Tricyclic cyclobutadiene complexes

The reaction of cyclic diynes with CpCo(CO>2 or CpRh(CO)2, or in some cases with Fe(CO)5, leads to the tricyclic cyclobutadiene complexes, as demonstrated for the reaction of 1,7-cyclododecadiyne (3) with CpM(CO)2 in Eq. (24). This reaction was discovered and explored 20 years ago [77, 79]. The availability of cyclic diynes with uneven chains such as 1,6-cyclodecadiyne (100), 1,8-cyclotetradecadiyne (120) and 1,10-cyclooctadecadiyne (168) led to the superphanes 169-171 and to the intramolecular complexes 172-174 [Eq. (25)] [1 c, 80]. 

Cp)Co(CO)2 to give (Cp)Co(alkadiyne) complexes in which the acetylene has cyclized to a tricyclic cyclobutadiene ring-size effects are discussed in cyclizations with iron carbonyls. 

Hogeveen and co-workers <82JOC1909 83JOC4275> also reported the synthesis of tricyclic sulfinamides by the reaction of cyclobutadiene aluminum halide o complexes (65 or 66) with 53 at low temperature. Treatment of 65 or 66 with 53 at -60 °C resulted in the formation of 67 or 68 in 52% and 55% yields, respectively (Scheme 18). 

By cobalt-lithium exchange, the group of Sekiguchi and coworkers generated several dilithium salts of variously substituted cyclobutadiene dianions . By the reaction of the functionalized acetylenes (e.g. compound 137) with CpCo(CO)2 (136), the corresponding cobalt sandwich complexes, related to compound 138, were obtained (Scheme 50). These can be interconverted into the dilithium salts of the accordant cyclobutadiene dianions (e.g. dilithium compound 139) by reaction with metallic lithium in THF. Bicyclic as well as tricyclic (e.g. dilithium compound 141, starting from cobalt complex 140) silyl substituted systems were generated (Scheme 51) . ... 

Cyclopropene provides isomeric tricycles upon reaction with cyclobutadiene generated from its iron tricarbonyl complex (equation 54) but this thermal reaction is more likely to... 

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