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.
Cyclopentadienylalkylphosphane chelate complexes have been investigated in depth for many transition matals, but to a much lesser extent for nickel. On the basis of earlier investigations of cyclopentadienylalkylphosphane nickel chelates, a number of new alkyl, aryl, alkenyl, and alkynyl complexes, including some bearing functional groups, were prepared and fully characterized. These include for the first time
Treatment of cyclopentadienylnickel chloro or bromo chelates bearing either a tertiary 2‐(di‐tert‐butyl)phosphanylethyl or a secondary 2‐(2,4,6‐trimethylphenyl)phosphanylethyl tether with imidazolylidene (Arduengo carbene) ligands results in cationic or electroneutral carbene complexes with either a decoordinated or a chelated tether. The outcome depends on the nature of the carbene, the counter anion, and the reactant stoichiometry. The results are the basis of ongoing investigations directed towards a deprotonation of the chelated cationic complexes with a secondary phosphorus atom.
The reaction occurs at very mild conditions and involves an oxyanion driven ring opening. -(KOHSER, S. C.; DONGOL, K. G.; BUTENSCHOEN*, H.; Heterocycles 74 (2007) 1, 339-350; Inst. Org. Chem., Univ. Hannover, D-30167 Hannover, Germany; Eng.) -K. Woydowski 25-137
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