A lithium-aluminium heterobimetallic dimetallocene.

Homobimetallic dimetallocenes exhibiting two identical metal atoms sandwiched between two η5 bonded cyclopentadienyl rings is a narrow class of compounds, with representative examples being dizincocene and diberyllocene. Here we report the synthesis and structural characterization of a heterobimetallic dimetallocene, accessible through heterocoupling of lithium and aluminylene fragments with pentaisopropylcyclopentadienyl ligands. The Al-Li bond features a high ionic character and profits from attractive dispersion interactions between the isopropyl groups of the cyclopentadienyl ligands. A key synthetic step is the isolation of a cyclopentadienylaluminylene monomer, which also enables the structural characterization of this species. In addition to their structural authentication by single-crystal X-ray diffraction analysis, both compounds were characterized by multinuclear NMR spectroscopy in solution and in the solid state. Furthermore, reactivity studies of the lithium-aluminium heterobimetallic dimetallocene with an N-heterocyclic carbene and different heteroallenes were performed and show that the Al-Li bond is easily cleaved.

Bis(tetrelocenes) - fusing tetrelocenes into close proximity.

We report the synthesis and structure of two bis(germanocenes) and a bis(stannocene), obtained by the reaction of unsymmetric ansa bis(cyclopentadienyl) ligands with germanium and tin dichloride. DFT calculations show that the formation of these bis(tetrelocenes) is energetically favoured over the formation of the corresponding [1]tetrelocenophanes. In the crystal structure authenticated structural motif, the two tetrel(II) centers are forced into close proximity to each other, resulting in weak donor-acceptor interactions, according to Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses.

Revisiting the origin of the bending in group 2 metallocenes AeCp2 (Ae = Be-Ba).

Metallocenes are well-established compounds in organometallic chemistry, and can exhibit either a coplanar structure or a bent structure according to the nature of the metal center (E) and the cyclopentadienyl ligands (Cp). Herein, we re-examine the chemical bonding to underline the origins of the geometry and stability observed experimentally. To this end, we have analysed a series of group 2 metallocenes [Ae(C5R5)2] (Ae = Be-Ba and R = H, Me, F, Cl, Br, and I) with a combination of computational methods, namely energy decomposition analysis (EDA), polarizability model (PM), and dispersion interaction densities (DIDs). Although the metal-ligand bonding nature is mainly an electrostatic interaction (65-78%), the covalent character is not negligible (33-22%). Notably, the heavier the metal center, the stronger the d-orbital interaction with a 50% contribution to the total covalent interaction. The dispersion interaction between the Cp ligands counts only for 1% of the interaction. Despite that orbital contributions become stronger for heavier metals, they never represent the energy main term. Instead, given the electrostatic nature of the metallocene bonds, we propose a model based on polarizability, which faithfully predicts the bending angle. Although dispersion interactions have a fair contribution to strengthen the bending angle, the polarizability plays a major role.

Polycobaltoceniumylmethylene - A Water-Soluble Polyelectrolyte Prepared by Ring-Opening Transmetalation Polymerization.

The synthesis of a water-soluble polycobaltoceniumylmethylene chloride (PCM-Cl) via ring-opening transmetalation polymerization is presented. Starting from a carba[1]magnesocenophane and cobalt(II) chloride, this route gives access to a polymer with methylene-bridged cobaltocenium moieties within the polymers' main-chain. The polymer was characterized by NMR spectroscopy, elemental analysis, TGA, DSC, XRD, and CV measurements, as well as UV-vis spectroscopy. Furthermore, GPC measurements in an aqueous eluent versus pullulan standards were conducted to gain insight into the obtained molar masses and distributions. In addition, the ion-dependent solubility was demonstrated by anion exchange, tuning the hydrophobic/hydrophilic properties of this redox-responsive material.

Phosphanyl-substituted tin half-sandwich complexes.

Phosphanyl-substituted tin(ii) half sandwich complexes are reported. Due to the Lewis acidic tin center and Lewis basic phosphorous atom they form head-to-tail dimers. Their properties and reactivities were investigated both experimentally and theoretically. Furthermore, related transition metal complexes of these species are presented.

Heavier N-heterocyclic half-sandwich tetrylenes.

ansa-Half-sandwich complexes of the group 14 elements germanium, tin and lead are reported, which represent a new class of Lewis amphiphilic tetrylenes and bridge the gap between classical N-heterocyclic systems and group 14 metallocenes. These compounds can form complexes both with carbenes and transition metal fragments.

Crystal structure of 1,1',2,2',4,4'-hexa-iso-propyl-magnesocene.

The title compound, 3Cp2Mg or [Mg(C14H23)2], was synthesized from the cor-res-ponding triiso-propyl-cyclo-penta-diene by treatment with n-butyl-sec-butyl-magnesium. The structural characterization by single-crystal X-ray diffraction revealed that the compound crystallizes in the triclinic space group P with half a mol-ecule per asymmetric unit and a staggered arrangement of the cyclo-penta-dienide ligands.

Bis(di-tert-butylindenyl)tetrelocenes.

The synthesis and characterization of bis(di-tert-butylindenyl) germanium(II), tin(II) and lead(II) complexes are reported, which includes the first structurally authenticated example of a bis(indenyl)germanocene. The species were studied in detail in solution and in the solid, which includes single crystal X-ray diffraction and NMR spectroscopy, as well as Mössbauer spectroscopy of the tin compound.

Diarylpnictogenyldialkylalanes─Synthesis, Structures, Bonding Analysis, and CO2 Capture.

Several new diphenylamino- and diphenylphosphanyldialkylalanes are reported, which were characterized in solution and in the solid state, assisted by in-depth bonding analysis within the DFT framework. In the case of bulky alkyl substituents on the aluminum atom, the species are stable in their monomeric form and were structurally characterized by single crystal X-ray diffraction, expanding the relatively small field of monomeric pnictogenylalanes. In the case of oligomeric diphenylpnictogenyldimethylalanes, their reactivity toward different σ-donor ligands was studied, and several examples of monomeric adducts could be structurally characterized, including the first cyclic(alkyl)(amino)carbene complexes. The reactivity of these CAAC complexes, their oligomeric precursors, and an unstabilized monomeric aminoalane toward CO2 was probed, leading to different insertion products that could be characterized. Additionally, the mechanism was elucidated by DFT calculations.

Rings and Chains: Synthesis and Characterization of Polyferrocenylmethylene.

The synthesis and characterization of polyferrocenylmethylene (PFM) starting from dilithium 2,2-bis(cyclopentadienide)propane and a Me2 C[1]magnesocenophane is reported. Molecular weights of up to Mw  = 11 700 g mol-1 featuring a dispersity, Ð, of 1.40 can be achieved. The material is studied by different methods comprising nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption/ionization time of flight (MALDI-ToF) mass spectrometry, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) measurements elucidating the molecular structure and thermal properties of these novel polymers. Moreover, cyclic voltammetry (CV) reveals quasi-reversible oxidation and reduction behavior and communication between the iron centers. Also, the crystal structure of a related cyclic hexamer is presented.

Diphosphanylmetallocenes of Main-Group Elements.

Several 1,1'-diphosphanyl-substituted metallocenes of magnesium (magnesocenes) were synthesized, structurally characterized, and their reactivity and coordination chemistry were investigated. Transmetalation of these magnesocenes gives access to group 14 metallocenes (tetrelocenes), as well as to group 15 stibonocenes. These s- and p-block metallocenes represent a novel class of bis(phosphanyl) ligands, exhibiting Lewis-amphiphilic character. Their coordination chemistry towards different transition-metal and main-group fragments was investigated and different complexes are presented.

Main-Group Metallocenophanes.

Metallocenes with interlinked cyclopentadienide ligands are commonly referred to as ansa-metallocenes or metallocenophanes. These can have drastically different properties than their unbridged parent compounds. While this concept is best known for transition metals such as iron, it can also be adopted for many main-group elements. This review aims to summarize recent advances in the field of metallocenophanes based on main-group elements of group 2, group 13, group 14 and group 15, focusing on synthesis, structure and properties of these compounds.

Donor-Stabilized Monocarba-Bridged Bis(cyclopentadienyl)alanes.

Five monocarba-bridged bis(cyclopentadienyl)aluminum halide NHC and thione complexes and one monocarba-bridged bis(cyclopentadienyl)phosphanylalane NHC complex are reported. The former were synthesized by transmetalation of a C[1]magnesocenophane with the corresponding aluminum(III) chloride and aluminum(III) bromide donor adducts. The phosphanylalane complex was obtained by a subsequent functionalization of the corresponding bromoalane with lithium diphenylphosphide. All complexes were characterized in solution by multinuclear NMR spectroscopy and in the solid state by single crystal X-ray diffraction. Bonding energies of the NHC and thione ligands to the aluminum centres were estimated by DFT calculations.

Magnesocenophane-Catalyzed Amine Borane Dehydrocoupling.

The Lewis acidities of a series of [n]magnesocenophanes (1 a-d) have been investigated computationally and found to be a function of the tilt of the cyclopentadienyl moieties. Their catalytic abilities in amine borane dehydrogenation/dehydrocoupling reactions have been probed, and C[1]magnesocenophane (1 a) has been shown to effectively catalyze the dehydrogenation/dehydrocoupling of dimethylamine borane (2 a) and diisopropylamine borane (2 b) under ambient conditions. Furthermore, the mechanism of the reaction with 2 a has been investigated experimentally and computationally, and the results imply a ligand-assisted mechanism involving stepwise proton and hydride transfer, with dimethylaminoborane as the key intermediate.

Synthesis, Structure, and Reactivity of Disiloxa[3]tetrelocenophanes.

Tetramethyldisiloxa[3]metallocenophanes of the heavy group 14 elements germanium, 2a, tin, 2b, and lead, 2c, (tetrelocenophanes) have been synthesized by the reaction of dilithiated ligand, 1, with the corresponding element(II) chloride. The plumbocenophane, 2c, forms one-dimensional coordination polymers in the solid state, while the germanocenophane, 2a, and the stannocenophane, 2b, are monomeric. Furthermore, the reactivity of the stannocenophane, 2b, and the plumbocenophane, 2c, toward N-heterocyclic carbenes was explored. Although the coordination of carbene is reversible in solution at room temperature, the corresponding carbene complexes, 3a,b, could be structurally characterized, illustrating the Lewis acidity of the central atom in these metallocenophanes.

A bis(aluminocenophane) with a short aluminum-aluminum single bond.

A bis(dicarba[2]aluminocenophane) was synthesized by reduction of a corresponding dichloro precursor with 1,3-ß-diketiminate magnesium(i). The bis(aluminocenophane) is stable under an inert gas atmosphere and was characterized in solution and in the solid state. The crystal structure reveals an unusually short Al-Al single bond and two η5 coordinated cyclopentadienyl groups on each aluminum atom which are disposed in an orthogonal fashion. The aluminum bond can be oxidized and cleaved by element chlorides and tert-butyl isonitrile. The bonding situation was studied within the DFT framework.

Permethylated Disila[2]metallocenophanes of Group 14 and 15 Elements.

Permethylated disila[2]metallocenophanes of silicon, germanium, tin, lead, 2 a-d, (tetrelocenophanes) and antimony, 3 a,b, (pnictogenocenophanes) are described. In the case of antimony, a chloro-substituted stibonocenophane, 3 a, as well as cationic stibonocenophanium tetrachloroaluminate and tetraphenylborate salts, 3 b[X] (X=[AlCl4 ], [BPh4 ]), were synthesized. These represent the first examples of metallocenophanes of any Group 15 element. All compounds were studied in solution and in the solid state. Without exception the ansa-bridge exerts a strong influence on the bending angle of the two Cp-ligands. For disila[2]plumbocenophane, 2 d, its reactivity towards Group 15 halides was probed. Treatment of disila[2]plumbocenophane, 2 d, with two equivalents of phosphorus(III) chloride or arsenic(III) chloride, results in a ring-opening reaction and gives the bis(dihalopnictogenyl)-substituted products, 4 a,b.

Lewis base complexes of sila[2]aluminocenophanes.

Several new sila[2]aluminocenophane Lewis base complexes are described, which were synthesized directly from the corresponding sila[2]magnesocenophane and AlX3·base precursors. The compounds are stable at room temperature for weeks, and were characterized in solution by multinuclear NMR spectroscopy and in the solid state by single crystal X-ray diffraction. In all cases, a dynamic structure was observed in solution, due to rapid sigmatropic rearrangements. Bonding energies of the Lewis base ligands to the aluminium center were calculated to be 162.9-213.3 kJ mol-1.

Carbene Complexes of Stannocenes.

Several stannocene carbene complexes, 3a-3g, were synthesized and examined in solution by NMR spectroscopy and in the solid state by single-crystal X-ray diffraction. In this new class of metallocene carbene complexes, coordination of the carbene to the tin atom was found to be comparably weak and mostly due to attractive dispersion forces, as indicated by density functional theory calculations. Furthermore, coordination of the N-heterocyclic carbenes results in a weakening of the Sn-Cp bonds, making these complexes very reactive and short-lived at room temperature.