ORGANOMETALLIC IRON(II) COMPLEXES CONTAINING P-SUBSTITUTED ACETOPHENONE-ARYLHYDRAZONE LIGANDS

a series of twelve new organometallic acetophenone-hydrazone complexes of general formula [(h 5-cp)fe(h 6-o-rc6h4)-nhn=cme-c6h4-p-r？]+pf6- (cp= c5h5; r,r？=h,me, [5]+pf6-; h,meo, [6]+pf6-; h,nme2, [7]+pf6-; me,me, [8]+pf6-; me,meo, [9]+pf6-; me,nme2, [10]+pf6-; meo,me, [11]+pf6-; meo,meo, [12]+pf6-; meo,nme2, [13]+pf6-; cl,me, [14]+pf6-; cl,meo, [15]+pf6-; cl,nme2, [16]+pf6-) has been prepared by reaction between their corresponding organometallic hydrazine precursors [(h 5-cp)fe(h 6-o-rc6h4)-nhnh2]+pf6- (r=h, [1]+pf6-; me, [2]+pf6-; meo, [3]+pf6-; cl, [4]+pf6-, and aromatic ketones of the type mec(=o)c6h4-p-r？ (r？=me, meo, nme2) in refluxing ethanol containing concentrated acetic acid. these mononuclear hydrazones were stereoselectively obtained as their trans-isomers about the n=c double bond, and were characterized by elemental analysis or high resolution mass spectrometry, i.r., uv-vis, and 1h nmr spectroscopies and, in the case of complex [11]+pf6- (r,r'=meo,me), by single-crystal x-ray diffraction analysis. the more salient features of this structure are: (i) the concomitant lengthening of the fe-cipso and the shortening of the cipso-n bond distances leading to a slight iminium-cyclohexadienyl character of the coordinated c6 ring, (ii) the intramolecular hydrogen bonding between the benzylic n-h group and the oxygen atom of the ortho-methoxo-substituent, with the n(1)···o(1) separation of ca. 2.627(4) ？, and (iii) the slight deviation of coplanarity between the coordinated and the free phenyl rings (dihedral angle=15.60(0.25)°). finally, the cyclic voltammetry studies reveal an irreversible one-electron reduction step for compounds [5-7]+pf6-, and the redox potentials clearly indicate that the reduction occurs at the cationic electron acceptor mixed sandwich unit.