Synthesis and Characterization of Group 4 Trianionic ONO^3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space ¹⁹F–¹⁹F Coupling

This report describes the synthesis and characterization of a new series of group 4 complexes supported by a trianionic ONO3– pincer-type ligand. Treating TiCl4 with the proligand [CF3–ONO]­H3 (1) and NEt3 in benzene afforded {[CF3–ONO]­TiCl3}­{HNEt3}2 (2). By means of a lithium transmetalation route, the neutral monochloride complex [CF3–ONO]­TiCl­(THF) (3) was synthesized in 91% yield. The analogous Hf­(IV) derivative could not be obtained using this method. Instead, transmetalation with thallium­(I) resulted in the formation of the seven-coordinate complex [CF3–ONHO]­HfCl2(THF)2 (4-(THF)2), which was characterized by combustion analysis and X-ray crystallography. Applying vacuum to 4-(THF)2 liberated the THF ligands to provide the five-coordinate THF-free complex [CF3–ONHO]­HfCl2 (4). Alkylation of complex 4 with alkyllithium or Grignard reagents resulted in a mixture of unidentifiable products. However, access to the neutral complex 3 enabled the subsequent preparation of organotitanium complexes [CF3–ONO]­TiR­(THF) (5-R; R = Me, Bn, Mes). Single-crystal X-ray analysis of 5-Me indicated that the organotitanium complexes are mononuclear. Single-crystal X-ray diffraction and NMR studies in solution confirmed that complex 5-Mes exhibits rare through-space 19F–19F coupling (5 Hz).