Diether functionalized rhodium(I)-N-heterocyclic carbene complexes and their catalytic application for transfer hydrogenation reactions

N-heterocyclic carbene (NHC) complexes of rhodium(I) (3 and 4) bearing one diether (MeOCH₂CH₂OCH₂CH₂-NHC) functionality on N¹ and bulky benzyl groups (CH₂-C₆H₂(CH₃)₃-2,4,6 and CH₂-C₆(CH₃)₅) on N³ of (5,6-dimethyl)benzimidazole were synthesized by deprotonation of the corresponding benzimidazolium salt with [Rh(μ-OMe)(1,5-cod)]₂ in dichloromethane at ambient temperature. All compounds have been fully characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. X-ray diffraction studies on single crystals of 3a and 3b confirm the cis square planar geometry. All of the new benzimidazol-2-ylidene rhodium(I) complexes were found to be effective catalysts for the transfer hydrogenation reaction.     

Aggregation of imino-phosphonate monoester complexes

The aggregates {[Zn(L¹)]H₂O}_∞ and {[Y(L²)]₄Na₃(H₂O)₂(MeOH)_1.2}(NO₃)₃·2H₂O·5.6MeOH have been assembled from complexes of imino-phosphonate monoester ligands [L¹]²⁻ {CH₂[CH₂NC(CH₃)PO₂(OMe)]₂}²⁻ and [L²]³⁻ {N[CH₂CH₂NC(CH₃)PO₂(OMe)]₃}³⁻, the topology of these materials differing from that of their imino-carboxylate analogues.     

Neutral and cationic rare-earth metal alkyl complexes that contain bis(2-methoxyethyl)(trimethylsilyl)amine, a neutral [ONO]-type ligand

Neutral tris(trimethylsilylmethyl) complexes [Ln(CH₂SiMe₃)₃(L)] (Ln = Sc (1), Lu (2)) and cationic bis(trimethylsilylmethyl) complexes [Ln(CH₂SiMe₃)₂(L)(THF)]⁺[BPh₄]⁻, (Ln = Sc (3), Lu (4)) that contain bis(2-methoxyethyl)(trimethylsilyl)amine (L = Me₃SiN(CH₂CH₂OMe)₂) as a neutral, tridentate ligand were synthesized and characterized by NMR spectroscopy. X-ray structural analysis was performed for the scandium complex 1 and exhibited a distorted octahedral coordination geometry with a facially arranged ligand at the neutral scandium center. NMR spectroscopy corroborated the coordination of the tertiary amine function of the ligand to the metal. Complexes 3 and 4 expand the still limited range of cationic rare-earth metal alkyl complexes with known neutral, multidentate ligands.     

Synthesis and characterization of new cationic hydride complexes of rhodium(III)

New cationic hydride complexes of rhodium(III) with PR₃ and R-DAB ligands have been prepared and characterised. The tertiary phosphines employed were PPh₃, PMePh₂, PEt₃ and the R-DAB ligands, (RN:CR′CR′:NR), c-Hex-DAB, Ph-DAB, NH2-DAB-(CH₃,CH₃). Hexacoordinate-dihydride complexes, characterized by ¹H and ³¹P NMR, with stoichiometry [RhH₂(R-DAB)(PR₃)₂]X were obtained. Compounds with other stoichiometries (R-DAB/PR₃=1 or 2) are also possible. Preliminary studies of the catalytic activity in hydrogenation of olefins have been carried out.     

Syntheses and structures of vinyl and aryl derivatives of carbonyl halide iron complexes

cis,trans-Fe(CO)₂(PMe₃)₂(p-Y-C₆H₄)X [X=Br, Y=H (4a), MeO (4b), Cl (4c), F (4d), Me (4e); X=I, Y=H (5); X=Cl, Y=H (6)] and cis,trans-Fe(CO)₂(PMe₃)₂(σ-CHCH₂)X [X=Br (7); X=I (8); X=Cl (9)] are prepared by reacting dihalide complexes cis,trans,cis- Fe(CO)₂(PMe₃)₂X₂ [X=Br (1), X=I (2), X=Cl (3)] with Grignard reagents p-Y-C₆H₄-MgBr (Y=H, OMe, Cl, F, Me) or CH₂CH-MgBr and with lithium reagents PhLi, CH₂CH-Li. With both reagents, the reaction proceeds following two parallel pathways: one is the metallation reaction which yields alkyl derivatives, the other affords 17 electron complexes [Fe(CO)₂(PMe₃)₂X] via monoelectron reductive elimination. The influence of the halides and organometallic reagents on the yield of the metallation reaction is discussed. The solution structure of the complexes is assigned on the basis of IR and ¹H, ¹³C, ¹⁹F, ³¹P NMR spectra. The solid state structure of complexes 4a, 5 and 6 is determined by single crystal X-ray diffractometric methods.     

Dynamic properties of the fluxional Rh2H(μ-PPh2)2(PPh3)3 complex

The rhodium dimer [Rh₂H(PPh₂)₂(PPh₃)₃]⁻ was prepared from RhCl(PPh₃)₃ and K₄Sn₉ in the presence of 2,2,2-cryptand in ethylenediamine/toluene solvent mixtures. The [K(2,2,2-crypt)]⁺ salt was isolated and characterized via NMR and X-ray diffraction studies. The solid state structure reveals a binuclear, diphenylphosphido-bridged, 32 electron Rh(I)-Rh(I) complex with edge-shared tetrahedral and square planar Rh centers with overall C_s point symmetry. 1-D and 2-D ¹H, ³¹P, and ³¹P{¹H} NMR experiments were used to characterize the complex.     

Titanium, zirconium and hafnium halide complexes of trithioether and triselenoether ligands

The reaction of TiX₄(X=Cl or Br) with the tripodal ligands MeC(CH₂SMe)₃ or MeC(CH₂SeMe)₃, (L³) in anhydrous n-hexane or CH₂Cl₂ produced the extremely moisture sensitive complexes [TiX₄(L³)]. These were characterised by microanalysis, IR, UV-Vis and variable temperature ¹H,¹³C{¹H} and ⁷⁷Se NMR spectroscopy. The NMR studies showed that in solution in CH₂Cl₂ the complexes contain L³ bound as bidentates, and that pyramidal inversion and exchange between the free and coordinated chalcogen donors is rapid at room temperature. Ligand dissociation/exchange increases TiCl₄<TiBr₄ and MeC(CH₂SMe)₃<MeC(CH₂SeMe)₃ and attempts to isolate TiI₄ analogues were unsuccessful. The reactions of [MCl₄(Me₂S)₂] (M=Zr or Hf) with (L³) in anhydrous CH₂Cl₂ produces white or cream 7-coordinate [MCl₄(L³)], which are insoluble in chlorocarbon solvents. The reactions of TiX₄ (X=Cl, Br or I) with the trithia-macrocycles [9]aneS₃ and [10]aneS₃ produced [TiX₃([n]aneS₃)]X, whilst reaction of TiCl_4, SbCl₅ and [9]aneS₃ in anhydrous CH₂Cl₂ gave [TiCl₃([9]aneS₃)]SbCl₆. Spectroscopic studies suggest these macrocyclic compounds contain 6-coordinate cations, [TiX₃([n]aneS₃)]⁺ (n=9 or 10) but with Zr and Hf the complexes [MCl₄([n]aneS₃)] are 7-coordinate and neutral.     

Siloxane functionalized cyclopentadienyl-molybdenum complexes: Synthesis, characterization and catalytic application

A series of compounds of the type CpMoR(CO)₃ and RCpMo(CO)₃CH₃ (R = (CH₂)₃Si(OMe)₃ or CH₂Si(OEt)₃), containing a (CH₂)_nSi(OR)₃ functionality as a side chain, either fixed to the metal itself or to the cyclopentadienyl ligand are prepared and spectroscopically characterized. These molecules are applicable as precursors for both homogeneous and heterogeneous phase catalysts. Their homogeneous catalytic activity in the olefin epoxidation is in the same order of magnitude as that of their methyl and chloro analogues of the types CpMo(CO)₃R and CpMo(CO)₃Cl.     

Synthesis of a series of ruthenium and rhodium complexes with tridentate pyridine-based ligands containing hydrogen bonding groups

A series of ruthenium and rhodium complexes with a urea-disubstituted pyridine ligand are reported. The X-ray crystal structures of three of these species, RuCl₂(L¹)(PPh₃) (1), [Ru(MeCN)₂(L¹)(PPh₃)][BF₄]₂ (3) and Rh(CH₂Cl)Cl₂(L¹) (9) (where L¹ = N,N′-(2,2′-(1E,1′E)-(1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))bis(azan-1-yl-1-ylidene)bis(ethane-2,1-diyl))diacetamide) have shown that the disubstituted pyridine acts as a tridentate ligand and its urea substituents engage in hydrogen bonding interactions with species coordinated to the metal centres. The reactivity of the ruthenium complexes towards coordination of other anions such as NCS⁻ has been investigated, as well as the oxidative-addition of alkyl chlorides to rhodium(I) centres (to yield species such as 9).     

New amino-dithiaphospholanes and phosphoramidodithioites and their rhodium and iridium complexes

New sulfur derivatives of phosphoramidite ligands were synthesized and the impact of the sulfur unit on the spectroscopic properties of their rhodium and iridium complexes was investigated. The new ligands Bn₂NPSCH₂CH₂S^a(P-S^a) (Bn = benzyl, 4), Bn₂NPSCHCHS^a(CH₂)₃C^aH₂(P-S^a)(C^a-S^a) (6) and Bn₂NP(4-XC₆H₄OMe)₂ (X = S, 7a; X = O, 7b) were converted to the rhodium and iridium complexes trans-[Rh(CO)Cl(L)₂] (L = 4, 6, 7), [RhCl(COD)(L)] (L = 4, 6, 7), [IrCl(COD)(7a)] and [IrCl₂Cp∗(6)]. For comparison, some phosphoramidite complexes of these formulations also were synthesized. The new metal complexes were spectroscopically analyzed. For the carbonyl complexes, the ν_CO IR stretching frequencies were lower than for the corresponding phosphite and phosphoramidite ligands. The ¹J_PRh coupling constants for the rhodium complexes with the new ligands were also smaller than for the respective phosphoramidite and phosphite complexes. Finally, the ¹J_PSe coupling constants of the selenides of the new ligands were lower than those of the phosphoramidite ligands but higher than for PPh₃. The spectroscopic data reveal that the new thio ligands 4, 6 and 7a are more electron donating than phosphites and phosphoramidites but less electron donating than PPh₃.     

Copper(I) and silver(I) tertiary phosphines complexes: Synthesis, X-ray structures and spectroscopic characterization

Six new complexes, [Cu₄I₄(PPh₂Cy)₄]·2H₂O (1), [CuI(PPhCy₂)₂] (2), [CuCl(PPhCy₂)₂] (3), and [CuBr(PPh₃)₃]·CH₃CN (4), [Ag(PPhCy₂)₂(NO₃)] (5), [Ag(PCy₃)(NO₃)]₂ (6) [where Ph = phenyl, Cy = cyclohexyl], have been synthesized and structurally characterized by X-ray diffraction, IR absorption spectra and NMR spectroscopic studies (except complex 4). The X-ray diffraction analysis of complex (1), pseudo polymorph of complex [Cu₄I₄(PPh₂Cy)₄], reveals a stella quadrangula structure. The four corners of the cube are occupied by copper(I) atoms and four I atoms are present at the alternative corners of the cube, further more the copper(I) atoms are coordinated to a monodentate tertiary phosphine. Complexes (2) and (3) are isostructural with trigonal planar geometry around the copper(I) atom. The crystal structure of complex (4) is a pseudo polymorph of complex [CuBr(PPh₃)₃] and the geometrical environment around the copper(I) centre is distorted tetrahedral. In the Ag^I complexes (5) and (6), the central metal atoms have pseudo tetrahedral and trigonal planar geometry, respectively. Spectroscopic and microanalysis results are consistent with the single crystal X-ray diffraction studies.     

Syntheses of some new methylcyclopentadienylmolybdenum complexes: Characterizations, crystal structures and comparisons with related complexes

As part of a long-term study of the substitution reactions of piano-stool type cyclopentadienylmetal carbonyl complexes, several new methylcyclopentadienylmolybdenum compounds have been prepared and characterized by methods including IR spectroscopy, electrospray ionization mass spectrometry and X-ray crystallography. The complexes reported here include [{Cp′Mo(CO)₃}₂I]BPh₄, cis-Cp′Mo(CO)₂(PPh₃)I and [Cp′Mo(CO)₃(CH₃CN)]BF₄ (Cp′ = η⁵-C₅H₄CH₃). In addition to their syntheses, comparisons are made between their IR spectroscopic and X-ray crystal structure data and those of similar complexes.     

Rhodium(I) and palladium(II) complexes with the Schiff base 2,2-bis((4S)-4-benzyl-2-oxazoline)

The Schiff base 2,2^′-bis((4S)-4-benzyl-2-oxazoline) (I) and its coordination complexes with rhodium(I) and palladium(II) (and with 1,5-cyclo-octadiene and allyl ligands) have been characterised by single-crystal X-ray diffraction, mass spectrometry, ¹³C and ¹H NMR spectroscopy: [Rh(C₂₀H₂₀N₂O₂)(C₈H₁₂)][Rh₂(C₂₀H₂₀N₂O₂)₂](CF₃SO₃)₃ · (CH₃CH₂O) (II) and [Pd(C₂₀H₂₀N₂O₂)(C₃H₅)]CF₃SO₃ (III). We discuss the reasons for the formation of two complex cations for Rh(I), [Rh(C₂₀H₂₀N₂O₂)(C₈H₁₂)]⁺ (IIa) and [Rh₂(C₂₀H₂₀N₂O₂)₂]²⁺ (IIb), and only one for Pd(II).     

Carbonyl trichlorostannate complexes of platinum: chemistry and 119Sn, 195Pt,and 13C NMR spectroscopy

The reactions of the carbonyl anion [PtCl₃(CO)]^- with SnCl₂ in the presence of CO in both methylene chloride and acetone are reported. In the former solvent, only Pt^II-SnCl₃ species are formed. These have been identified by ¹³C, ¹¹⁹Sn and ¹⁹⁵Pt NMR measurements as cis-[PtCl₂(SnCl₃)(CO)]^-, (I), trans- [PtCl(SnCl₃)₂(CO)]^-, (II), and [Pt(SnCl₃)₄(CO)]^2-, (III). Salts of these complexes have been isolated. In contrast, when acetone is the solvent, reduction of the platinum occurs to give two new complexes. On the basis of NMR measurements, we assign one of these as the Pt^I dimer [Pt₂(SnCl₃)₄(CO)₂]^2-, (IV), and the other as a platinum triangle (VI) containing terminal CO ligands and two types of Sn ligand. The Pt^II compound (IV) can also be generated by treating a CH₂Cl₂ solution of trans-[PtCl(SnCl₃)_2- (CO)]^-, (II), with dihydrogen. NMR spectroscopic data, including those from measurements on samples of the complexes containing ¹³C-enriched CO, are reported and discussed.     

Structure and dynamic behaviour of lanthanide nitrate complexes with bis(diphenylphosphorylmethyl)mesitylene in solutions: The nature of unexpected P NMR spectra

The solution structures of the lanthanide complexes, [Ln(L)(NO₃)₃] and [Ln(L)₂(NO₃)₃], where L = bis(diphenylphosphorylmethyl)mesitylene and Ln = La, Ce, Nd, Er, were investigated by ³¹P NMR and IR spectroscopy, conductivity and sedimentation analysis. Variable-temperature ³¹P{¹H} NMR spectroscopy was used to identify species present in solution and to monitor their interconversions. The results indicate that equilibrium between molecular complexes [Ln(L)_n(NO₃)₃]⁰ and cationic species (as ion pairs [Ln(L)_n(NO₃)₂]⁺ · (NO₃)⁻ and as free ions [Ln(L)_n(NO₃)₂]⁺, throughout n = 1, 2) in solutions can be observed by ³¹P{¹H} NMR spectroscopy due to separate detection of the molecular complexes and cationic species. The chelate coordination of the ligand and nitrate ions is retained in all complex species at ambient temperature except for [Er(L)₂(NO₃)₃]. The crystal structure of [Nd(L)(NO₃)₃(MeCN)]MeCN was determined by X-ray diffraction.     

Synthesis of cyclopentadienyl ruthenium(II) complexes containing tethered functionalities

The reaction of [C₅H₄(CH₂)_nX]Tl (1: n = 2, X = NMe₂, OMe, CN; n = 3, X = NMe₂) with [(η⁶-C₆H₆)RuCl(μ-Cl)]₂, 2, afforded the sandwich compounds [{η⁵-C₅H₄(CH₂)_nX}Ru(η⁶-C₆H₆)]PF₆, 3, and [η⁵-C₅H₄(CH₂)_nX]₂Ru, 4. Photolytic cleavage of 3 in acetonitrile afforded the tethered products [{η⁵:κN-C₅H₄(CH₂)_nX}Ru(CH₃CN)₂]PF₆, 5.     

First synthesis of a dihydrido functionalized double-cored oligosilane dendrimer

The reaction of (R₂MeSi)₂SiHCl (2) [R=SiMe₃] with Na-K-alloy yields the double-cored dendritic oligosilane [(R₂MeSi)₂SiH]₂ (4). The structure of 4 was obtained from X-ray diffraction data, which verify a total of 14 silicon atoms and a longest chain of six silicon atoms. The UV-Vis spectra of 4 and the structurally analogous [(R₂MeSi)₂SiMe]₂ (5) exhibit absorption maxima (shoulders) at 269 nm (ε=2.0×10⁴) and 276 nm (ε=2.3×10⁴), respectively, which are the longest so far observed for alkyl substituted oligosilanes with hexasilane chains.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

Transformations of the Vaska-type complex trans-[RhCl(CO)(PTA)2] (PTA = 1,3,5-triaza-7-phosphaadamantane) during stepwise addition of HCl: Synthesis, characterization and crystal structure of trans-[RhCl2(PTA)(PTAH)]

The new aqua-soluble rhodium(I) complex trans-[RhCl₂(PTA)(PTAH)] (1) {PTAH = N-protonated form of 1,3,5-triaza-7-phosphaadamantane (PTA)} has been synthesized via the reaction of trans-[RhCl(CO)(PTA)₂] with aqueous HCl or N-chlorosuccinimide, or by the treatment of RhCl₃ with PTA. Compound 1 has been characterized by IR, ¹H and ³¹P{H} NMR spectroscopies, ESI-MS(+), elemental and single crystal X-ray diffraction analyses, the latter showing a square planar {RhCl₂P₂} geometry. Besides, the stepwise addition of diluted HCl to an aqueous solution of trans-[RhCl(CO)(PTA)₂] has been monitored by ³¹P{¹H} NMR and ESI-MS(+) techniques, allowing to detect a number of intermediate Rh(I) species.     

The synthesis, structure, and luminescence of two silver(I)-dppm complexes based on sulfate anion and nitrogen heterocyclic ligands

At ambient temperature, two silver(I) complexes [Ag₄(SO₄)₂(dppm)₄]·5CH₃CH₂OH·1/2H₂O (1) and [Ag₂(SO₄)(dppm)₂(2-ampz)]·CH₃OH·H₂O (2) (dppm = bis(diphenylphosphino)methane, 2-ampz = 2-aminopyrazine) were obtained by the reaction of Ag₂SO₄ with dppm in the presence of pyrazine or 2-aminopyrazine. They are characterized by IR, X-ray crystallography, luminescence and ¹H, ³¹P NMR spectroscopy. Complex 1 is a tetranuclear cluster. In complex 2, the units [Ag₂(SO₄)(dppm)₂] are connected by 2-aminopyrazine to form a 1D linear polymer. Due to the subtle interactions of different nitrogen heterocyclic ligands with silver ions, two SO₄²⁻ anions in 1 adopt μ₃-O, O′, O′ and unique μ₄-O, O, O′, O′ bonding modes respectively, while SO₄²⁻ anion in 2 adopts μ-O, O′ bonding mode.