Structural characterization of the coordination behavior of 4,4′-di-methoxy,2,2′-di-ol-benzophenone modified metal alkoxides

Abstract

For the first time, the coordination behavior of the 4,4′-di-methoxy,2,2′-di-ol-benzophenone (H 2-OBzP) ligand with a series of early transition metal alkoxides (Group 4, 5, and 6) was determined to adopt either the ‘bridging, chelating bridging’ (μ,μ c-OBzP) or the ‘bichelating bridging’ (μ c2-OBzP) arrangement. The main products were found to be dimeric with pseudo-octahedral (O h ) bound metal centers. The μ,μ c-OBzP mode was noted for the larger cations (Hf, Nb, and Ta) and the solvated smallest (Ti/py) whereas the μ c2-OBzP coordination was observed for the larger Group 4 metal congeners: [(py)(OPr i) 2Ti(μ,μ c-OBzP)] 2 ( 1), ‘{[(OBu t) 2Ti(μ-OBu t)] 2(μ c2-OBzP)} n ’ ( 2), [(ONep) 2Ti(μ-ONep)] 2(μ c2-OBzP) ( 3), [(OBu t) 2Zr(μ-OBu t)] 2(μ c2-OBzP) ( 4), [(MeIm) 2(ONep) 2Zr(μ,μ c-OBzP)] 2 ( 5), [(ONep) 2Zr(μ c2-OBzP)(μ-ONep)(μ 3-O)Zr(ONep)] 2 ( 5a), [(OBu t) 2Hf(μ c2-OBzP)] 2 (6), ‘{[(ONep) 2Hf(μ,μ c-OBzP)] 2·py} n ’ ( 7), ‘{[(OEt) 3Nb(μ,μ c-OBzP)] 2} n ’ ( 8), [(ONep) 3Nb(μ,μ c-OBzP)] 2 ( 9), [(OEt) 3Ta(μ,μ c-OBzP)] 2 ( 10), [(ONep) 3Ta(μ,μ c-OBzP)] 2 ( 11), and [(OEt) 2(O)W(μ,μ c-OBzP)] 2 ( 12), [(ONep) 2W(O)(μ,μ c-OBzp)] 2 ( 13), [(py)(O) 2W(μ,μ c-OBzP)] 2 ( 13a), and [(Me 2Al(μ, 2μ c-OBzP)Al(py) 2] ( 14) where Me = CH 3, OEt = OCH 2CH 3, OPr i = OCHMe 2, OBu t = OCMe 3, ONep = OCH 2CMe 3, py = pyridine, MeIm = 1-methyl imidazole, and 2μ c-refers to the chelation occurs on the same metal. Compounds 2, 7, and 8 are represented by quotation marks since they could not be crystallographically characterized, however, their structural arrangements were deduced from the FTIR spectroscopic data. The coordination mode of the OBzP ligand for 1– 13 appears to be driven by the need to fill the O h geometry, which is achieved by either binding solvent molecules or additional bridging ligands, dictated by the charge and size of the cations employed. The metal alkyl alkoxide compound 14 employs a unique μ, 2μ c-OBzP mode, yielding a +2/+4 charge separated molecular Al complex.