Synthesis and structures of tris(2-pyridyl)aluminate sandwich compounds [{RAl(2-py′)2}2M] (py′ = 2-pyridyl, M = Ca, Mn, Fe)

Abstract

Reactions of the lithium salts [{RAl(2-py′)₃Li·THF] [2-py′ = 2-py (2-pyridyl), R = ⁿBu (1), R = ^secBu (2); py′ = 5-Me-2-py (5-methyl-2-pyridyl), R = Me (3); 6-Me-2-py (6-methyl-2-pyridyl), R = Et (4b)] with the corresponding metal(II) halides give the new heterobimetallic sandwich compounds [{RAl(2-py)₃}₂M] [R = ⁿBu, M = Ca (5), Mn (6), Fe (7); R = ^secBu, M = Ca (8), Mn (9)], [{MeAl(5-Me-2-py)₃}₂Ca] (10) and [{EtAl(6-Me-2-py)₃}₂Ca] (11) and the co-complex [{EtAl(6-Me-2-py)₃}Mn(μ-Cl)Li{(6-Me-2-py)₃AlEt}] (12). While neither the bridgehead group (R) nor remote ring Me-groups have any impact on metal coordination in 5–10, the introduction of Me groups into the pyridyl substituent at the 6-position (i.e., adjacent to the donor pyridyl-N atoms) has a marked effect on the ability of the ligands to form sandwich arrangements, as seen in the distorted structure of the sandwich compound 11 and in the formation of the co-complex 12, consisting of a two half-sandwich arrangement linked by a μ-Cl ion. The syntheses and solid-state structures of the new precursor 4b and the new compounds 5–12 are reported.