Coordination modes in zirconium β-diketiminate complexes

Reaction of β-diketiminate lithium salts, nacnacRLi(THF) (R = 2,6-xylyl (1a), R-CH(Me)Ph (1b)), with ZrCl4 or ZrCl4·THF yielded the mono-diketiminate complexes nacnacRZrCl3(THF), 2a and 2b. Complex 2a did not react further with a second equivalent of 1a, but with CpLi or IndLi to form pseudo-tetrahedral complexes 3 and 4. No product could be isolated from reaction of 2b with CpLi. Coordination of the diketiminate ligand in 2a is best described as a distorted κ2-, in-plane coordination. Complexes 3 and 4, however, display a haptotropic shift of the diketiminate ligand and its coordination is best described as κ2,η2-coordination. Although not previously described, analyses of available structures in the literature reveal that non-symmetric κ2,η2-coordination is an independent coordination mode, which exists next to the previously described “η5-like” coordination.