Bulky Cyclopentadienyl Ligands Research Articles

Synthesis, Characterization, and Catalytic Activity of a Cubic [Mo3S4Pd] Cluster Bearing Bulky Cyclopentadienyl Ligands

AbstractA cubic metal‐sulfur cluster containing three Mo ions and a Pd ion, [CpSiEt33Mo3S4Pd]Cl (Mo3Pd, CpSiEt3=C5Me4SiEt3), was synthesized by the incorporation of the Pd ion into a Mo3S4 cluster [CpSiEt33Mo3S4] (Mo3). Mo3Pd was characterized by 1H NMR, UV‐vis, X‐ray crystallography, and cyclic voltammetry measurements. The electrochemical measurements demonstrated reversible one‐ and two‐electron reduction processes for Mo3Pd, which suggested potential catalytic activity for two‐electron substrate reductions such as hydrogen evolution reaction. Controlled potential electrolysis in the presence of Mo3Pd and trifluoroethanol in THF solvent displayed H2 formation with a constant current over 60 min. The amount of generated H2 by Mo3Pd was two times higher than Mo3, indicating the catalytic activity facilitated by the Pd center. The mechanism of the catalytic cycle was determined by density functional theory.

Biomimetic Transition Metal Cluster Complexes: Synthetic Studies and Applications in the Reduction of Inert Small Molecules

Abstract Transition metal cluster complexes, particularly those containing iron and sulfur, are used as catalysts for the biological reduction of inert small molecules such as N2 and CO2. The structures of these biological clusters are complicated and the protein backbones around the clusters often play important roles in catalysis, hence reproducing or mimicking the enzymatic functions with synthetic cluster complexes remains a challenge. Appropriate assumptions and hypotheses on the relationships between the structures and functions of biological clusters are needed to develop synthetic molecular catalysts inspired by enzymes. This account reviews recent studies by the author and his coworkers on iron-containing biomimetic cluster complexes. Cubic Mo-Fe-S clusters supported by bulky cyclopentadienyl ligands on molybdenum were designed and synthesized, and their Fe sites captured and catalytically converted N2 under reducing conditions. Iron-hydride clusters, which are relevant to the active species of biological and industrial nitrogen fixation, also served as catalysts for the reduction of N2. Furthermore, various metal-sulfur clusters, ranging from a structural mimic of the complex active site of the N2-reducing enzyme to a simple and cubic [Fe4S4] cluster, were found to catalyze the biologically inaccessible direct conversion of CO2 to short-chain hydrocarbons. These studies have demonstrated the potential utility of biomimetic approaches to the catalytic reduction of inert small molecules, through the rational design and synthesis of simple yet appropriate iron-containing cluster complexes.

Tromancenium complexes with steric and electronic modulation

A series of new heteroleptic cationic (η7-cycloheptatrienyl)(η5-cyclopentadienyl)manganese(I) (“tromancenium”) sandwich complexes containing the cycloheptatrienyl ligand and various sterically bulky cyclopentadienyl ligands was synthesized in a one-pot two-step procedure via their cymantrene precursors by high-power LED photochemistry followed by oxidation. In comparison to their less-substituted congeners which display only partially reversible redox events, these new air-stable tromancenium salts show reversible Mn(I)/Mn(II) and quasi-reversible Mn(I)/Mn(0) redox couples, as intended by the conceptual design of this work. Full spectroscopic and structural characterization of by 1H, 13C, 55Mn NMR, IR, UV–vis spectroscopy, high-resolution mass spectrometry and single crystal structure analysis is reported.

Synthesis, Characterization, and Catalytic Reactivity of Dithiolate-Bridged Diiron Complexes Supported by Bulky Cyclopentadienyl Ligands

Synthesis, Characterization, and Catalytic Reactivity of Dithiolate-Bridged Diiron Complexes Supported by Bulky Cyclopentadienyl Ligands

Rh(III)-Catalyzed Annulation of 2-Biphenylboronic Acid with Diverse Activated Alkenes.

Rhodium(III)-catalyzed annulation of 2-biphenylboronic acids with three classes of activated alkenes has been realized, leading to the synthesis of fused or bridged cyclic skeletons via transmetalation-initiated C-H activation. In the annulative coupling of 2-biphenylboronic acid with a CF3-substituted enone, the bulky cyclopentadienyl ligand (CptBu) in the catalyst proved effective to promote the reductive elimination process prior to protonolysis, affording the [4 + 2] annulated products instead of the simple 1,4-addition product. Seven-membered rings were obtained when disubstituted cyclopropenones were employed. Bridged cycles were isolated from the coupling of 2-biphenylboronic acid with benzoquinones as a result of 2-fold Michael additions. The substrate scopes were found to be broad with up to 99% yield under air-tolerant conditions.

Frontispiece: Rhodium(III) Complex with a Bulky Cyclopentadienyl Ligand as a Catalyst for Regioselective Synthesis of Dihydroisoquinolones through C−H Activation of Arylhydroxamic Acids

Frontispiece: Rhodium(III) Complex with a Bulky Cyclopentadienyl Ligand as a Catalyst for Regioselective Synthesis of Dihydroisoquinolones through C−H Activation of Arylhydroxamic Acids

Rhodium(III) Complex with a Bulky Cyclopentadienyl Ligand as a Catalyst for Regioselective Synthesis of Dihydroisoquinolones through C−H Activation of Arylhydroxamic Acids

Catalytic reaction of arylhydroxamic acids with alkenes represents a convenient method for preparation of biologically active dihydroisoquinolones. Here, the rhodium(III) complex [(C5 H2 tBu2 CH2 tBu)RhCl2 ]2 , which allows one to carry out such reactions with high regioselectivity to obtain 4-substituted dihydroisoquinolones in 72-97 % yields, is described. The regioselectivity is provided by the bulky cyclopentadienyl ligand of the catalyst, which is formed through a [2+2+1] cyclotrimerization of tert-butylacetylene. The catalytic reaction tolerates various distant functional groups in alkenes, but is inhibited by bulky (e.g., tBu) or strongly coordinating (e.g., imidazolyl) substituents. Some of the prepared dihydroisoquinolones effectively inhibit growth of phytopathogenic fungi.

Syndiotactic polymerization of styrene and copolymerization with ethylene catalyzed by chiral half-sandwich rare-earth metal dialkyl complexes

The syndiotactic polymerization of styrene (St) and the copolymerization of St with ethylene (E) were carried out by using a series of chiral half-sandwich rare-earth metal dialkyl complexes (Cp x *) as the catalysts. The complexes are Ln(CH2SiMe3)2(THF) (1−4: Ln = Sc (1), Ln = Lu (2), Ln = Y (3), Ln = Dy (4)) bearing chiral cyclopentadienyl ligand containing bulky cylcohexane derivatives in the presence of activator and Al i Bu3. For the St polymerization, a high activity up to 3.1 × 106 g of polymer molLn−1·h−1 and a high syndiotactic selectivity more than 99% were achieved. The resulting syndiotactic polystyrenes (sPSs) have the molecular weights (Mn) ranging from 3700 g·mol−1 to 6400 g·mol−1 and the molecular weight distributions (Mw/Mn) from 1.40 to 5.03. As for the copolymerization of St and E, the activity was up to 2.4 × 106 g of copolymer molSc−1·h−1·MPa−1, giving random St-E copolymers containing syndiotactic polystyrene sequences with different St content in the range of 15 mol%−58 mol%. These results demonstrate that the bulky cyclopentadienyl ligands of the chiral half-sandwich rare-earth metal complexes effectively inhibit the continued insertion of St monomers into the (co)polymer chain to some extent in comparison with the known half-sandwich rare-earth metal complexes.

Reversible Formation of a Cerium‐Bound Terminal Hydride: Ce(C5Me4SiMe3)2(H)(thf)

The use of the bulky cyclopentadienyl ligand Cp′ (Cp′ = C5Me4SiMe3) to stabilize cerium hydrides has resulted in the preparation of two novel tuck‐in complexes with C–H activated SiMe3 groups. Subsequent reaction of these with H2 in thf gives a lanthanide terminal hydride species Ce(Cp′)2(H)(thf) which reversibly regenerates the tuck‐in complex under sustained vacuum. This compound is only the second structurally characterized terminal cerium hydride. This new hydride is a catalyst in H/D exchange reactions between with both sp3‐CH and sp2‐CH bonds, and for the hydrogenation of unsaturated alkene bonds.

Pentaarylcyclopentadienyl Iron, Cobalt, and Nickel Halides.

The preparation of new stable half-sandwich transition metal complexes, having a bulky cyclopentadienyl ligand C5(C6H4-4-Et)5 (Cp(Ar1)) or C5(C6H4-4-nBu)5 (Cp(Ar2)), is reported. The tetrahydrofuran (THF) adduct [Cp(Ar1)Fe(μ-Br)(THF)]2 (1a) was synthesized by reacting K[Cp(Ar1)] with [FeBr2(THF)2] in THF, and its molecular structure was determined by X-ray crystallography. Complex 1a easily loses its coordinated THF molecules under vacuum to form the solvent-free complex [Cp(Ar1)Fe(μ-Br)]2 (1b). The analogous complexes [Cp(Ar1)Co(μ-Br)]2 (2), [Cp(Ar1)Ni(μ-Br)]2 (3), and [Cp(Ar2)Ni(μ-Br)]2 (4) were synthesized from CoBr2 and [NiBr2(1,2-dimethoxyethane)]. The mononuclear, low-spin cobalt(III) and nickel(III) complexes [Cp(Ar2)MI2] (5, M = Co; 6, M = Ni) were prepared by reacting the radical Cp(Ar2) with NiI2 and CoI2. The complexes were characterized by NMR and UV-vis spectroscopies and by elemental analyses. Single-crystal X-ray structure analyses revealed that the dimeric complexes 1a, 1b, and 3 have a planar M2Br2 core, whereas 2 and 4 feature a puckered M2Br2 ring.

ChemInform Abstract: Rhodium‐Catalyzed syn‐Carboamination of Alkenes via a Transient Directing Group.

AbstractThe syn‐carboamination of various disubstituted alkenes is achieved using a novel bulky cyclopentadienyl ligand that alters the inherent chemoselectivity of the reaction.

Synthesis of Titanium and Zirconium Complexes with 2‐­Pyridonate and 2, 6‐Pyridinedithiolate Ligands

AbstractTreatment of complex [Cp2TiCl2] with the lithium salt of 2‐hydroxypyridine afforded complex [Cp2Ti(Opy)2] (1), whereas the same synthetic strategy applied to the analogous zirconium compound [Cp2ZrCl2] did not worked. However, the use of the metallocene [Cptt2ZrMe2] with protic ligands allowed directing the reactivity towards protonation of the methyl groups attached to zirconium. To check this approach we reacted [Cptt2ZrMe2] with methanol affording complex [Cptt2ZrMe(OMe)] (2), which was characterized in situ by NMR techniques. In the same line, the reaction of [Cptt2ZrMe2] with 2‐hydroxypyridine gave complex [Cptt2Zr(Me)(Opy)] (3); forcing the conditions of this reaction did not lead to the expected complex [Cptt2Zr(Opy)2], most probably due to the steric hindrance exerted by the bulky cyclopentadienyl ligands. Further reactions of complex 3 with ligands having acidic protons also led to the recovery of the starting complex. However, when shifting to the bifunctional ligand 2, 6‐dimercaptopyridine [py(SH)2] a double protonation of the methyl ligands in [Cptt2ZrMe2] occurred, allowing the isolation of mononuclear complex [Cptt2Zr(κS,κS,κN‐pyS2)] (4), upon evolution of methane. The molecular structure of complex 4 was determined by X‐ray methods, showing the zirconium atom in a highly distorted trigonal bipyramidal arrangement; structural parameters indicate a conventional Zr–N bond, but rather weak Zr–S interactions.

A structural investigation of heteroleptic lanthanide substituted cyclopentadienyl complexes

The synthesis and structural authentication of novel heteroleptic lanthanide complexes supported by bulky cyclopentadienyl ligands is herein presented. Steric effects play a fundamental role in the coordination motifs.

How big is a Cp? Novel cycloheptatrienyl zirconium complexes with tri-, tetra- and pentasubstituted cyclopentadienyl ligands.

The new bulky cyclopentadienyl anions 1,2,4-tri(cyclopentyl)cyclopentadienide and 2,3-diisopropyl-1,4-dimethyl-5-trimethylsilyl-cyclopentadienide were prepared. These and the already known 1,2,4-tri(cyclohexyl)-, 1,2,4-tri(isopropyl)-, 2,3-diisopropyl-1,4-dimethyl-, 1,3,4-triisopropyl-2,5-dimethyl-, pentaphenyl-, and p-butylphenyl-tetraphenyl-cyclopentadienide as well as tert-butylindenide were coordinated to the cycloheptatrienylzirconium fragment [(CHT)ZrCl(tmeda)]. The nine zirconium complexes of the [(CHT)Zr(Cp)] type were characterized by elemental analysis and NMR spectroscopy. For five of the sandwich complexes X-ray crystal structure determination could be carried out; structures of the four others were obtained by DFT calculations. The data serve as a basis for cone angle measurements of cyclopentadienyl ligands to evaluate the steric demand of these ligands.

Cover Picture: Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [EuII(CpBIG)2] (CpBIG=(4-nBu-C6H4)5-Cyclopentadienyl) (Chem. Eur. J. 37/2013)

High luminescence is observed for an Eu2+ ion sandwiched between two bulky cyclopentadienyl ligands, as described by S. Harder et al. in their Full Paper on page 12272 ff. In contrast to [Eu(Cp*)2] (Cp* = pentamethylcyclopentadienyl), which hardly shows luminescence, a quantum yield of 45% is found for the europocene [Eu(CpBIG)2] (CpBIG=(4-nBu-C6H4)5-cyclopentadienyl). Magnetic susceptibility measurements, and Mössbauer as well as EXAFS spectroscopy rule out possible oxidation-state ambiguities for the lanthanide(II) metallocenes of Sm, Eu, and Yb.

Mono-cyclopentadienyl complexes of lanthanum: synthesis and characterization of anilido derivatives

Mono-ligand lanthanide complexes utilizing the bulky tris(trimethylsilyl)cyclopentadienyl ligand are reported. Achiral mono-anilido complexes, in which the iodide and anilido groups are trans -disposed, are readily converted to chiral analogues, where the iodide and anilido groups are oriented in a cis fashion, by the addition of a chelating bidentate ligand such as 2,2 ′ -bipyridine. Use of the bulky cyclopentadienyl ligand [η 5 -C 5 H 2 (SiMe 3 ) 3 -1,2,4] − (Cp‴) allows for the isolation of monomeric, mono-ring lanthanide species. As previously reported, (Cp‴)K reacts with LaI 3 (THF) 4 (THF=tetrahydrofuran) in THF/pyridine to form the mono-ring complex (Cp‴)LaI 2 (py) 3 ( 1 ) (py=pyridine); a minor product of this reaction is the bis-ring species (Cp‴) 2 LaI(py) ( 2 ). The solid state structure of 2 reveals a monomeric compound containing a pseudo-tetrahedral metal center exhibiting no unusual intramolecular contacts. Addition of one equiv of KNHAr (Ar=2,6- i Pr 2 C 6 H 3 ) to complex 1 in THF generates the mono-anilido compound (Cp‴)LaI(NHAr)(THF) 2 ( 3 ), which may be converted to the more stable pyridine adduct (Cp‴)LaI(NHAr)(py) 2 ( 4 ) by the addition of pyridine to 3 . An X-ray crystal structure of 3 indicated a trigonal bipyramidal metal center with the anilido group oriented trans to the iodide atom (N1–La1–I1=123.1(3)°). A structural study on the bis-pyridine adduct 4 revealed a similar C s -symmetric structure with a slightly increased N anilido –La–I angle of 132.1(2)°. Addition of KNHAr to the di-iodo bipyridine adduct (Cp‴)LaI 2 (bipy)(py) ( 5 ), in which the two iodide atoms are cis -disposed, yields the mono-anilido complex (Cp‴)LaI(NHAr)(bipy)(py) ( 6 ) (bipy=2,2 ′ -bipyridine); this compound may also be prepared by the addition of bipy to (Cp‴)LaI(NHAr)(py) 2 ( 4 ). An X-ray diffraction study shows that the lanthanum center in 6 is octahedrally coordinated by a Cp‴ ring, an iodide, an anilido group, a pyridine molecule and two nitrogens of a bipy molecule. In this case, the anilido moiety and the iodide ligand are arranged in a cis fashion (N anilido –La–I=111.2(2)°), resulting in a complex with C 1 symmetry. Both (Cp‴)LaI(NHAr)(py) 2 ( 4 ) and (Cp‴)LaI(NHAr)(bipy)(py) ( 6 ) are inactive as catalysts for the hydroamination/cyclization of 2-amino-hex-5-ene.

Mono-cyclopentadienyl complexes of lanthanum: synthesis and characterization of anilido derivatives

Use of the bulky cyclopentadienyl ligand [η 5-C 5H 2(SiMe 3) 3-1,2,4] − (Cp‴) allows for the isolation of monomeric, mono-ring lanthanide species. As previously reported, (Cp‴)K reacts with LaI 3(THF) 4 (THF=tetrahydrofuran) in THF/pyridine to form the mono-ring complex (Cp‴)LaI 2(py) 3 ( 1) (py=pyridine); a minor product of this reaction is the bis-ring species (Cp‴) 2LaI(py) ( 2). The solid state structure of 2 reveals a monomeric compound containing a pseudo-tetrahedral metal center exhibiting no unusual intramolecular contacts. Addition of one equiv of KNHAr (Ar=2,6- i Pr 2C 6H 3) to complex 1 in THF generates the mono-anilido compound (Cp‴)LaI(NHAr)(THF) 2 ( 3), which may be converted to the more stable pyridine adduct (Cp‴)LaI(NHAr)(py) 2 ( 4) by the addition of pyridine to 3. An X-ray crystal structure of 3 indicated a trigonal bipyramidal metal center with the anilido group oriented trans to the iodide atom (N1–La1–I1=123.1(3)°). A structural study on the bis-pyridine adduct 4 revealed a similar C s-symmetric structure with a slightly increased N anilido–La–I angle of 132.1(2)°. Addition of KNHAr to the di-iodo bipyridine adduct (Cp‴)LaI 2(bipy)(py) ( 5), in which the two iodide atoms are cis-disposed, yields the mono-anilido complex (Cp‴)LaI(NHAr)(bipy)(py) ( 6) (bipy=2,2 ′-bipyridine); this compound may also be prepared by the addition of bipy to (Cp‴)LaI(NHAr)(py) 2 ( 4). An X-ray diffraction study shows that the lanthanum center in 6 is octahedrally coordinated by a Cp‴ ring, an iodide, an anilido group, a pyridine molecule and two nitrogens of a bipy molecule. In this case, the anilido moiety and the iodide ligand are arranged in a cis fashion (N anilido–La–I=111.2(2)°), resulting in a complex with C 1 symmetry. Both (Cp‴)LaI(NHAr)(py) 2 ( 4) and (Cp‴)LaI(NHAr)(bipy)(py) ( 6) are inactive as catalysts for the hydroamination/cyclization of 2-amino-hex-5-ene.

Synthesis and characterisation of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3.

Cyclopentadienyl complexes Ba(C5Me5)2(THF)2 (1), Ba(C5Me5)2(A) (A = THF, dien, trien, diglyme, triglyme) (2-5), Ba(Pr(i)3C5H2)2(THF)2 (6), Ba(Bu(t)3C5H2)2(THF) (7), Ba(Me2NC2H4C5Me4)2 (8) and Ba(EtOC2H4C5Me4)2 (9) were prepared and characterised with TGA/SDTA, NMR and MS. Crystal structures of 2, 4, 5, 7, 8 and 9 are presented. All complexes prepared sublime under reduced pressure and complexes 1, 6 and 7 showed volatility also under atmospheric pressure. Complexes 1, 6 and 7 lose the coordinated THF when evaporated while complexes 2-5 are sublimable as complete molecules under reduced pressure. Complexes with bulky cyclopentadienyl ligands (6 and 7) are the most thermally stable and volatile among the prepared barocenes. X-ray structure determinations reveal that all the complexes studied are monomeric. Complexes 1, 7 and 8 were successfully tested in BaTiO3 thin film depositions by atomic layer deposition (ALD).

Organometallic Compounds of the Lanthanides. 127 [1] Synthesis of Monomeric Bis(cyclopentadienyl)lanthanide Tetrahydroborates with Bulky Cyclopentadienyl Ligands. Single Crystal X-ray Structures of [(η5-C5Me5)2SmBH4(THF)] and [(η5-C5Me4Et)2Y(μ-H)2BH2(THF)

The trichlorides of yttrium, samarium, and lutetium react with 2 equivalents of Na[C5H4 tBu] and 1 equivalent of NaBH4 to give [(η5-C5H4 tBu)2LnBH4(THF)] (Ln = Y (1), Sm (2), Lu (3)) or with 2 equivalents of Na[C5Me4R] and 1 equivalent of NaBH4 to form [(η5-C5Me4R)2 · LnBH4(THF)] (R = H, Ln = Y (4), Sm (5), Lu (6); R = Me, Ln = Y (7), Sm (8), Lu (9); R = Et, Ln = Y (10), Sm (11), Lu (12); R = iPr, Ln = Y (13), Sm (14), Lu (15)). The new compounds have been characterized by elemental analysis, NMR spectroscopy and mass spectrometry. The crystal structures of 8 and 10 were determined by single crystal X-ray diffraction. Organometall-Verbindungen der Lanthanoide. 127 Synthese von monomeren Bis(cyclopentadienyl)lanthanoid-tetrahydroboraten mit sperrigen Cyclopentadienyl-Liganden. Einkristallstrukturen von [(η5-C5Me5)2SmBH4(THF)] and [(η5-C5Me4Et)2Y(μ-H)2BH2(THF)] Die Trichloride von Yttrium, Samarium und Lutetium reagieren mit 2 Aquivalenten Na[C5H4 tBu] und 1 Aquivalent NaBH4 zu [(η5-C5H4 tBu)2LnBH4(THF)] (Ln = Y (1), Sm (2), Lu (3)) oder mit 2 Aquivalenten Na[C5Me4R] und 1 Aquivalent NaBH4 zu [(η5-C5Me4R)2 · LnBH4(THF)] (R = H, Ln = Y(4), Sm (5), Lu (6); R = Me, Ln = Y (7), Sm (8), Lu (9); R = Et, Ln = Y (10), Sm (11), Lu (12); R = iPr, Ln = Y (13), Sm (14), Lu (15)). Die Verbindungen wurden elementaranalytisch, NMR-spektroskopisch und massenspektrometrisch charakterisiert. Die Kristallstrukturen von 8 und 10 wurden aus Einkristallstruktur-Daten bestimmt.

The preparation of mixed ligand ruthenocenes containing bulky cyclopentadienyl ligands. Crystal structures of pentaphenylruthenocene, [Ru( η5-C 5Ph 5)( η5-C 5H 5)], pentaparatolylruthenocene, [Ru{ η5-C 5( p-MeC 6H 4) 5}( η5-C 5H 5)] and pentaphenylpentamethylruthenocene, [Ru( η5-C 5Ph 5)( η5-C 5Me 5)

The preparations of the mixed ligand ruthenocenes [Ru( η 5-C 5R 5)( η 5-C 5H 5)] [R 5=Ph 5 ( 1), Ph 4H ( 2) and ( p-MeC 6H 4) 5 ( 3)] and [Ru( η 5-C 5Ph 5)( η 5-C 5Me 5)] ( 4) are reported. The molecular structures of 1 ( Pbca, a=14.234(3), b=20.276(3), c=20.625(4) Å), 3 ( P1̄, a=19.319(7), b=21.007(7), c=10.436(3) Å, α=103.76, β=95.07(3), γ=112.59(2)°) and 4·H 2O ( P1̄, a=12.145(2), b=12.696(4), c=14.281(2) Å, α=80.41(2), β=66.43(1), γ=62.80(2)°) were determined by single crystal X-ray diffraction studies; the cyclopentadienyl rings in each structure are almost parallel and nearly eclipsed. For 1, 2 and 3, two oxidative processes, but no reductive electrochemical processes, were observed. The precipitated product from the reaction of Ru 3(CO) 12, C 5Ph 5Br and Zn in xylenes yielded, after subsequent reaction with NaBPh 4, [Ru( η 5-C 5Ph 5){ η 6-C 6H 4(CH 3) 2}] +BPh 4 − ( 5).