Stoichiometric and catalytic reactivity of tris(oxazolinyl)phenylborato zinc and magnesium compounds
Recently, our research group has synthesized a new class of monoanionic tridentate ligands, ToR (ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate and ToP = tris(4-S-isopropyl-2-oxazolinyl)phenylborate), and developed the corresponding stoichiometric and catalytic chemistry of zirconium, yttrium, rhodium, iridium, and magnesium complexes. This thesis begins with the comparison of this new class of scorpionate-type ligands (ToM and ToP) with more classical Tp (tris(pyrazolyl)borates) and Cp (cyclopentadienyl) analogues, both in terms of relative electron donating ability as well as steric bulk. Group 7 metal tricarbonyl complexes of ToM and ToP (ToMM(CO)3 and ToPMC(O)3; M = Re, Mn) were synthesized in this purpose and the corresponding νCO IR stretching frequency data were used for the electron donating ability comparison. Solid angles of these ancillary ligands were calculated using coordinates from crystal structures or molecular models with the program Solid-G to obtain a quantitative assessment of the relative steric properties. The thesis then mainly focuses on the chemistry of four-coordiante zinc complexes using ToM as the supportive ancillary ligand. The main interest lies on the synthesis of molecular terminal zinc hydride and its catalytic activity in Si−O bond formation reactions, as well as the isolation and reactivity study of alkylperoxy zinc compounds (ToMZnOOR) obtained from the reactions of the corresponding zinc alkyls (ToMZnR) with molecular O2. The later part of this thesis also discusses the chemistry of ToM-supported magnesium complexes and the comparison with analogous zinc complexes. It starts with the synthesis of ToM-supported zinc and magnesium bulky silyl complexes, both comprising with and without β-SiH moieties (ToMM−SiR3; M = Zn, Mg; R = SiHMe2, SiMe3). The study further extends to divergent reaction pathways of ToMMSi(SiHMe2)3 (M = Zn, Mg) towards CO2. Finally, the thesis discusses the catalytic activity of ToMZnH and ToMMgMe in carbonyl reduction. ToMMgMe mediated catalytic Tischenko coupling of aldehydes, reversible trans-esterification, and reductive ester cleavage are also discussed in details.