in dichloromethane stirred for 4 d at room temp.; concd. (vac.), toluene added, filtered after 1 h, crystals washed with toluene, dried (vac.);

in tetrahydrofuran byproducts: H2, HP(O2C6H4)2; absence of air and moisture; pptn. on mixing Nb-complex with 2 equiv. ofphosphine; decantation;

CH2Cl2 in dichloromethane CH2Cl2 (-78°C) added to cold (-78°C) mixt. of Nb complex and (Cp2Fe)PF6 in 2:1 molar ratio under inert atm., cold bath removed, allowed to stir for 3 h; volatiles removed, extd. with Et2O, evapn. of ext. gave Cp2Fe (NMR); residue extd. with acetone, quickly filtered, pumped, washed with Et2O to give (Cp2Nb(CH2SiMe3)Cl)PF6 (NMR); remaining powder identified by IR to be Cp2NbCl2; Me3SiHal identified by GC;

in diethyl ether absence of air and moisture; pptn. on standing for some d, decantation, drying (vac.);

in toluene byproducts: cyclopentadiene; (Ar); addn. of a pyridinium salt (double excess) to a suspn. of niobium complex in toluene at room temp., stirring for 60 h at room temp.; filtration, washing with toluene, drying in vac.;

in toluene absence of air and moisture; pptn. on mixing Nb-complex with 2 equiv. ofphosphine; decantation, crystn. (room temp., 1 week), decantation, drying (vac.); elem. anal.;

hydrogenchloride in tetrahydrofuran introduction HCl gas during stirring of solution for some min; evapn., residue washed with heptane several times;

HCl in tetrahydrofuran under N2, bubbling HCl gas through THF soln. of Nb complex;

in tetrahydrofuran; diethyl ether in inert atmosphere; to soln. of Nb complex in THF added soln. of FeCl3in Et2O, stirred for 0.5 h at room temp.; concd., Nb(Cp)2Cl2 pptd. by cooling overnight, mother liquid concd. andadded pentane, ppt.of (Cp)2NbCl4Fe washed with cold pentane, dried in vac.; elem. anal.;

in benzene dropwise addn. of equimolar amt. of C6H5ICl2 in benzene to rapidly stirred soln. of Nb-complex in benzene at 0 or 25°C; not isolated, detected by ESR-spectroscopy;