Rhodium(I) Complexes of New Ferrocenyl Benzimidazol-2-ylidene Ligands: The Importance of the Chelating Effect for Ketone Hydrosilylation Catalysis

Synthesis and catalytic properties of palladium(II) complexes with P,π-chelating ferrocene phosphinoallyl ligands and their non-tethered analogues

Hybrid phosphines usually combine a phosphine moiety with another heteroatom secondary donor group in their structures while compounds equipped with hydrocarbyl π-donor moieties remain uncommon. This contribution reports the synthesis and structural characterization of the first P/π-allyl-chelating complexes that were obtained using the structurally flexible and redox-active ferrocene unit as the scaffold, viz. [PdCl(R2PfcCHCHCH2-η3:κP)] (1R; R = Ph and cyclohexyl (Cy); fc = ferrocene-1,1'-diyl). These compounds were synthesized from the respective phosphinoferrocene carboxaldehydes R2PfcCHO via reaction with vinylmagnesium bromide to generate 1-(phosphinoferrocenyl)allyl alcohols, which were subsequently acetylated. The resulting allyl acetates reacted smoothly with [Pd2(dba)3]/[Et3NH]Cl (dba = dibenzylideneacetone) to produce the target compounds. Complexes 1R and their nontethered analogues [PdCl(η3-C3H5)(FcPR2-κP)] (5R; Fc = ferrocenyl) were evaluated as pre-catalysts for the Pd-catalysed allylic amination of cinnamyl acetate with aliphatic amines and Suzuki-Miyaura-type cross-coupling of 4-tolylboronic acid with benzoyl chloride. In these reactions, better results were achieved with compounds 5R (particularly with 5Ph), presumably because they form more stable LPd(0)-type catalysts.

Forever young: the first seventy years of ferrocene

The discovery of ferrocene, [Fe(η5-C5H5)2], seventy years ago has significantly influenced chemical research and provided a key impetus for establishing and rapidly expanding organometallic chemistry, which has continued at a...

Amphiphilic polymeric nanoreactors containing Rh(i)–NHC complexes for the aqueous biphasic hydrogenation of alkenes

A rhodium(i) complex bearing a monodentate N-heterocyclic carbene ligand has been confined into the core of amphiphilic core-crosslinked micelles (CCMs).

New anionic rhodium complexes as catalysts for the reduction of acetophenone and its derivatives

New anionic rhodium(iii) complexes, obtained by a simple reaction of RhCl3 with organic chlorides (derivatives of imidazole and pyridine), have been employed as catalysts for hydrosilylation (reduction) of acetophenone derivatives. The reactions, in which 1,1,1,3,5,5,5-heptamethyltrisiloxane was a reducing agent, proceeded in a biphasic system because the above complexes are insoluble in the reaction medium. Thereby easy isolation of the complexes from post-reaction mixtures was possible after reaction completion. This is the first example of the application of rhodium complexes of this type as catalysts for ketone reduction. The complexes have shown high activity and enabled obtaining the hydrosilylation product in a very short time and in the range of low concentrations (0.1 mol%). By using FT-IR in situ analysis that enables measuring product concentrations in real time, a comparison has been made of the catalytic activity for hydrosilylation of acetophenone and methoxyacetophenone isomers shown by four rhodium complexes ([C+][RhCl4 -]) differing in cations and the most effective catalyst for this process has been distinguished.

Ferrocenylmethylation reactions with a phosphinoferrocene betaine

A phosphinoferrocene betaine, N-{[1'-(diphenylphosphino)ferrocenyl]methyl}-N,N-dimethyl-3-sulfo-1-propanaminium, inner salt, Ph2PfcCH2NMe2(CH2)3SO3 (; fc = ferrocene-1,1'-diyl), was prepared by alkylation of Ph2PfcCH2NMe2 () with 1,3-propanesultone, and was studied as a ferrocenylmethylation agent. The treatment of with NaOH in hot water-dimethyl sulfoxide produced phosphinoalcohol Ph2PfcCH2OH () in a 64% yield, whereas a similar reaction with MeONa in dimethylsulfoxide-methanol furnished the corresponding ether, Ph2PfcCH2OMe (), in a 47% yield. In subsequent experiments, betaine was employed in the synthesis of phosphinoferrocene sulfones, Ph2PfcCH2SO2R, where R = Me (), Ph (), and 4-tolyl (). Compounds and some by-products of the ferrocenylmethylation reactions, namely alcohol , 1'-(diphenylphosphino)-1-methylferrocene (), and 1-{[diphenyl(2,4-cyclopentadien-1-ylidene)phosphoranyl]methyl}-1'-(diphenylphosphino)ferrocene () structurally characterised. Reactions of as the representative with ZnX2/NaX (X = Br and I) afforded unique coordination polymers [ZnNaX3()(CH3OH)]n featuring tetrahedral Zn(ii) and octahedral Na(i) centres bridged by halide ions, solvating methanol and the sulfone ligands. The reaction of with ZnBr2/KBr produced an analogous product, [ZnKBr3()(CH3OH)]n, while that with ZnBr2/LiBr furnished a different, pseudodimeric complex [Zn2Li2Br6()2(CH3OH)4(H2O)]·CH3OH, featuring tetrahedrally coordinated Zn(ii) and Li(i) centres bridged by . Reactions of with ZnBr2/MBr (M = Rb, Cs) and NaCl/ZnCl2 did not yield similar products because of an easy precipitation (low solubility) of the respective alkali metal halides.

Hydroxyl and ester functionalized N-heterocyclic carbene complexes of iridium(i): efficient catalysts for transfer hydrogenation reactions

Iridium(i)–NHC catalyzed transfer hydrogenation reaction of aldehydes and ketones with up to 10 000 TON has been achieved.

1-Ferrocenylmethyl-3-(2,4,6-trimethylbenzyl)-1H-imidazolidin-3-ium iodide and trans-bis(3-benzyl-1-ferrocenylmethyl-1H-imidazolidin-2-ylidene)diiodidopalladium(II)

Owing to increasing interest in the use of N-heterocyclic carbenes (NHCs) based on imidazolidinium ions as ligands in the design of highly efficient transition-metal-based homogeneous catalysts, the characterizations of the 1-ferrocenylmethyl-3-(2,4,6-trimethylbenzyl)imidazolidin-3-ium iodide salt, [Fe(C(5)H(5))(C(19)H(24)N(2))]I, (I), and the palladium complex trans-bis(3-benzyl-1-ferrocenylmethyl-1H-imidazolidin-2-ylidene)diiodidopalladium(II), [Fe(2)Pd(C(5)H(5))(2)(C(16)H(17)N(2))(2)I(2)], (II), are reported. Compound (I) has two iodide anions and two imidazolidinium cations within the asymmetric unit (Z' = 2). The two cations have distinctly different conformations, with the ferrocene groups orientated exo and endo with respect to the N-heterocyclic carbene. Weak C-H donor hydrogen bonds to both the iodide anions and the π system of the mesitylene group combine to form two-dimensional layers perpendicular to the crystallographic c direction. Only one of the formally charged imidazolidinium rings forms a near-linear hydrogen bond with an iodide anion. Complex (II) shows square-planar coordination around the Pd(II) metal, which is located on an inversion centre (Z' = 0.5). The ferrocene and benzyl substituents are in a trans-anti arrangement. The Pd-C bond distance between the N-heterocyclic carbene ligands and the metal atom is 2.036 (7) Å. A survey of related structures shows that the lengthening of the N-C bonds and the closure of the N-C-N angle seen here on metal complexation is typical of similar NHCs and their complexes.

1,1'-Bis(N-benzimidazolylidene)ferrocene: synthesis and study of a novel ditopic ligand and its transition metal complexes

Diiridum complexes containing 1,1'-bis(N-benzimidazolylidene)ferrocene, a novel ditopic ligand comprised of two N-heterocyclic carbenes (NHCs) linked directly via their N-substituents to each cyclopentadienyl ring of a ferrocene moiety, were synthesized. Crystallographic analyses of these C(2)-symmetric bimetallic complexes revealed the benzimidazolylidene moieties were intramolecularly stacked in nearly opposing orientations, effectively forming Janus-type bis(NHC) structures in the solid state. Using a variety of electrochemical techniques, the oxidation potentials of the ferrocenyl groups in these complexes were found to depend on the auxillary ligands coordinated to the Ir centers (i.e., 1,5-cyclooctadiene vs. carbonyl). Similarly, the nu(CO) of carbonyls ligated to the Ir centers varied in accord with the oxidation state of the ferrocene contained with the bis(NHC) ligand. These results suggest that the Ir and Fe centers in these complexes are electronically coupled and that the electron donating ability of the bis(NHC) ligand reported herein can be tuned electrochemically.