Synthesis, characterization and functionalization of titanium κ amidinato complexes from carbodiimides.

A series of titanium amidinato complexes were synthesized by stoichiometric insertion reactions of carbodiimides into bis(π-η:σ-η-pentafulvene)titanium complexes. NMR studies and single-crystal X-ray diffraction showed κ coordination of the former carbodiimides to the metal center. DFT calculations were performed, confirming the clear preference for a single nitrogen atom coordinating to the metal center with a high energy transition state for the formation of a chelating heteroallyl ligand.

From Coordination to Noncoordination: Syntheses and Substitution Lability Studies of Titanium Triflato Complexes.

A new concept for obtaining cationic complexes with triflate counteranions from coordinating triflato ligands was developed. Various routes are leading to titanium(IV) and titanium(III) triflato complexes efficiently. The reactions of pentafulvene titanium complexes with either triflic acid or silver triflate give the corresponding titanium(IV) triflato complexes in excellent yields.

Syntheses, Characterization, and Redox Activity of Ferrocene-Containing Titanium Complexes.

The chemistry of bis(π-η:σ-η-pentafulvene)titanium complexes is characterized by a broad range of E-H activation and Ti-C functionalization reactions, whereas ferrocene derivatives are easily accessible and redox-active compounds. The reaction of ferrocenealdehyde and -ketones with bis(π-η:σ-η-pentafulvene)titanium complexes result in the formation of bimetallic complexes via insertion of the C=O double bond of the aldehyde/ketone into the Ti-C bond of the pentafulvene moiety. The reaction of bis(π-η:σ-η-pentafulvene)titanium complexes with ferrocenyl alcohols leads to alcoholate complexes via deprotonation of the OH group by the pentafulvene ligand.

Syntheses, Characterization, and Multifaceted Coordination Chemistry of Hydrazonido Titanium Complexes.

The reaction of hydrazones with bis(π-η:σ-η-pentafulvene)titanium complexes leads to both hydrazonido and hydrazido complexes depending on the interaction of the hydrazone with the fulvene ligand of the metal complex. The molecular structures mostly reveal κ, side-on coordination of the hydrazonido ligand due to the deprotonation of the N-H bond by one of the fulvene moieties. Instead of deprotonation, the reaction of the bis(adamantylidene fulvene)titanium complexes with cinnamon aldehyde phenylhydrazone leads to κ coordination.

Titanium-Catalyzed Polymerization of a Lewis Base-Stabilized Phosphinoborane.

The reaction of the Lewis base-stabilized phosphinoborane monomer tBuHPBH NMe (2 a) with catalytic amounts of bis(η :η -adamantylidenepentafulvene)titanium (1) provides a convenient new route to the polyphosphinoborane [tBuPH-BH ] (3 a). This method offers access to high molar mass materials under mild conditions and with short reaction times (20 °C, 1 h in toluene). It represents an unprecedented example of a transition metal-mediated polymerization of a Lewis base-stabilized Group 13/15 compound.

Density Functional Theory Calculations for Multiple Conformers Explaining the Regio- and Stereoselectivity of Ti-Catalyzed Hydroaminoalkylation Reactions.

Hybrid Density Functional Theory (DFT) calculations for multiple conformers of the insertion reactions of a methylenecyclopropane into the Ti-C bond of two differently α-substituted titanaaziridines explain the experimentally observed differences in regioselectivity between catalytic hydroaminoalkylation reactions of methylenecyclopropanes with α-phenyl-substituted secondary amines and corresponding stoichiometric reactions of a methylenecyclopropane with titanaaziridines, which can only be achieved with α-unsubstituted titanaaziridines. In addition, the lack of reactivity of α-phenyl-substituted titanaaziridines as well as the diastereoselectivity of the catalytic and stoichiometric reactions can be understood.

Elemental Magnesium as an Early Transition Metal Substitute: From Pentafulvene Coordination to Deprotonation of Amines.

The reaction of magnesium turnings and 6,6-di-para-tolylpentafulvene was investigated. Under mild conditions, the magnesium dissolves, forming the Mg complex 1 with a π-η  : σ-κ coordinating ligand of the dimerized pentafulvene, analyzed by NMR and XRD investigations. As a magnesium pentafulvene complex was a possible intermediate, amines were employed as intercepting agents.

Vanadium Pentafulvene Complexes: Synthon for Unprecedented Vanadocene Derivatives.

The benzene ligand at CpV(η -C H ) (1) is exchanged for pentafulvenes. Using sterically demanding pentafulvenes gives a clean exchange reaction, yielding vanadium pentafulvene (2 a and 2 b) and benzofulvene complexes (3 a and 3 b). The molecular structures of the target compounds suggest a π-η :σ-η coordination mode with a vanadium center.

(Carbazol-9-ido-κ)di-chlorido-(η:η-2,3,4,5-tetra-methyl-penta-fulvene)tantalum(V).

The reaction of (η:η-2,3,4,5-tetra-methyl-penta-fulvene)tantalum(V) dicarbazolide chloride () with etheric HCl results in the formation of the title compound (), [Ta(CH)(CHN)Cl]. The Ta atom has a distorted tetra-hedral coordination environment in a three-legged piano-stool fashion. The conformation of the penta-fulvene exocyclic C atom to the three other ligands is staggered and not eclipsed, as found in the crystal structure of .

Crystal structures of the Lewis acid-base adducts {[(CH)N]Ti-}[MeB(CF)]·1.5CH; LB = (CH)PO (1), -F-CHCN (2).

The reaction of [(CH)N]Ti-CH with the Lewis acid B(CF), followed by addition of the Lewis bases (CH)PO and -F-CHCN led to the complex salts tris-(di-cyclo-hexyl-amido)(tri-phenyl-phosphine oxide)titanium methyl-tris(penta-fluoro-phen-yl)borate toluene sesquisolvate, [Ti(CHN)(CHOP)](CHFB)·1.5CH, (), and tris-(di-cyclo-hexyl-amido)(4-fluoro-benzo-nitrile)-titanium methyl-tris-(penta-fluoro-phen-yl)borate toluene sesquisolvate, [Ti(CHN)(CHFN)](CHFB)·1.5CH, (), both crystallizing with 1.

A niobium pentafulvene ethylene complex: synthesis, properties and reaction pathways.

The π-η:σ-η coordination mode of early transition metal pentafulvene ligands yields a strongly nucleophilic exocyclic carbon atom (C). The substitution of the chlorido ligand of bis(η:η-(di--tolyl)pentafulvene)niobium chloride (1) by reaction with ethyl magnesium bromide is subsequently followed by a β-C-H activation employing this C, forming the pentafulvene niobium ethylene complex 2. The intermediately formed ethyl complex can be intercepted with water, protonating both pentafulvene moieties and thereby retaining the ethyl moiety to give the terminal oxo complex 3.

Reaction of a bis(pentafulvene)titanium complex with an N-heterocyclic olefin: C-H-activation leads to resonance between a titanium vinyl and titanium alkylidene complex.

The N-heterocyclic olefin (NHO) ImMeCH (2) (ImMeCH = (MeCNMe)CCH) was employed for the synthesis of the titanium complex 3 derived from an NHO ligand precursor. By reacting 2 with the bis(π-η:σ-η-pentafulvene)titanium complex 1a, the terminal ylidic methylene unit of 2 is deprotonated by the quaternary exocyclic carbon atom of one pentafulvene ligand of 1a yielding the titanium complex 3 which bears an anionic NHO ligand (ImMeCH). 3 was characterized by NMR spectroscopy, single crystal X-ray diffraction and quantum chemical calculations.

Selective propargylic C(sp)-H activation of methyl-substituted alkynes [2 + 2] cycloaddition at a titanium imido template.

The reaction of the titanium imido complex with 2-butyne leads to the formation of the titanium azadiene complex at ambient temperature instead of yielding the archetypical [2 + 2] cycloaddition product (titanaazacyclobutene) which is usually obtained by combining titanium imido complexes and internal alkynes. The formation of is presumably caused by an initial propargylic C(sp)-H activation step and quantum chemical calculations suggest that the outcome of this unexpected reactivity is thermodynamically favored. The previously reported titanaazacyclobutene (which is obtained by reacting with 1-phenyl-1-propyne) undergoes a rearrangement reaction at elevated temperature to give the corresponding five-membered titanium azadiene complex .

Intermolecular Hydroaminoalkylation of Alkynes.

Intermolecular hydroaminoalkylation reactions of alkynes with secondary amines, which selectively give access to allylic amines with E configuration of the alkene unit, are achieved in the presence of titanium catalysts. Successful reactions of symmetrically substituted diaryl- and dialkylalkynes as well as a terminal alkyne take place with N-benzylanilines, N-alkylanilines, and N-alkylbenzylamines.

Electronic Transitions in Different Redox States of Trinuclear 5,6,11,12,17,18-Hexaazatrinaphthylene-Bridged Titanium Complexes: Spectroelectrochemistry and Quantum Chemistry.

Multinuclear transition metal complexes bridged by ligands with extended π-electronic systems show a variety of complex electronic transitions and electron transfer reactions. While a systematic understanding of the photochemistry and electrochemistry has been attained for binuclear complexes, much less is known about trinuclear complexes such as hexaphenyl-5,6,11,12,17,18-hexaazatrinaphthylene-tristitanocene [(Cp Ti) HATN(Ph) ]. The voltammogram of [(Cp Ti) HATN(Ph) ] shows six oxidation and three reduction waves.

Tetra-kis(di-cyclo-hexyl-amido)-zirconium(IV).

The reaction of ZrCl with three equivalents of LiNCy (Cy is cyclo-hex-yl) resulted in the formation of tris-(di-cyclo-hexyl-amido)-zirconium chloride and the title compound, [Zr(CHN)]. The latter is isotypic with its cerium(IV) analogue and crystallizes with three independent mol-ecules in the asymmetric unit. One mol-ecule is located about a twofold rotation axis, and the other two on fourfold inversion axes.

Intermolecular Hydroaminoalkylation of Propadiene.

Intermolecular hydroaminoalkylation reactions of propadiene with selected secondary amines take place in the presence of a 2,6-bis(phenylamino)pyridinato titanium catalyst. The corresponding products, synthetically useful allylamines, are formed in convincing yields and with high selectivities. In addition, propadiene easily inserts into the titanium-carbon bond of a titanaaziridine.

Spin Transition of an Iron(II) Organoborate Complex in Different Polymorphs and in Vacuum-Deposited Thin Films: Influence of Cooperativity.

Two polymorphic modifications ( and ) of the new spin crossover (SCO) complex [Fe{HB(pz)(pypz)}] (pz = pyrazole, pypz = pyridylpyrazole; ) were prepared and investigated by differential scanning calorimetry (DSC), magnetic measurements, Mößbauer, vibrational, and absorption spectroscopy as well as single-crystal and X-ray powder diffraction. DSC measurements reveal that upon heating the thermodynamically metastable form to ∼178 °C it transforms into in an exothermic reaction, which proves that these modifications are related by monotropism. Both forms show thermal SCO with values of 390 K () and 270 K ().

Synthesis of a titanium ethylene complex via C-H-activation and alternative access to CpTi(η-MeSiCSiMe).

The synthesis of the novel room temperature stable titanacyclopropane derivative Cp*Ti(η-CH)(η-CHAdH) (2) in a one-step-two-transformation protocol and first insights into its reactivity are presented, including the synthesis of the corresponding bis(trimethylsilyl)acetylene complex Cp*Ti(η-MeSiCSiMe)(η-CHAdH) (4). Given these results, a novel one-pot procedure toward CpTi(η-MeSiCSiMe) was subsequently developed.

Titanium-Catalyzed Hydroaminoalkylation of Ethylene.

The first examples of titanium-catalyzed hydroaminoalkylation reactions of ethylene with secondary amines are presented. The reactions can be achieved with various titanium catalysts and they do not require the use of high pressure equipment. In addition, the first solid-state structure of a titanapyrrolidine that is formed by insertion of an alkene into the Ti-C bond of a titanaaziridine is reported.

Unexpected Selective Methyl Group Abstractions from SiMe Moieties of CH SiMe Ligands To Give New Cationic Titanium Complexes.

The synthesis of the alkylated pentafulvene titanium complex Cp*Ti(CH SiMe )(π-η :σ-η -C H =CR ) (CR =adamantylidene) is described. The coordination mode of the pentafulvene ligand in this complex allowed for the subsequent synthesis of a series of nitrile-insertion products. By reacting these neutral compounds with the strong Lewis acid B(C F ) , unprecedented selective methyl-group abstractions from the SiMe moieties under formation of novel cationic titanium complexes with the corresponding MeB(C F ) anion are demonstrated.

FLP behaviour of cationic titanium complexes with tridentate Cp,O,N-ligands: highly efficient syntheses and activation reactions of C-X bonds (X = Cl, F).

The synthesis of cationic titanium complexes 4a,b with tridentate Cp,O,N-ligand frameworks, starting from the monopentafulvene complex Cp*Ti(Cl)(π-η5:σ-η1-C5H4CR2 (CR2 = adamantylidene) (1) and bidentate O,N-ligand precursors CH3C(O)CH2CH2NR2 (R = Et, CH2Ph) (L1a,b), in a high-yielding and efficient two-step synthetic pathway is described. The β-aminoketones L1a,b were synthesized by a herein reported solvent- and catalyst-free reaction. The reaction pathway involves insertion reactions, subsequent methylations and final activations with B(C6F5)3.

Teaching c-phosphanylimines the titanaaziridine coordination mode.

The c-phosphanylimine L1 was employed for the synthesis of the novel titanaaziridine 1 with an intramolecular phosphine donor side following a reductive complexation route. This coordination mode is new for c-phosphanylimines and compound 1 is the first group 4 complex featuring a c-phosphanylimine ligand.

Synthesis, Crystal Structures, and Magnetic and Electrochemical Properties of Highly Phenyl Substituted Trinuclear 5,6,11,12,17,18-Hexaazatrinaphthylene (HATNPh)-Bridged Titanium Complexes.

Trinuclear titanium complexes coordinated by one ligand with three coordination sites have shown properties of mixed valency and a high number of reversible redox steps. Herein we report on the hexaphenyl-substituted derivative (CpTi)(μ-HATNPh) (2). On reaction of 2 with the ferrocenium salt [CpFe]BF, the cationic complexes [(CpTi)(μ-HATNPh)] ( n = 1-3; 3-5) become available in a selective way.

Bis(η :η -pentafulvene)niobium(V) Complexes: Efficient Synthons for Niobium Carbene and Imido Derivatives.

Transition-metal carbene complexes and their reactivities are a key topic of chemistry. They are an integral part of researches in catalysis, organic synthesis, coordination chemistry, and numerous other areas. In this context, we report the synthesis of a low-valent bis(η :η -(di-p-tolyl)-pentafulvene)niobium chloride.