The First η⁵-Indenylnickel Chelate Complexes with a Pendant Phosphane Tether

The synthesis of the first indenylnickel chelate complexes with a pendant phosphane ligand is described. In contrast to earlier attempts by others directed to chelates with a tethered diphenylphosphino ligand in our hands, the synthesis was successful with a di-tert-butylphosphino ligand. The anionic ligand system was generated by a nucleophilic ring-opening of spiroindene 3 with lithium di-tert-butylphosphide, a reaction that was significantly accelerated by microwave irradiation. Alternatively, the borane-protected ligand was obtained by using the lithiated borane adduct of di-tert-butylphosphane. Reaction of the anionic ligand with nickel(II) chloride gave chloro chelate 8, which was transformed to azido, cyano, and isothiocyanato complexes 9−11, the cationic acetonitrile complex 12, and representatives containing nickel−carbon bonds, including the methyl and the ethynyl derivatives 13 and 18. A crystal structure analysis of methyl chelate 13 is also included. The 13C NMR data of a quarternized 2-pyridylethynyl derivative 20 suggest a significant contribution of the respective allenylidene resonance formulas 21 and 22. Finally, bimetallic ferrocenylethynyl complex 23 has been included as a bimetallic representative. Some of the complexes were characterized by cyclovoltammetry.