Synthesis of 1,2-cyclopentadienyl diimine anions and their zirconium complexes

Abstract: 1,2-disubstituted cyclopentadienyl diimine anions are examples of extended -systems that bind metals through the nitrogen atoms. Reaction of Cp2Mg with benzonitrile gives the product (1,2-C5H3(C(Ph)NH)2)CpMg(NCPh) (1) in 98% yield. In an analogous manner, the related complexes (1,2-C5H3(C(Ph)NH)2)CpMg(OEt2) (2) and ((4-Me3SiC5H2)(1,2-(C(Ph)NH)2)(Me3SiC5H4)Mg(OEt2) (3) were prepared in situ. Demetalation of these complexes 1-3 yields the corresponding free diimine ligands of formulation H[(1,2-C5H3(C(Ph)NH)2)] (4) and H[4-Me3SiC5H2-1,2-(C(Ph)NH)2] (5). Hydrolysis of compound 4 leads to the fulvene derivative 1-(C(OH)Ph)-2-(O=C(Ph))C5H3 (6). The zirconium complexes (C5H3-1,2-(C(Ph)NH)2)ZrCl3(THF) (7) and (C5H3-1,2-(C(Ph)NH)2)3ZrCl (8) were isolated from reactions of 4 with ZrCl4(THF)2. X-ray crystallographic studies of 1, 7, and 8 are reported. Evidence suggests that these new 1,2-disubstituted cyclopentadienyl diimine anions impart some charge delocalization, thus offering a new approach to electrophilic metal centers. This view is supported by EHMO calculations.