COMMUNICATIONSin which the ring atoms are also coplanar. However, in 2 the ring strain is increased by the central double bond.In summary, tBuC=C-C=CtBu and M e , S i C d -C-CSiMe, react completely differently with zirconocene complexes. The latter cleaves [51 or couples [Eq. (a), ref. [9]] when treated with "Cp,Zr".In contrast. the less reactive rBuC=C-C-CtBu remains intact to yield the mononuclear complex 2. One possible explanation for these differences in reactivity lies in the different electronic influences the substituents exert on the butadiyne system. For R = SiMe, a withdrawal of electron density from the central C atoms through drc(Si)-prc(C) interactions is conceivable; this situation is described by the limiting structureMe, Si = C = C -C =C= SiMe,. For R = tBu the central double bond (essential for coordination as a cumulene) is stabilized in the complex. Coordination is therefore favored over cleavage or coupling (as observed for R = SiMe,).( -)
I + ) I + )I -)
E.uperii~irtitc11 ProcedureAll ireiictioiis were conducted under anaerobic and anhydrous conditions.1 : To a n orange solution of [CplZr(py)(Me,SiC,SiMe,)] (400 mg, 0.85 mmol) in ir-hexanc (10 mL) WAS added ii solution of bis(trimethylsily1)-I .3-butadiyne (330 mg. 1.7 inmol) in ri-hexane (10 mL). and the mixture was stirred for 48 h at room temperature. The ~olvciit was removed under vacuum, the residue redissolved in n-hexiine and filtcred through a frit. and the filtrate was then allowed to crystallize in the cold. Yellow crystalr of 1 formed and were washed w i t h cold ri-hexane and dried under v:icuuni. Yield-210 mg (51 %). m.p. 187-188 C. correct elemental analysis.
.At room tcmperature, a solution of di-rrrr-butyl-1.3-butadiyne (183 mg, 1 .I3 inmol) in tr-hexanc (10 mL) was added to a stirred solution of [Cp,Zr(p\i)lMe,SiCrSiMe,)] (532 mg. 1.13 mmol) in fr-hexane (15 mL). The solution's color changed froin dark red to green. After 24 h all volatile components were removed undcr vacuum and ri-hexane was added. Following filtration, 2 crystallized upon cooling in form of light green needles: these were washed with cold whexane and dried under vacuum. . correct elrinental ariiilysis.