Investigations of cyano-substituted polypyrazolylborate ligands as possible motifs for transition metal complexes and coordination polymers
Polypyrazolylborates, also called scorpionates, have been one of the most popular ligands in inorganic and organometallic chemistry since their discovery. In our research lab, we have been working with a class of polypyrazolylborate ligands that have alkyl or aryl substituents at the 3- and 5-positions and a CN substituent at the 4-position of the pyrazole rings. Reaction of TpPh, 4CN with chloride salts of Co(II), Mn(II) and Ni(II) produced sandwich complexes, TpPh,4CNBpPh,4CNM. The source of Bp ligands in these complexes was the degradation of Tp ligands, which was verified when Ni(HpzPh,4CN)4Cl2 was isolated from the same reaction that produced TpPh,4CNBpPh,4CNNi. These sandwich complexes of Co, Mn and Ni, plus the Fe analog, were again produced rationally when one equivalent each of the Tp ligand, the Bp ligand and the respective metal chlorides were reacted. When Tpt-Bu,4CN was reacted with chloride salts of Co(II) and Ni(II), M(Hpzt-Bu,4CN)4Cl2 complexes were isolated. Isolation of these complexes indicates the degradation of Tp ligands to pyrazoles, which is not an uncommon phenomenon. With the TpPh, 4CN ligand, we were able to isolate the first half-sandwich complex, [Et4N][TpPh,4CNMo(CO)3]. Methodology for the synthesis of HpzPh, 4CN and Hpzt-Bu,4CN was simplified. New methodologies for the syntheses of tri-substituted cyanopyrazoles were developed. With the aid of these new methodologies, several new pyrazoles were synthesized. Reaction of TpPh,4CN with CuNO3 again produced the Cu(I) polymer, [TpPh,4CNCu.3THF]n. Reaction of TpPh,4CN with the perchlorate salt of Co(II), serendipitously produced the Co(II) coordination polymer, [Co(TpPh,4CN)(HpzPh,4CN)(pzPh,4CN)]n. Further studies are underway to optimize the synthesis of this complex as well as synthesize heterometallic coordination polymers.
Thesis (Ph.D.)-- Wichita State University, Fairmount College of Liberal Arts & Sciences, Dept. of Chemistry