Tungsten alkylidynes [CF3-ONO]W≡CC(CH3)3(THF)2 (1) and [(t)BuOCO]W≡CC(CH3)3(THF)2 (3) react with ethylene. Complex 1 reacts reversibly with ethylene to give the metallacyclobutene (2). Complex 3 reacts with ethylene to form the tethered alkylidene (4) featuring a tetraanionic pincer ligand. Complexes 1 and 3 initiate the polymerization of norbornene at room temperature. The polymerization of norbornene by 1 is not stereoselective, whereas 3 generates a highly cis and syndiotactic cyclic polynorbornene. Comparison of the intrinsic viscosity, radius of gyration, and elution time of the synthesized cyclic polynorbornene with those of linear analogues provides conclusive evidence for a cyclic topology.

Synthetic protocols for a pyrrolide-centered ONO3– trianionic pincer-type ligand are presented. Treating ( t BuO)3WC t Bu with the proligand [pyr-ONO]­H3 (2) results in the formation of the trianionic pincer alkylidene complex [pyr-ONO]­WCH t Bu­(O t Bu) (3). Addition of a mild base to complex 3 provides the trianionic pincer alkylidyne complex {MePPh3}­{[pyr-ONO]­WC t Bu­(O t Bu)} (4). All new compounds were characterized by NMR spectroscopy, combustion analysis, and, in the case of complex 4, single-crystal X-ray crystallography. DFT calculations performed on 4 provide insight into its electronic structure and indicate that the HOMO is ligand-based and localized on the pyrrolide π orbitals.

A chemically non-innocent pyrrole-based trianionic (ONO)(3-) pincer ligand within [(pyr-ONO)TiCl(thf)2 ] (2) can access the dianionic [(3H-pyr-ONO)TiCl2 (thf)] (1-THF) and monoanionic [(3H,4H-pyr-ONO)TiCl2 (OEt2 )][B{3,5-(CF3 )2 C6 H3 }4 ] (3-Et2 O) states through remote protonation of the pyrrole γ-C π-bonds. The homoleptic [(3H-pyr-ONO)2 Zr] (4) was synthesized and characterized by X-ray diffraction and NMR spectroscopy in solution. The protonation of 4 by [H(OEt2 )2 ][B{C6 H3 (CF3 )2 }4 ] yields [(3H,4H-pyr-ONO)(3H-pyr-ONO)Zr][B{3,5-(CF3 )2 C6 H3 }4 ] (5), thus demonstrating the storage of three protons.

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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).