PROGRAM | Chemistry and Biochemistry

By: Eric Sirianni Chair: Klaus Theopold

ABSTRACT

The successful synthesis and structural characterization of a new family of second and third generation ferrocenyl-substituted tris(pyrazolyl)borate ligands was achieved. These ligands employ ferrocenyl (Fc) moieties for increased C-H bond strengths as well as maintaining the steric demands necessary to remain “tetrahedral enforcers”. The thallium(I) salts of the TpFc* (1) and TpFc,Me* (2) ligands were isolated as N-confused asymmetric isomers. However, TpFc,iPrTl (3) was isolated as the symmetric ligand as a dimer with an apparent Tl – Tl interaction. Cyclic voltammetry of 1, 2, and 3 revealed single, reversible, three electron redox processes which suggests a lack of electronic communication between the ferrocenyl moieties when bound to a hydrotris(pyrazolyl)borate ligand. Conversely, TpCF3,FcTl (4) displays an irreversible redox process that is accompanied by decomposition during the oxidation wave of the CV.
Thallium salts 1 and 2 undergo borotropic rearrangements to form the symmetric TpFcTl (7) and TpFc,MeTl (8), respectively. These ligands react with CoX2 (X: Cl, I) to form their symmetric TpCoX complexes. Salt metathesis of 3 with CoI2 led to the isolation of TpFc,iPrCoI (13) as the only observable product. However, the reaction of 3 with CoCl2 yielded an N-confused TpFc,iPr*CoCl (14) complex. The electronic characterization of TpFc,R (R: H, Me, i-Pr) has been sought through the synthesis of their corresponding copper(I) carbonyl complexes. Although the reaction of 7 and 8 with CuI under CO yields the symmetric TpFcCu(CO) (16) and TpFc,MeCu(CO) (17), respectively, the reaction of 3 with CuI under CO yielded the singly N-confused TpFc,iPr*Cu(CO) (19) and doubly N-confused TpFc,iPr**Cu(CO) (18) complexes.
The TpFc,Me ligand has been employed in cobalt oxygen chemistry and has displayed its ability to resist C-H bond activation on the ligand. TpFc,MeCo(η3-C3H5) (22) reacted with O2 to form an apparent TpFc,MeCoOOC3H5 intermediate which underwent O – O bond homolysis to form TpFc,MeCoOH (21). 22 reacted with CO to form TpFc,MeCo(CO) (23). 23 reacts with O2 to form the side-on superoxo complex, TpFc,MeCo(O2), which has been structurally characterized by X-ray diffraction. Furthermore, the terminal imido complex, TpFc,MeCoNAd (25), displayed greater thermal stability than its analogous alkyl-substituted TptBu,MeCoNR complexes.

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