The reaction of nickelocene with tert-butyllithium has been studied. It was found that unstable species {CpNiC(CH 3 ) 3 }, formed in this reaction, reacted further in two directions: β-H elimination and homolytic cleavage of Ni-C bond. Hydrogen elimination product formed trinickel cluster (NiCp) 3 CCH(CH 3 ) 2 1, while t-butyl radical alkylated cyclopentadienyl rings to form several compounds. One of these compounds, {Ni[C 5 H 4 C(CH 3 ) 3 ]} 2 [C 5 H 5 C(CH 3 ) 3 ] 3, has been isolated and fully characterised. The compound crystallizes from hexane in a triclinic crystal system and P1 space group. Corresponding unit cell parameters were determined as a=7.520(2) 9; b=13.150(5) 9; c=13.625(4) 9; α=113.77(3) o ; β=97.42(3) o ; γ=90.02(3) o ; V=1220.7(7) 9 3 ; Z=2. It is the first example of alkylation of cyclopentadienyl rings bonded to nickel by organolithium compounds.