C–O Bond Activation by a Tantalum‐Bonded Pincer Ligand – Ligand Modification Effects on the Selectivity of C–H Bond Cleavage Processes

The tantalum complexes [TaCp*Me{(OCH2)(OCHCO2)py-(4)-N,O,O,O}](2) (2, Cp* = (5)-C5Me5, py = pyridyl) and [TaCp*Me{(OCH2)(OCHCONAr)py-(4)-N,O,O,O}](2) (3, Ar = p-tolyl) have been synthesized by the reactions of [TaCp*Me{(OCH2)(OCH)py-(3)-N,O,O}] (1) with CO2 and p-tolyl isocyanate, respectively. The reaction of 3 with an excess of water renders the corresponding tantalum hydroxide [TaCp*Me(OH){(OCH2)(OCHCONHAr)py-(3)-N,O,O}] (4). Compound 1 reacts with pyridyl triflate (pyOTf) to afford the new pyridyl-functionalized pincer derivative [TaCp*Me{(OCH2)(OCHpy)py-(3)-N,O,O}(OTf)] (5). Compound 5 reacts with water to yield the aqua adduct [TaCp*Me(OH2){(OCH2)(OCHpy)py-(3)-N,O,O}]OTf (6). The reaction of 5 with LiN(SiMe3)(2) gives rise to the new tantalum compound [TaCp*Me{(OCH2)(OCpy)py-(3)-N,O,O}] (7). Complex 7 reacts with pyOTf to give the dipyridyl-functionalized pincer derivative [TaCp*Me{(OCH2)(OCpy(2))py-(3)-N,O,O}(OTf)] (8). The molecular structures of complexes 2, 4 and 6 have been established by single-crystal X-ray diffraction studies.