Aluminum-Stabilized Low-Spin Iron(II) Hydrido Complexes of 1,4,7-Trimethyl-1,4,7-triazacyclononane

We
investigated herein the reactions of (Me3tacn)­FeCln (1a: n = 3, 1b: n = 2) with common aluminum hydride reagents
and a bulky dihydridoaluminate {Li­(ether)2}­{Al­(OC6H3-2,6-tBu2)}­(μ-H)2, which yielded the diamagnetic hydrido complexes 2–4 containing Fe­(II) and Al­(III). In particular,
the use of divalent 1b afforded excellent isolated yields.
The structures of 2–4 were determined
using spectroscopic and crystallographic analyses. The crystal structures
showed distorted octahedral Fe centers and fairly short Fe–Al
distances [2.19–2.24 Å]. The structures of cation moiety 2 and neutral complex 4 were further probed using
DFT calculations, which indicated a stable low-spin Fe­(II) state and
strongly electron-donating nature of the (Me3tacn)­FeH3 fragment toward the Al­(III) center.