Perdita Arndt

Reactions of group 4 metallocene alkyne complexes with carbodiimides: experimental and theoretical studies of the structure and bonding of five-membered hetero-metallacycloallenes.

The reaction of the low-valent metallocene(II) sources Cp(2)Ti(η(2)-Me(3)SiC(2)SiMe(3)) (7) and Cp(2)Zr(py)(η(2)-Me(3)SiC(2)SiMe(3)) (11, Cp = η(5)-cyclopentadienyl, py = pyridine) with carbodiimides RN═C═NR (R = Cy, i-Pr, p-Tol) leads to the formation of five membered hetero-metallacycloallenes Cp(2)M{Me(3)SiC═C═C[N(SiMe(3))(R)]-N(R)} (9M-R) (M = Ti, R = i-Pr; M = Zr, R = Cy, i-Pr, p-Tol). Elimination of the alkyne (as the hitherto known reactivity of titanocene and zirconocene alkyne complexes would suggest) was not observed. The molecular structures of the obtained complexes were confirmed by X-ray studies. Moreover, the structure and bonding of the complexes 9Zr-Cy and 9Zr-p-Tol was investigated by DFT calculations.

Titanocene and zirconocene σ-alkynyl complexes in CC single bond coupling and cleavage reactions

Group 4 metallocene mono- and bis-σ-alkynyl complexes of the type L2M(σ-CCR) and L2M(σ-CCR)2 with M=titanium and zirconium in the oxidation states +3 and +4 and L=Cp (η5-cyclopentadienyl) and Cp* (η5-pentamethylcyclopentadienyl) are important compounds for stoichiometric and catalytic CC single bond coupling and cleavage reactions. Detailed investigations show five-membered metallacyclocumulenes L2M(η4-1,2,3,4-RC4R) as the key intermediates in both reactions of a CC single bond cleavage of different 1,4-substituted 1,3-butadiynes RCCCCR to alkynyl groups and the opposite reaction of CC single bond formation starting from alkynyl groups under the formation of 1,4-substituted 1,3-butadiynes. Depending on different metals M and ligands L, coupling or cleavage is favoured. Combination of both reactions offered the first CC single bond metathesis in homogeneous solution, which is photocatalyzed and titanocene-mediated. It proceeds via titanocene–mono-alkynyl complexes, which are interesting species also for other stoichiometric and catalytic CC coupling reactions. Some similarities regarding the σ-to-π conversion exist between the coupling of the alkynyl groups at titano- and zirconocenes to complexed 1,3-butadiynes on one side and the coupling of phenyl groups at chromium to complexed diphenyl on the other side.

Novel Amidoniobium Complexes with a Functional Relationship to the [Cp2ZrR]+ Ion*

Partial abstraction of apical methyl groups is observed in aminopyridinatoniobium alkyne complexes, as exemplified with the synthesis and characterization of 1. This results in cationic complex fragments, which facilitate the polymerization of ethylene and in the presence of methylalumoxane the selective dimerization of 1-butene.

Intramolekulare Insertion eines η5-cyclopentadienyl-ringes in einem bis-η5-cyclopentadienyltitanacyclopentadien

Abstract The reaction of in situ-generated titanocene “Cp 2 Ti” with 2 equiv. of alkynes Me 3 SiCCR yields a mixture of symmetrically ( R = Ph ( 3 ), Py ( 6 ) ) and unsymmetrically ( R = Ph ( 4 ) , Py ( 7 ) substituted titanacyclopentadienes. Complex 7 is unstable and rearranges with an intramolecular insertion of one Cp of the titanocene fragment into the unsymmetrically substituted titanacyclopentadiene to produce the dihydroindenyl complex 8 , which was characterized by an X-ray structure analysis.

Formation of a 1-Zircona-2,5-disilacyclopent-3-yne: Coordination of 1,4-Disilabutatriene to Zirconocene?†

Alkyne under stress: a novel metallacycle containing one Zr atom, two Si atoms, and a C≡C bond has been prepared and its structure elucidated (Zr green, Si blue, C gray). According to X-ray data, spectral properties, and DFT calculations, the bonding situation in this compound is characterized as a 1-metalla-2,5-disilacyclopent-3-yne with a weak metal-triple-bond interaction.

Bimetallic Titanocene or Zirconocene/Aluminium Complexes as Active Catalysts in Lactone Polymerization Reactions

The metallocene alkyne complexes [Cp2M(L)(η2-Me3SiC2R)] react with diisobutylaluminium hydride at room temp. by addition of HAl(iBu)2 to yield the heterobimetallic complexes [{Cp2M}(μ-η1:η2-RCCSiMe3)(μ-H){Al(iBu)2}] [{Cp2M}: (η5-C5H5)2Ti, R = Ph 1, R = SiMe32; {Cp2M}: (η5-C5H5)2Zr, R = SiMe33; {Cp2M}: (ebthi)Zr, R = SiMe34] {ebthi: rac-[1,2-ethylene-1,1′-bis(η5-tetrahydroindenyl)]}. Complexes 1−4 were characterized by NMR spectroscopy and 1, 2 and 4 investigated by X-ray crystal structure analysis. Compounds 1−4 were tested as initiators in the ring-opening polymerization of lactones. The results are discussed in comparison to the corresponding monometallic titanocene and zirconocene alkyne complexes.

Homoleptic trisaminopyridinato MIII complexes (MTi, V and Cr), synthesis, structure and EPR investigations

Abstract The synthesis of a series of trisaminopyridinato metal(III) complexes (metalTi, V and Cr) is reported. The titanium complex is synthesized by reduction of the monochloro TiIV complex (4-Me-TMS-APy)2Ti(NMe2)Cl (4-methyl-2-trimethylsilylaminopyridine = 4-Me-TMS-APyH) using sodium amalgam as a reducing agent. The vanadium complex is prepared via a salt elimination route using VCl3(THF)3 and 3 equiv of in situ lithiated 4-Me-TMS-APyH. The chromium complex is made via benzene elimination from Ph3Cr(THF)3 and 3 equiv of 4-Me-TMS-APyH. All three compounds are paramagnetic and the IR spectra of the compounds fit very well in the finger print range. The X-ray crystal structure analyses of the titanium and the chromium complexes establish their mononuclear structures with a strongly disturbed octahedral coordination geometry. The EPR spectra of the TiIII and CrIII complexes are reported.

Si-H Bond Activation of Alkynylsilanes by Group 4 Metallocene Complexes

The reactivity of variously substituted alkynylsilanes toward selected group 4 metallocene complexes was investigated. Reactions of the alkynylsilanes R(1)C(2)SiR(2)(2)H (R(1) = SiMe(3), R(2) = Me, 1; R(1) = SiMe(3), R(2) = Ph, 2; R(1) = SiMe(2)H, R(2) = Me, 5) with Cp(2)TiMe(2) (Cp = eta(5)-cyclopentadienyl) resulted, upon methyl group transfer to the silyl group, in the previously described titanocene alkyne complexes Cp(2)Ti(R(1)C(2)SiR(2)(2)R(3)) (R(1) = Me(3)Si, R(2) = R(3) = Me, 3; R(1) = HMe(2)Si, R(2) = R(3) = Me, 6) or the unreported complex 4 (R(1) = Me(3)Si, R(2) = Ph, R(3) = Me). The Cp(2)TiCl(2)/n-BuLi system yielded alkyne complexes 6 and 7 (R(1) = HMe(2)Si, R(2) = Me, R(3) = H); no alkyl group transfer was detected. On the other hand, reactions utilizing the Cp(2)ZrCl(2)/n-BuLi system afforded inseparable mixtures; however, complexes of the type Cp(2)Zr[R(1)C(2)SiMe(2)(n-Bu)] (R(1) = Me(3)Si, 8; R(1) = HMe(2)Si, 9) were detected. Cp(2)Hf(n-Bu)(2) reacted with the alkynylsilanes in a diverse way, depending on the substituents of the alkyne substrate. The reaction with an excess of alkyne 1 (R(1) = Me(3)Si, R(2) = Me) afforded only an intractable mixture, which contained Me(3)SiC(2)SiMe(2)(n-Bu) (10). Hafnacyclopentadienes 13-15 as precedented product types were obtained when alkyne 12 (R(1) = Ph, R(2) = Me) was used. In sharp contrast, the symmetrically substituted alkynes 5 (R(1) = HMe(2)Si, R(2) = Me) and H(2)PhSiC(2)SiPhH(2) (18) yielded the hitherto unknown Si-containing metallacycles 16 and 19. A reaction mechanism leading to these products was proposed and subsequently supported by DFT calculations. In addition, the reduction of Cp(2)HfCl(2) with magnesium in THF in the presence of alkynylsilanes was shown to be an alternative route to compounds 14-16 and 19. Presumably due to steric reasons, alkyne 1 could not form any of the product types described above. Nevertheless, it was utilized for the preparation of the PMe(3)-stabilized hafnocene alkyne complex 11.

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

Cp2Ti(Me3SiC2SiMe3) 1 reagiert mit alicyclischen und aliphatischen O-silylierten Ketoximen vom Typ R1R2C=NOSiMe3 (2: R1R2 = (CH2)5; 3: R1 = R2 = Me) unter N–O-Bindungsspaltung zu den entsprechenden Titanocen-Komplexen Cp2Ti(OSiMe3)(N=CR1R2) 6 (R1R2 = (CH2)5) und 7 (R1 = R2 = Me). Die Struktur von 6 konnte durch eine Rontgenkristallstrukturanalyse aufgeklart werden (6: triklin, Raumgruppe P1, Z = 2, a = 9.486(1), b = 9.865(1), c = 12.305(2) A, α = 107.19(1), β = 96.08(1), γ = 111.08(1)°). 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) A, α = 107.19(1), β = 96.08(1), γ = 111.08(1)°).

Yttrat-vermittelter Ligandentransfer und Direktsynthese als Wege zu Amidopalladium-Komplexen

Ein Ligandentransfer vom Yttrium zum Palladium und die Ruckbildung von 1 sind die entscheidenden Schritte bei einer effizienten Synthese des stark gespannten Amidopalladium-Komplexes 2 aus [(cod)PdCl2] und 1 (cod=Cyclooctadien. Dieses Syntheseprinzip sollte angesichts der Vielzahl von bekannten at-Komplexen fruher Ubergangsmetalle ein enormes Potential haben.