Tetrahydroquinolinyl Amido and Indolinyl Amido Complexes of Tantalum as Models for Substrate−Catalyst Adducts in Hydrodenitrogenation Catalysis

The reactions of TaCl 5 with Me 3 SiNC 9 H 10 or LiNC 9 H 10, where [NC 9 H 10 ] - = tetrahydroquinolinyl (the amido anion of tetrahydroquinoline), afford selective preparative routes to the complete series of amido halide complexes of tantalum(V) Ta(NC 9 H 10 ) n Cl 5 - n for n = 1−5 (compounds 1 − 5, respectively). The monokis(tetrahydroquinolinyl) complex is isolated as an ether adduct Ta(NC 9 H 10 )Cl 4 (OEt 2 ) while the complexes Ta(NC 9 H 10 ) n Cl 5 - n ( n = 2−5) are found to be base-free, monomeric species. The related complexes of indolinyl [NC 8 H 8 ] - (the amido anion of indoline), Ta(NC 8 H 8 ) n Cl 5 - n (THF) for n = 1 ( 6 ) or 2 ( 7 ), have been prepared from TaCl 5, Me 3 SiNC 8 H 8, and THF. An X-ray structural determination of Ta(NC 9 H 10 ) 2 Cl 3 ( 2 ) reveals that it adopts a trigonal bipyramidal geometry with equatorial amido ligands that are closer to lying parallel (within) than perpendicular to the TBP equatorial plane. Routes to mixed-ligand aryloxide−amide complexes have been developed from either aryloxide or amido precursors but not from both. Thus, Ta(NC 9 H 10 )(OAr)Cl 3 (OEt 2 ) ( 8 ), where Ar = 2,6-C 6 H 3 i Pr 2, and Ta(NC 8 H 8 )(OAr)Cl 3 (OEt 2 ) ( 9 ) are available from reacting Ta(OAr)Cl 4 (OEt 2 ) with Me 3 SiNC 9 H 10 and Me 3 SiNC 8 H 8, respectively, while Ta(NC 9 H 10 ) 2 (OAr) 2 Cl ( 10 ) is available from Ta(NC 9 H 10 ) 2 Cl 3 ( 2 ) and excess LiOAr·OEt 2 . The alkyl derivatives Ta(NC 9 H 10 )(OAr)Me 2 Cl ( 11 ), Ta(NC 9 H 10 )(OAr)Et 2 Cl ( 12 ), Ta(NC 9 H 10 ) 2 (OAr) 2 Me ( 13 ), and Ta(NC 9 H 10 )Me 2 Cl 2 ( 14 ) are prepared from AlR 3 or ZnR 2 reagents and the appropriate precursor. Thermolyzing compounds 4, 5, and 11 − 14 in solution afforded no evidence for the formation of any η 2 ( N,C )-heterocyclic complexes arising from metalation of a NC 9 H 10 ligand.