With  NbCl3(CH3OCH2CH2OCH3) in  ethylene glycol dimethyl ether  under Ar; addn. of Cr-complex/DME (1-2 equiv) to Nb-compd./DME at room temp., mixt. stirred; addn. of satd. Na2CO3, extd. (ether, twice), combined organics dried (MgSO4), filtered, evapn. (vac.), flash chromy. (silica gel, light petroleum-diethyl ether (7/3));