Structural Characterization and Self-Association of (Arylimido)vanadium(V) Triisopropoxides

Alkoxide ligand controlled self-assembling of (imido)vanadium(V) compounds having a tetrahedral VO3N geometry

The reaction of (1S,2S)-(-)-1,2-diphenylethylenediamine with VO(OⁱPr)₃ in the presence of NaH was found to afford the binuclear (imido)vanadium(V) triisopropoxide, [(OⁱPr)₃V(N-meso-1,2-DPE-N)V(OⁱPr)₃] (DPE = diphenylethylene), (1a_RS/SS). Using (1R,2R)-(+)-1,2-diphenylethylenediamine as a starting material, one-step reaction also proceeded to form the binuclear (imido)vanadium(V) triisopropoxide, [(OⁱPr)₃V(N-meso-1,2-DPE-N)V(OⁱPr)₃], (1a_RS/RR). The single-crystal X-ray structure determination of 1a_RS/SS revealed the hydrogen-bonded self-assembled structure utilizing the advantage of anti-conformation through the intermolecular hydrogen bonds of C-H···O pattern between phenyl and isopropoxide moieties, wherein each vanadium atom is coordinated in a nearly tetrahedral VO₃N geometry (τ₄ = 0.017 and 0.057). On the contrary, a discrete (imido)vanadium(V) tris(triphenylsiloxide) unit, which possesses a nearly tetrahedral VO₃N arrangement around the vanadium metal center (τ₄ = 0.060), was observed in the crystal structure of the (4-methoxyphenylimido)vanadium(V) tris(triphenylsiloxide), [(p-MeOC₆H₄N)V(OSiPh₃)₃], (1b) with bulky triphenylsiloxide ligands.

Design and redox function of conjugated complexes with polyanilines or quinonediimines

Because of their potential application as new electrical materials that depend on their redox properties, π-conjugated polymers and oligomers have attracted much attention. Polyanilines, which are chemically stable, are one of the promising classes of conducting π-conjugated polymers. Polyanilines exist in three different discrete redox forms, which include the fully reduced leucoemeraldine, the semioxidized emeraldine, and the fully oxidized pernigraniline base form. The redox-active 1,4-phenylenediamine (PD) and 1,4-benzoquinonediimine, unit molecules of the emeraldine base form, can bind to transition metals to afford novel conjugated complexes. The introduction of metal centers into π-conjugated polymers is expected to dramatically change their functions. In this Account, we describe our ongoing research into the construction of conjugated complexes with redox-active π-conjugated polyanilines and 1,4-benzoquinonediimines. These systems can form architecturally controlled functionalized systems that depend on their dynamic redox properties, resulting in highly selective and versatile electron-transfer reactions and functionalized materials. Complexation with metals (Pd, V, Cu, etc.) occurred via the two nitrogen atoms of the quinonediimine moiety of the emeraldine base form of poly(o-toluidine) to afford the single-strand or cross-linked network conjugated complexes with d,π-conjugation. The complexation of the redox-active π-conjugated 1,4-benzoquinonediimines, unit molecules of the emeraldine base form, with palladium(II) compounds yielded a variety of conjugated complexes. Through regulation of the coordination mode of the quinonediimine moiety, we were able to architecturally control the formation of conjugated bimetallic, polymeric, or macrocyclic complexes. Complexation modulated the redox function of the quinonediimine moiety. Introduced metals act as a metallic dopant, and the complexed quinonediimine is stabilized as an electron sink. Furthermore, chirality could be induced into a π-conjugated backbone through complexation with optically active transition compounds, resulting in chiral d,π-conjugated complexes. We could also modulate the functional properties of conjugated complexes based on the redox states of the redox-active π-conjugated moieties. We also demonstrated how complexes with redox-active π-conjugated molecules can control the architecture of redox-functionalized systems through the metal imido bonds of these systems. Using the one-pot preparation of (arylimido)vanadium(V) compounds from the corresponding anilines, we synthesized binuclear complexes with axial chirality and trinuclear complexes with a tridendritic centrosymmetric structural motif. Such structures showed a strong tendency to self-assemble.