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The first [4]radialene complex of zirconocene 1Zr-Ph was obtained by the reaction of Negishi’s reagent with 1,4-diphenylbutadiyne. The structure of 1Zr-Ph has been determined by X-ray diffraction. ...

The interaction of the seven-membered zirconacyclocumulene complex Cp2Zr[η4-Me3SiC4(SiMe3)–C(C2SiMe3)=CSiMe3] (1) with an equimolar amount of HCl in dioxane at 20 °C results in the formation of the...

The interaction of the Buchwald seven-membered zirconacyclocumulene Cp2Zr[η4-Me3SiC4(SiMe3)–C(C2SiMe3)=CSiMe3] (1) with a 2-fold excess of benzophenone in toluene at 100 °C for 20 h results in the ...

On prolonged heating of the Buchwald seven-membered zirconacyclocumulene Cp2Zr[η4-Me3SiC4(SiMe3)–C(C2SiMe3)═CSiMe3] (1) in toluene at 100 °C, the isomerization of 1 takes place with the formation of a seven-membered zirconacyclocumulene complex, Cp2Zr[η4-Me3SiC4(SiMe3)–C(SiMe3)═C(C2SiMe3)] (8), containing the Me3SiC≡C group in α-position and the SiMe3 group in β-position with respect to the Zr atom. A remarkable peculiarity of complex 8 is its ability to undergo a rapid degenerate rearrangement at room temperature in toluene solution, as a result of which only two rather than four singlets of the Me3Si groups are observed in the 1H NMR spectrum of 8 under such conditions. At temperatures below 200 K, the rate of this rearrangement decreases and, as a consequence, the 1H NMR spectrum of 8 acquires the normal view. If 1 is heated at 100 °C in the presence of acetylenes such as 1,4-bis(tert-butyl)butadiyne (tBuC≡C–C≡CtBu) and tolane, the corresponding seven-membered zirconacyclocumulenes, viz., Cp2Zr[η4-tBuC...

Reactions of the five-membered metallacyclocumulenes Cp2M(η4-t-Bu-C4-t-Bu) (M = Ti, Zr) with the Lewis Acid i-Bu2AlH were studied. Cp2Ti(η4-t-Bu-C4-t-Bu) (1) reacts with i-Bu2AlH to give a heterobi...

The previously described hafnacyclocumulene Cp2Hf(η4-t-Bu-C4-t-Bu) (1) reacts with B(C6F5)3 to give the dinuclear complex 2, which consists of a cationic part with two hafnocene centers bridged uns...

The bonding nature of metallocene acetylene complexes Cp2M(eta(2)-H3SiC2SiH3) 1M and CP2M (eta(2)- HC2H) 1M' (M = Ti, Zr, Hf) wits studied by density functional theory method. It is found that this acetylene complex has indeed it metallacyclopropene moiety with two in-plane M-C sigma-bonds and one out-of-plane pi-bond interacting with the metal center, resulting in the formation of it delocalized three-center and two-electron (3c-2e) system. Along with its delocalized out-of-plane bonding, this complex has been characterized its aromatic on the basis of the computed stabilizing energy and negative nucleus-independent chemical shifts (NICS). The aromatic stabilization increases from Ti to Zr and Hf, and this is because of the increased charge separation between the CP2M fragment and the H3SiC2SiH3 (also HC2H) unit. The decrease of the M-C bond length from Zr to Hf is ttributed to the increased s character of both M and C hybridization of the M-C a-bonds.

The previously described hafnocene alkyne complexes are of limited applicability for the generation of the hafnocene fragment in stoichiometric and catalytic reactions. For this reason di-n-butylhafnocene (1-Hf) was fully characterized and used as a hafnocene source in reactions with alkynes and diynes. With bis(trimethylsilyl)acetylene and pyridine the alkyne complex Cp2Hf(py)(η2-Me3SiC2SiMe3) (2-Hf) was obtained and coordination of di-tert-butylbutadiyne yielded the first structurally characterized hafnacyclocumulene, Cp2Hf(η4-t-BuC4-t-Bu) (4-Hf). By the coupling of 2 equiv of the 1,3-butadiyne RC4R at the hafnocene center, hafnacyclopentadienes were formed regioselectively (R = t-Bu, 5-t-Bu-Hf; R = SiMe3, 5-SiMe3-Hf). In the case of 1,4-diphenylbutadiyne the hafnocene-substituted [4]radialene 6-Hf was formed. Treatment of the latter with acid gave the free [4]radialene 7. In the reaction of 4-Hf with diphenylacetylene, the alkyne inserted into the Hf−Cα bond to give the hafnacyclopentadiene 8.

Reaction of the menthyl-substituted metallocene dichlorides (η5-menthyl-C5H4)2MCl2 (M = Ti (1-Ti), Zr (1-Zr)) with magnesium in the presence of Me3SiC2SiMe3 in THF gives the chiral group 4 metallocene alkyne complexes of titanium and zirconium (η5-menthyl-C5H4)2M(Me3SiC2SiMe3) (M = Ti (2-Ti), Zr (2-Zr)). Both complexes show a similar complexation behavior and reactivity to their achiral metallocene congeners. For example, the reaction with ethylene was studied; whereas the zirconium complex 2-Zr yields the zirconacyclopentane 3 in a well-defined reaction, the titanium analogue 2-Ti produces only an as yet unseparable mixture of different compounds. 2-Ti, 2-Zr, and 3 were characterized by X-ray crystal structure analysis.

The complexation of phenyl(trimethylsilyl)acetylene by decamethylhafnocene gave the complex Cp*2Hf(η2-PhC2SiMe3) (1-Hf). By comparison of detailed spectroscopic and structural data as well as of so...

The reactions of the 1-zirconacyclopent-3-ynes Cp‘2Zr(η4-H2C4H2) with Cp‘2 = Cp2 (1), (η5-t-Bu-C5H4)2 (2), and Me2Si(η5-C5H4)2 (3) and of the zirconacyclopropene Me2Si(η5-C5H4)2Zr(THF)(η2-Me3SiC2SiMe3) (8) toward t-Bu-NC are described. In the case of the 1-zirconacyclopent-3-ynes 2 equiv of t-Bu-NC were inserted into the β-Zr−C bonds of the zirconacycle. After subsequent rearrangement the substituted 1-zircona-2,5-diazacyclopent-3-enes 4, 5, and 6, possessing an anellated cyclobutene ring having two exocyclic double bonds, were obtained. In the protolysis of 6 with MeOH the metal-free cyclobutene 7 was formed. The alkyne complex 9 reacted with the isocyanide to give end-on complexation instead of an expected insertion, resulting in the alkyne complex Me2Si(η5-C5H4)2Zr(η1-CN-t-Bu)(η2-Me3SiC2SiMe3) (11).

The reduction of certain group 4 metallocene dichlorides by magnesium or lithium in the presence or absence of Me3SiC2SiMe3 in THF or toluene was investigated, giving in the case of titanium the dinuclear Ti(III) complex [rac-(ebthi)Ti(μ-Cl)]2 (1). For zirconium the 1-oxa-2-zirconacyclohexane 2 was formed by ring-opening reaction of rac-(ebthi)Zr(η2-Me3SiC2SiMe3) with THF. As a byproduct from the synthesis of Cp*2Zr(η2-Me3SiC2SiMe3) starting from Cp*2ZrCl2 another 1-oxa-2-zirconacyclohexane (3) was obtained by ring-opening reaction of THF via the dinuclear complex Cp*2Zr(Cl)-(CH2)4O−Zr(Cl)Cp*2 (4). In the case of hafnium the analogous dinuclear complex Cp*2Hf(Cl)−(CH2)4O−Hf(Cl)Cp*2 (5) and 1-oxa-2-hafnacyclohexane (6) were the main products of the reaction, inhibiting the synthesis of Cp*2Hf(η2-Me3SiC2SiMe3) (7). The tendency for ring opening of THF initiated by metallocenes increases in the series Ti, Zr, Hf, thus leading to consequences for the synthesis of metallocene complexes.

The synthesis and reactions of ansa-dimethylsilanediyl−dicyclopentadienyl−zirconacyclopent-3-yne, Me2Si(η5-C5H4)2Zr(η4-H2C4H2) (7), are described. Complexation by Ni(0) complexes gives an external coordination of the triple bond and formation of the complex Me2Si(η5-C5H4)2Zr[μ(η4-H2C4H2)]Ni(PPh3)2 (8), representing a μ-“cis”-complexation of 1,2,3-butatrienes, which is described and compared with the coordination of similar complexes. The reaction of complex 7 with B(C6F5)3 results in ring opening of the 1-zirconacyclopent-3-yne and formation of the zwitterionic complex [Me2Si(η5-C5H4)2Zr]+−CH2C⋮CCH2−[B-(C6F5)3] (9), with the but-2-yne-1,4-diyl ligand bridging the zirconocenium center and the formed boranate. All complexes were characterized by X-ray analysis.

The well-known zirconafuranone, obtained by the reaction of the decamethylzirconocene bis(trimethylsilyl)acetylene complex Cp*2Zr(η2-Me3SiC2SiMe3) with carbon dioxide, rearranges upon thermolysis to a complex with the [C5Me4−CH2−CH(Me3Si)C(CO)]2- ligand resulting from an electrophilic substitution of a hydrogen atom at one of the methyl groups of a Cp* ligand, a cleavage of the CO bond in the starting zirconafuranone, and a movement of the Me3Si groups from β-carbon to oxygen. Another example of the functionalization of a pentamethylcyclopentadienyl ligand by carbon dioxide was found with a complex obtained by the reaction of Cp*2ZrCl2 with magnesium in the presence of the butadiyne t-BuC⋮CC⋮Ct-Bu. This complex reacts by formally inserting 1 equiv of carbon dioxide into each of two ZrC bonds, but yields a dinuclear complex with twofold functionalized Cp* ligands acting as bridging dicarboxylato ligands, [O2C−CH2−C5Me3−CH2−CH(t-Bu)C(CCH-t-Bu)−CO2]3-. Both complexes result from a simple method of functional...

In the reaction of the decamethylzirconocene-bis(trimethylsilyl)acetylene complex Cp* 2 Zr(η 2 -Me 3 -SiC 2 SiMe 3 ) (1) with i-Bu 2 AlH, CH bond activation, an electrophilic substitution, and alumination of the pentamethylcyclopentadienyl ligand resulted in formation of the η 5 -C 5 Me 4 CH 2 -Al(i-Bu) 2 H ligand. The final product contains an alkenyl complex that shows an agostic C-H···Zr interaction, Cp*Zr[-C(SiMe 3 )= CH(SiMe3)](μ-H)[η 5 -C5Me4CH2-Al(ι-Bu) 2 ] (2). Heating complex 2 gives the heterobimetallic complex Cp*Zr[-C(SiMe3)=C(SiMe3)Al(i-Bu)(μ-H)(CH 2 -η 5 -C5Me4)] (3), which is formed by an intramolecular reaction, analogous to intermolecular reactions of titanocene- and zirconocene-alkyne complexes with i-Bu 2 AlH, which yield the well-known heterobimetallic complexes with tetracoordinated planar carbon atoms. Both complexes were characterized by NMR spectroscopy and X-ray crystal structure analysis. Complex 2 catalyzes the ethene polymerization and the ring-opening polymerization of e-caprolactone.

The complexation of the uncommon 1-zirconacyclopent-3-yne Cp2Zr(η4-H2C4H2) by Ni(0) complexes is described and compared to the coordination of similar 1-metallacyclopenta-2,3,4-trienes Cp2M(η4-PhC4Ph) of titanium and zirconium, both showing μ-“cis”-complexation of 1,2,3-butatrienes and 1,3-butadiynes in addition to the well-known μ-“trans”-complexation.

The five-membered zirconacyclocumulenes Cp*2Zr(η4-1,2,3,4-RC4R) (Cp* = η5-pentamethylcyclopentadienyl, R = Me3Si 1a, Me 1b, Ph 1c) each react differently with B(C6F5)3. For 1a (R = Me3Si) a bond cl...

In reactions of the zirconocene 2-vinylpyridine complex Cp2Zr(2-vipy) (1) with iBu2AlH and iBu2AlF the isostructural complexes [Cp2Zr(μ-η1:η2-2-CH2CH−C5H4N)(μ-H)][iBu2Al] (3) and [Cp2Zr(μ-η1:η2-2-CH2CH−C5H4N)(μ-F)][iBu2Al] (5) were formed. These complexes can serve as models for the transfer of fluorine from zirconium to aluminum (Zr−F with Al−H to Zr−H and Al−F) found in the reaction of rac-(ebthi)ZrF2 with iBu2AlH to form the dimeric complex [rac-(ebthi)ZrH(μ-H)]2 (6). The compounds are important in obtaining an understanding of the activation of zirconocene fluoro complexes by iBu3Al and of the role of iBu2AlH in activation processes for the catalytic polymerization of olefins.

Different products of the reaction of the five-membered zirconacyclocumulenes (zirconacyclopenta-2,3,4-trienes) Cp*2Zr(η4-1,2,3,4-RC4R) (Cp* = η5-pentamethylcyclopentadienyl, R = Me (1a), Me3Si (1b...

Starting from zirconocene bis(trimethylsilyl)acetylene complexes Cp‘2Zr(L)(η2-btmsa) via the 2-vinylpyridine complexes Cp‘2Zr(2-vipy) a novel synthetic method for zirconocene difluoride and alkyl m...

The zirconocene−alkyne complex Cp2Zr(py)(η2-Me3SiC2SiMe3) reacts with methyl vinyl ketone to yield the zirconadihydrofuran (1). In contrast, rac-(ebthi)Zr(η2-Me3SiC2SiMe3) (ebthi = 1,2-ethylene-1,1‘-bis(η5-tetrahydroindenyl) reacts with methyl vinyl ketone giving, for the first time, the 1,4-conjugated insertion product (2) in good yield. An X-ray crystallographic structure determination of 2 shows that the seven-membered ring is twisted in such a way to fit the steric demands of the “ebthi” and SiMe3 groups. Treating rac-(ebthi)Zr(η2-Me3SiC2SiMe3) with tert-butyl acrylate gives the zirconadihydrofuran (3). The monomeric structure of 3 has been established by X-ray crystallography. A different type of zirconadihydrofuran, (4), results from the reaction with mesityl oxide. Complexes analogous to 4 and 2 were observed consecutively by NMR in the reaction of Thi2Zr(η2-Me3SiC2SiMe3) (Thi = η5-tetrahydroindenyl) with methyl vinyl ketone. This lets one conclude that the carbonyl insertion products (e.g. 4) are ...

The reactions of the titanium(III) complex Cp*2TiCl with lithium acetylides RC⋮CLi depend strongly on the solvents used. In THF only the lithium tweezer compounds [Cp*2Ti(C⋮CR)2Li(THF)n] (Cp* = η5-C5Me5; R = SiMe3, n = 1 (1); R = t-Bu, n = 1 (2); R = Ph, n = 2 (3)), not the expected mono(σ-alkynyl) titanocene(III) complexes, were obtained, whereas in n-hexane these complexes Cp*2Ti(C⋮CR) were isolated for R = Me (4), t-Bu (5). The reaction of the complex [Cp*2Ti(C⋮CSiMe3)2Li(THF)] (1) with carbon dioxide results in the titanafuranone 6, which presumably is formed by insertion of carbon dioxide into the η2-butadiyne complex Cp*2Ti(η2-Me3SiC⋮CC⋮CSiMe3). The complex [Cp*2Ti(C⋮C-t-Bu)2Li(THF)] (2) reacts with carbon dioxide to yield the permethyltitanocene carboxylate Cp*2Ti(O2CC⋮C-t-Bu) (7) via insertion into the σ-acetylide bond of the in situ formed titanium(III) intermediate [Cp*2Ti−C⋮C-t-Bu]. Compound 7 was also obtained in the reaction of the isolated titanium(III) complex Cp*2Ti−C⋮C-t-Bu (5) with carbo...

The reaction of (η5-iPrC5H4)2Ti(Me3SiC2SiMe3) (2) with B(C6F5)3 in toluene at room temperature produces the zwitterionic titanium(III) complex (η5-iPrC5H4)[η5-{1,3-iPrC5H3B(C6F5)3}]Ti (3) in which the 3-hydrogen atom of one of the C5 rings is substituted by a B(C6F5)3 group. The complex is analogous in its structure to the previously described titanium(III) zwitterion Cp[η5-C5H4B(C6F5)3]Ti (1) formed in the interaction of B(C6F5)3 with Cp2Ti(Me3SiC2SiMe3). A characteristic feature of both zwitterionic complexes is the presence of coordinative bonds between the ortho-fluorine atoms of two C6F5 substituents and the positively charged titanium center. Complex 1 is also obtained by the reaction of B(C6F5)3 with Cp2Ti(PhC2SiMe3). The oxidation of 1 and 3 by air oxygen affords the zwitterionic titanoxanes {Cp[η5-C5H4B(C6F5)3]Ti}2O (4) and {(η5-iPrC5H4)[(η5-{1,3-iPrC5H3B(C6F5)3}]Ti}2O (5), respectively, which contain two zwitterionic units in the molecule. In each of these units, only one ortho-fluorine atom of ...

The new class of compounds arising from unconventinal additions of 1,4-disubstituted 1,3-butadiynes to activated permethylmetallocene species of Ti and Zr can be used in facile functionalizations. For example, the chiral product 5, obtained from the addition of tBuC⋮CC⋮CtBu to activated permethyltitanocene, has been derivatized by simple means, e.g., hydrogen chloride, bromine, or dihydrogen, affording practically useful functionalized titanocene compounds containing a chiral auxiliary ligand with an intramolecularly coordinated (compound 7) or a free double bond (compounds 8a,b). The new complexes have been characterized spectroscopically. Additionally, X-ray crystal structure analyses were performed for 7 and 8a,b.

Reactions of the branched polyynes tris(tert-butylbutadiynyl)benzene (1,3,5-(tBuC⋮CC⋮C)3C6H3) (1) with the metallocene sources Cp2Ti(η2-Me3SiC⋮CSiMe3) (2) and Cp2Zr(THF)(η2-Me3SiC⋮CSiMe3) (3; THF = tetrahydrofuran) led to diverse novel organometallic Ti6 (4), Zr3 (5), and Zr6 (6) complexes depending on the metals, the polyynes, and the stoichiometries employed in the conversions. The new complexes have been characterized spectroscopically. Additionally X-ray crystal structure analyses were performed for 4 and 6.

In reactions of the zirconocene derivative Cp2ZrC(SiMe3)C(SiMe3)(THF) with ketones and aldehydes the influence of the various substituents of the carbonyl compounds upon the formation of different products was investigated. Formaldehyde reacts by an insertion of the carbonyl unit into a Zr−C bond to give a metallacycle which is additionally stabilized by the formation of a coordination dimer [Cp2ZrOCH2C(SiMe3)C(SiMe3)]2 (1). Benzaldehyde yields a monomeric metallacycle Cp2ZrOCHPhC(SiMe3)C(SiMe3) (2). Complex 2 is less stable than 1, and at higher temperatures it loses half of its moiety Me3SiC2SiMe3, leaving {[Cp2ZrOCHPhC(SiMe3)C(SiMe3)][Cp2Zr(η2-OCHPh)]} (3). Benzophenone gives no insertion, and the monomeric η2-ketone complex Cp2Zr(THF)(η2-OCPh2) (4) was obtained.

Reactions of the branched tetraalkynylsilanes (RC⋮C)4Si (1a: R = Ph, 1b: tBu, 1c: SiMe3) with the metallocene source Cp2Ti(η2-Me3SiC⋮CSiMe3) (2) led to complexes 4−6, and those of 1a with Cp2Zr(THF)(η2-Me3SiC⋮CSiMe3) (3) to complex 7. These, via 2-fold migration and C−C coupling of the alkynyl groups, gave a novel type of dinuclear carbon-rich spiro complexes. The conversions proved to be independent of the metals, the substituents R, and the stoichiometries employed. All new complexes have been characterized spectroscopically. Additionally, an X-ray crystal structure analysis was performed for 7.