Investigating metal size effects in the Ln2(mu-eta2:eta2-N2) reduction system: reductive reactivity with complexes of the largest and smallest trivalent lanthanide ions, La3+ and Lu3+.

Metal size effects in reductive chemistry using [(C(5)Me(4)H)(2)Ln(THF)](2)(mu-eta(2):eta(2)-N(2)) complexes have been evaluated using the extremes in ionic radii of the lanthanide series, Ln = La, 1, and Lu, 2. Comparisons have been made using 1,3,5,7-cyclooctatetraene, phenazine, carbon dioxide, and anthracene as substrates. Complexes 1 and 2 react similarly with 1,3,5,7-cyclooctatetraene to form (C(5)Me(4)H)(3)Ln and (C(5)Me(4)H)Ln(C(8)H(8))(THF)(x) (Ln = La, x = 2, or Lu, x = 0) in a reaction analogous to the reduction of this substrate with divalent (C(5)Me(5))(2)Sm. Complexes 1 and 2 differ in their reactions with phenazine in that 1 forms at least three products, including [(C(5)Me(4)H)(2)La](mu-eta(4):eta(2)-C(12)H(8)N(2))[La(THF)(C(5)Me(4)H)(2)], 3, and (C(5)Me(4)H)(3)La, whereas 2 forms a single product, [(C(5)Me(4)H)(2)Lu](2)(mu-eta(3):eta(3)-C(12)H(8)N(2)), 4, in quantitative yield. Complexes 3 and 4 are similar to the product obtained from the reaction of (C(5)Me(5))(2)Sm and phenazine, [(C(5)Me(5))(2)Sm](2)(mu-eta(3):eta(3)-C(12)H(8)N(2)), since all three complexes contain a reduced phenazine dianion, but the phenazine ligand displays structural variations depending on the size of the metal. With CO(2), complex 1 forms multiple products, but 2 reacts cleanly to form the reductively coupled oxalate complex, [(C(5)Me(4)H)(2)Lu](2)(mu-eta(2):eta(2)-C(2)O(4)), 5, in high yield. With anthracene, 1 forms a complex product mixture from which only (C(5)Me(4)H)(3)La(THF), 9, characterized by X-ray crystallography, could be identified. In contrast, 2 is unreactive toward anthracene even upon heating to 75 degrees C after 24 h.