6] Addition of crown ether has been reported to increase the reactivity of the silyl anion by forming a crown ether-sodium ion complex; A. Sekiguchi, T. Yatabe, C. Kabuto, H. Sakurai, Angew. Chem. f O 1 (1989) 778; Angew. Chem. Int. Ed. Engl. 28 (1989) 757; M. FuJino, H. Isaka, J. Chem. SOC., Chem. Commun. 1989,466. 171 A single crystal with dimensions of 0.5 x 0.2 x 0.2 mm, obtained from ethanol was used for the X-ray analysis. Lattice constants were determined by the least-squares method with an angular setting of 25 reflections within the range 11 < 6 < 13". Intensity data were obtained on a Enraf-Nonius CAD4 diffractometer equipped with graphite monochromatized Mo,, radiation and using thew-28 scan technique (26 < 50"). Duringdata collection three standards, measured every 120 min, indicated a total loss in intensity of 18.4%. A h e a r decay correction was applied. Of 3158 independent reflections measured, only 2298 were considered as observed on the basis of the criterion I > 3.0 o(1). All intensities were corrected for Lorentz and polarization effects but not for absorption. Crystal data for 1: M , = 483.19; orthorhombic; P,,,; a = 15.037(3), b = 9.029(3), c = 23.231(5) A; V = 3154.3 A3; 2 = 4; = 1.02 g ~m -~; p (Mo~.) = 3.0 cm-I. The structure of 1 was solved by direct methods and refined by full-matrix least-squares methods. The final refinements with anisotropic temperature factors for the non-hydrogen atoms lowered Rand R, values to 0.059 and 0.072, respectively.

Die mehrfache Insertion von Ethylen in die TiCH3‐Bindung, ein erster direkter Nachweis für die Rolle kationischer Zwischenstufen in Polymerisationsreaktionen, beobachtet man bei niedriger Temperatur bei der Umsetzung der kationische Ti‐ und Zr‐Komplexe 3, die aus 1 und 2 unter Methanabspaltung entstehen. Ethylen im Überschuß wird unter gleichen Bedingungen polymerisiert (M  Ti, Zr).

The reaction of [(η5-C5Me5)Co(η4-1,5-cyclooctadiene)] with HBF4·Me2O affords, at room temperature, an agostic η3-cyclooctenyl complex which undergoes a facile ring opening to afford anti-[(η5-C5Me5)Co(η5-1-propylpentadienyl)]BF4.

The fluxional, agostic, norborn-5-en-2-ylcobalt(iii) cations [Co(q-C5R5)(2 : 5,6-q-C7Hs)]+ (R = H, Me) under o C-C bond cleavage at -20 "C to give 4-~inylcyclopentenylcobalt(111) complexes [Co(q-C5R5)(l -3 : 6,7-q-CH2=CH €-% H(CH)3 H2)]+ [R = H (4) (structurally characterized by X-ray crystallography), Me ( 7 ) ] ,which react with LiAIH4 or LiBHEt, to give neutral 4-vinylcyclopentenecobalt(i) complexes [Co(q-C5R5)( 1,2 : 6,7-q-CH2=CHcHCH,CH=CHcH*)] [R = H (8), Me (9a)l;(9a) is protonated at 0 "C to give the 4-ethylcyclopentenyl complex [Co(q-C5Me5){ l-3-q-C5H6(endo-Et-4)}]+ (1 I), which is stabilized by an agostic interaction between cobalt and the endo-hydrogen-carbon bond of the 5-position, and readily undergoes conrotatory ring-opening to afford [Co(q-C5Me5){q-c5H6(syn-Et-5)}]+ (12) containing an acyclic 5-ethylpentadienyl ligand, as shown by X-ray crystallography.