Using Diamagnetic Yttrium and Lanthanum Complexes to Explore Ligand Reduction and C-H Bond Activation in a Tris(aryloxide)mesitylene Ligand System

[Y(N(SiMe3)(2))(3)] reacts with ((ArOH)-Ar-Ad,Me)(3)mes to form the Y3+ complex [(((ArO)-Ar-Ad,Me)(3)mes)Y], 1-Y. This complex reacts with potassium metal in the presence of 2.2.2-cryptand to give a cocrystallized mixture of [K(2.2.2-cryptand)]-[(((ArO)-Ar-Ad,Me)(3)mes)Y], 2-Y, and [K(2.2.2-cryptand)]-[(((ArO)-Ar-Ad,Me)(3)mes)YH], 3-Y. The electron paramagnetic resonance spectrum of this crystalline mixture exhibits an isotropic signal at 77 K (g(iso) = 2.000, W-iso = 1.8 mT), suggesting that 2-Y is best described as a Y3+ complex of the tris(aryloxide)mesitylene radical (((ArO)-Ar-Ad,Me)(3)mes)(4-). Evidence of the hydride ligand in 3-Y was obtained by Y-89-H-1 heteronuclear multiple quantum coherence NMR spectroscopy, and a coupling constant of J(YH) = 93 Hz was observed. A single crystal of 3-Y was also obtained in pure form and structurally characterized for comparison with the crystal data on the mixed component 2-Ln/3-Ln crystals. The origin of the hydride in 3-Ln is unknown, but further studies of the reduction of 1-La, previously found to form 2-La, revealed a possible source. Ligand-based C-H bond activation and loss of hydrogen can occur under reducing conditions to form a tetraanionic ligand derived from (((ArO)-Ar-Ad,Me)(3)mes)(3-), as observed in [K(2.2.2-cryptand)][(((ArO)-Ar-Ad,Me)(3)(C6Me3(CH2)(2)CH)La], 4-La.