We report the enhanced reactivity of hydroxyl substituted CuN 3 + derivatives, where N 3 = tris(picolinyl) methane (tripic) and related derivatives, upon deprotonation of the O-H functionality. The work capitalizes on new methodology for incorporating hydroxyl groups into the second coordination sphere of copper centers. The key synthetic methodology relies on Pd-catalyzed coupling reactions of dilithiated 6-methyl-2-pyridone with bromopyridyl derivatives. These building blocks allow the preparation of tridentate N 3 ligands with OH and OMe substituents flanking the fourth coordination site of a tetrahedral complex. Coupling of these tridendate ligands gives the corresponding hydroxy- and methoxy-functionalized bistripodal ligands. [Cu[bis(2-methylpyrid-6-yl)(2- hydroxypyrid-6-yl)methane](NCMe)] + ([Cu(2H)(NCMe)] +) oxidizes readily in air to afford the mixed valence Cu 1.5 dimer ([Cu 2(2) 2] +). Formation of [Cu 2(2) 2] + is accelerated in the presence of base and can be reversed with a combination of decamethylferrocene and acid. The reactivity of [Cu(2H)(NCMe)] + with dioxygen requires deprotonation of the hydroxyl substituent: neither [Cu(tripic)(NCMe)] + nor the methoxy-derivatives displayed comparable reactivity. A related mixed valence dimer formed upon oxidation of the dicopper(I) complex of a tetrahydroxy bis(tridentate) ligand, [Cu 2(6H 4)(NCMe) 2] 2+. The dicopper(I) complex of the analogous tetramethoxy N 6-ligand, [Cu 2(5)(NCMe) 2] 2+, instead reversibly binds O 2. Deprotonation of [Cu(2H)(CO)] + and [Cu(2H)(NCMe)] + afforded the neutral derivatives Cu(2)(CO) and Cu 2(2) 2, respectively. The dicopper(I) derivative Cu 2(2) 2 can be reoxidized, reprotonated, and carbonylated. The silver(I) complex, [Ag(2H)(NCMe)]BF 4, forms an analogous neutral dimer (Ag 2(2) 2) upon deprotonation of the hydroxyl group. The structures of ligand 2H, [Cu 2(5)(NCMe) 2] +, [Cu 2(2) 2] +, [Cu 2(6H 2)] +, [Ag(2H)(NCMe)]BF 4, and Ag 2(2) 2 were confirmed by single crystal X-ray diffraction.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry