A thorough investigation of the reactions of diynes, R(C&tbd1;C)(2)R, and polyynes, R(C&tbd1;C)(n)()R, with titanocene and zirconocene was performed using the metallocene sources Cp(2)M(L)(eta(2)-Me(3)SiC&tbd1;CSiMe(3)) (M = Ti, L = -; M = Zr, L = THF, pyridine). The conversions show an array of different products generated in complexation, coupling, and cleavage reactions. These results include remarkable structures (e.g., five-membered metallacyclocumulenes) and reactions (e.g., C-C single-bond cleavage). In addition, the first C-C single-bond metathesis in homogeneous solution was discovered. The presented findings have been supported by theoretical studies.

This paper describes the reactivity of permethylzirconocene and permethyltitanocene toward different 1,3-butadiynes. A pointed dependence on the metals and the diyne substituents was found. Unusual, but still stable, five-membered zirconacyclocumulenes (η4-diyne complexes, zirconacyclopenta-2,3,4-trienes) Cp*2Zr(η4-1,2,3,4-RC4R), R = Ph and SiMe3, were prepared using two new and effective synthetic routes. One starts with the permethylzirconocene bisacetylides Cp*2Zr(C⋮CR)2, R = Ph (1a), SiMe3 (1b), which rearrange in sunlight to form the stable five-membered zirconacyclocumulenes Cp*2Zr(η4-1,2,3,4-RC4R), R = Ph (2a), SiMe3 (2b). The alternative route to 2a and 2b is the reduction of Cp*2ZrCl2 with Mg in the presence of the adequate disubstituted butadiynes RC⋮C−C⋮CR. Both methods failed to produce the analogous titanacyclocumulenes, which seemed extremely unstable. Nevertheless, we were able to obtain distinct products employing the reduction pathway with permethyltitanocene. For R = SiMe3, the novel titanacyclopropene (η2-complex) Cp*2Ti(η2-1,2-Me3SiC2C⋮CSiMe3) (3) was isolated. For R = Ph, an activation of both pentamethylcyclopentadienyl ligands was observed resulting in the complex [η5-C5Me4−(CH2)−]Ti[−C(CHPh)C(CHPh)CH2-η5-C5Me4] (4). The reaction of 4 with carbon dioxide led to the Cp*-substituted titanafuranone Cp*Ti[−OC(O)C(Ph)C(−)C(CHPh)CH2-η5-C5Me4] (5). The zirconacyclocumulene 2b surprisingly inserted two molecules of CO2 to give the unprecedented cumulenic dicarboxylate Cp*2Zr [−OC(O)C(SiMe3)CCC(SiMe3)C(O)O−] (6). The η2-complex 3 (titanacyclopropene) took up one molecule of carbon dioxide to afford the titanafuranone Cp*2Ti[OC(O)C(SiMe3)C(C⋮CSiMe3)−] (7).

Herein we describe different C-C coupling reactions of permethyltitanocene and -zirconocene with disubstituted 1,3-butadiynes. The outcomes of these reactions vary depending on the metals and the diyne substituents. The reduction of [Cp2*MCl2] (Cp* = C5Me5; M = Ti, Zr) with Mg in the presence of disubstituted butadiynes RC triple bond C-C triple bond CR' is suitable for the synthesis of different C-C coupling products of the diyne and the permethylmetallocenes, and provides a new method for the generation of functionalized pentamethyl-cyclopentadienyl derivatives. For M = Zr and R = R' = tBu, the reaction gives, by a twofold activation of one pentamethylcyclopentadienyl ligand, the complex [Cp*Zr[-C(=C=CHtBu)-CHtBu-CH2-eta5-C5Me3-CH2-]] (3), containing a fulvene ligand that is coupled to the modified substrate (allenic subunit). When using the analogous permethyltitanocene fragment "Cp2*Ti", the reaction depends strongly on the substituents R and R'. The coupling product of the butadiyne with two methyl groups of one of the pentamethylcyclopentadienyl ring systems, [Cp*Ti[eta5-C5Me3-(CH2-CHR-eta2-C2-CHR'-CH2)]], is obtained with R = R' = tBu (4) and R = tBu, R' = SiMe3 (5). In these complexes one pentamethylcyclopentadienyl ligand is annellated to an eight-membered ring with a C-C triple bond, which is coordinated to the titanium center. A different activation of both pentamethylcyclopentadienyl ligands is observed for R = R' = Me, resulting in the complex [[eta5-C5Me4(CH2)-]Ti[-C(=CHMe)-C(=CHMe)-CH2-eta5-C5Me4]] (6), which displays a fulvene as well as a butadienyl-substituted pentamethylcyclopentadienyl ligand. The influence exerted by the size of the metal is illustrated in the reaction of [Cp2*ZrCl2] with MeC triple bond C-C triple bond CMe. Here the five-membered metallacyclocumulene complex [Cp2*Zr(eta4-1,2,3,4-MeC4Me)] (7) is obtained. The reaction paths found for R = R' = Me are identical to those formerly described for R = R' = Ph.

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