in diethyl ether; pentane byproducts: C2H4; Ar atmosphere; dropwise addn. of PCC(CH3)3 (20.0 mmol) in ether/pentaneto a soln. of the Co complex (7.8 mmol) in ether/pentane at -30°C; mixt. was kept at -5°C for 1 h;; evapn.; residue was dissolved in pentane; filtration through Florisil; filtrate was cooled at -78°C for 12 h; removal of solvent; dryingat 1E-3 torr; elem. anal.;;

in diethyl ether; pentane Ar atmosphere, molar ratio complex/PC-t-Bu 1:1; chromy (Al2O3, toluene);

in toluene CpCo(C2H4)2 (9.4 mmol) and Me3SiCCSiMe3 (20 mmol) dissolved in toluene and heated to reflux, at this temp. t-BuCP (7 mmol) and Me3SiCCSiMe3 (10 mmol) in toluene added over 5 h, further stirred for 2 h; filtered through Florisil, evapd., chromd. (column, Kieselgel 60, hexane), CpCo((CSiMe3)4) isolated from 1st yellow eluate, next red eluate yielded CpCo(t-BuCP(CSiMe3)2) after evapn., last eluate contained CpCo((t-BuCP)2); elem. anal.;