Structural characterization of ((9-fluorenylidene) (ferrocenyl)methyl)palladium iodide as the catalytic intermediate in the synthesis of 9-(ferrocenyl (ferrocenylethynyl)methylene)-9<i>H</i>-fluorene

The reaction of 2,2′-diiodo-1,1′-biphenyl (1a) with ethynyl ferrocene (2) gave trace amounts the expected 2,2′-bis(ferrocenylethynyl)-1,1′-biphenyl (3) together 9-(ferrocenyl(ferrocenylethynyl)methylene)-9H-fluorene (4), formed via a cyclization process during Sonogashira cross-coupling reaction, as major product. In contrast, similar 2,2′-diiodo-1,1′-diphenyl ether analogue 2 anticipated 2,2′-bis(ferrocenylethynyl) substituted product (11). Reaction 11 tetracyanoethylene its bis-[2 + 2] cycloaddition in high yield (12), while alkynyl motif fluorenylidene 4 proved to be inert towards such reactions. Studies mechanism leading formation using Pd/dppf (dppf = 1,1′-bis(diphenylphosphino)ferrocene) catalyst combination allowed for isolation {C C(Fc)–PdI(dppf)} intermediate (13), which was structurally characterized by single crystal X-ray diffraction. Electrochemical investigations 4, 11, 12 and 13 revealed series essentially ferrocene-based oxidation processes, case could better resolved non-coordinating anion based electrolyte. Electronic structure studies at DFT level (B3LYP/def2-TZVP/CPCM(CH2Cl2) suggest that first event can assigned vinyl-bonded ferrocenyl moiety.