Zur Kenntnis des Aluminiumchlorids. Die Umsetzung von AlCl3 mit PCl5 und Methylamin

Aluminium trichloride forms the adducts AlCl₃ · NH₂CH₃, AlCl₃ · 2NH₂CH₃, AlCl₃ · 4NH₂CH₃; AlCl₃ · NH₃CH₃Cl, AlCl₃ · 2NH₃CH₃Cl. The interaction between AlCl₃, PCl₅ and NH₃CH₃Cl in the molar ratio 1:3:2 proceeds according to the reaction equation in “Inhaltsübersicht”. On applying other stoichiometric amounts, [Cl₂(NHCH₃)P? N(CH₃)? AlCl₃] · HCl and [Cl₃P? N(CH₃)? AlCl₃] · HCl are obtained; the latter reacts as [Cl₃P? NHCH₃][AlCl₄]. At the molar ratio AlCl₃:PCl₅:NH₃CH₃Cl = 1:2:4 a compound is formed being presumably the six-membered heterocycle formulated in “Inhaltsübersicht”. With [Cl₃P?N? PCl₃] and aluminium chloride [Cl₃P?N? PCl₃][AlCl₄] is formed.     

Katalysatordesaktivierungen bei der Acetylen-Polymerisation mit Titanocen- bzw. Zirconocen-Komplexen des Bis(trimethylsilyl)acetylens

Desactivation of Catalysts in the Polymerization of Acetylene by Bis(trimethylsilyl)acetylene Complexes of Titanocene or Zirconocene Unexpected inactive byproducts were observed in the catalytic polymerization of acetylene using metallocene alkyne complexes Cp₂M(L)(η²-Me₃SiC₂SiMe₃), 1 : M = Ti, without L; 2 : M = Zr, L = thf. The reaction of 1 was investigated in detail by NMR to give quantitatively at –20 °C the titanacyclopentadiene Cp₂Ti–CH=CH–C(SiMe₃)=C(SiMe₃) ( 3 ). Around 0 °C 3 starts to rearrange to yield the dihydroindenyl complex 4 via coupling of one Cp-ligand with the titanacyclopentadiene. In the reaction of 2 under analogous conditions a zirconacyclopentadiene Cp₂Zr–CH=CH–C(SiMe₃)=C(SiMe₃) ( 5 ) and the dimeric complex [Cp₂Zr(C(SiMe₃)=CH(SiMe₃)]₂[μ-σ(1,2)-C≡C] ( 6 ) were observed. Whereas 5 decomposes to a mixture of unidentified paramagnetic species, 6 was isolated and investigated by NMR spectroscopy and X-ray analysis. In the reaction of rac-(ebthi)Zr(η²-Me₃SiC₂SiMe₃) (ebthi = ethylenbistetrahydroindenyl) with 2-ethynyl-pyridine the complex rac-(ebthi)ZrC(SiMe₃)=CH(SiMe₃)](σ-C≡CPy) 7 was obtained, which was investigated by an X-ray analysis.     

Die CuCl-katalysierte Reaktion von Trimethylsilyl(t-butyl)chlorphosphan mit Dimethylzirconocen: Ein Beispiel der Tandem-Katalyse

The CuCl-catalyzed Reaction of Trimethylsilyl(t-butyl)chlorophosphane with Dimethylzirconocene: An Example for Tandem Catalysis t-BuP(SiMe₃)Cl was prepared from t-BuP(SiMe₃)₂ and hexachloroethane and reacted in situ with Cp₂ZrMe₂ in the presence of catalytic amounts of copper(I) chloride yielding t-Bu(Me)P? P(Cl)t-Bu ( 1 ) (2 : 1 reaction) or t-Bu(Me)P? P · (Me)t-Bu ( 2 ) (1 : 1 reaction) and Cp₂ZrCl(Me). To understand the course of reaction, the reaction of dimethylzirconocene with CuCl and the decomposition of t-BuP(SiMe₃)Cl in the presence of CuCl and tetrachloroethene were studied. The results suggest that CuCl reacts with t-BuP(SiMe₃)Cl in the presence of C₂Cl₄ to give t-Bu(Cl)P? P(Cl)t-Bu ( 3 ); simultaneously, CuCl reacts with Cp₂ZrMe₂ with formation of methylcopper, which reacts with 3 to give 1 or 2 , respectively.     

Zur Bildung von Vinylverbindungen des Lanthans und Lutetiums

On Preparation of Vinyl Compounds of Lanthanum and Lutetium At reaction of permethyllanthanocene chloride with vinyl lithium coupling of vinyl groups takes place with formation of the butadiene complex [Li(dme)₃][Cp₂*La(C₄H₆)] ( 1 ). The corresponding lutetium compound yields the expected vinyl complex Cp₂*Lu(CH?CH₂) · LiCl · dme ( 4 ) with low stability. Furthermore, the more stable alkenyl compounds Cp₂*LaCPh?CMe₂ · 2 thf ( 2 ) and Cp₂*LuCPh?CMe₂ · MgCl₂ · dme ( 3 ) could be obtained. The new complexes were characterized by their ¹H and ¹³C-n.m.r. spectra.     

Metallocene ion pairs: A direct insight into the reaction equilibria and polymerization by 13C NMR spectroscopy

The reaction equilibria of Cp₂Ti¹³CH₃Cl and Cp₂Ti(CH₃)₂ with AlMe₃ (TMA) and/or methylaluminoxane (MAO) have been investigated by ¹³C NMR. Several adducts have been identified. A study of the ¹³C 90% enriched ethylene polymerization in an NMR tube in the presence of the above catalytic systems, in the most experimentally significant conditions, and a comparison of the NMR data with the catalytic activity have been made as well. It has been shown that: i) some species are side products, inactive for addition ethylene polymerization; ii) active cation-like species such as Cp₂TiMe⁺Cl·[AlMeO]_n- and Cp₂TiMe⁺Me·[AlMeO]_n- are formed in titanocene-MAO systems. Concerning the role of AlMe₃, contained in MAO solutions, it has been shown that: a) AlMe₃ is mainly bound to MAO; b) if some “free” AlMe₃ exists in solution it is not the actual cocatalyst in the metallocene-MAO based catalytic systems; c) the amount of AlMe₃ influences either active or inactive species.     

Titanium and zirconium chloro, oxo and alkyl derivatives containing silyl-cyclopentadienyl ligands. Synthesis and characterisation

The reaction of the tetramethylcyclopentadiene-silyl substituted derivative C₅Me₄(SiMe₃)(SiMe₂Cl) with MCl₄ afforded the trichloro mono-tetramethylcyclopentadienyl complexes M(η⁵-C₅Me₄SiMe₂Cl)Cl₃ [M=Ti (1), Zr (2)] with selective elimination of SiMe₃Cl. Compound 1 reacts with deoxygenated water in methylene chloride, with the evolution of HCl, to give the dinuclear titanium compound {Ti[μ-(η⁵-C₅Me₄SiMe₂O-κO)]Cl₂}₂ (3), which was converted into the μ-oxo complex {Ti[μ-(η⁵-C₅Me₄SiMe₂O-κO)]Cl}₂(μ-O) (4) by a further hydrolysis reaction which occurred when a solution of 3 in toluene was refluxed for a long period of time in the air. Depending on the size of the alkyl ligand, reactions of the mononuclear compound 1 with an appropriate alkylating reagent rendered the peralkylated Ti(η⁵-C₅Me₄SiMe₂R)R₃ [R=Me (5), CH₂Ph (6)] or partially alkylated {Ti[(η⁵-C₅Me₄SiMe₂(CH₂SiMe₃)]Cl(CH₂SiMe₃)₂} (7) compounds by a salt metathesis route. Attempts to synthesise a partially methylated or benzylated complex were unsuccessful. Treatment of the dinuclear compound 3 with four equivalents of MgClMe yielded the tetramethyl derivative {Ti[μ-(η⁵-C₅Me₄SiMe₂O-κO)]Me₂}₂ (8), while the same reaction carried out with MgCl(CH₂Ph) or Mg(CH₂Ph)₂·2THF gave the chloro-benzyl derivative {Ti[μ-(η⁵-C₅Me₄SiMe₂O-κO)]Cl(CH₂Ph)}₂ (9) as an equimolar mixture of diastereomers, regardless of the molar ratio of the alkylating reagent used. All of the new compounds were characterised by elemental analysis and NMR spectroscopy.     

N–O-Bindungsspaltung in O-silylierten Oximen bei der Reaktion mit einem Titanocen-Alkin-Komplex

N–O Bond Cleavage in O-silylated Oximes by Reaction with a Titanocene-Alkyne Complex Cp₂Ti(Me₃SiC₂SiMe₃) 1 reacts with alicyclic and aliphatic O-silylated ketoximes of type R¹R²C=NOSiMe₃ ( 2 : R¹R² = (CH₂)₅; 3 : R¹ = R² = Me) under N–O bond breaking to the titanocene complexes Cp₂Ti(OSiMe₃)(N=CR¹R²) 6 (R¹R² = (CH₂)₅) and 7 (R¹ = R² = Me). The structure of 6 was obtained by X-ray crystal structure analysis ( 6 : triclinic, space group P1, Z = 2, a = 9.486(1), b = 9.865(1), c = 12.305(2) Å, α = 107.19(1), β = 96.08(1), γ = 111.08(1)°).     

Investigation and mechanistic study into intramolecular hydroalkoxylation of unactivated alkenols catalyzed by cationic lanthanide complexes

Cationic lanthanide complexes of the type [Ln(CH₃CN)₉]³⁺[(AlCl₄)₃]^3–·CH₃CN (Ln = Pr, Nd, Sm, Gd, Er, Yb, Y) served as effective catalysts for the intramolecular hydroalkoxylation/cyclization of unactivated alkenols to yield the cyclic ethers with Markovnikov regioselectivity under mild conditions. Novel cationic complexes, [AlCl(CH₃CN)₅]²⁺[(AlCl₄)₂]^2–·CH₃CN and [Nd(CH₃CN)₉]³⁺[(FeCl₄)₃]^3–·CH₃CN, were synthesized and evaluated for the intramolecular hydroalkoxylation/cyclization of unactivated alkenols for comparison. The active sequence of [Nd(CH₃CN)₉]³⁺[(FeCl₄)₃]^3–·CH₃CN < [AlCl(CH₃CN)₅]²⁺[(AlCl₄)₂]^2–·CH₃CN < [Nd(CH₃CN)₉]³⁺[(AlCl₄)₃]^3–·CH₃CN observed indicated that both the cation and anion have great influence on the activity. Comparative study on the activity of AlCl₃ and its cationic complex [AlCl(CH₃CN)₅]²⁺[(AlCl₄)₂]^2–·CH₃CN revealed the formation of the cationic Al center enhanced the activity greatly. The ¹H NMR studies indicated the activation of hydroxyl and olefin by the cationic Ln³⁺ center were involved in the reaction pathways.     

Biphasic ethylene polymerisation using ionic liquid over a titanocene catalyst activated by an alkyl aluminium compound

1-n-Butyl-3-methylimidazolium tetrachloroaluminate ([BMIM]⁺[AlCl₄]⁻) was applied to biphasic ionic liquid/hexane ethylene polymerisation as a medium of the Cp₂TiCl₂ titanocene catalyst activated by alkylaluminium compounds (MAO, AlEt₂Cl, AlEt₃). The best results were obtained using AlEt₂Cl. The results show that catalyst recycling, higher ethylene pressure, and greater Al/Ti molar ratio along with a greater volume of the ionic liquid phase enhance catalyst activity. The polyethylene gathered from the hexane phase is characterised primarily by its high purity. Its physical properties remain polyethylene obtained over a heterogeneous metallocene catalyst. Thus, biphasic ionic liquid polymerisation using a metallocene catalyst is possible and offers interesting technological implications.     

On the nature and reactivity of Cp2TiCH3

Reaction of Cp₂TiCl with 1 eq. of CH₃Li in ether at ?78°C yields the green, thermally unstable, trivalent Ti compound Cp₂TiCH₃. EPR studies on ether solutions of this compound reveal it to be present in solution as the adduct Cp₂TiCH₃ · OEt₂ · By reaction with DCl Cp₂TiCl₂ and CH₃D are formed. Reaction with 2,6 xylylisocyanide leads to insertion of the isocyanide into the TiCH₃ bond, while reaction with CS₂ yields the disproportionation products Cp₂-Ti(CH₃)₂ and Cp₂TiCS₂. Thermal decomposition studies on deuteriated analogues confirm the TiCH₃ structure. The rate determining step in the decomposition process is the abstraction of a Cp proton by the methyl group. Under nitrogen the decomposition reaction yields NH₃ and N₂H₄ in amounts of up to 0.28 moles N/Ti. Some catalytic applications of Cp₂TiCH₃ for hydrogenation and isomerisation of olefins and acetylenes are briefly mentioned.     

[Li(12-Krone-4){(Me3Si)2N}2TiCH2SiMe2NSiMe3] – ein Ionenpaar mit gestreckter Li–C–Ti-Achse

[Li(12-Crown-4){(Me₃Si)₂N}₂TiCH₂SiMe₂NSiMe₃] – an Ion-Pair with a Linear Li–C–Ti-Axis The title compound ( 1 ) has been prepared from Ti[N(SiMe₃)₂]₃ and n-butyllithium in OEt₂/n-hexane in the presence of 12-crown-4. Smaragd-green single crystals of 1 · C₇H₈ which were suitable for X-ray crystallography were formed from toluene solutions at –18 °C. According to the crystal structure determination 1 forms ion pairs between the lithium atom and the CH₂-carbon atom which is member of a planar Ti–C–Si–N heterocycle. The coordination geometry of the Li–C–Ti axis is linear (bond angle 172.8° in average of the two symmetry independent species) with coordination number five at the CH₂-carbon atom.     

Crystallographic report: The [bis(η5‐cyclopentadienyl)titanium(IV)‐bis(L‐methionine)] dichloride

The structure of ionic complex [Cp₂Ti(L -Met)₂]²⁺[Cl⁻]₂ (where Cp = η⁵-C₅H₅) possessing C₂ symmetry is presented. Discrete cationic units with distorted tetrahedral geometry around the central titanium atom are connected through intermolecular H···Cl bonds between ammonium group protons of α-amino acid ligands and chloride anions. Copyright © 2004 John Wiley & Sons, Ltd.     

Liquid-phase isobutane alkylation with butenes over aluminum chloride complexes synthesized in situ from activated aluminum and <Emphasis Type="Italic">tert</Emphasis>-butyl chloride

The liquid-phase interaction between isobutane and butenes at 303 K and 2.5–3.0 MPa has been investigated using activated aluminum (Al*)-tert-butyl chloride (TBC) model system (TBC: Al* = 0.35−4 mol/mol). It has been demonstrated by attenuated total reflection FT-IR (ATR-FT-IR) spectroscopy that the catalytically active aluminum chloride complexes forming in situ in the hydrocarbon medium vary in composition. Alkylation as such takes place at equimolar proportions of the reactants (TBC: Al* = 1: 1) and butenes feed 1mass flow rate of 5 h⁻¹ per gram of Al*. According to ATR-FT-IR data, the most abundant aluminum complexes resulting under these conditions are the AlCl₄⁻ and Al₂Cl₇⁻ ions and, probably, the molecular complex AlCl₃ · sec-C₄H₉Cl. In a fourfold excess of TBC over Al* at butenes mass feed rate of 2.5 h⁻¹, isobutane undergoes self-alkylation. In this case, the Al₂Cl₇⁻ ion is not detected and the most abundant complexes are AlCl₄⁻, Al₃Cl₁₀⁻ and the molecular species AlCl₃ · tert-C₄H₉Cl. It is hypothesized that the Al₂Cl₇⁻ ion plays the key role in the liquid-phase alkylation of isobutane with butenes.     

Über die natur der übergangsmetall-kohlenstoff-σ-bindung: X. Über die darstellung,charakterisierung und thermische zersetzung von bis(η5-cyclopentadienyl)-titan-bis(thioanisolyl) und natrium-thioanisolylphthalo-cyaninato-ferrat(II)·4THF

Cp₂TiCl₂ (Cp = η⁵-C₅H₅; H₂Pc = phthalocyanine) reacts with 1.9 equivalents of PhSCH₂Li to give Cp₂Ti(CH₂SPh)₂ (I), the structure of which follows from the results of elemental analysis, ¹H NMR and mass spectroscopic investigations and protolysis to form PhSCH₃. I decomposes in toluene at 100°C, with the methylene group being liberated to form [Cp₂TiSPh]₂ (II) (ca. 31%) and Cp₂Ti(SPh)₂ (III) (ca. 16%). Na[PcFeCH₂SPh]·4THF (IV) (μ_eff. 0.12 BM) has been obtained as green-black, air-sensitive crystals in an oxidative addition reaction from PhSCH₂Cl and iron(0) phthalocyanine. In boiling THF the organyl group is gradually split off without formation of a considerable amount of the corresponding thiophenolato complex. The results are in agreement with the assumption that the formation of an η²-thioanisolyl structure as an unstable intermediate is essentially important for the conversion of the thioanisolyl into the thiophenolato complexes.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)methanide Ligands

A study of the coordination chemistry of different bis(diphenylphosphino)methanide ligands [Ph₂PC(X)PPh₂] (X=H, SiMe₃) with Group 4 metallocenes is presented. The paramagnetic complexes [Cp₂Ti{κ²‐P,P‐Ph₂PC(X)PPh₂}] (X=H ( 3 a ), X=SiMe₃ ( 3 b )) have been prepared by the reactions of [(Cp₂TiCl)₂] with [Li{C(X)PPh₂}₂(thf)₃]. Complex 3 b could also be synthesized by reaction of the known titanocene alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with Ph₂PC(H)(SiMe₃)PPh₂ ( 2 b ). The heterometallacyclic complex [Cp₂Zr(H){κ²‐P,P‐Ph₂PC(H)PPh₂}] ( 4 aH ) has been prepared by reaction of the Schwartz reagent with [Li{C(H)PPh₂}₂(thf)₃]. Reactions of [Cp₂HfCl₂] with [Li{C(X)PPh₂}₂(thf)₃] gave the highly strained corresponding metallacycles [Cp₂M(Cl){κ²‐P,P‐Ph₂PC(X)PPh₂}] ( 5 aCl and 5 bCl ) in very good yields. Complexes 3 a , 4 aH , and 5 aCl have been characterized by X‐ray crystallography. Complex 3 a has also been characterized by EPR spectroscopy. The structure and bonding of the complexes has been investigated by DFT analysis. Reactions of complexes 4 aH , 5 aCl , and 5 bCl did not give the corresponding more unsaturated heterometallacyclobuta‐2,3‐dienes.     

Half-sandwich dibenzyl complexes of scandium: Synthesis, structure, and styrene polymerization activity

Half-sandwich dibenzyl complexes of scandium have been prepared by stepwise treatment of scandium trichloride with lithium derivatives of silyl-functionalized tetramethylcyclopentadienes (C₅Me₄H)SiMe₂R (R = Me, Ph) and benzyl magnesium chloride. The resulting complexes [Sc(η⁵-C₅Me₄SiMe₃)(CH₂Ph)₂(THF)] and [Sc(η⁵-C₅Me₄SiMe₂Ph)(CH₂Ph)₂(1,4-dioxane)] show structure related to that of the corresponding bis(trimethylsilylmethyl) compounds [Sc(η⁵-C₅Me₄SiMe₂R)(CH₂SiMe₃)₂(THF)]. The four-coordinate complexes display η¹-coordinated benzyl ligands without significant interaction of the ipso-carbon of the phenyl moiety. Conversion of [Sc(η⁵-C₅Me₄SiMe₃)(CH₂Ph)₂(THF)] into the cationic species by treatment with triphenylborane in THF led to the formation of a stable charge separated complex [Sc(η⁵-C₅Me₄SiMe₃)(CH₂Ph)(THF)_x][BPh₃(CH₂Ph)]. Benzyl cation formed using [Ph₃C][B(C₆F₅)₄] in toluene resulted in a moderately active syndiospecific styrene polymerization catalyst.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)amide Ligands

A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph₂P‐N‐PPh₂ at Group 4 metallocenes is presented herein. Coordination of N,N‐bis(diphenylphosphino)amine ( 1 ) to [(Cp₂TiCl)₂] (Cp=η⁵‐cyclopentadienyl) generated [Cp₂Ti(Cl)P(Ph₂)N(H)PPh₂] ( 2 ). The heterometallacyclic complex [Cp₂Ti(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Ti ) can be prepared by reaction of 2 with n‐butyllithium as well as from the reaction of the known titanocene–alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with the amine 1 . Reactions of the lithium amide [(thf)₃Li{N(PPh₂)₂}] with [Cp₂MCl₂] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp₂M(Cl){κ²‐N,P‐N(PPh₂)₂}] ( 4 Zr and 4 Hf ). Reduction of 4 Zr with magnesium gave the highly strained heterometallacycle [Cp₂Zr(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Zr ). Complexes 2 , 3 Ti , 4 Hf , and 3 Zr were characterized by X‐ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations.     

The methylenation of enolizable ketones and esters using organotitanium chemistry

The titanium methylidene fragment, Cp₂TiCH₂, resulting from Tebbe's reagent, Cp₂TiCH₂·AlMe₂Cl or the β,β-disubstituted metallacycle, CP₂TiCH₂C(Me)(n-Pr)CH₂, methylenates enolizable acidic ketones and converts α,α-disubstituted ketones into titanium enolates. The reagent reacts selectively with ketones over esters.     

Insertions of nitriles and pyridine into the ZrSi bond of (η5-C5H5)(η5-C5Me5)Zr[Si(SiMe3)3]Me

The zirconium silyl complex CpCpZr[Si(SiMe₃)₃]Me (1; Cp = η⁵-C₅H₅; Cp = η⁵-C₅Me₅) reacts with nitriles RCN (R = Me, CHCH₂, Ph) to form the azomethine derivatives CpCpZr[NC(R)Si(SiMe₃)₃]Me (2, R = Me; 3, R = CHCH₂; 4, R = Ph). Pyridine reacts with 1 to give a 75% yield of CpCpZr[NC₅H₅Si(SiMe₃)₃]Me (5), which results from 1,2-addition of the ZrSi bond of 1 to pyridine. These reactions provide the first examples of nitrile and pyridine insertions into a transition metal-silicon bond. The related silyl complexes Cp₂Zr[Si(SiMe₃)₃]Me and CpCpZr[Si(SiMe₃)₃]Cl are much less reactive toward nitriles and pyridine.     

Four‐Membered Heterometallacyclic d0 and d1 Complexes of Group 4 Metallocenes with Amidato Ligands

A study of the coordination chemistry of different amidato ligands [(R)N?C(Ph)O] (R=Ph, 2,6‐diisopropylphenyl (Dipp)) at Group 4 metallocenes is presented. The heterometallacyclic complexes [Cp₂M(Cl){κ²‐N,O‐(R)N?C(Ph)O}] M=Zr, R=Dipp ( 1 a ), Ph ( 1 b ); M=Hf, R=Ph ( 2 )) were synthesized by reaction of [Cp₂MCl₂] with the corresponding deprotonated amides. Complex 1 a was also prepared by direct deprotonation of the amide with Schwartz reagent [Cp₂Zr(H)Cl]. Salt metathesis reaction of [Cp₂Zr(H)Cl] with deprotonated amide [(Dipp)N?C(Ph)O] gave the zirconocene hydrido complex [Cp₂M(H){κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 3 ). Reaction of 1 a with Mg did not result in the desired Zr(III) complex but in formation of Mg complex [(py)₃Mg(Cl) {κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 4 ; py=pyridine). The paramagnetic complexes [Cp′₂Ti{κ²‐N,O‐(R)N?C(Ph)O}] (Cp′=Cp, R=Ph ( 7 a ); Cp′=Cp, R=Dipp ( 7 b ); Cp′=Cp*, R=Ph ( 8 )) were prepared by the reaction of the known titanocene alkyne complexes [Cp₂′Ti(η²‐Me₃SiC₂SiMe₃)] (Cp′=Cp ( 5 ), Cp′=Cp* ( 6 )) with the corresponding amides. Complexes 1 a , 2 , 3 , 4 , 7 a , 7 b , and 8 were characterized by X‐ray crystallography. The structure and bonding of complexes 7 a and 8 were also characterized by EPR spectroscopy.