Cyclobutadiene capped

Cation 615 with C4v symmetry can be viewed1078 as square cyclobutadiene capped ... 

A first structural characterization of a cyclobutadiene dianion was performed by Boche and coworkers, who generated the dilithium salt of the 1,2-diphenylbenzocyclobutadiene dianion (143) (by deprotonation with n-butyllithium in the presence of TMEDA) (Figure 17) . Nevertheless, the molecular structure of 143 resembles more the structures of dilithiated alkenes, synthesized by reaction of the corresponding alkynes with metallic lithium. In that class of compounds, carbon-carbon bonds, capped by two lithium centres, are the structural motif (see Section II. E). 

Other superphanes of note are CpCo-capped cyclobutadiene and cyclopentadienone-contain-ing superphanes prepared by Gleiter s group. Examples of these are 55-57 (Scheme 13) [41]. 

Cation 215 with 4 symmetry can be viewed as a square cyclobutadiene moiety capped by a CI I group (see Chapter 1). Several calculations of the structure of (CH)5 at more sophisticated levels have appeared. - MINDO/3 calculations indicated that the pyramidal cation 215 is less stable by 14.4 kcal mol than the isomeric singlet cyclopentadienyl cations of 2 symmetry (216 and 217). The triplet ion 218 of D i, symmetry was calculated to be more stable than the singlet ions but only by 1.6 kcal mol. The triplet... 

Another factor, besides strain, that can destabilize a molecule is an unfavorable electronic interaction, for example that manifested as antiaromaticity, in, say cyclobutadiene [39], but unlike strain, electronic interactions can be favorable and stabilizing. Minyaev et al. proposed that orbital interactions between the two capping (CH)n and the adjacent C moieties stabilize [3 n]- and [4,n]-prismanes by CT-overlap of rr-type ring orbitals, and precedent for snch stabihzation in simple... 

Co, Rh and Ir - The synthesis, properties and reactions of (T]5-bicyclo[3.2.01hcpta-l,3-dienyl)(il -COD)cobalt(I) have been reported, including the X-ray crystal structure of the tetraphenylcyclobutadiene complex, (17), the product of its reaction with diphenylethyne. The reaction of [(Ti5-C5H4R)Co( n -COD)] with 1,6-cyclodecadiyne afforded the (q. C5H4R)cobalt-capped cyclobutadiene superphane. The yield of the reaction was reported to vary with the substituent R. 

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