Two Faces of the Bi-O Bond: Photochemically and Thermally Induced Dehydrocoupling for Si-O Bond Formation

Abstract

The diorgano(bismuth)alcoholate [Bi((C₆H₄CH₂)₂S)OPh] (1-OPh) has been synthesized and fully characterized. Stoichiometric reactions, UV/Vis spectroscopy, and (TD-)DFT calculations suggest its susceptibility to homolytic and heterolytic Bi-O bond cleavage under given reaction conditions. Using the dehydrocoupling of silanes with either TEMPO or phenol as model reactions, the catalytic competency of 1-OPh has been investigated (TEMPO=(tetramethyl-piperidin-1-yl)-oxyl). Different reaction pathways can deliberately be addressed by applying photochemical or thermal reaction conditions and by choosing radical or closed-shell substrates (TEMPO vs. phenol). Applied analytical techniques include NMR, UV/Vis, and EPR spectroscopy, mass spectrometry, single-crystal X-ray diffraction analysis, and (TD)-DFT calculations.

Keywords: Bismuth; Catalysis; Chalcogens; Dehydrocoupling; Radical reactions.

Figure 1

Synthesis (a) and molecular structure in the solid state (b) of compound 1‐OPh. Displacement parameters are drawn at the 50 % probability level. Selected bond lengths (Å) and angles (°): Bi1−C1, 2.263(3); Bi1−C14, 2.249(3); Bi1−O1, 2.2176(18); Bi1−S1, 2.8995(7); C1−Bi1−C14, 97.25(9); C1−Bi1−O1, 89.27(8); C14−Bi1−O1, 85.99(8); S1−Bi1−O1, 151.49(5).

Figure 2

Experimental UV/Vis spectrum of 1‐OPh in acetonitrile at a concentration of c=0.78 mmol ⋅ L⁻¹ (solid black line), lowest energy calculated transitions (blue bars), and molecular orbitals involved in the two lowest calculated absorptions. Isovalue=0.03.