Bis(trimethylsilyl)acetylene Complexes of Titanocenes and Zirconocenes: Their Recent Chemistry and Reactions with Lewis Acids

• Published in: European journal of inorganic chemistry Vol. 2004; no. 24; pp. 4739 - 4749
• Main Authors: Rosenthal, Uwe, Burlakov, Vladimir V., Arndt, Perdita, Baumann, Wolfgang, Spannenberg, Anke, Shur, Vladimir B.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.12.2004; WILEY‐VCH Verlag
• Subjects: Lewis acids; Metallocenes; Polymerization; Titanium; Zirconium
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200400749

The chemistry of the metallocene bis(trimethylsilyl)acetylene complexes [Cp2M(L)(η2‐Me3SiC2SiMe3)] [M = Ti, without L (1); M = Zr, L = THF (2a); M = Zr, L = pyridine (2b)], the pentamethylcyclopentadienyl complexes [Cp*2M(η2‐Me3SiC2SiMe3)] [M = Ti (3), Zr (4)], and the ethylenebis(tetrahydroindenyl) (ebthi) complexes rac‐[(ebthi)M(η2‐Me3SiC2SiMe3)] [M = Ti (5), Zr (6)] has been described in several reviews. A fine‐tuning of the reactions is possible by varying the Cp ligands (Cp, Cp*, ebthi), additional the co‐ligands (THF, pyridine), and/or metals (Ti, Zr), and it has been pointed out that these complexes offer a number of compelling advantages over other, similar, widely used metallocene reagents. In this microreview recent (2000−2004) examples of the chemistry of complexes 1−6 are summarized, and some special interactions with Lewis acids are described. In these reactions the metallocene cores “Cp′2Ti” and “Cp′2Zr” (Cp′ = substituted Cp ligands) are mostly formed after dissociation of the alkyne. As examples of this, a new selective zirconocene coupling route to large, functionalized macrocycles has been established from 2b and polyynes, complex 1 catalyses the first anti‐Markovnikov hydroamination of terminal alkynes, complexes 1 and 3 selectively form polynuclear titanium complexes by C−C coupling of N‐containing heterocycles, and complexes 1, 2b, 3, and 6 promote selective C−H and C−F bond‐cleavage reactions of fluorinated N‐containing heterocycles. Beside this recent chemistry, this microreview also focuses on the reactions of the above‐mentioned complexes with the Lewis acids diisobutylaluminum hydride and tris(pentafluorophenyl)borane. For example, complexes 1, 2b, and 6 react with iBu2AlH to give heterodimetallic complexes containing tetracoordinate planar carbon atoms. The titanium complex 1 reacts with B(C6F5)3 with elimination of the alkyne and gaseous hydrogen to give an electrophilic substitution of the Cp or Cp* ligand in which zwitterionic TiIII complexes are formed. The zirconium complexes 4 and 6 do not liberate hydrogen in the reaction with B(C6F5)3, although, after C−H activation of one methyl group of the Cp* or Cp part of the ebthi ligand and a B−C bond formation, zwitterionic complexes containing alkylidene groups with agostic interactions with the metal center are obtained. Complex 5 reacts with B(C6F5)3 with Si−C bond cleavage of the alkyne and formation of an alkynylboranate [Me3SiC≡CB(C6F5)3]−, which is complexed by the “rac‐(ebthi)Ti” fragment to give a zwitterionic complex. Some of the formed heterodinuclear complexes and the zwitterionic complexes are active catalysts in the ring‐opening polymerization of lactones, cyclic carbonates, and epoxides, as well as the polymerization of ethylene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)