(Di-tert-butylphosphanyl-P-ethyl)cyclopentadienylcobalt(I) complexes 1 and 2 were treated with 3,3-disubstituted cyclopropenes to give isoprene and vinylcarbene complexes. The diphenylvinylcarbene complex reacted with tert-butylphosphaethyne to give unusual coupling products.

Reactions of cyclopropenone derivatives with the [2-(di-tert-butylphosphanyl)ethyl]cyclopentadienylcobalt(I) chelate system were investigated. Ethene complex 2 reacts with diphenylcyclopropenone under cobalt insertion to give cobaltacyclobutenone chelate complex 6 in 91% yield. 6 was characterized crystallographically and shows a structure similar to that of a known platinacyclobutenone. Thermoanalysis of 6 indicated a reaction at elevated temperature, which was shown to be a cycloreversion at 60°C leading to known diphenylethyne and carbonyl complexes 7 and 9. Attempts to reduce the metallacyclobutenone with lithium tetrahydridoaluminate resulted in the cycloreversion reaction at a temperature as low as -100 to -90°C, the lithium cation acting as a Lewis acid. The reaction of dimethoxycyclopropene complex 4 with zinc triflate unexpectedly resulted in the formation of methyl acrylate complex 13, which was characterized crystallographically.

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Treatment of {eta(5):eta(1)[2-(di-tert-butylphosphanyl-P)ethyl]cyclopentadienyl}cobalt(I) chloride (5) with methylenecyclopropane (3) or bicyclopropylidene (4), as well as with their spirocyclopropanated analogues methylenespiropentane (7), cyclopropylidenespiropentane (10), or 7,7'-bi(dispiro[2.0.2.1]heptylidene) (15) in the presence of sodium amalgam at -50 degrees C, furnished the stable cobalt complexes 6, 9, 8, 11, and 16, respectively, in 72, 83, 84, 86, and 54 % isolated yield, respectively. The complexes 14 and 16 were also obtained by ligand exchange of the ethene complex {eta(5):eta(1)[2-(di-tert-butylphosphanyl-P)ethyl]cyclopentadienyl}(eta(2)-ethene)cobalt(I) (12) with 13 and 15 in 79 and 52 % yield, respectively. The X-ray crystal-structure analyses of complexes 9, 14, and 16, as well as the NMR-spectroscopic data of all complexes, reveal that they can be regarded as linear and branched cobalta[n]triangulanes. The thermal stability of complexes 6, 8, and 9 up to 109, 145, and 160 degrees C was determined by differential thermal analysis-thermogravimetry (DTA-TG) analysis.

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