Versatile Coordination of Cyclopentadienyl-Arene Ligands and Its Role in Titanium-Catalyzed Ethylene Trimerization

Cationic titanium(IV) complexes with ansa-(η5-cyclopentadienyl,η6-arene) ligands were synthesized and characterized by X-ray crystallography. The strength of the metal-arene interaction in these systems was studied by variable-temperature NMR spectroscopy. Complexes with a C1 bridge between the cyclopentadienyl and arene moieties feature hemilabile coordination behavior of the ligand and consequently are active ethylene trimerization catalysts. Reaction of the titanium(IV) dimethyl cations with CO results in conversion to the analogous cationic titanium(II) dicarbonyl species. Metal-to-ligand backdonation in these formally low-valent complexes gives rise to a strongly bonded, partially reduced arene moiety. In contrast to the η6-arene coordination mode observed for titanium, the more electron-rich vanadium(V) cations [cyclopentadienyl-arene]V(NiPr2)(NC6H4-4-Me)+ feature η1-arene binding, as determined by a crystallographic study. The three different metal-arene coordination modes that we experimentally observed model intermediates in the cycle for titanium-catalyzed ethylene trimerization. The nature of the metal-arene interaction in these systems was studied by DFT calculations.

Use of ring-expanded diamino- and diamidocarbene ligands in copper catalyzed azide-alkyne "click" reactions

The two-coordinate ring-expanded N-heterocyclic carbene copper­(I) complexes [Cu­(RE-NHC)₂]⁺ (RE-NHC = 6-Mes, 7-<i>o</i>-Tol, 7-Mes) have been prepared and shown to be effective catalysts under neat conditions for the 1,3-dipolar cycloaddition of alkynes and azides. In contrast, the cationic diamidocarbene analogue [Cu­(6-MesDAC)₂]⁺ and the neutral species [(6-MesDAC)­CuCl]₂ and [(6-MesDAC)₂(CuCl)₃] show good activity when the catalysis is performed on water

CYCLOPENTADIENYL COMPOUNDS WITH NITROGEN DONORS IN THE SIDE-CHAIN

Jutzi P, SIEMELING U. CYCLOPENTADIENYL COMPOUNDS WITH NITROGEN DONORS IN THE SIDE-CHAIN. JOURNAL OF ORGANOMETALLIC CHEMISTRY. 1995;500(1-2):175-185.The coordination chemistry of cyclopentadienyl ligands bearing either a dimethylaminoethyl side-chain or a pendant pyridyl group is described. The influence of these N donor functionalities on the structure and the physical as well. as chemical properties of relevant metal complexes is discussed. In several cases, a relatively weak intramolecular coordination of the pendant amine is found; the hemilabile coordination profile of the N functionalised cyclopentadienyl ligands towards d-block elements may prove useful for the development of single-component catalysts

TRINUCLEAR HOMOMETALLIC AND HETEROMETALLIC COMPLEXES OF A DOUBLY BRIDGED CYCLOPENTADIENYL LIGAND

SIEMELING U, Jutzi P. TRINUCLEAR HOMOMETALLIC AND HETEROMETALLIC COMPLEXES OF A DOUBLY BRIDGED CYCLOPENTADIENYL LIGAND. CHEMISCHE BERICHTE-RECUEIL. 1992;125(1):31-35.Metal complexes that are derived from the doubly bridged cyclopentadiene system 2,2,8,8-tetramethyl-2,8-disilatricyclo-[7.3.0.0(3,7)]dodeca-3,5,9,11-tet raene (LH2) are investigated. The dilithio salt of this compound (LLi2) reacts with (Me3Si)3-C5H2FeCl to give, amongst other products, the trinuclear ferrocene [(Me3Si)3C5H2FeL]2Fe (2). A starting material well suited for the selective preparation of similar trinuclear complexes is the mononuclear ferrocene (HL2)Fe (3) which is formed by reaction of HLLi with iron(II) chloride. Reaction of dilithiiated 3 with trimethyltin chloride yields (Me3SnL)2Fe (4). Cocomplexation of dilithiated 3 and Cp*Li(Cp* = C5Me5) with iron(II) chloride leads to the trinuclear ferrocene (Cp*FeL)2Fe (5). By reaction of 3 with octacarbonyldicobalt the heterometallic complex [(CO)2CoL]2Fe (6) is obtained, which yields [(CO)I2CoL]2Fe (7) by oxidative decarbonylation with iodine. The stereochemistry of the complexes presented is discussed. The trinuclear complexes 2, 5, 6, and 7 are model systems for organometallic polymers with spatially directed structures, whose stability even in mixed-valence states is evidenced by the mass spectra of these complexes

[3]Ferrocenophanes with a tetramethyldisiloxane bridge: synthesis and molecular structure

Siemeling U, Krallmann R, Jutzi P, Neumann B, Stammler H-G. [3]Ferrocenophanes with a tetramethyldisiloxane bridge: synthesis and molecular structure. Monatshefte für Chemie. 1994;125(5):579-586.6,6,8,8-Tetramethyl-7-oxa-6,8-disila[3]-ferrocenophan 2 entsteht aus dem Di(alkoxysilyl)ferrocen (H4C5SiMe2OR)2Fe (R=CH2CH2OCH2CH2OCH2CH2OMe) durch Hydrolyse und anschließende intramolekulare Disiloxan-Bildung. 2,2',3,3',4,4',5,5',6,6,8,8-Dodecamethyl-7-oxa-6,8-disila[3]ferrocenophan 3 wurde durch Luftoxidation von 2,2',3,3',4,4',5,5',6,6,7,7-Dodecamethyl-6,7-disila[2]ferrocenophan erhalten. Die Kristallstrukturen beider Verbindungen wurden durch Einkristall-Röntgenstrukturanalyse bestimmt (2:a=8.5330(10), b=15.610(3), c=18.774(5)Å, [alpha]=70.68(2), [beta]=77.94(2), [gamma]=75.150(10)°, V=2259.8(8)Å3, Z=6, Raumgruppe P1, R=0.045, Rw =0.044; 3:a=12.388(3), b=9.924(3), c=19.136(10)Å, [beta]=105.11(3)°, V=2271.2(15)Å3, Z=4, Raumgruppe P21/c, R=0.076, Rw =0.060). Wegen der Flexibilität der Disiloxan-Brücke sind 2 und 3 ungespannte Moleküle

Molecular Suction Pads: Self-Assembled Monolayers of Subphthalocyaninatoboron Complexes on Gold

Subphthalocyaninatoboron complexes with six long-chain alkylthio substituents in their periphery are applicable for the formation of self-assembled monolayers (SAMs) on gold. Such films were prepared from solution with the axially chlorido substituted derivatives and characterised by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results are in accord with the formation of SAMs assembled by the chemisorption of both covalently bound thiolate-type as well as coordinatively bound thioether units. The adsorbate molecules adopt an essentially ‘flat’ adsorption geometry on the substrate, resembling a suction pad on a surface

BINUCLEAR TRANSITION-METAL COMPLEXES OF CYCLOPHANOID CYCLOPENTADIENONE AND CYCLOPENTADIENYL LIGANDS

Jutzi P, SIEMELING U, Müller A, Bögge H. BINUCLEAR TRANSITION-METAL COMPLEXES OF CYCLOPHANOID CYCLOPENTADIENONE AND CYCLOPENTADIENYL LIGANDS. ORGANOMETALLICS. 1989;8(7):1744-1750

METAL-METAL INTERACTIONS IN COMPLEXES WITH A DOUBLE DIMETHYLSILANDIYL-BRIDGED DICYCLOPENTADIENYL LIGAND

SIEMELING U, Jutzi P, BILL E, TRAUTWEIN AX. METAL-METAL INTERACTIONS IN COMPLEXES WITH A DOUBLE DIMETHYLSILANDIYL-BRIDGED DICYCLOPENTADIENYL LIGAND. JOURNAL OF ORGANOMETALLIC CHEMISTRY. 1993;463(1-2):151-154.The metal-metal interaction in the mixed-valence ferrocenium salt [trans-Cp*FeLFeCp*]+PF6- ([5(+)]PF6-) (Cp* = C(5)Me(5), L = [C(5)H(3)SiMe(2)](2)) was investigated by cyclic voltammetry, electron spectroscopy, EPR and temperature dependent Mossbauer spectroscopy. The compound is best described as a valence-localised system (class I according to Robin and Day)