Cobalt complex amplification imaging system with blocked dye precursor

Claim 1

An imaging element comprising at least one image-providing layer, said layer including (a) an inert cobalt (III) complex containing amine ligands, said complex being reducible to a form which releases the ligands, and (b) a blocked dye precursor which is amine activatable to form an unblocked dye precursor capable of an oxidation-reduction reaction with said complex to form a dye, said dye precursor being a blocked leuco dye having the formula ##STR12## wherein COUP is a photographic color-forming coupler connected to the nitrogen atom through a carbon atom at the coupling position; Ar is a substituted or unsubstituted para-phenylene group containing from 6 to about 20 carbon atoms, the substituents of which are halogen atoms in the ortho or meta position of the ring; and X is either an amino group, a hydroxyl group, or the group: --O--R.sup.1 wherein R 1 is a hydrolyzable carbonyl-containing group of the formula ##STR13## wherein R 4 is a group containing 1 to 12 carbon atoms and is an alkyl group or an aryl group; and R 2 is a hydrogen atom or the same substituent as R 1 , provided that at least one of X and R 2 is a carbonyl-containing group.