Zirconocene derivatives for dehydrocoupling of acetylenes and carbene-phosphinidene adducts and their metal complexes

Abstract

Anionic Group 4 metallocenes have seen a significant amount of attention over the last 20 years with particular interest in titanocene and zirconocene derivatives.[superscript 1-5] The synthesis and characterization of dichlororbis([eta superscript 5]-cyclopentadienyl)zirconium (zirconocene dichloride or Cp[subscript 2]ZrCl[subscript 2] where Cp = [eta superscript 5]-C[subscript 5]H[subscript 5]) first described in 1954 by Wilkinson and Birmingham spurred extensive research in this field.[superscript 6] A particularly interesting area of these zirconocene derivatives comes from the work by Negishi et al. where an anionic zirconocene compound can be oxidized resulting in the coupling of two phenylacetylene molecules.[superscript 2] Similar to the Negishi zirconocene chemistry, Stephan et al. published a synthetic route for an anionic zirconocene trihydride.[superscript 7] Using both areas of research as a starting block, a catalytic process was investigated to dehydrocouple phenylacetylene using similar zirconocene derivatives. Although it was confirmed via Nuclear Magnetic Resonance (NMR) spectroscopy that a possible catalytic precursor was formed, no catalysis was successfully completed in this research. A second aspect of fundamental main group chemistry involves the synthesis of carbene-phosphinidene adducts first described by Arduengo in 1997.[superscript 8] The bonding scenario of the P-C bond of the carbene-phosphinidene adduct was confirmed to have both single and double bond character.[superscript 9] With this unique property in mind, novel carbene-phosphinidene adducts were synthesized and characterized via single crystal X-ray diffraction techniques. Due to the interesting bonding nature of the carbene-phosphinidene adduct, the newly synthesized carbene-phosphinidene adducts were used in attempts to form metal complexes. Preliminary results indicate the formation of the first stable carbene-phosphinidene metal complex. Other preliminary results indicate the possibility of insertion reactions occurring with weaker P-C bonds in the carbene-phosphinidene adducts.