No abstract

The utility of the bulky aryloxide ligands 2,6-Ad 2 -4-Me-C 6 H 2 O − ( Ad,Ad,Me ArO − ) and 2,6-Ad 2 -4-t-Bu-C 6 H 2 O − ( Ad,Ad,t-Bu ArO − ; Ad = 1-adamantyl) for stabilizing the Y(II) ion is reported and compared with the results with 2,6-t-Bu 2 -4-Me-C 6 H 2 O − (Ar′O − ). In contrast to the reduction product obtained from reducing Y(OAr′) 3 with potassium graphite, which is only stable in solution for 60 s at room temperature, KC 8 reduction of Y(OAr Ad,Ad,t-Bu ) 3 in THF in the presence of 2.2.2-cryptand (crypt) produces the room-temperature stable, crystallographically characterizable Y(II) aryloxide [K(crypt)]-[Y(OAr Ad,Ad,t-Bu ) 3 ]. The X-band EPR spectrum at 77 K shows an axial pattern with resonances centered at g ⊥ = 1.97 and g ∥ = 2.00 and hyperfine coupling constants of A ⊥ = 156.5 G and A ∥ = 147.8 G and at room temperature shows an isotropic pattern with g iso = 1.98 and A iso = 153.3 G, which is consistent with an S = 1/2 spin system with nuclear spin I = 1/2 for the 89 Y isotope (100% natural abundance).

To evaluate the relative reducing capacities of rare-earth metal complexes of Sc­(II), Y­(II), and complexes of the lanthanide metals in their +2 oxidation state, a series of reactions of trivalent LnIIIA3 compounds with divalent [Ln′IIA′3]1– complexes has been examined, where Ln = Sc, Y, or a lanthanide and A is C5H4SiMe3 (Cp′), C5H3(SiMe3)2 (Cp″), C5Me4H (Cptet), N­(SiMe3)2 (NR2), 2,6- t Bu2-C6H3O (OAr), or 2,6- t Bu2-4-Me-C6H2O (OAr′). The specific combinations were chosen to allow evaluation by EPR spectroscopy of the Ln­(II) complex. The [LnIICp′3]1– complexes of Y­(II), La­(II), and Lu­(II) have similar reducing abilities in that they all reduce LnIIICp′3 complexes of the other metals in this group. However, these Y­(II), La­(II), and Lu­(II) complexes all are stronger reductants than [GdIICp′3]1–, which cannot reduce LnIIICp′3 complexes of Y, La, and Lu. These results do not apply to all ligand sets, since [GdII(NR2)3]1– can reduce YIII(NR2)3 to [YII(NR2)3]1–. The amide and aryloxide complexes of Y and Sc are similar in that [YII(NR2)3]1– reduces ScIII(NR2)3 and [YII(OAr′)3]1– reduces ScIII(OAr′)3. Both [YII(NR2)3]1– and [YII(OAr′)3]1– reduce YIIICp′3. [LaIICptet 3]1– has reductive capacity similar to that of [LaIICp′3]1–, and both are stronger reductants than [LaIICp″3]1–. None of the LnIII2 complexes of Sm, Tm, Dy, and Nd can reduce LnIIIA3 complexes of Y and La to [LnIIA3]1–. In the “same-metal-different-ligands” reactions, multiple EPR signals are found, suggesting that ligand exchange occurs alongside the electron transfer reactivity.

The suitability of aryloxide ligands for stabilizing +2 oxidation states of Sc and Y has been examined and EPR evidence indicating the first O-donor complexes of Sc and Y has been obtained, as well as an X-ray crystal structure of a Sc aryloxide complex. The trivalent rare-earth metal aryloxide precursors, Ln(OAr') , 1-Ln (Ln=Sc, Y, Gd, Dy, Ho, Er; OAr'=OC H tBu -2,6-Me-4), were synthesized from the corresponding rare-earth metal trichlorides and LiOAr'⋅OEt . Reduction of THF solutions of 1-Ln with potassium graphite in the presence of 2.2.2-cryptand (crypt) yielded dark-colored solutions, 2-Ln, whose EPR spectra at 77 K are characteristic of the Ln ions: a two-line spectrum (g =1.99, g =1.97, A =154 G) for 2-Y and an eight-line spectrum (g =2.01 and A =291 G) for 2-Sc. Solutions of 2-Y decompose within one minute at room temperature, wheras 2-Sc persists up to 40 min at room temperature. 2-Sc was identified by X-ray crystallography as [K(crypt)][Sc(OAr') ], which has a trigonal-planar arrangement of oxygen-donor atoms around Sc . Analogous reductions of 1-Ln for Ln=Gd, Dy, Ho, and Er also gave dark solutions of limited stability. Theoretical analysis using time-dependent density functional theory (TD-DFT) along with complete active space self-consistent field (CASSCF) methods, and structural analysis with the Guzei ligand solid angle G-parameter method are presented.

The possibility that the relative reactivity of complexes of actinidem etalsi nt he + 2a nd + 3o xidation states could be investigated by examining reactions between An III and An II species of Th and Uw ithr are-earth metal reagents that provide EPR confirmation of electron transfer reactivity has been explored. 2 ). 1À ,r espectively, which wereidentified by EPR spectroscopy.The reverse reactions also occur which indicates that the reduction potentials are similar.[ Cp'' 3 La II ] 1À reduces Cp' 3 Y III and the reverse Y II /La III combination also occurs.I nb othc ases, the reactions generate EPR spectra indicative of multiple species in the mixtures of La II and Y II ,w hich is consistent with ligand exchange and demonstrates that numeroush eteroleptic complexes of these Ln II ions exist.Ar ecent development in rare-earth and actinide chemistry is the discovery that the + 2oxidation state is availableincrystallographically characterizable molecular speciesf or many more metals than was previously expected. Specifically, the first crystallographically-characterizable