Ligand‐Modification Effects on the Reactivity, Solubility, and Stability of Organometallic Tantalum Complexes in Water

Tantalum complexes [TaCp*Me{κ 4 ‐ C,N,O,O ‐(OCH 2 )(OCHC(CH 2 NMe 2 )CH)py}] ( 4 ) and [TaCp*Me{κ 4 ‐ C,N,O,O ‐(OCH 2 )(OCHC(CH 2 NH 2 )CH)py}] ( 5 ), which contain modified alkoxide pincer ligands, were synthesized from the reactions of [TaCp*Me{κ 3 ‐ N,O,O ‐(OCH 2 )(OCH)py}] (Cp*=η 5 ‐C 5 Me 5 ) with HCCCH 2 NMe 2 and HCCCH 2 NH 2 , respectively. The reactions of [TaCp*Me{κ 4 ‐ C,N,O,O ‐(OCH 2 )(OCHC(Ph)CH)py}] ( 2 ) and [TaCp*Me{κ 4 ‐ C,N,O,O ‐(OCH 2 )(OCHC(SiMe 3 )CH)py}] ( 3 ) with triflic acid (1:2 molar ratio) rendered the corresponding bis‐triflate derivatives [TaCp*(OTf) 2 {κ 3 ‐ N,O,O ‐(OCH 2 )(OCHC(Ph)CH 2 )py}] ( 6 ) and [TaCp*(OTf) 2 {κ 3 ‐ N,O,O ‐(OCH 2 )(OCHC(SiMe 3 )CH 2 )py}] ( 7 ), respectively. Complex 4 reacted with triflic acid in a 1:2 molar ratio to selectively yield the water‐soluble cationic complex [TaCp*(OTf){κ 4 ‐ C,N,O,O ‐(OCH 2 )(OCHC(CH 2 NHMe 2 )CH)py}]OTf ( 8 ). Compound 8 reacted with water to afford the hydrolyzed complex [TaCp*(OH)(H 2 O){κ 3 ‐ N,O,O ‐(OCH 2 )(OCHC(CH 2 NHMe 2 )CH 2 )py}](OTf) 2 ( 9 ). Protonation of compound 8 with triflic acid gave the new tantalum compound [TaCp*(OTf){κ 4 ‐ C,N,O,O ‐(OCH 2 )(HOCHC(CH 2 NHMe 2 )CH)py}](OTf) 2 ( 10 ), which afforded the corresponding protonolysis derivative [TaCp*(OTf) 2 {κ 3 ‐ N,O,O ‐(OCH 2 )(HOCHC(CH 2 NHMe 2 )CH 2 )py}](OTf) ( 11 ) in solution. Complex 8 reacted with CN t Bu and potassium 2‐isocyanoacetate to give the corresponding iminoacyl derivatives 12 and 13 , respectively. The molecular structures of complexes 5 , 7 , and 10 were established by single‐crystal X‐ray diffraction studies.