Synthesis and characterization of thiosemicarbazone derivatives of 2-chloro-4-hydroxy-benzaldehyde and their rhenium(I) complexes

N-Thioamide thiosemicarbazone derived of 2-chloro-4-hydroxy-benzaldehyde (R = H, HL¹; R = Me, HL² and R = Ph, HL³) have been prepared and their reaction with fac-[ReX(CO)₃(CH₃CN)₂] (X = Br, Cl) in chloroform gave the adducts [ReX(CO)₃(HL)] (1a X = Cl, R = H; 1a′ X = Br, R = H; 1b X = Cl, R = CH₃; 1b′ X = Br, R = CH₃; 1c X = Cl, R = Ph; 1c′ X = Br, R = Ph) in good yield. Complexes 1a′ and 1b’ were also obtained by the reaction of HL¹ and HL³ with [ReBr(CO)₅] in toluene.All the compounds have been characterized by elemental analysis, mass spectrometry (FAB), IR and ¹H NMR spectroscopic methods. Moreover, the structures of HL², HL³ and 1a·H₂O were also established by X-ray diffraction. In 1a, the rhenium atom is coordinated by the sulphur and the azomethine nitrogen atoms, forming a five-membered chelate ring, as well as three carbonyl carbon and chloride atoms. The resulting coordination polyhedron can be described as a distorted octahedron.The study of the crystals obtained by slow evaporation of methanol and DMSO solutions of the adducts 1a′ and 1b, respectively, showed the formation of dimer structures based on rhenium(I) thiosemicarbazonates [Re₂(L¹)₂(CO)₆]·3H₂O (2a)·3H₂O and [Re₂(L²)₂(CO)₆]·(CH₃)₂SO (2b)·2(CH₃)₂SO. Amounts of these thiosemicarbazonate complexes [Re₂(L)₂(CO)₆] (2) were obtained by reaction of the corresponding free ligands with [ReCl(CO)₅] in dry toluene.In 2a·3H₂O and 2b·2(CH₃)₂SO the dimer structures are established by Re–S–Re bridges, where S is the thiolate sulphur from a N,S-bidentate thiosemicarbazonate ligand. In both structures the rhenium coordination sphere is similar; the dimers are in the same diamond Re₂S₂ face.     

Metal complexes of azo compounds derived from 4-acetamidophenol and substituted aniline

The Ni(II) and Cu(II) complexes of four azo compounds (H₂L^1–4), namely, 2-(p-X-phenylazo)-4-acetamidophenol (X = OCH₃, NO₂, Br, and H for H₂L¹, H₂L², H₂L³, and H₂L⁴, respectively) were prepared and characterized on the basis of their analytical, spectroscopic, magnetic, and conductance data. The isolated complexes are found to have the general formulae [M(HL^1–4)Cl(H₂O)₃] (M = Ni(II) and Cu(II)). The chelates are found to have octahedral structure. The infrared spectra show that H₂L^1–4 ligands are coordinated to the metal ions in a uninegative bidentate manner, with NO donor sites of the azo N and the deprotonated phenolic O. The ligands and their chelates are subjected to thermal analysis. The biological activity of the synthesized ligands and their metal complexes also are screened against the adult Tribolium confusum mortality. They showed remarkable biological activity.     

Synthesis,spectroscopy and structures of halogen and sulfur-bridged dinuclear silver(I) complexes with N1-substituted thiophene-2-carbaldehyde thiosemicarbazone

The reactions of silver(I) halides (Cl or Br) with thiophene-2-carbaldehyde N¹-methyl thiosemicarbazone (HttscMe) in the presence of Ph₃P (1:1:1 molar ratio) yield halogen-bridged dimers, [Ag₂(μ-X)₂(η¹-S-HttsMe)₂(PPh₃)₂] (X = Cl, 1; Br, 2). The use of 2,2′-bipyridine in lieu of Ph₃P in the reaction of silver(I) chloride with HttscMe yields the sulfur-bridged dimer, [Ag₂(μ-S-HttscMe)₂(η¹-HttsMe)₂] · 2CHCl₃ 3. The substituents have altered the nature of bridge between the two silver atoms. The Ag···Ag separation (3.4867(5) Å) in complex 3 is less than that in the halogen-bridged dimers (3.734(4) Å 1; 3.746(5) Å 2). Unlike PPh₃ the co-ligand 2,2′-bipyridine did not coordinate to the silver center, but was necessary for crystallization in the reaction with the thio-ligand. NMR spectroscopy revealed that the complexes remained unchanged in the solution state (CDCl₃).     

Heterofunctionalized phosphines derived from (2-formylphenyl)diphenylphosphine and their reactions with oxorhenium(V) complexes

Reactions of [ReOCl₃(PPh₃)₂] with a potentially tridentate Schiff base derived from (2-formylphenyl)diphenylphosphine and 2-aminophenol, HL¹P, (HL¹P = Ph₂PC₆H₄-2-HCN(C₆H₄-2-OH)) result in a rapid decomposition of the Schiff base and the formation of a large number of hitherto non-identified metal-containing species, while from similar reactions with the analogoue phosphine oxide HL¹PO, (HL¹PO = Ph₂P(O)C₆H₄-2-HCN(C₆H₄-2-OH)) products of the compositions [ReOCl₂(PPh₃)(L¹PO)] (1) and [Re(NC₆H₄-2-OH)Cl₃(PPh₃)₂] (2) could be isolated. The structure of 2 is an experimental proof of the preceding, metal-induced cleavage of the C–N double bond. A subsequent reaction of the released 2-aminophenol forms the final phenylimido ligand.Reduction of HL¹P with NaBH₄ gives the phosphine amine H₂L²P (H₂L² = Ph₂P(C₆H₄-2-CH₂NH(C₆H₄-2-OH))) in good yield. Reactions of H₂L²P with common oxorhenium(V) complexes result in the formation of the stable rhenium(V) complex [ReOCl₂(HL²P)] (3) with a facially coordinated HL²P^? ligand.     

Functionalized N-heterocyclic carbene iridium complexes: Synthesis,structure and addition polymerization of norbornene

Picolyl, pyridine, and methyl functionalized N-heterocyclic carbene iridium complexes [Cp¹Ir(C^N)Cl]Cl (4, C^N = 3-Methyl-1-picolyimidazol-2-ylidene), [Cp¹Ir(C^N)Cl][Cp¹IrCl₃] (5), [Cp¹Ir(C-N)Cl]Cl (6, C-N = 3-Methyl-1-pyridylimidazol-2-ylidene) and [Cp¹Ir(L)Cl₂] (7, L = 1,3-dimethylimidazol-2-ylidene) have been synthesized by transmetallation from Ag(I) carbene species, and characterized by ¹H NMR, ¹³C NMR spectra and elemental analyses. The molecular structures of 5–7 have been confirmed by X-ray single-crystal analyses. The iridium carbene complexes 4 and 6 show moderate catalytic activities (3.03 × 10⁵ g PNB (mol Ir)^?1 h^?1 and 1.70 × 10⁶ g PNB (mol Ir)^?1 h^?1) for the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as co-catalyst. The produced polynorbornene have been characterized by IR, ¹H NMR and ¹³C NMR spectra, showing it follows the vinyl-addition-type of polymerization.     

Electrochemical characterization of common catalysts and initiators for atom transfer radical polymerization in [BMIm][OTf]

The redox properties of some largely employed ATRP initiators and copper catalysts (Cu/L/X⁻) were investigated in 1-butyl-3-methylimidazolium trifluoromethanesulfonate (L = amine ligand, X = Br or Cl). Both Cu(II) and Cu(I) complexes are stable in the IL and, as required by ATRP, X⁻ stabilizes more Cu(II) than Cu(I). The activation rate constants of initiators by [Cu^ITPMA]⁺ were measured and a good correlation between k_act and the C-X bond dissociation free energy (BDFE) was observed. Overall, the results indicated that [BMIm][OTf] behaves much like organic solvents; the reported data launch the bases for a useful database to select the appropriate catalyst/initiator couple for ATRP in ILs.     

Luminescent coordination polymers with extended Au(I)–Ag(I) interactions supported by a pyridyl-substituted NHC ligand

Reaction of [Ag(CH₃impy)₂]PF₆, 1, with Au(tht)Cl produces the monometallic Au(I)-species [Au(CH₃impy)₂]PF₆, 2. Treatment of 2 with excess AgBF₄ in acetonitrile, benzonitrile or benzylnitrile produces the polymeric species {[AuAg(CH₃impy)₂(L)](BF₄)₂}_n, (L = CH₃CN,3; L = C₆H₅CN, 4; L = C₆H₅CH₂CN, 5) where the Au(I) centers remain bound to two carbene moieties while the Ag(I) centers are coordinated to two alternating pyridyl groups and a solvent molecule (L). Reaction of 2 with AgNO₃ in acetonitrile produces the zig-zag mixed-metal polymer {[AuAg(CH₃impy)₂(NO₃)]NO₃}_n, 6, that contains a coordinated nitrate ion in place of the coordinated solvent species. All of these polymeric materials are dynamic in solution and dissociate into their respective monometallic components. Compounds 2–6 are intensely luminescent in the solid-state and in frozen solution. All of these complexes were characterized by ¹H, ¹³C NMR, electronic absorption and emission spectroscopy and elemental analysis.     

Metal–metal bond cleavage of carbene complexes by halogens: The crystal and molecular structures of ax-[Mn2(CO)9{C(OEt)2-thienyl}], [Mn(CO)4(I){C(OEt)2-thienyl}] and eq-[Mn2(CO)9{C(NH2)2-thienyl}]

The metal–metal bond in [M₂(CO)₉{C(OEt)R}] (M = Mn (1), Re (2), R = 2-thienyl (a), 2-bithienyl (b)) is readily cleaved with halogens to afford cis-[M(CO)₄(X){C(OEt)R}] (M = Mn (3), X = I; M = Re (4), X = Br). In the binuclear manganese complex, the carbene ligand is found in an axial position due to steric reasons, whereas the electronically favoured equatorial position is found for the carbene ligands in the corresponding rhenium complexes and in [Mn₂(CO)₉{C(NH₂)thienyl}] (5a), containing a sterically less demanding NH₂-substituent.     

Uranium(VI) bis(imido) disulfonamide and dihalide complexes: Synthesis density functional theory analysis

Novel cis- and trans-bis(imido) uranium disulfonamide derivatives have been prepared from iodide metathesis reactions between two equivalents of K[N(Me)(SO₂Ar’)] (Ar’ = 4-Me-C₆H₄) and U(N^tBu)₂(I)₂(L)_x (L = OPPh₃, x = 2; Me₂bpy, x = 1; Me₂bpy = 4,4’-dimethyl-2,2’-bipyridyl). These bis(amide) derivatives serve as useful precursors for the synthesis of the trans-diphenolate complex U(N^tBu)₂(O-2-^tBuC₆H₄)₂(OPPh₃)₂ (5), cis- and trans-dithiolate complexes U(N^tBu)₂(SPh)₂(L)_x (L = OPPh₃ (6); Me₂bpy (7)), and cis- and trans-dihalide complexes with the general formulas U(N^tBu)₂(X)₂(L)_x (X = Cl, L = OPPh₃ (8), L = Me₂bpy (10); X = Br, L = OPPh₃ (9), L = Me₂bpy (11)). DFT calculations performed on the trans-dihalide series U(N^tBu)₂(X)₂(L)₂ and the UO₂²⁺ analogues UO₂X₂(OPPh₃)₂ suggest that the uranium centers in the [U(N^tBu)₂]²⁺ ions possess more covalent character than analogous UO₂²⁺ derivatives but that the U-X bonds in the U(N^tBu)₂X₂L₂ complexes possess a more ionic nature.     

Structures and spin states of mono- and dinuclear iron(II) complexes of imidazole-4-carbaldehyde azine and its derivatives

Mononuclear [Fe(H₂L^R)₂]X₂ (R = H, 2-Me, 5-Me, 2-Et-5-Me; X = ClO₄, BF₄) and dinuclear [Fe₂(H₂L^R)₃]X₄ complexes containing imidazole-4-carbaldehyde azine (H₂L^H) and its derivatives prepared by condensation of 4-formylimidazole, 2-methyl- or 5-methyl-4-formylimidazole, or 2-ethyl-4-methyl-5-formylimidazole, with hydrazine in a 2:1 mole ratio in methanol, were prepared and their magnetostructural relationships were studied. In the mononuclear complexes, H₂L^R acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H₂L^R acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate structure. At room temperature, [Fe₂(H₂L^H)₃](ClO₄)₄ and [Fe₂(H₂L^2-Me)₃](ClO₄)₄ were in the high-spin (HS) and low-spin (LS) states, respectively. The results are in accordance with the ligand field strength of H₂L^2-Me with electron-donating methyl groups being stronger than H₂L^H, with the order of the ligand field strengths being H₂L^2-Me > H₂L^H. However, in the mononuclear [Fe(H₂L^H)₂](ClO₄)₂ and [Fe(H₂L^2-Me)₂](ClO₄)₂ complexes, a different order of ligand field strengths, H₂L^H > H₂L^2-Me, was observed because [Fe(H₂L^H)₂](ClO₄)₂ was in the LS state while [Fe(H₂L^2-Me)₂](ClO₄)₂ was in the HS state at room temperature. X-ray structural studies revealed that the interligand steric repulsion between a methyl group of an H₂L^2-Me ligand and the other ligand in [Fe(H₂L^2-Me)₂](ClO₄)₂ is responsible for the observed change in the spin state. The same is true for [Fe(H₂L^2-Et-5-Me)₂](ClO₄)₂, while [Fe(H₂L^5-Me)₂](ClO₄)₂ does not involve such a steric congestion and stays in the LS state over the temperature range 5–300 K. Two kinds of crystals (polymorphs) were isolated for [Fe₂(H₂L^H)₃](BF₄)₄ and [Fe₂(H₂L^2-Et-5-Me)₃](ClO₄)₄, and they exhibited different magnetic behaviors.     

Mass spectrometric study of the dissociation of Group XI metal complexes with fatty acids and glycerolipids: Ag2H+ and Cu2H+ ion formation in the presence of a double bond

Results of mass spectrometric studies are reported for the collisional dissociation of Group XI (Cu, Ag, Au) metal ion complexes with fatty acids (palmitic, oleic, linoleic and α-linolenic) and glycerolipids. Remarkably, the formation of M₂H⁺ ions (M = Cu, Ag) is observed as a dissociation product of the ion complexes containing more than one metal cation and only if the lipid in the complex contains a double bond. Ag₂H⁺ is formed as the main dissociation channel for all three of the fatty acids containing double bonds that were investigated while Cu₂H⁺ is formed with one of the fatty acids and, although abundant, is not the dominant dissociation channel. Also, Cu(I) and Ag(I) ion complexes were observed with glycerolipids (including triacylglycerols and glycerophospholipids) containing either saturated or unsaturated fatty acid substituents. Interestingly, Ag₂H⁺ ion is formed in a major fragmentation channel with the lipids that are able to form the complex with two metal cations (triacylglycerols and glycerophosphoglycerols), while lipids containing a fixed positive charge (glycerophospocholines) complex only with a single metal cation. The formation of Ag₂H⁺ ion is a significant dissociation channel from the complex ion [Ag₂(L–H)]⁺ where L = Glycerophospholipid (GP) (18:1/18:1). Cu(I) also forms complexes of two metal cations with glycerophospholipids but these do not produce Cu₂H⁺ upon dissociation. Rather organic fragments, not containing Cu(I), are formed, perhaps due to different interactions of these metal cations with lipids resulting from the much smaller ionic radius of Cu(I) compared to Ag(I).     

Synthesis and investigations of mixed-ligand lanthanide complexes with N,N′-dipyrrolidine-N′′-trichloracetylphosphortriamide,dimethyl-N-trichloracetylamidophosphate, 1,10-phenanthroline and 2,2′-bipyrimidine

Coordination compounds with general formula [Ln(L¹)₃phen], where Ln = Nd, Eu, Er, Yb, HL¹ = N,N′-dipyrrolidine-N′′-trichloracetylphosphortriamide, phen = 1,10-phenanthroline; [Ln(L¹)₃bpm], where Ln = La, Nd, Eu, Gd, Er, Y, bpm = 2,2′-bipyrimidine and [{Ln(L²)₃}₂(μ-bpm)], where Ln = La, Nd, Eu, Gd, Er, Y, HL² = dimethyl-N-trichloracetylamidophosphate have been synthesized and characterized by means of IR and UV–Vis spectroscopy. Crystal structures of [Nd(L¹)₃phen] (1), [Nd(L¹)₃bpm] (2) and [{Nd(L²)₃}₂(μ-bpm)] (3) have been determined. It was found, that in the deprotonated form the phosphoryl ligands (L¹)^? and (L²)^? are coordinated to the neodymium atoms in a bidentate manner via the oxygen atoms of the phosphoryl and the carbonyl groups with formation of six-membered metallocycles. In the case of compounds 1 and 2 the 1,10-phenanthroline (or 2,2′-bipyrimidine) molecules are coordinated to the metals in a bidentate manner via the nitrogen atoms. In contrast 2,2′-bipyrimidine acts in the bidentate-bridge mode forming binuclear complex 3. Variable-temperature magnetic susceptibility measurements of 3 and [{Gd(L²)₃}₂(μ-bpm)] (4) reveal a weak antiferromagnetic interaction between the two magnetic centres, whereas in the case of [{Eu(L²)₃}₂(μ-bpm)] (5) the presence of spin–orbit coupling leads to a deviation from the Curie and Curie–Weiss laws.     

Two highly unsymmetrical tetradentate (N3O) Schiff base copper(II) complexes: Template synthesis,structural characterization,magnetic and computational studies

Two new copper(II) complexes, [Cu₂(L¹)₂](ClO₄)₂ (1) and [Cu(L²)(ClO₄)] (2), of the highly unsymmetrical tetradentate (N₃O) Schiff base ligands HL¹ and HL² (where HL¹ = N-(2-hydroxyacetophenone)-bis-3-aminopropylamine and HL² = N-(salicyldehydine)-bis-3-aminopropylamine) have been synthesised using a template method. Their single crystal X-ray structures show that in complex 1 two independent copper(II) centers are doubly bridged through phenoxo-O atoms (O1A and O1B) of the two ligands and each copper atom is five-coordinated with a distorted square pyramidal geometry. The asymmetric unit of complex 2 consists of two crystallographically independent N-(salicylidene)-bis(aminopropyl)amine-copper(II) molecules, A and B, with similar square pyramidal geometries. Cryomagnetic susceptibility measurements (5–300 K) on complex 1 reveal a distinct antiferromagnetic interaction with J = ?23.6 cm^?1, which is substantiated by a DFT calculation (J = ?27.6 cm^?1) using the B3LYP functional. Complex 1, immobilized over highly ordered hexagonal mesoporous silica, shows moderate catalytic activity for the epoxidation of cyclohexene and styrene in the presence of TBHP as an oxidant.     

Formation of chiral ionic liquids and imidazol-2-ylidene metal complexes from the proteinogenic aminoacid l-histidine

Treatment of the amino acid derivative Bz-His-OMe with excess n-propyl bromide gave the corresponding histidinium salt [Bz-His(n-propyl)₂-OMe⁺Br⁻]. It features a melting point of 39 °C and may serve as a useful readily available optically active ionic liquid. Its subsequent treatment with silver oxide gave the corresponding l-histidine derived chiral N-heterocyclic carbene complex [“(carbene)₂Ag · AgBr₂”]. Transmetallation by treatment with Pd(CH₃CN)₂Cl₂ or [Rh(cod)Cl]₂ led to the formation of the respective chiral late metal imidazol-2-ylidene complexes [“(carbene)₂PdCl₂”] and [“(carbene)RhCl(cod)”], respectively. Four diastereomers of the square planar palladium system were observed. Due to the additional chirality center in the l-histidine-derived “Arduengo-carbene ligand” two diastereomers of the rhodium carbene complex were formed.     

Synthesis and characterization of organophosphine/phosphite stabilized N-silver(I) succinimide: crystal structure of [(Ph3P)3 · AgNC4H4O2]

Six organophosphine/phosphite stabilized N-silver(I) succinimide complexes of the type L_n · AgNC₄H₄O₂ (L = PPh₃; n = 1, 2a; n = 2, 2b; n = 3, 2c; L = P(OEt)₃; n = 1, 2d; n = 2, 2e; n = 3, 2f) have been prepared by reacting [AgNC₄H₄O₂], which can be synthesized from succinimide and excessive Ag₂O in boiling water, with triphenylphosphine or triethylphosphite in dichloromethane under a nitrogen atmosphere. These complexes were obtained in high yields and characterized by elemental analysis, ¹H, ¹³C{H} NMR, IR spectroscopy and thermal analysis (TG and DSC). The molecular structure of 2c has been determined by X-ray single crystal analysis, in which the silver atom is in a distorted tetrahedral geometry.     

Application of carboxyl functionalized graphene oxide as mimetic peroxidase for sensitive voltammetric detection of H2O2 with 3,3′,5,5′-tetramethylbenzidine

A sensitive electrochemical method for H₂O₂ determination was proposed with carboxyl functionalized graphene oxide (GO-COOH) as mimetic peroxidase and 3,3′,5,5′-tetramethylbenzidine (TMB) as substrate. GO-COOH exhibited intrinsic peroxidase-like activity that could catalyze the oxidation of TMB with H₂O₂. The generated product exhibited a sensitive second order derivative linear sweep voltammetric reduction peak at − 0.93 V (vs. Ag/AgCl) in Britton–Robinson buffer. Under the optimal conditions the reduction peak current was proportional to H₂O₂ concentration in the linear range from 0.006 to 0.8 μmol L^− 1 with the detection limit of 1.0 nmol L^− 1 (3σ). This proposed method was further applied to determine H₂O₂ content in fresh milk samples with satisfactory results.     

Synthesis,characterization and fluorescence properties of hexanuclear zinc(II) complexes

Two hexanuclear zinc(II) complexes, [Zn₆(L¹)₂(μ₂-OH)₂(μ₂-CH₃COO)₈] · CH₃CN (1 · CH₃CN) and [Zn₆(L²)₂(μ₂-OH)₂(μ₂-CH₃COO)₈] · 4CH₃CN (2 · 4CH₃CN), where HL¹ = 4-methyl-2,6-bis(cyclohexylmethyliminomethyl)-phenol and HL² = 4-methyl-2,6-bis(1-naphthalylmethyliminomethyl)-phenol, have been synthesized and characterized by elemental analysis, FT-IR and fluorescence spectroscopic methods, and by X-ray diffraction analysis. In the asymmetric unit of complex 1, two of the three zinc atoms have pentacoordinate geometries and the other is tetrahedrally coordinated, whereas the three distinct Zn atoms in complex 2 adopt three different coordination environments, namely distorted octahedral, trigonal bipyramidal and tetrahedral. The fluorescence properties of the ligands and complexes have been investigated.     

Cyclic (alkyl)(amino)carbene gold(I) complexes: A synthetic and structural investigation

A series of mono- and dicarbene gold(I) complexes of types Au(CAAC)(Cl) [CAAC = cyclic (alkyl)(amino)carbene] (1) and [Au(CAAC)₂]⁺[X]^? (X = Cl, AuCl₂) (2) have been prepared through reaction of AuCl(SMe₂) with free carbenes a–e, and structurally characterized by single X-ray diffraction studies (1a, 1b, 2d, 2e). In addition two new free cyclic (alkyl)(amino)carbenes (c and e) have been synthesized.     

A N,N′-diacetate benzodioxotetraazamacrocycle and its transition metal complexes

Reaction of 2,9-dioxo-1,4,7,10-tetraazabicyclo[1.10.1]hexadeca-1(11),13,15-triene-4,7-diacetic acid (H₂L1) with CuCl₂ · 2H₂O in ethanol at pH 6 led to the monomeric benzodioxochlorocomplex [Cu(L′1)Cl] (1) (HL′1 = monoethylesther of H₂L1). X-ray structural analysis has shown that in complex 1 the Cu is five-coordinated by two nitrogen and two oxygen atoms of the macrocycle and by a chloride, displaying a square pyramidal coordination geometry. One of the acetate arms does not coordinate to the Cu and has suffered an in situ ethanolic esterification reaction. The protonation constants of H₂L1 and the stability constants of its complexes with Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were determined by potentiometric methods and in some cases by ¹H NMR spectroscopy. The stability constants of the complexes follow the trend [Ni(H₋₁L1)]⁻ > [Cu(H₋₁L1)]⁻ ≫ [Pb(H₋₁L1)]⁻ > [Zn(H₋₁L1)]⁻ > [Cd(H₋₁L1)]⁻, probably due to steric requirements. Spectroscopic measurements (absorption and EPR) at different pH values have shown the effect of the pH on the coordination sphere of the Cu complexes.     

Oxidative addition of MeI to cationic Rh(I) carbonyl complexes with pyridyl bis(carbene) ligands

A series of cationic Rh(I) carbonyl complexes of the form [Rh(CO)(L)]PF₆ (where L = 2,6-bis (alkylimidazol-2-ylidene)-pyridine; alkyl = Me (1a), Et (1b), CH₂Ph (1c)) have been prepared by the reactions of [Rh(CO)₂(OAc)]₂ with diimidazolium pyridine salts in the presence of NEt₃. The ν(CO) values for 1 are ca. 1982 cm⁻¹, indicating that the N-heterocyclic carbene ligands impart high electron density on the Rh(I) centres, despite the overall cationic charge. Each of the Rh(I) complexes reacts with MeI to form two isomeric Rh(III) methyl species, and a third unidentified species. Kinetic measurements on the MeI oxidative addition reactions give second-order rate constants (MeCN, 25 °C) of 0.0927, 0.0633 and 0.0277 M⁻¹ s⁻¹ for 1a, 1b and 1c, respectively. Comparison of these data with those for related Rh(I) carbonyl complexes shows that 1 have remarkably high nucleophilicity for cationic species.