ortho- and meta-(Diethynylcyclopentadienyl)tricarbonylmanganese: Building Blocks toward the Construction of Metal Fragment Supported Fullerenynes?

Starting from [(trimethylsilyl)ethynyl]cymantrene (1), the two isomeric 1,2- and 1,3-[bis-(trimethylsilyl)ethynyl] cymantrenes (3a, 4a ) were prepared by a deprotonation/iodination/coupling sequence. The coupling reaction was performed on the mixed ortho-/meta-iodo[(trimethylsilyl)ethynyl]cymantrenes (2) by using Stille methodology (tin alkynes and PdCl{sub 2}(CH{sub 3}CN){sub 2} as catalyst in ethyl ether/DMF). Separation of the isomers (3a, 4a) is achieved by chromatography over flash silica gel. The ortho-diethynylcymantrene 3a is isolated in 42%, while the corresponding meta compound 4a is formed in 26%. If the deprotonation reaction of 1 in pentane/TMEDA is performed under carefully controlled conditions (-78{degree}C), the formation of only ortho 2 is observed in 67% yield. Coupling with trimethylstannyl(trimethylsilyl)acetylene furnished 3a in 57%. Crystal structures have been carried out for complexes 3a. Removal of the alkyne-bound trimethylsilyl groups is achieved in yields of >80% by treatment of 3a and 4a with potassium carbonate in methanol. The parent diethynylcymantrenes (3b, 4b) are stable compounds. Treatment of 1,2-diethynylcymantrene 3b under Hay conditions gives coupled material, a polymer poly[(ortho-cymantrene)butadiynylene] (6) in 68% yield (M{sub n} = 9300). 15 refs., 4 figs., 1 tab.