Cyclopentadienyl Rhodium Complexes Research Articles

Concise Synthesis of Functionalized Cyclopentadienyl Rhodium(III) Complexes via Suzuki–Miyaura Cross Coupling

AbstractHerein, we report a concise method for the preparation of functionalized cyclopentadienyl rhodium complexes via Suzuki–Miyaura cross-coupling. We successfully converted 2,3,4,5-tetramethylcyclopent-2-en-1-one into the corresponding cyclopentadienylboronic acid pinacol ester, which could be used as a coupling partner with aryl halides. Several functionalized cyclopentadienyl rhodium complexes were synthesized in two steps from readily available aryl bromides. We also demonstrated the rapid synthesis of a novel chiral cyclopentadienyl rhodium complex that could be used as a precatalyst for an asymmetric C–H functionalization reaction.

Chiral Bicyclo[2.2.2]octane-Fused Cyclopentadienyl Rhodium Complexes: Synthesis and Potential Use in Asymmetric C—H Activation

Chiral Bicyclo[2.2.2]octane-Fused Cyclopentadienyl Rhodium Complexes: Synthesis and Potential Use in Asymmetric C—H Activation

Enantioselective Synthesis of Spiroindenes by Enol-Directed Rhodium(III)-Catalyzed C-H Functionalization and Spiroannulation.

Chiral cyclopentadienyl rhodium complexes promote highly enantioselective enol-directed C(sp2)-H functionalization and oxidative annulation with alkynes to give spiroindenes containing all-carbon quaternary stereocenters. High selectivity between two possible directing groups, as well as control of the direction of rotation in the isomerization of an O-bound rhodium enolate into the C-bound isomer, appear to be critical for high enantiomeric excesses.

Enantioselective Synthesis of Spiroindenes by Enol‐Directed Rhodium(III)‐Catalyzed CH Functionalization and Spiroannulation

AbstractChiral cyclopentadienyl rhodium complexes promote highly enantioselective enol‐directed C(sp2)‐H functionalization and oxidative annulation with alkynes to give spiroindenes containing all‐carbon quaternary stereocenters. High selectivity between two possible directing groups, as well as control of the direction of rotation in the isomerization of an O‐bound rhodium enolate into the C‐bound isomer, appear to be critical for high enantiomeric excesses.

Half-sandwich cyclopentadienyl rhodium complexes bearing pendant sulfur or oxygen ligands and their catalytic behaviors in ethylene polymerization

Two half-sandwich rhodium complexes with sulfur or oxygen functionalized cyclopentadienyl ligands [η 5-C 5H 4(CH 2) 2SCH 2CH 3]RhI 2 3, {[η 5-C 5H 4(CH 2) 2OCH 3]RhI 2} 2 4 have been synthesized and characterized by IR, 1H-NMR spectra and Elemental analyses. The molecular structures of complexes 3 and 4 have been determined by X-ray crystallographic analysis. Complexes 3, 4 with a pendent arm on cyclopentadienyl ligand have been tested as catalysts for ethylene and norbornene polymerization in the presence of MAO. Complexes 3 and 4 kept high activities of ca. 10 6 g PE mol −1 Rh h −1 with morderate molecular weight ( M w ≈ 10 5 g mol −1) of polyethylene in the ethylene polymerization. Catalytic activities, molecular weights of polyethylene have been investigated under the various reaction conditions.

Ancillary Ligand-Controlled Selectivity for Metal or Cyclopentadienyl Ring Fluoroalkylation in Reactions of Fluoroalkyl Iodides with Cyclopentadienylrhodium Complexes

Reactions of [Rh(η5-C5H5)(CO)2] with isomeric primary and secondary fluoroalkyl iodides proceed by selective fluoroalkylation at the metal center to give [Rh(η5-C5H5)(CO)(RF)I], and treatment of these compounds with excess PMe3 affords cationic fluoroalkyl complexes [Rh(η5-C5H5)(PMe3)2(RF)]+I-. In contrast, reactions of [Rh(η5-C5H5)(PMe3)2] with the same fluoroalkyl iodides proceed with completely different selectivity to afford ring-exo-fluoroalkylated products [Rh(η4-C5H5RF)(PMe3)2I], which, in turn, react with Ag+BF4- to give the cationic hydrido complexes [Rh(η5-C5H4RF)(PMe3)2H]+[BF4]-.

Redox-rotational phenomena in organometallic chemistry. Unique features of the crystal structure and stereodynamic behaviour of acetylacetonato- and cyclopentadienylrhodium complexes with potentially dipolar two-ring semiquinoid ligands in solution

Replacement of the acac group in the 16-electron (metal oxidation state Rh 1) (acac)Rh(L) complex A (where L is 4-methyl-A-trichloromethyl-1-(4,4-dimethyl-2,6-dioxocyclohexylidene)-2,5-cyclohexadiene) with Cp, under the action of CpTl, gives the 18-electron CpRh(L) complex B, in which, according to 1H and 13C NMR spectral data, the η 4-diene structure of the ligand L rearranges into the dipolar delocalized form of 1-(4,4-dimethyl-2,6-dioxocyclohexylide)-4-methyl-4-trichloromethylbenzolonium with η 5-coordination by the cyclohexadienyl ring to the Rh IIII atom, in a reaction we have termed a ligand redox-exchange. An X-ray diffraction has revealed that the dimedone ring of molecule B in the crystal is twisted around the central polarized ▪ bond by an angle of 28.9°, and 1H and 13C DNMR spectroscopy has shown that the dimedone fragments of the complexes A and B in solution undergo internal rotation about this band. The effects of solvent on this process, including the enhancing effect by the presence of H +, has been studied. The rotation in the case of complex B is faster than that in complex A (“redox-rotation”). The kinetic parameters of the stereodynamics of the process (including the accompanying dimedone ring inversion) have been measured (e.g. in acetone- d 6 Δ H ≠ 18.4 kJ/mol, δ S ≠ −125.8 J mol −1 K −1, Δ G ≠ 298 56.0 kJ/mol). Treatment of B with CF 5COOH gives a stable η 5-cyclohexadienyl complex of Rh III, CpRh(LH)OCOCF 3, with a protonated oxygen in the CO group of the ligand. A periodic system for virtually all the rotatable β-charged organometallic molecules has been proposed, which includes four structural types (and two classes) of models capable of undergoing either isovalent-odd or anisovalent-even internal rotations, depending on the evenness of the ligand fragment coordinated with the metal.

Synthesis of pyridines from alkynes and nitriles catalyzed by polymer-anchored rhodium complexes

Cyclopentadienylrhodium(I) complexes have been attached to polymers by first binding cyclopentadiene to polystyrene resins in a variety of crosslink densities and then converting the resulting species to the cyclopentadiene anion. On subsequent reaction of the resin-bound anions with rhodium compounds of general formula [RhXL 2] n (X = chloro or acac, L = C 2H 4 or CO; L 2 = 1,5-C 8H 12), various rhodium-containing resins were obtained which were then analyzed by X-ray fluorescence and IR spectroscopies. These resin-attached cyclopentadienylrhodium complexes were active in the cocyclization of alkynes and nitriles to pyridine derivatives, at temperatures between 90 and 170 °C. In all cases, variable amounts of benzene derivatives were also formed, owing to the parallel self-trimerization of alkyne. A detailed study was carried out of the activity, chemo- and regio-selectivities of these catalysts as a function of the reaction parameters. The activity was seen to depend markedly upon the nature of the rhodium ancillary ligands and the crosslink density of the support: the ethylene complexes anchored to lightly crosslinked resins were the most active, all other variables being the same. Analogies and differences between heterogeneously and homogeneously rhodium-catalyzed pyridine syntheses are discussed.

Disubstituted norbornadiene ? -complexes. Communication 1. Synthesis and some chemical properties of 2,3-disubstituted norbornadiene complexes of rhodium

1. We have obtained a series of new π complexes of rhodium with 2,3-dicarboalkoxy- and 2,3-dicarboxynorbornadiene ligand, for which we have found mild conditions for selective hydrolysis and esterification of one of the ester or acid groups. 2. Using the IR and PMR spectroscopy method, we have studied the structure of the 2,3-disubstituted norbornadiene complexes in the solid state and in dilute solutions. Depending on the structure and the phase state, the carboxylic acids of this series form intramolecular, intermolecular, and possibly three-center hydrogen bonds. 3. We have studied the reaction of protonation of (2,3-dicarboalkoxynorbornadiene)-cyclopentadienylrhodium complexes with the acids HPF6 or HBF4· Et2O, as a result of which we have obtained stable cationic products of composition 1:1 with a strong hydrogen bond of the O...H...O type.

Highly active rhodium catalysts for the [2+2+2] cycloaddition of acetylenes

The catalytic activity of the complexes [Rh(π 5-indenyl)L 2] (L = ethylene or cyclooctene; L 2 = 1,5-cyclooctadiene), ( I) - ( III), and [Rh(π 5-fluorenyl) (1,5-cyclooctadiene)], ( IV), in the cyclotrimerization reaction of alkynes to benzene derivatives has been investigated. Compounds I - IV were very active in comparison with the isostructural cyclopentadienyl rhodium complexes. The catalytic activity depended markedly upon the nature of the substituents attached to the carbon-carbon triple bond, decreasing in the order: dimethyl acetylenedicarboxylate > methyl propiolate > diphenylacetylene > 1-hexyne > 3-hexyne > 1-octyne. In almost all cases the reaction has shown a high chemoselectivity. Some influence of the nature of the cyclopentadienyl-like ligand on both the catalytic activity and the regioselectivity has been observed. By reacting diphenylacetylene (dpa) with roughly stoichiometric amounts of I and III, the complexes [Rh 2π 5-indenyl) 2(dpa) 2], ( VI), and [Rh(π 5-indenyl)(π 4-tetraphenylcyclobutadiene)], ( VII), have been obtained, respectively. VI was poorly active and VII inactive in dpa cyclotrimerization. The mechanism of these cyclotrimerization reactions is discussed with reference to the role played by the indenyl and fluorenyl ligands in determining the activity of the catalyst precursors I - IV.

Retention of configuration during ligand-substitution reactions of cyclopentadienylrhodium complexes containing an acyl ligand

Retention of configuration during ligand-substitution reactions of cyclopentadienylrhodium complexes containing an acyl ligand

Reactions of transition metal compounds with macrocyclic alkadiynes : IV*. Intramolecular transannular cyclizations with cyclopentadienyldicarbonylrhodium

The macrocyclic alkadiynes, 1,7-cyclododecadiyne, 1,7-cyclotridecadiyne, 1,7- and 1,8-cyclotetradecadiyne, and 1,8-cyclopentadecadiyne react with C 5H 5Rh(CO) 2 in boiling cyclooctane to give pale yellow to white volatile compounds of the compositon C 5H 5Rh(alkadiyne) in which the macrocyclic alkadiyne has undergone an intramolecular transannular cyclization to form a tricyclic cyclobutadiene derivative. The reaction of 1,7-cyclododecadiyne with C 5H 5Rh(CO) 2 also gives a dimer of 1,7-cyclododecadiyne containing a benzene ring. Corresponding reactions of the simple alkynes RCCR (R = C 2H 5 and C 6H 5) with C 5H 5Rh(CO) 2 in boiling cyclooctane failed to give any rhodium—cyclobutadiene derivatives. Instead the reaction of 3-hexyne with C 5H 5Rh(CO) 2 under these conditions gave orange-red (C 5H 5) 2Rh 2(CO)C 4(C 2H 5) 4 and purple-black (C 5H 5) 3Rh 3(CO)(C 2H 5CCC 2H 5) and the reaction of diphenylacetylene with C 5H 5Rh(CO) 2 gave a low yield of the orange complex (C 5H 5) 3Rh 3(C 6H 5CCC 6H 5). The infrared, 1H NMR, and mass spectra of these new cyclopentadienylrhodium complexes are described.

Insertion reactions of hexafluoroacetone with tricarbonyl(diene)iron and π-cyclopentadienyl(diene)rhodium complexes

The reaction of hexafluoroacetone (HFA) with various tricarbonyl-(1,3-diene)iron complexes affords adducts containing one or two molecules of HFA, the latter adducts being transformed on heating into products, in which HFA has formally inserted into carbon–hydrogen bonds; analogous reactions with cyclopentadienylrhodium complexes lead to insertion of one or two HFA molecules into cyclopentadienyl carbon–hydrogen bonds.