Cyclopentadienide Ligands Research Articles

Cover Feature: A Route toward (Aminomethyl)cyclopentadienide Ligands and Their Group 4 Metal Complexes (Eur. J. Inorg. Chem. 34/2018)

Cover Feature: A Route toward (Aminomethyl)cyclopentadienide Ligands and Their Group 4 Metal Complexes (Eur. J. Inorg. Chem. 34/2018)

A Route toward (Aminomethyl)cyclopentadienide Ligands and Their Group 4 Metal Complexes

A new method is described, by which N‐functionalized cyclopentadienide ligands are synthesized via the nucleophilic substitution of sodium cyclopentadienide onto Katritzky's (benzotriazolyl) compounds. This route enables the introduction of bulky and basic amines, separated from the cyclopentadienyl ring by a methylene spacer. The method thus represents a valuable alternative to the general fulvene route. The resulting ligands have been coordinated to titanium and zirconium, producing a series of discrete metallocene derivatives with a pendant amine arm. These complexes are extremely sensitive towards moisture, but they can easily be converted into benchtop‐stable ammonium chloride derivatives. The ligands and their complexes have been fully characterized by NMR and IR spectroscopy, elemental analysis and/or high resolution ESI‐MS. The solid‐state structures of ten complexes have been established by single‐crystal X‐ray diffraction analysis.

Bimetallic nickel complexes supported by 2,5-bis(phosphine)-1,4-hydroquinonate ligands. Structural, electrochemical and theoretical investigations

The coordination chemistries of several 2,5-bis(phosphine)-1,4-hydroquinones, (2,5-bis(PiPr2)-3,6-difluoro-1,4-hydroquinone (1a), 2,5-bis(PiPr2)-1,4-hydroquinone (1b), (2,5-bis(PPh2)-3,6-difluoro-1,4-hydroquinone (1c), and 2,5-bis(PPh2)-1,4-hydroquinone (1d)) were investigated. Reactions of these ligands 1a–d with excess (∼2.5) of bis(cyclopentadienide)nickel, and in case of 1a, with bis(pentamethylcyclopentadienide)nickel, resulted in the formation of bimetallic nickel complexes 2a–d and 3a, where both [P,O] chelating pockets of the ligands were occupied by CpNi or Cp∗Ni moieties, respectively. Cyclic voltammetric (CV) scans on complexes 2a–d contained a common feature of two reversible/quasi-reversible waves and one irreversible redox event. Complex [2a][PF6] was isolated by the oxidation of 2a with ferrocenium hexafluorophosphate. Spectroscopic, structural, and synthetic studies were carried out in order to elucidate the nature of these redox processes. Our results suggest that the reversible and quasi-reversible redox events are ligand-based processes (hydroquinone/semiquinone/quinone), while the irreversible process was assigned as metal-based. These conclusions were supported by additional experimental data and by theoretical calculations. Investigations of chemical reactivity showed that cyclopentadienide ligands in complexes 2a–d can be displaced from the metal centers upon reactions with o-aminothiophenol. One of these derivatives, 4a, containing capping [N,S] o-aminothiophenolate ligands was isolated and fully characterized. A CV scan of complex 4a contained one reversible wave and an irreversible wave at higher potentials. The assignment is complicated by the proton transfer processes accompanying the electron transfer events. Complexes 1a, 2a–c, [2a][PF6] and 4a were characterized by single crystal X-ray diffraction experiments.

Transmetalation of Chromocene by Lithium-Amide, -Phosphide, and -Arsenide Nucleophiles

The pnictogen-centered nucleophiles LiE(SiMe3)2 (E = N, P, or As) substitute a cyclopentadienide ligand of chromocene (Cp2Cr), with elimination of lithium cyclopentadienide, to give the series of pnictogen-bridged compounds [(μ:η(2):η(5)-Cp)Cr{μ-N(SiMe3)2}2Li] (1) and [(η(5)-Cp)Cr{μ-E(SiMe3)2}]2, with E = P (2) or E = As (3). Whereas 1 is a heterobimetallic coordination polymer, 2 and 3 are homometallic dimers, with the differences being due to a structure-directing influence of the hard or soft character of the bridging group 15 atoms. For compound 1, the experimental magnetic susceptibility data were accurately reproduced by a single-ion model based on high-spin chromium(II) (S = 2), which gave a g-value of 1.93 and an axial zero-field splitting parameter of D = -1.83 cm(-1). Determinations of phosphorus- and arsenic-mediated magnetic exchange coupling constants, J, are rare: in the dimers 2 and 3, variable-temperature magnetic susceptibility measurements identified strong antiferromagnetic exchange between the chromium(II) centers, which was modeled using the spin Hamiltonian H = -2J(S(CrA)·S(CrB)), and produced large coupling constants of J = -166 cm(-1) for 2 and -77.5 cm(-1) for 3.

Group 11 complexes containing the [C5(CN)5]− ligand; ‘coordination-analogues’ of molecular organometallic systems

The reactions of Na[C(5)(CN)(5)] (Na[1]) with group 11 phosphine complexes [(P)(n)MCl] (M = Cu, Ag, Au, P = Ph(3)P; M = Cu, P = dppe (Ph(2)PCH(2)CH(2)PPh(2))] give a range of compounds containing the pentacyanocyclopentadienide ligand, [C(5)(CN)(5)](-) (1). The new complexes [(Ph(3)P)(2)M{1}](2) [M = Cu (3); M = Ag (5)], [(Ph(3)P)(3)Ag{1}] (4), [(dppe)(3)Cu(2){1}(2)] (6) and [Au(PPh(3))(2)][1] (7) include the first complete series of group 11 complexes of any cyclopentadienide ligand to be structurally characterised.

Exploring the Concept of Aromaticity on Complexes of a Fourfold Benzannulated Cyclopentadienyl Ligand

The ligand dibenzo[c,g]fluorenide (Dbf(-)), combines a cyclopentadienide ligand and 1,1'-binaphthyl fragment in one molecule. Preliminary investigations confirmed the special electronic situation in this 6pi-electron donor by way of a series of novel transition-metal complexes. Herein, the electron delocalization was investigated in detail by means of DFT calculations in combination with calculations on the nucleus-independent chemical shifts (NICS). These results clearly prove that the Dbf(-) ion gains the largest aromatic stabilization among all benzannulated fluorenides, and there are two almost olefinic C=C bonds in this structure. These bonds undergo cyclopropanation when treated with ZnEt(2) and ClCH(2)I in a modified Simmons-Smith reaction.

Continuous Shape Measures as a Stereochemical Tool in Organometallic Chemistry

The continuous shape measures of homoleptic organometallic compounds of the transition elements relative to the classical coordination polyhedra offer a tool for their accurate stereochemical description, including geometries along polyhedral interconversion pathways. The use of the centroid of π-bonded carbon atoms to define a coordination position allows us to show that polyhedral continuous shape measures may serve as excellent stereochemical descriptors for complexes with such ligands as olefins, alkynes, and allyls. Such an approach can be extended to treat π-bonded diolefins as bidentate ligands, defining their bite and establishing comparisons with classical chelating ligands such as diamines, carboxylates, and diketonates. The adequacy of considering the η5-coordinated cyclopentadienide ligand as occupying one or three coordination positions in the piano-stool [M(η5-Cp)L3] complexes is also discussed.

Coordination chemistry of neutral quinolyl- and aminophenylcyclopentadiene derivatives

The cyclopentadiene and indene derivatives 1– 4 being functionalised by a dimethylaniline and quinolyl group, respectively, were treated with metal carbonyl complexes. Whereas cyclopentadienes (C 5R 5H) normally loose one hydrogen atom prior or during metal complex formation, leading to negatively charged cyclopentadienide ligands, the compounds 1– 4 are able to act as neutral ligands without hydrogen loss. Consequently transition metal complexes with coordination of the nitrogen donor and a CC double bond of the five membered ring have been obtained. In some cases a hydrogen atom is eliminated and the expected η 5-(C 5R 5) complexes are formed. Reaction of Ru 3(CO) 12 with 2 leads to the binuclear η 6-fulvene complex 8. The octahedral molybdenum complex 9 and the square planar rhodium(I) complexes 10 and 11 which were obtained from Mo(CO) 6 and [Rh(CO) 2Cl] 2, respectively, are rare examples of η 2-(C 5R 5H) coordination to metal atoms.

Synthesis of (s-trans-η4-Butadiene)tantalocene Cation and Its CC-Coupling Reactions with Ketones, Nitriles, and Alkynes

(η4-Butadiene)(η5-cyclopentadienyl)tantalum dichloride (6), synthesized by treatment of CpTaCl4 (5) with (butadiene)magnesium (7), was treated with 2 molar equiv of sodium cyclopentadienide to yield Cp3Ta(butadiene) (9). The spectroscopic analysis revealed the (η5-Cp)2(η1-Cp)(η2-C4H6)Ta structure of 9. Treatment of 9 with 1 molar equiv of the salt [(Cp2Zr−CH3)+(CH3B(C6F5)3)-] (11) resulted in the clean transfer of a cyclopentadienide ligand from tantalum to zirconium with formation of the neutral zirconium compound Cp3Zr−CH3 (12) and the cation Cp2Ta(butadiene)+ (10; with CH3B(C6F5)3- counteranion). The spectroscopic characterization and an X-ray crystal structure analysis has revealed that 10 is a cationic (s-trans-η4-butadiene)bis(η5-cyclopentadienyl)tantalum complex. It reacts cleanly with a variety of ketones at 60 °C to form the respective 7,7-disubstituted tetrahydrotantalaoxepines 13. These cationic seven-membered metallacyclic σ-allyl complexes undergo a rapid topomerization process on the NMR tim...

Coordination Modes of 2,5-Di(tert-butyl)pyrrolide – Crystal Structures of HPyr*, Pyr*H·thf, (thf)2LiPyr*, and [(Me3Si)3C-Zn]2(μ-Cl)(μ-Pyr*) (Pyr* = 2,5-tBu2NC4H2)

The lithiation of 2,5-di(tert-butyl)pyrrole (1) yields bis(tetrahydrofuran)lithium 2,5-di(tert-butyl)pyrrolide (2), which is monomeric in solution as well as in the solid state. Due to the coordination number of three for the lithium atom, short Li–O and Li–N bond lengths of 193 pm are observed. The metathesis reaction of 2 with tris(trimethylsilyl)-methylzinc chloride (3) gives colorless bis[tris(trimethyl-silyl)methylzinc] chloride 2,5-di(tert-butyl)pyrrolide (4). The pyrrolide ligand and the chlorine atom bridge the zinc atoms. One of the zinc atoms is bonded to the nitrogen atom of the pyrrolide substituent, while the other bonds to the opposite C–C bond. At 215 pm, the Zn–N bond is very long compared to those in alkylzinc amides, whereas the Zn–C distances lie in the range of Zn–C bond lengths found between zinc and η5-bonded cyclopentadienide ligands. The molecular structures of 1 and of the low-melting THF adduct 1·thf show a similar 2,5-di(tert-butyl)pyrrole molecule, but in the latter case a weak N–H···O bond is observed (N–H 97 pm, O···H 199 pm).

Use of Tl(C 5H 5) for the synthesis of In(C 5H 5) 3−nX n: Crystal structure of [In(C 5H 5)Cl 2{O(CH 2CH 2) 2{ 2

Reaction of thallium(I) cyclopentadienide with InCl 3 and InI 3 led to the stepwise replacement of halide ions by cyclopentadienides. The complex [In(C 5H 5)Cl 2 {O(CH 2CH 2) 2} 2] was isolated and its solid-state structure was established by single-crystal X-ray diffraction. In this pentacoordinated complex, the central indium(III) ion is bonded to two tetrahydrofuran molecules in the axial position, one cyclopentadienide ligand and two chloride ions in the equatorial positions in a trigonal bipyramidal arrangement.

Synthesis and characterization of substituted cyclopentadienide ligands that may form chelates or metal dimers

Nine different substituted cyclopentadienyl ligands, which have substituents that may either chelate or bridge to second metal center, have been prepared from nucleophilic substitution reactions of esters or alkyl halides with NaCp. The sodium or thallium salts of these ligands were isolated as solids and characterized by 1H NMR. The alkyl halide and NaCp reaction proved to yield the purer salts of the ligands because of the milder reaction conditions. These salts were reacted futher with Mn(CO) 5Br to form the corresponding manganese tricarbonyl derivatives (i.e. (C 5H 4R)Mn(CO) 3; where R = C(O)CH 2OCH 3, C(O)CH 2SCH 3, C(O)CH 2CH 2SCH 3, CH 2CO 2CH 3, CH 2CO 2CH 2CH 3, CH 2CH 2CO 2CH 3, CH 2CH 2CO 2CH 2CH 3, CH 2CH 2O 2CCH 3, and CH 2CH 2OCH 3) and Na(C 5H 4C(O)CH 2OCH 3) was reacted with Co 2(CO) 8 to form (C 5H 4C(O)CH 2OCH 3)Co(CO) 2. The manganese and cobalt compounds were characterized by elemental analysis, IR, 1H, and 13C NMR spectra.

Alkenylsubstituierte calcocene

The reaction of calcium bis[bis(trimethylsilyl)amide] with 6-methyl-6-organylfulvene yields calcium bis(1-organyl-ethen-1-yl- cyclo-pentadienide) with organyl groups such as methyl ( 1), phenyl ( 2) and iso-butyl ( 3). Compound 2 crystallizes in the monoclinic space group P2/n with a = 1266.8(2), b = 1225.6(2), c = 1831.4(2) pm, β = 97.65° and Z = 4. The asymmetric unit contains two half-molecules, both the calcium atoms are coordinated distorted tetrahedrally by two cyclo-pentadienide ligands and two THF molecules. The metathesis reaction of the calcocene 1 with iron(II) chloride leads to the corresponding ferrocene derivative 4 in good yield.

ChemInform Abstract: Syntheses and Structures of Rhodium-Osmium Clusters Derived from the Reaction of (μ-H)2Os3(CO)10 with (η5-C5H5)Rh(CO)2.

Abstract The reaction between (μ-H) 2 Os 3 (CO) 10 and (η 5 -C 5 H 5 )Rh(CO) 2 in toluene at 90°C produces (η 5 -C 5 H 5 )RhOs 2 (CO) 9 (I) and (μ-H) 2 (η 5 -C 5 H 5 )RhOs 3 (CO) 10 (II), as the principal products while the pentanuclear cluster (μ-H) 2 (η 5 -C 5 H 5 )RhOs 4 (CO) 13 (III) is obtained in low yield. When added hydrogen is present during the reaction, replacement of the cyclopentadienide ligand by toluene occurs and the principal product is (μ-H) 3 (η 6 -C 6 H 5 CH 3 )RhOs 3 (CO) 9 (VI). Also produced in this reaction are (μ-H) 2 (η 5 -C 5 H 5 ) 2 Rh 2 Os 2 (CO) 7 (IV) and cluster II, but in low yields. In benzene in the presence of H 2 , an analogous reaction occurs. The cyclopentadienide ligand is replaced by benzene to give (μ-H) 3 (η 6 -C 6 H 6 )RhOs 3 (CO) 9 (VII) as the main product and clusters II and (μ-H) 4 (η 5 -C 5 H 5 )RhOs 3 (CO) 9 (V) are formed in small yields. Conversion of clusters I and II to clusters IV and V, respectively, was achieved by bubbling H 2 through toluene solutions of I and II at 90°C. Cluster V is moderately unstable in solution, with significant decomposition occurring during the reaction. The molecular structures of clusters II, III, IV, and VII have been determined by single crystal X-ray diffraction studies. Clusters II, IV, and VII have tetrahedral metal cores, while the pentanuclear cluster III has an Os tetrahedral core which is edge bridged by a Rh atom. For compound II: space group P 2 1 / n , a 8.120(3), b 14.932(3), c 16.277(3) A, β 91.29(4)°, V 1972.9 A 3 , Z = 4, mol wt = 1020.73, ρ calcd 3.434 gm cm −3 , and μ calcd 201.5 cm −1 for Mo- K α ; 3885 independent reflections ⩾ 3σ( I ); 4 ⩽ 2θ ⩽ 55° obtained at −35°C; final R f 5.7%, R wf 7.4%. For compound III: space group P 2 1 / c , a 11.134(2), b 16.649(2), c 14.015(2) A, β 109.98(1)°, V 2441.6 A 3 , Z = 4, mol wt = 1294.95, ρ calcd = 2.773 gm cm −3 , and μ calcd 162.6 cm −1 for Mo- K α ; 5695 independent reflections ⩾ 3σ( I ); 4 ⩽ 2θ ⩽ 50° at −30°C; final R f 2.95%, R wf 4.0%. For compound IV: space group P 2 1 / c , a 8.186(3), b 15.651(5), c 15.723(2) A, β 97.32°, V 1998.25 A 3 , Z = 4, mol wt = 914.49, ρ calcd 3.038 gm cm −3 , and μ calcd 143.34 cm −1 for Mo- K α ; 3619 independent reflections ⩾ 3σ( I ); 4 ⩽ 2θ ⩽ 55° at 25°C; final R f 3.3%, R wf 4.5%. For compound VII: space group R , a = b = c = 10.003(4) A, α = β = γ = 92.16(3)°, V = 998.3 A 3 , Z = 2, mol wt = 1006.5, ρ calcd 3.34 gm cm −3 , and μ calcd 214.8 cm −1 Mo- K α ; 3017 independent reflections ⩾ 3σ( I ); 4 ⩽ 2θ ⩽ 50° at 25°C; Final R f 4.4%, R wf 6.3%.

Syntheses and structures of rhodium-osmium clusters derived from the reaction of (μ-H) 2Os 3(CO) 10 with (η 5-C 5H 5)Rh(CO) 2

The reaction between (μ-H) 2Os 3(CO) 10 and (η 5-C 5H 5)Rh(CO) 2 in toluene at 90°C produces (η 5-C 5H 5)RhOs 2(CO) 9 (I) and (μ-H) 2(η 5-C 5H 5)RhOs 3(CO) 10 (II), as the principal products while the pentanuclear cluster (μ-H) 2(η 5-C 5H 5)RhOs 4(CO) 13 (III) is obtained in low yield. When added hydrogen is present during the reaction, replacement of the cyclopentadienide ligand by toluene occurs and the principal product is (μ-H) 3(η 6-C 6H 5CH 3)RhOs 3(CO) 9 (VI). Also produced in this reaction are (μ-H) 2(η 5-C 5H 5) 2Rh 2Os 2(CO) 7 (IV) and cluster II, but in low yields. In benzene in the presence of H 2, an analogous reaction occurs. The cyclopentadienide ligand is replaced by benzene to give (μ-H) 3(η 6-C 6H 6)RhOs 3(CO) 9 (VII) as the main product and clusters II and (μ-H) 4(η 5-C 5H 5)RhOs 3(CO) 9 (V) are formed in small yields. Conversion of clusters I and II to clusters IV and V, respectively, was achieved by bubbling H 2 through toluene solutions of I and II at 90°C. Cluster V is moderately unstable in solution, with significant decomposition occurring during the reaction. The molecular structures of clusters II, III, IV, and VII have been determined by single crystal X-ray diffraction studies. Clusters II, IV, and VII have tetrahedral metal cores, while the pentanuclear cluster III has an Os tetrahedral core which is edge bridged by a Rh atom. For compound II: space group P2 1/ n, a 8.120(3), b 14.932(3), c 16.277(3) Å, β 91.29(4)°, V 1972.9 Å 3, Z = 4, mol wt = 1020.73, ρ calcd 3.434 gm cm −3, and μ calcd 201.5 cm −1 for Mo- K α; 3885 independent reflections ⩾ 3σ( I); 4 ⩽ 2θ ⩽ 55° obtained at −35°C; final R f 5.7%, R wf 7.4%. For compound III: space group P2 1/ c, a 11.134(2), b 16.649(2), c 14.015(2) Å, β 109.98(1)°, V 2441.6 Å 3, Z = 4, mol wt = 1294.95, ρ calcd = 2.773 gm cm −3, and μ calcd 162.6 cm −1 for Mo- K α; 5695 independent reflections ⩾ 3σ( I); 4 ⩽ 2θ ⩽ 50° at −30°C; final R f 2.95%, R wf 4.0%. For compound IV: space group P2 1/ c, a 8.186(3), b 15.651(5), c 15.723(2) Å, β 97.32°, V 1998.25 Å 3, Z = 4, mol wt = 914.49, ρ calcd 3.038 gm cm −3, and μ calcd 143.34 cm −1 for Mo- K α; 3619 independent reflections ⩾ 3σ( I); 4 ⩽ 2θ ⩽ 55° at 25°C; final R f 3.3%, R wf 4.5%. For compound VII: space group R ▪, a = b = c = 10.003(4) Å, α = β = γ = 92.16(3)°, V = 998.3 Å 3, Z = 2, mol wt = 1006.5, ρ calcd 3.34 gm cm −3, and μ calcd 214.8 cm −1 Mo- K α; 3017 independent reflections ⩾ 3σ( I); 4 ⩽ 2θ ⩽ 50° at 25°C; Final R f 4.4%, R wf 6.3%.

Photoexchange of η 5-cyclopentadienide ligands in selected systems

Cyclopentadienide ligands are exchanged between molecules of di-η 5 cyclopentadienyltitanium monochloride in benzene, and between bis(methyl-η 5-cyclopentadienyl)vanadium dichloride and di-η 5-cyclopentadienylvanadium dichloride in benzene by a photochemical process. A small amount of dimer is produced upon photolysis of benzene solutions containing both 1,1′-trimethylene titanocene dichloride and titanocene dichloride.