The reactions of bicyclopropylidene 2 with bis(cyclopentadienyl)bis(trimethylphosphane)titanium(II) 1 and with the cobalt chelate 4 give the first known metal complexes of bicyclopropylidene 3 and 7, respectively, in good yields; the bicyclopropylidene cobalt complex 7 is characterized by an X-ray crystal structure analysis which shows a severe out-ofplane bending of the alkenic ligand, indicating considerable back-bonding which goes along with a release of strain in the ligand.

4]heptane derivativesBicyclopropylidene (1) readily undergoes a palladium(0)-caates 2aϪ5 with the electron deficient alkenes and the cycloadducts 6 and 7 with the strained alkenes in acceptable to talyzed [3 + 2] co-cyclization with electron deficient alkenes (methyl acrylate, methyl trans-crotonate, methyl cinnamate good yields (56 to 83%). In contrast to palladium(0) catalysts nickel(0) complexes catalyze both distal ring opening of 1 and diethyl fumarate) as well as with some strained alkenes (norbornene, norbornadiene) by distal ring cleavage of one and oxidative coupling of the two double bonds when 1 is reacted with e.g. diethyl fumarate. The result is a mixture of the three-membered rings of 1. All these co-cyclizations are regioselective with respect to 1 as well as regio-and steof the methylenecyclopentane derivative 5 with the [2 + 2] cycloadduct 8 and the cotrimer 9. reoselective with respect to the alkenes to give the corresponding 4-methylenespiro[2.4]heptane-trans-6-carboxyl- Introductionderivatives thereof as building blocks for a (trimethylenemethane)palladium [PdTMM] intermediate which acts as Cycloaddition reactions are the archetypes for synthetic the cycloaddend [7] [8] . A closer look at both methods reveals efficiency, as they are highly atom economical and fre-that the [PdTMM] intermediates responsible for the [3 ϩ 2] quently regio-as well as diastereoselective. The prototype co-cyclizations cannot be the same, since the species derived is the widely used [4 ϩ 2] cycloaddition (Diels-Alder reac-from methylenecyclopropanes undergo [3 ϩ 2] cycloadtion) to yield six-membered carbo-or heterocycles in one ditions with both electron-rich and electron-poor alkenes, step. For the construction of five-membered carbocycles whereas the reactive species in the Trost reagents only react our group [1a] have de-with electron-poor alkenes. In addition, the palladium(0)-veloped a metal-catalyzed [3 ϩ 2] cycloaddition methology catalyzed "cyclodimerization" of substituted methylenein recent years. Crucial for the general applicability of this cyclopropanes occurs with poor regioselectivity [1a] , while methodology is the selection of a suitable and conveniently the Trost reagents derived from mono-or disubstituted deaccessible C 3 -building block which can be modified with rivatives cycloadd with good regioselectivity [8] . Indeed, a wide range of substituents. We have demonstrated that computational studies have revealed that different reaction methylenecyclopropane and its derivatives with substituents mechanisms with different [PdTMM] intermediates are reon the three-membered ring or on the double bond fulfill sponsible for the observed differences in reactivities and these conditions and undergo [3 ϩ 2] co-cyclizations in the product distributions of the palladium-catalyzed [3 ϩ 2] presence of a catalytically active nickel(0) or palladium(0) cycloadditions between substituted methylenecycloprocomplex [2] [3] with a wide range of alkenes bearing both panes and substituted 2-(trimethylsilylmethyl)all...

Bis(trimethy1phosphane)titanocene (1) and ($-Ethene)(trimethy1phosphane)titanocene ( 2 ) react with one equivalent of allene (3a), phenylallene (3b), 1,l-dimethylallene (3c), and 1,l-diphenylallene ( 3 4 readily by displacement of one trimethylphosphane from 1 and of ethene from 2 to give regiospecifically the corresponding (q2-allene)(trimethylphosphane)-titanocene complexes 4a-d in good yields. From (q2-l-butene)(trimethylphosphane)zirconocene (6) and 3d the corresponding ( 1,2 -4 2-3, 3-diphenylallene)zirconocene complex 7d is obtained in the same manner. The structures of these new allene complexes have been established unambiguously by 'H-and 13C-NMR-spectroscopy. A crystal structure analysis of the titanocene complex 4d confirms the spectroscopic structure determination. All the above mentioned allene-metallocene complexes consume readily a second equivalent of the allene derivatives to produce, in most cases, regiospecifically the corresponding 1 -metalla-2,5-dimethylenecyclopentane derivatives 5a-d (M = Ti) and 8c, d (M = Zr); only the (al1ene)zirconocene complex 7a gives rise to a 1 : 1 mixture of the regioisomers 8a and 9. More conveniently 5a-d and 8c, d are synthesized directly from metallocene dichloride and the corresponding allenes 3.Nach jiingsten Untersuchungen verlauft die Synthese von I, 1 -Bis(qs-cyclopentadienyl)-l -metallacyclopentanen (M = Ti, Zr) aus Metallocendichloriden, Hauptgruppenmetallorganylen, wie Alkyllithiumverbindungen oder Alkylmagnesiumhalogeniden, und Alkenen uber (q2-Alken)metallocene, die dann mit iiberschussigem Alken unter oxidativer Kupplung weiterreagieren[1%2] (Schema 1). In Anwesenheit geeigneter Triorganylphosphane, z. B. Trimethylphosphan, konnen die q2-Alkenkomplexe des Zirkonocens als Triorganylphosphan-Addukte in kristalliner Form abgefangen werdent". Mit M = Ti entsteht hierbei Bis(trimethy1phos-phan)titano~en[~~I, das aber seinerseits als Ausgangsmaterial zur Gewinnung von (qZ-Alken)-oder (q2-A1kin)titanocenkomplexen eingesetzt werden kannL4I. Die Bildung der (A1ken)zirconiumkomplexe aus Dialkylzirconocen ist offensichtlich ein intramolekularer ProzeD, wobei ein P-H-Atom einer Alkylgruppe direkt auf das a-C-Atom der zweiten Alkylgruppe ubertragen wirdc51.Starkere 7c-Komplexbildner, wie Alkine oder gespannte Olefine, konnen Ethylen oder 1-Alkene aus ihren (q2-A1ken)metallocenkomplexen verdrangen, woraus sich neue Moglichkeiten zur Darstellung von q2-Alkin-oder q2-A1-kenkomplexen e r g e b e~~t~~] .Dieser Syntheseweg ist aber in manchen Fallen nicht brauchbar, da mit bestimrden Alkenen oder Alkinen die Weiterreaktion zu den entsprechenden Metallacyclen schneller ist als die n-Komplexbildung [6].Wir haben die Reaktionsmoglichkeiten nach Schema 1 genutzt, um einerseits uber die Titankomplexe 1 und 2 sowie die Zirconiumkomplexe 6 (q2-Allen)(trimethylphosphan)-Komplexe des Titanocens und Zirconocens darzustellen, andererseits auf direktem Weg uber den thermischen Zerfall der Metallocendialkyle in Anwesenheit von mindestens zwei Aquivalenten eines Allens Dimethylenmet...

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Tetratrifylpropene (TTP) has been developed as a highly acidic, allylic C-H acid for Brønsted and Lewis acid catalysis. It can readily be obtained in two steps and consistently shows exceptional catalytic activities for Mukaiyama aldol, Hosomi-Sakurai, and Friedel-Crafts acylation reactions. X-ray analyses of TTP and its salts confirm its designed, allylic structure, in which the negative charge is delocalized over four triflyl groups. NMR experiments, acidity measurements, and theoretical investigations provide further insights to rationalize the remarkable reactivity of TTP.