Synthesis and Characterization of Binucleating Bis(amidinate) Ligands and Their Dialuminum Complexes

Two general routes to binucleating bis(amidinate) ligands based on dibenzofuran and 9,9-dimethylxanthene backbones
are reported. The free-base form of one of the ligands, Ph,MesLDBFH2, forms a 1:1 adduct with acetone. Single-crystal
X-ray diffraction of this adduct reveals bidentate H-bonding of the bis(amidine) to the ketone oxygen. Bond lengths
suggest that the individual H-bonds are relatively weak, yet IR spectroscopy shows a significant −26 cm-1 shift
for the carbonyl stretch relative to free acetone. Additionally, the new dialuminum complexes iPrLDBFAl2Me4 (3),
iPrLXanAl2Me4 (4), tBu,EtLDBFAl2Me4 (5), and tBu,EtLXanAl2Me4 (6) are prepared by reaction of Al2Me6 with the bis(amidines)
in toluene solution. 1H NMR spectroscopic studies indicate that 3 and 4 interact weakly with certain Lewis bases
(DMSO, DMF, pyridine) to effect the exchange of the Al-bound Me groups. Other bases, such as THF and TMEDA,
fail to interact. Solid-state structures for 3 and 4 are reported.