N′-bis(4-pyridylmethylidene)benzene-1,4-diamine, 2,5-di(pyridylmethylidene)cyclopentanone, 2,6-di(4-pyridylmethylidene)cyclohexanone (LL, 2a-2g) can successfully be used to span heterobimetallic π-tweezer units of the type [{[Ti](μ-σ,π-CCSiMe₃)₂}M]⁺ ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; M = Cu, Ag). The thus accessible di-cationic species [{[Ti](μ-σ,π-CCSiMe₃)₂}MLLM{(Me₃SiCC-μ-σ,π)₂[Ti]}]²⁺ (4), which are formed via the formation of [{[Ti](μ-σ,π-CCSiMe₃)₂}MLL]⁺ (3) complexes, can be isolated in yields between 66% and 99%.However, when C₅H₄NCHCHC₆H₄CHCHNC₅H₄ (5a) and C₅H₄NCHNC₆H₄CHCHNC₅H₄ (5b), respectively, are reacted with {[Ti](μ-σ,π-CCSiMe₃)₂}AgBF₄(1c) in a 1:1 molar ratio, then the silver(I) ion is released from the organometallic π-tweezer 1c and coordination polymers [AgBF₄ · 5a]_n (6a) and [AgBF₄ · 5b]_n (6b) along with [Ti](CCSiMe₃)₂ (7) are formed in quantitative yield.     

Diffusion NMR studies on neutral and cationic square planar palladium(II) complexes

Diffusion NMR investigations were carried out in CD₂Cl₂ for a series of neutral (1-7) and cationic (8-10) square planar palladium complexes. Diffusion data were elaborated through a modified Stokes-Einstein equation that takes into account the size and shape of molecules. The hydrodynamic volume at infinite dilution of all complexes was found to be similar to the crystallographic volume and always much larger than the van der Waals volume. The self-aggregation tendency of [Pd(N,C⁻)(N,N)][PF₆] ionic complexes [(N,C⁻) = (C₆H₄-(Ph)C(O)-CN-Et); 8, (N,N) = 2,2′-bipirydine; 9, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(Me)-C(Me)N(2,6-(iPr)₂-C₆H₃); 10, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(R′)-C(R′)N(2,6-(iPr)₂-C₆H₃), R′₂ = naphthalene-1,8-diyl] was investigated by performing ¹H and ¹⁹F diffusion experiments as a function of the concentration. Clear evidence for the formation of ion triples containing two cationic units was obtained for 8, most likely due to the establishment of a weak Pd?O interaction. The tendency to form ion triples was much reduced in 9 and 10, having an increased steric hindrance in the apical positions. While 9 showed the usual tendency to afford a mixture of free ions and ion pairs, solvated ions were the predominant species in the case of 10 even at high concentration values (approaching 100 mM).