Disubstituted 1,8-Diamidonaphthalene Ligands as a Flexible, Responsive, and Reactive Framework for Tantalum Complexes

Deprotonated N,N′-disubstituted 1,8-diaminonaphthalenes (R2DAN2−; R = (CH3)2CH, C6H5, 3,5-Me2C6H3) were incorporated into Ta(V) complexes employing two methods. The direct proton transfer reaction of the parent amine, 1,8-(RNH)2C10H6, with TaMe3Cl2 led to elimination of methane and formation of TaCl3[1,8-(RN)2C10H6] (1, 2). Reaction of the dilithiated amido species, Li2R2DAN, with TaMe3Cl2 or [Ta(NEt2)2Cl3 ] yielded TaMe3[1,8-(RN)2C10H6] (3, 4) and TaCl(NEt2)2[1,8-(RN)2C10H6] (5, 6), respectively. X-ray structural studies of these complexes revealed the flexible coordination behavior of R2DAN2− by demonstrating that the ligand bonded to Ta with a coordination array dependent on the identity of the other ligands bonded to tantalum. Computational analysis of these complexes confirmed that the energetic components for binding of R2DAN2− to these TaX32+ fragments were dominated by the electronic features of the metal fragment. Chemical transformations of the bound ligand were evaluated by reaction of compounds 5 and 6 with LiNMe2 and MeLi. Simple metathesis products Ta(NEt2)2NMe2[1,8-(iPrN)2C10H6] (R = iPr 7, R = 3,5-Me2(C6H3) 8) were obtained from reactions with LiNMe2. In contrast, when the R group of the DAN ligand was iPr, reaction with MeLi ultimately led to activation of the isopropyl group and formation of the metallaziridine [κ3-(Me2CN)(iPrN)C10H6]Ta(NEt2)2 (9) species via the elimination of methane.