Synthesis and reactivity with amines of new diiron alkynyl methoxy carbene complexes

The new diiron alkynyl methoxy carbene complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO){C(OMe)CCR′}(Cp)₂]⁺ (R = 2,6-Me₂C₆H₃ (Xyl), R′ = Tol, 3a; R = Xyl, R′ = Ph, 3b; R = Xyl, R′=Buⁿ, 3c; R = Xyl, R′=SiMe₃, 3d; R = Me, R′ = Tol, 3e; R = Me, R′ = Ph, 3f) are obtained in two steps by addition of R′CCLi (R′ = Tol, Ph, Buⁿ, SiMe₃) to the carbonyl aminocarbyne complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)₂(Cp)₂]⁺ (R = Xyl, 1a; Me, 1b), followed by methylation of the resulting alkynyl acyl compounds [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO){C(O)CCR′}(Cp)₂] (R = Xyl, R′ = Tol, 2a; R = Xyl, R′ = Ph, 2b; R = Xyl, R′ = Buⁿ, 2c; R = Xyl, R′ = SiMe₃, 2d; R = Me, R′ = Tol, 2e; R = Me, R′ = Ph, 2f). Complexes 3 react with secondary amines (i.e., Me₂NH, C₅H₁₀NH) to give the 4-amino-1-metalla-1,3-dienes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO){C(OMe)CHC(R′)(NMe₂)}(Cp)₂]⁺ (R = Xyl, R′ = Tol, 4a; R = Xyl, R′ = Ph, 4b; R = Me, R′ = Ph, 4c) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CHC(Tol)(NC₅H₁₀)}(Cp)₂]⁺, 5. The addition occurs stereo-selectively affording only the E-configured products. Analogously, addition of primary amines R′NH₂ (R′ = Ph, Et, Prⁱ) affords the 4-(NH-amino)-1-metalla-1,3-diene complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CHC(R)(NHR′)}(Cp)₂]⁺ (R = Ph, 6a; Et, 6b; Prⁱ, 6c). In the case of 6a, only the E isomer is formed, whereas a mixture of the E and Z isomers is present in the case of 6b,c, with prevalence of the latter. Moreover, the two isomeric forms exist under dynamic equilibrium conditions, as shown by VT NMR studies. Complexes 6 are deprotonated by strong bases (e.g., NaH) resulting in the formation of the neutral vinyl imine complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CHC(NR)(Tol)}(Cp)₂] (R = Ph, 7a; Et, 7b; Prⁱ, 7c); the reaction can be reverted by addition of strong acids. X-ray crystal structures have been determined for 3a[CF₃SO₃] · Et₂O, 4c[CF₃SO₃], 6a[BF₄] · CH₂Cl₂, 6c[CF₃SO₃] · 0.5Et₂O and 7a · CH₂Cl₂.     

Platinum allenylidene complexes and formation of platinum and palladium acetonitrile alkynyl complexes

The platinum(0) complex [Pt(PPh₃)₄] reacts with brominated propargylic amides and esters in benzene by oxidative addition to give trans-[Br(PPh₃)₂Pt-CC-C(O)R] complexes whereas no reaction occurs when halogenated solvents (CH₂Cl₂, CHCl₃) are used. The cis-ligands PPh₃ can be replaced by P(ⁱPr)₃ and the bromide by trifluoroacetate. O-Alkylation of those trans-[X(PR′₃)₂Pt-CC-C(O)R] complexes (X = Br, CF₃COO; R′ = Ph, ⁱPr) derived from propargylic amides with MeOTf or [Me₃O]BF₄ in CH₂Cl₂ gives the first cationic monoallenylidene complexes of platinum, trans-[X(PR′₃)₂PtCCC(OMe)NR₂]⁺Y⁻ (Y = OTf, BF₄). In contrast, trans-[Br(PPh₃)₂Pt-CC-C(O)OMenthyl] derived from a propargylic ester does not react with MeOTf in CH₂Cl₂. However, in acetonitrile instead of O-methylation the substitution of acetonitrile for the bromide ligand to yield the cationic acetonitrile alkynyl platinum complex trans-[MeCN(PPh₃)₂Pt-CC-C(O)OMenthyl]⁺OTf⁻ is observed. The related palladium complexes trans-[X(PR′₃)₂Pd-CC-C(O)OR] (X = Br, CF₃COO; R′ = Ph, ⁱPr, R = menthyl, Et) react with MeOTf or [Et₃O]BF₄ analogously affording trans-[MeCN(PR′₃)₂Pd-CC-C(O)OR]⁺Y⁻ (Y = OTf, BF₄).     

Stereoselective aldol addition reactions of Fischer carbene complexes via electronic tuning of the metal center for enolate reactivity

The aldol reactions of tetracarbonyl(phosphine)methyl(methoxy)methylene chromium complexes and pentacarbonylmethyl (dialkylamino)methylene chromium complexes with aldehydes and ketones were examined. The reactions of the phosphine complexes give only aldol condensation products, but the desired aldol addition products can be isolated from the reactions of amino carbene complexes. This was attributed to the greater reactivity of the enolates of amino carbene complexes which is supported by a determination of the thermodynamic acidity of the dimethylamino complex 13 (pK_a=20.4). The aldol reactions of amino complexes with -chiral aldehydes occur with very high facial selectivities rivaling the best methods that have been developed for facial selectivity in the aldol reaction. The aldol reactions of amino complexes can be considered as direct synthons for amides since amide functions can be obtained in the oxidative cleavage of the aldol adducts of these complexes. As illustrative of the versatility of carbene complexes, it is also demonstrated in a photo-induced carbon-homologative demetallation, that in combination with the aldol addition reaction the unique reactions of carbene complexes provide powerful and novel overall transformations.     

Bridged dinucleating N-heterocyclic carbene ligands and their double helical mercury(II) complexes

A series of six 3,6-bis(imidazolium-3-yl)pyridazine derivatives with different imidazole-N substituents have been synthesized and isolated as the salts [H₂L]Cl₂ (1a)-(6a) and [H₂L](PF₆)₂ (1b)-(6b). Solid state structures have been determined crystallographically for eleven out of the twelve compounds, revealing diverse hydrogen bonding patterns that involve the imidazolium-C²H units and the anions. N-heterocyclic carbene (NHC) mercury(II) complexes [Hg₂L₂](PF₆)₄ (7)-(9) are readily formed in good yields from ligand precursors [H₂L](PF₆)₂ and Hg(OAc)₂, as long as imidazole-N substituents are not too bulky. X-ray crystallography reveals double helical bimetallic arrangements for the stable [Hg₂L₂]⁴⁺ cations. Ligand scrambling in [Hg₂L₂]⁴⁺ occurs only in the presence of free carbene precursor, presumably via an associative mechanism.     

Application of silver N-heterocyclic carbene complexes in O-glycosidation reactions

We report the efficient O-glycosidation of glycosyl bromides with therapeutically relevant acceptors facilitated by silver N-heterocyclic carbene (Ag–NHC) complexes. A set of four Ag–NHC complexes was synthesized and evaluated as promoters for glycosidation reactions. Two new bis-Ag–NHC complexes derived from ionic liquids 1-benzyl-3-methyl-1H-imidazolium chloride and 1-(2-methoxyethyl)-3-methylimidazolium chloride were found to efficiently promote glycosidation, whereas known mono-Ag complexes of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride and 1,3-bis(2,6-di-isopropylphenyl)imidazolium chloride failed to facilitate the reaction. The structures of the promoters were established by X-ray crystallography and these complexes were employed in the glycosidation of different glycosyl bromide donors with biologically valuable acceptors, such as estrone, estradiol, and various flavones. The products were obtained in yields considered good to excellent, and all reactions were highly selective for the β isomer regardless of neighboring group effects.     

A study of the reactivity and structure of cyclic α,β-unsaturated Fischer-type carbene complexes

Cycloaddition reactions with α,β-unsaturated carbene complexes of the Fischer-type bearing the carbene carbon atom and the double bond incorporated in the same ring are described. Pentacarbonyl(2H-benzopyran-2- ylidene)chromium(0) complexes (2a-c) and pentacarbonyl(4-methoxy-3,3-dimethyl-2-oxacyclopentylidene)- chromium(0) (3) show a rather low reactivity towards 1,3-dipoles and 1,3-dienes. The reactions with diazomethane are regioselective but not chemoselective; compounds 2 and 3 show two sites of attack: the α,β carbon-carbon and the carbon-metal double bond. The crystal and molecular structures of 2a and 3 have been elucidated by single crystal X-ray analysis. Crystals of 2a are monoclinic, space group P2₁/c, a=7.614(3), b=14.033(3), c=12.766(3) Å, β=95.24°, V=1358.3(7) Å Z=4; crystals of 3 are triclinic, space group P , a=6.553(1), b=9.408(1), c=10.620(1) Å α=92.70(1), β=92.30(1), γ=92.12(1)°, V=653.0(1), ų, Z=2. Final agreement indices for 2a and 3 are R=0.034 and 0.033, respectively. Vibrational properties of the Cr(CO)₅ moiety were interpreted by FT-IR and FT-Raman spectroscopy. Electronic spectra and π electron distribution were interpreted by resonance Raman spectroscopy.     

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.     

Synthesis, characterization and antimicrobial activity of new silver complexes with N-heterocyclic carbene ligands

Synthesis, structure, and antimicrobial studies of silver complexes of N-heterocyclic carbene (NHC) are reported. All the silver-NHC complexes (1a-f) were prepared from the benzimidazolium salts by the reactions with Ag₂O in dichloromethane as a solvent at room temperature. The new compounds characterized by ¹H NMR, ¹³ C NMR, IR and elemental analysis techniques which support the proposed structures. Chloro[1-(2,4,6-trimethylbenzyl)-3-(methoxyethyl)benzimidazol-2-ylidene]silver(I) complex was structurally characterized by single-crystal X-ray diffraction. A series of new Ag-NHC complexes were screened for their in vitro antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria as well as for their antifungal activity against a Candida albicans and Candida tropicalis.     

Reactions of the haloalcohols HO(CH2)nCl (n = 2, 3) with platinum(II) - alkynyl and -alkyne complexes. X-ray crystal structure of trans-[Pt(Me) {C(OCH2CH2Cl) (CH2Ph)} (PPh3)2] [BF4]

The chloro complexes trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄, react with 1-alkynes HC---C---R in the presence of NEt₃ to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh₃)₂] (R = p-tolyl (1), Ph (2), C(CH₃)₃ (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH₂)_nCl (n = 2, 3) in the presence of 1 equiv. of HBF₄ to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH₂)_nCl](CH₂R) } (PPh₃)₂][BF₄] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)₂(PMe₂Ph)₂] with 2 equiv. HBF₄ and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH₂CH₂CH₂Cl)(CH₂Ph) } (PMe₂Ph)₂][BF₄] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH₂CH₂Cl)(CH₂Ph) } (PPh₃)₂][BF₄] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄ in HOCH₂CH₂Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe₂Ph)]₂ with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl₂{C(OCH₂CH₂CH₂Cl)(CH₂C₆H₄-p-Me}(PMe₂Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2₁, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) ų and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry.     

Ruthenium(II) carbonyl chloride complexes containing pyridine-functionalised bidentate N-heterocyclic carbenes: Synthesis, structures, and impact of the carbene ligands on catalytic activities

A series of new ruthenium(II) carbonyl chloride complexes with pyridine-functionalised N-heterocyclic carbenes [Ru(Py-NHC)(CO)₂Cl₂], [Py-NHC = 3-methyl-1-(2-pyridyl)imidazol-2-ylidene, 1 (1a and 1b); 3-methyl-1-(2-picoyl)imidazol-2-ylidene, 2 (2a and 2b); 3-methyl-1-(2-pyridyl)benzimidazolin-2-ylidene, 3 (3b); 3-methyl-1-(2-picoyl)benzimidazolin-2-ylidene, 4 (4a and 4b); 1-methyl-4-(2-pyridyl)-1,2,4-triazoline-5-ylidene, 5 (5a and 5b)] have been prepared by transmetallation from the corresponding silver carbene complexes and characterized by NMR, IR spectroscopy and elemental analysis. In these complexes with bidentate Py-NHC ligands, one CO ligand is trans to the Py ligand. In 1a, 2a, 4a, and 5a, the NHC ligand is trans to the other CO ligand, thus leaving the two Cl⁻ ligands trans to each other. In 1b, 2b, 3b, 4b, and 5b, the NHC ligands are trans to one Cl⁻ ligand, and the two Cl⁻ ligands are cis to each other. The structures for 1b, 2b, 3b and 4b have been determined by single-crystal X-ray diffraction. These complexes are efficient catalysts in the transfer hydrogenation of acetophenone and their catalytic activities are found to be influenced by electronic effect of the N-heterocyclic carbene ligands.     

Spectroscopic properties of mono- and binuclear platinum(II) alkynyl complexes with phosphine ligands: A theoretical study

Based on their MP2 optimized structures in the ground states, we obtained solution absorption spectra for trans-[Pt^II(CCR)₂(PH₃)₂] (R = H (1) and Ph (2)) and trans-[Pt^II(CCH)₂(PH₂CH₂PH₂)]₂ (3) under the time-dependent density functional theory calculations. These absorptions agree with experimental observations. The unrestricted MP2 optimization performed for 3 in the lowest-energy triplet excited state shows that upon excitation the PtPt distance shortens about 0.347 Å with respect to the 3.188 Å one in the ground state. The UMP2 calculations estimated that its ³[σ^∗(d_z²)σ(p_z)] excited state produces the 531 nm emission, corresponding to the 580 nm one of trans-[Pt^II(CCPh)₂(PPh₂CH₂PPh₂)]₂ in the solid state at 298 K.     

Properties of monovalent nickel complexes with tetraaza-macrocyclic ligands in aqueous solutions

The effects of N-alkylation on the redox potential of the couples NiLⁱ²⁺/NiLⁱ⁺, L = tetraaza-14-membered-macrocyclic ligands, and on the properties of the monovalent nickel complexes in aqueous solutions are reported for 14 complexes. The spectra and lifetimes of the NiLⁱ⁺ complexes are reported. The self-exchange rates for the couples NiLⁱ²⁺/NiLⁱ⁺ were determined. Two of the ligands were synthesized for the first time for this study. Cyclic voltammetry and pulse radiolysis were used. The results point out that: (i) N-alkylation always shifts the redox potential to a less cathodic one; this effect stems to a large degree from the decrease in the solvation energy of the complex caused by the N-alkylation of the ligand. (ii). The lifetime of the monovalent complexes is not linearly related to the redox potential of the NiLⁱ²⁺/NiLⁱ⁺ couples. (iii) The NiLⁱ⁺ complexes exist in several isomeric forms; the rate of the isomerization depends on the structure of the ligand. (iv) Different isomers of NiLⁱ⁺ may be formed when the complex NiLⁱ²⁺ is reduced by different reagents; therefore, the pulse-radiolytically formed NiLⁱ⁺ complexes might have different properties than those formed electrochemically.     

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.     

Regioselective addition of bifunctional oximehydroxamic acid by the hydroxamic group to Pt(IV)-coordinated nitriles

The metal-mediated coupling between the nitriles RCN in the platinum(IV) complexes trans-[PtCl₄(RCN)₂] (RMe, Et, CH₂Ph, Ph), cis/trans-[PtCl₄(MeCN)(Me₂SO)] and the newly synthesized bifunctional oximehydroxamic acid, viz. N,2-dihydroxy-5-(1-hydroxyiminoethyl)benzamide, proceeds smoothly in CH₂Cl₂ at 40-45 °C to accomplish the new metallaligands HNC(R)ONHC(O)C₆H₃(2-OH)(5-C(Me)NOH) with pendant oxime functionalities due to the regioselective addition of the reagent via its hydroxamic groups. The obtained iminoligands exist in hydroxamic/hydroximic tautomeric equilibrium in solution. The structures of the isolated compounds are based on elemental analyses (C, H, N), IR, 1D ¹H, ¹³C{¹H}, and 2D NMR correlation experiments, i.e. ¹H,¹³C-COSY, ¹H,¹³C long range COSY, ¹H,¹⁵N-COSY, and ¹H,¹⁵N long range COSY.     

Palladium(II) complexes of imidazolin-2-ylidene N-heterocyclic carbene ligands with redox-active dimethoxyphenyl or (hydro)quinonyl substituents

Four novel imidazolium salts, precursors to N-heterocyclic carbene (NHC) ligands, with 2,5-dimethoxybenzyl or 2,5-dihydroxybenzyl (i.e., p-hydroquinone) substituents have been prepared. The crystal structure of the hydroquinone-substituted imidazolium salt H₃L³Br reveals Br⁻?H-O bridged chiral chains of alternating [H₃L³]⁺ cations and Br⁻ counter-ions parallel to the x-axis. Palladium(II) complexes were accessible from reactions of the dimethoxyphenyl-substituted imidazolium precursors with palladium(II) acetate, but not from reactions of imidazolium cations with hydroquinonyl substituents. The crystal structure of the bis(dimethoxybenzyl)-substituted bis(NHC)Pd complex, cis-[PdBr₂(L²)] (2), is described. Puckering of the bis(NHC) ligand leads to a cleft in which an included molecule of dimethylformamide is situated. The cleft is closed by one of the dimethoxybenzyl groups which π-stacks with the dimethylformamide; the other dimethoxybenzyl group points away from the cleft and Pd(II) centre. Reaction of complex 2 with BBr₃ afforded the targeted bis(hydroquinone)-substituted bis(NHC)Pd(II) complex 3 (97% yield) which, in turn, was oxidised by 2,3-dichloro-5,6-dicyano-benzoquinone to the corresponding p-benzoquinone-substituted bis(NHC)Pd(II) complex 4 (98% yield). The cyclic voltammograms of the Pd(II) complexes 2-4 reveal waves that are attributed to an admix of the anticipated ligand-centred and [Pd(C-NHC)₂Br₂]-centred processes.     

First example of an imine addition to coordinated isonitrile

The interplay between cis-[PtCl₂{CNC₆H₃(2,6-Me₂)}₂] and Ph₂CNH results in the addition of benzophenone imine to one isonitrile ligand to yield the aminoimino-carbene cis-[PtCl₂{CNC₆H₃(2,6-Me₂)}{C(NCPh₂)N(H)C₆H₃(2,6-Me₂)}]. The formulation of the latter compound is based on the coherent ¹H and ¹³C{¹H} NMR and ESI-MS data. This adduct is not stable in solution even at room temperature leading to diamino-carbene cis-[PtCl₂{CNC₆H₃(2,6-Me₂)}{C(NH₂)N(H)C₆H₃(2,6-Me₂)}], which is, formally, the product of the addition of ammonia to one isonitrile ligand in cis-[PtCl₂{CNC₆H₃(2,6-Me₂)}₂].     

Optically active iridium complexes with cyclopentadienyl-phosphine ligands: synthesis and oxidative addition of methyl iodide

The dimer [Ir(μ-Cl)(C₈H₁₄)₂]₂ reacts with the ligands (S)-(C₅H₄CH₂CH(Ph)PPh₂)Li and (R)-(C₅H₄CH(Cy)CH₂PPh₂)Li to give (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(C₈H₁₄)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(C₈H₁₄)], which upon treatment with CH₃I at room temperature afford the cationic iridium(III) compounds (S,S_Ir)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(C₈H₁₄)][I] as a single diastereomer, and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(C₈H₁₄)][I] as a 9:1 mixture of two diastereomers. If the oxidative addition reaction is performed at reflux in methylene chloride, the starting complexes convert to the neutral compounds (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(I)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(I)] as 1.6:1 and 3.3:1 mixtures of diastereoisomers, respectively. Carbonyl iridium complexes are synthesized by reacting [IrCl(CO)(PPh₃)₂] with the ligands to afford (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CO)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CO)]. They give upon treatment with CH₃I the cationic species (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(CO)][I] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(CO)][I] as 1.6:1 and 3:1 mixture of diastereomers, respectively. No migratory-insertion of the methyl group into the carbonyl-metal bond has been observed even after prolonged heating.     

Dicarbonyliridium(I) complexes of pyridine ester ligands and their reactivity towards various electrophiles

The reaction of dimeric precursor [Ir(CO)₂Cl]₂ with two molar equivalent of the pyridine-ester ligands (L) like methyl picolinate (a), ethyl picolinate (b), methyl nicotinate (c), ethyl nicotinate (d), methyl isonicotinate (e) and ethyl isonicotinate (f) affords the tetra coordinated neutral complexes of the type [Ir(CO)₂ClL] (1a-f). The single crystal X-ray structure of 1d reveals that the Ir atom occupies the centre of an approximately square planar geometry with two CO groups cis- to each other. Intermolecular C-H?O and Ir?C interactions greatly stabilize the supramolecular structure of 1d in the solid state. The oxidative addition (OA) reactions of 1a-f with different electrophiles such as CH₃I, C₂H₅I and I₂ undergo decarbonylation of one CO group to generate the oxidized products of the type [Ir(CO)RClIL] where R = -CH₃ (2a-f); -C₂H₅ (3a-f) and [Ir(CO)ClI₂L] (4a-f). Kinetic study of the reaction of 1c-f with CH₃I indicates a first order reaction which follow the order 1d > 1c > 1f > 1e. All the synthesized complexes were characterized by elemental analyses, IR, and multinuclear NMR spectroscopy.     

Non-innocent bma ligand in a dissymetrically disubstituted diiron dithiolate related to the active site of the [FeFe] hydrogenases

The purpose of the present study was to evaluate the use of a non-innocent ligand as a surrogate of the anchored [4Fe4S] cubane in a synthetic mimic of the [FeFe] hydrogenase active site. Reaction of 2,3-bis(diphenylphosphino) maleic anhydride (bma) with [Fe₂(CO)₆(µ-pdt)] (propanedithiolate, pdt = S(CH₂)₃ S) in the presence of Me₃NO-2H₂O afforded the monosubstituted derivative [Fe₂(CO)₅(Me₂NCH₂PPh₂)(µ-pdt)] (1). This results from the decomposition of the bma ligand and the apparent C-H bond cleavage in the released trimethylamine. Reaction under photolytic conditions afforded [Fe₂(CO)₄(bma)(µ-pdt)] (2). Compounds 1 and 2 were characterized by IR, NMR and X-ray diffraction. Voltammetric study indicated that the primary reduction of 2 is centered on the bma ligand.     

Palladium(II) complexes of a bis-2-aminobiphenyl N-heterocyclic carbene: Synthesis, structural studies and catalytic activity

A new imidazolinium [(SIBiphen)H](BF₄) was synthesized in three steps from 2-aminobiphenyl. The reaction of the salt with Pd(OAc)₂, NaI and t-BuOK gave a dimeric Pd(II) complex [(SIBiphen)PdI₂]₂, which was analyzed by an X-ray diffraction study. The reaction of [Pd(allyl)Cl]₂, the imidazolinium salt and t-BuOK in THF at −78 °C gave the monomeric Pd complex, in which the N-heterocyclic carbene was bound to the metal centre, as confirmed by a single-crystal X-ray diffraction study. A preliminary catalytic study showed that these new systems were moderately active in the Suzuki-Miyaura coupling of aryl halides.