Three-legged Piano Stool Research Articles

The First Imido Complex of Osmium(VI), [CpOs(NH)(CH2SiMe3)2][SO3CF3

Protonation of Os(η5-C5H5)(N)(CH2SiMe3)2 with either HBF4 or CF3SO3H at low temperature produces a thermally unstable imido complex, [Os(η5-C5H5)(NH)(CH2SiMe3)2][X] (X = BF4, SO3CF3). The imido com...

Tricarbonyl[η6-(R)-N,N-dimethyl-1-phenylethylamine]chromium(0)

The title complex, [Cr(C10H15N)(CO)3], has a typical three-legged piano-stool structure, as is expected for an η6-arene–tri­carbonyl­chromium compound. The conformation is staggered with respect to the side chain and one of the carbonyl ligands. The side chain bearing the stereogenic centre adopts a conformation with the H atom pointing downwards, leaving the di­methyl­amine group above the ring plane.

Tricarbonyl{η6-(S,S)-1-[2-methoxy-3,6-bis(trimethylsilyl)phenyl]-N,N-dimethylethylamine}chromium(0)

The title complex, [Cr(C17H33NOSi2)(CO)3], has the typical three-legged piano-stool structure expected for η6-arenetri­carbonyl­chromium compounds. The conformation is staggered with respect to the methoxy group of the arene ring and one of the carbonyl ligands.

Crystal Structure of the Monomeric Half-Sandwich Complex [RuCl(NCCH3)2(.ETA.6-C6H5OCH2CH2OH)]PF6

The crystal structure of the title compound was determined by the X-ray diffraction method. The crystal system is triclinic, space group P1 with Z = 2. The unit-cell parameters are: a = 7.4417(8)A, b = 10.7676(12)A, c = 11.3576(13)A, with α = 108.599(2)°, β = 91.892(2)° and γ = 92.532(2)°. The final R value is 0.0561 for 3165 reflections measured. The geometry for the complex ion corresponds to the characteristic “three-legged piano stool” configuration.

Tricarbonyl(η6-N,N-dimethylaniline)chromium(0)

The title compound, [Cr{(C6H5N(CH3)2}(CO)3], exhibits the three-legged piano-stool structure expected for a tri­carbonyl­metal with an η6-coordinated arene. The arene moiety is distorted with the amino functional group bent away from the chromium atom.

Cp*Cr(C6F5)(Me)(Py)] as a Living Chromium(III) Catalyst for the “Aufbaureaktion”

The reaction of [Cp*Cr(C6F5)(μ-Cl)]2 (1) with 2 equiv of MeLi in THF yields the methyl-bridged Cr(III) dimer [Cp*Cr(C6F5)(μ-Me)]2 (2). This dinuclear compound is very soluble in hydrocarbon solvent and has been isolated in low yield (6%). Compound 2 reacts with pyridine to afford [Cp*Cr(C6F5)(Me)(Py)] (3), which has been isolated in a 67% yield. Compound 3 is a 15-electron, coordinatively saturated chromium(III) species that has been characterized by NMR, magnetometry, and EA. The structures of 1, 2, and 3 have been determined by single-crystal X-ray diffraction. Compounds 1 and 2 exist in the form of centrosymmetrical dimers with bridging chloride and methyl ligands, respectively. Mononuclear compound 3 adopts the expected three-legged piano stool geometry. Compound 2 polymerizes ethylene in toluene under 1 atm of ethylene at room temperature in the absence of any activators. Compound 3 is not catalytically active by itself. Yet, the addition of excess AlEt3 to a solution of 3 in toluene leads to a catal...

Tricarbonyl(η6-trifluoromethylbenzene)chromium(0)

The title compound, [Cr(C6H5CF3)(CO)3], exhibits the three-legged piano-stool structure expected for a tri­carbonyl­metal complex with an η6-coordinated arene. The tri­fluoro­methyl functional group is tilted towards the Cr(CO)3 center.

Tricarbonyl(η6-fluorobenzene)chromium

The title compound, [Cr(C6H5F)(CO)3], exhibits the three-legged piano stool structure expected for a metal tri­carbonyl complex with a η6-coordinated arene. The fluoro functional group is tipped away from the Cr(CO)3 center.

Tricarbonyl(η6-1,3-dimethoxybenzene)chromium

The title compound, [Cr{1,3-(MeO)2C6H4}(CO)3], exhibits the three-legged piano stool structure expected for a metal tri­carbonyl with an η6-coordinated arene. Two independent mirror-symmetric mol­ecules are found in the unit cell. The methoxy groups display an out-of-plane distortion.

Tricarbonyl(η6-1,3-dimethylbenzene)chromium

The title compound, [Cr(1,3–Me2C6H4)(CO)3], exhibits the three-legged piano stool structure expected for a metal tri­carbonyl with an η6-coordinated arene. The compound displays mirror symmetry in the solid state.

A new family of monocyclopentadienyl organoscandium bis-alkyls supported by a bulky trialkylphosphine oxide ancillary

Treatment of the oligomeric compound [Cp*ScCl2]n (Cp* = C5Me5) with tri-tert-butylphosphine oxide in THF leads to the monocyclopentadienyl scandium dichloride [Cp*(t-Bu3P=O)ScCl2] as a monomeric, THF-free solid in 72% yield. This compound can be alkylated with MeLi to give the corresponding dimethyl derivative, [Cp*(t-Bu3P=O)ScMe2], 1. The crystal structures of these two compounds have been done and reveal a three-legged piano stool geometry about the scandium center. The coordinated phosphine oxide ligand exchanges with free donor in both compounds via an associative mechanism, as indicated by the activation parameters (ΔH‡ = 6.4–8.4 kcal mol–1-; ΔS‡ = –22.5 to –26.6 eu). Thus, the Cp*(t-Bu3P=O) ligand set provides a stable platform for organoscandium chemistry. This was demonstrated by the activation of 1 by treatment with B(C6F5)3 to form the fully characterized contact ion pair [Cp*(t-Bu3P=O)ScMe]+[MeB(C6F5)3]–, 2, which is an active ethylene polymerization catalyst.Key words: organoscandium compounds, olefin polymerization, cationic complexes.

Tricarbonyl(η6-1,3,5-trimethoxybenzene)chromium(0)

The title compound, (1,3,5-(MeO)3C6H3)Cr(CO)3 or [Cr(C9H12O3)(CO)3], exhibits the three-legged piano-stool structure expected for a metal tri­carbonyl with an η6-coordinated arene. The mol­ecule exhibits threefold symmetry. The methoxy groups display an out-of-plane distortion.

Tricarbonyl(η6-4-fluoroaniline)chromium

The title compound, [Cr(C6H6FN)(CO)3], exhibits the three-legged piano-stool structure expected for a metal tri­carbonyl with an η6-coordinated arene. A crystallographic mirror plane bisects the mol­ecule. The amine and fluoro­arene functional groups display an out-of-plane distortion.

Synthesis of the sterically constrained ligand precursor cyclopentadienyl-2,6-diphenylbenzene and structure of [(2,6-Ph 2–C 6H 3-η 5-C 5H 4)Zr(NEt 2) 3

A Pd-catalysed Stille coupling of 2,6-diphenyliodobenzene with tributylcyclopentadienyltin gave the sterically constrained ligand precursor cyclopentadienyl-2,6-diphenylbenzene ( 1). Treatment of this precursor with tetrakis(diethylamido)zirconium(IV) gave the three-legged piano-stool complex [(2,6-Ph 2–C 6H 3-η 5-C 5H 4)Zr(NEt 2) 3] ( 2). Complex 2 was characterised by 1H- and 13C{ 1H}-NMR spectroscopy as well as by X-ray crystallography which showed significant distortions of the three-legged piano-stool geometry as a result of steric interactions with the bulky aryl substituent.

Piano-stool inversion in arene complexes of Ru(ii): modelling the transition state

In the solid-state, the [RuH(arene)(Binap)]CF3SO3, complexes, 1, arene = η6-benzene and 2, arene = η6-toluene, distort markedly from a classical three-legged piano-stool structure with the former having the P–Ru–P plane approximately perpendicular to the plane of the arene; this structure for 1 is what one would expect for a transition state leading from one diastereomer to another via inversion at ruthenium.

Chloro(methyl)(η5-pentamethylcyclopentadienyl)(trimethylphosphine)rhodium(III)

The title compound, RhCp*Me(Cl)(PMe3) or [RhCl(CH3)(C10H15)(C3H9P)], where Cp* is penta­methyl­cyclo­penta­dienyl, has a pseudo-tetrahedral coordination geometry. The Cp* ligand is planar and η5-coordinated. The molecular structure can be described as a so-called three-legged piano-stool. The rhodium–methyl, rhodium–chlorine and rhodium–phospho­rus distances are 2.255 (4), 2.3764 (18) and 2.2436 (13) A, respectively.

Molecular structures of tris(dimethylamido)-pentamethy-1-cyclopentadienyl-titanium and -zirconium, (η-C5Me5)M(NMe2)3, M=Ti or Zr, by gas electron diffraction; DFT calculations on the model compound (η-C5H5)Ti(NMe2)3

The molecular structures of (η-C5Me5)M(NMe2)3, M=Ti or Zr, Me=methyl, have been determined by gas electron diffraction (GED). Both compounds have three-legged piano–stool structures with propeller-like orientations of the dimethylamido groups and planar N atoms. The most important bond distances and valence angles are Ti–C=245.3(9)pm;Ti–N=195.4(5)pm, ∠(ring centroid) TiN=117.7(10)°; Zr–C=255.8(14)pm;Zr–N=207.1(10)pm, ∠(ring centroid) ZrN=117.1(9)°.

Chloro(1-{3-[2-(diphenylphosphanyl-κP)ethyl]-η6-benzyl}-3,5-dimethyl-1H-pyrazole-κN2)ruthenium(II) trifluoromethanesulfonate

To address the question of the role of chirality at the metal in enantioselective catalysis, a pseudo-tetrahedral three-legged piano-stool complex has been prepared, i.e. [RuCl(C26H27N2P)](CF3SO3). Anchoring a phosphine and a pyrazole tether to an arene (PArN) yields, after η6:η1:η1 coordination to ruthenium, [{η6:η1:η1-(PArN)}RuCl]+ as a 1:1 mixture of enantiomers. Unfortunately, all attempts to resolve the enantiomers failed. The structure solution revealed the presence of racemic crystals.

Tribenzyl(η5-pentamethylcyclopentadienyl)hafnium(IV)

The title compound, [Hf(C7H7)3(C10H15)], adopts a monomeric three-legged piano-stool structure. One benzyl ligand is disordered between two sites (44:56%) related by a ∼30° rotation about an axis defined by the Hf atom and the ipso-C atom of the benzyl ligand.

(eta 6-hexamethylbenzene)(mesidine)ditriflatoruthenium(II)

The crystal structure of the title complex, (η6-hexamethylbenzene)bis(trifluoromethanesulfonato-O)(2,4,6-trimethylanil­ine-N)ruthenium(II), [Ru(CF3O3S)2(C12H18)(C9H13N)], is described. The complex has the classic three-legged piano-stool structure with a planar arene 1.667 Å from the metal, two monodentate O-bound tri­fluoro­methane­sulfonate ligands [Ru—O 2.169 (2) and 2.174 (2) Å] and one N-bound mesidine ligand [Ru—N 2.198 (2) Å]. The Ru—N distance is relatively long and the average Ru—O distance is relatively short when compared with previously characterized RuII complexes.