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

• Published in: Inorganic chemistry 1996-10, Vol.35 (21), p.6027-6036
• Main Authors: Fox, Peter A, Gray, Steven D, Bruck, Michael A, Wigley, David E
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic960298n

The reactions of TaCl5 with Me3SiNC9H10 or LiNC9H10, where [NC9H10]- = tetrahydroquinolinyl (the amido anion of tetrahydroquinoline), afford selective preparative routes to the complete series of amido halide complexes of tantalum(V) Ta(NC9H10) n Cl5 - n for n = 1−5 (compounds 1−5, respectively). The monokis(tetrahydroquinolinyl) complex is isolated as an ether adduct Ta(NC9H10)Cl4(OEt2) while the complexes Ta(NC9H10) n Cl5 - n (n = 2−5) are found to be base-free, monomeric species. The related complexes of indolinyl [NC8H8]- (the amido anion of indoline), Ta(NC8H8) n Cl5 - n (THF) for n = 1 (6) or 2 (7), have been prepared from TaCl5, Me3SiNC8H8, and THF. An X-ray structural determination of Ta(NC9H10)2Cl3 (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(NC9H10)(OAr)Cl3(OEt2) (8), where Ar = 2,6-C6H3 iPr2, and Ta(NC8H8)(OAr)Cl3(OEt2) (9) are available from reacting Ta(OAr)Cl4(OEt2) with Me3SiNC9H10 and Me3SiNC8H8, respectively, while Ta(NC9H10)2(OAr)2Cl (10) is available from Ta(NC9H10)2Cl3 (2) and excess LiOAr·OEt2. The alkyl derivatives Ta(NC9H10)(OAr)Me2Cl (11), Ta(NC9H10)(OAr)Et2Cl (12), Ta(NC9H10)2(OAr)2Me (13), and Ta(NC9H10)Me2Cl2 (14) are prepared from AlR3 or ZnR2 reagents and the appropriate precursor. Thermolyzing compounds 4, 5, and 11−14 in solution afforded no evidence for the formation of any η2(N,C)-heterocyclic complexes arising from metalation of a NC9H10 ligand.