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{(OCH 2 )(OCHCO 2 )py‐κ 4 ‐ N , O , O , O }] 2 ( 2 , Cp* = η 5 ‐C 5 Me 5 , py = pyridyl) and [TaCp*Me{(OCH 2 )(OCHCONAr)py‐κ 4 ‐ N , O , O , O }] 2 ( 3 , Ar = p ‐tolyl) have been synthesized by the reactions of [TaCp*Me{(OCH 2 )(OCH)py‐κ 3 ‐ N , O , O }] ( 1 ) with CO 2 and p ‐tolyl isocyanate, respectively. The reaction of 3 with an excess of water renders the corresponding tantalum hydroxide [TaCp*Me(OH){(OCH 2 )(OCHCONHAr)py‐κ 3 ‐ N , O , O }] ( 4 ). Compound 1 reacts with pyridyl triflate (pyOTf) to afford the new pyridyl‐functionalized pincer derivative [TaCp*Me{(OCH 2 )(OCHpy)py‐κ 3 ‐ N , O , O }(OTf)] ( 5 ). Compound 5 reacts with water to yield the aqua adduct [TaCp*Me(OH 2 ){(OCH 2 )(OCHpy)py‐κ 3 ‐ N , O , O }]OTf ( 6 ). The reaction of 5 with LiN(SiMe 3 ) 2 gives rise to the new tantalum compound [TaCp*Me{(OCH 2 )(OCpy)py‐κ 3 ‐ N , O , O }] ( 7 ). Complex 7 reacts with pyOTf to give the dipyridyl‐functionalized pincer derivative [TaCp*Me{(OCH 2 )(OCpy 2 )py‐κ 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.