172164-68-0Relevant academic research and scientific papers
Studies of six-coordinate adducts all-trans-[M(OAr)2(X)2(L)2] (M = Nb, Ta; X = Cl, Br; L = tertiary phosphine, pyridine)
Schweiger, Scott W.,Freeman, Emily E.,Clark, Janet R.,Potyen, Mark C.,Fanwick, Phillip E.,Rothwell, Ian P.
, p. 64 - 71 (2008/10/08)
An extensive series of d1-derivatives of niobium and tantalum [M(OAr)2(X)2(L)2] (M = Nb, Ta; X = Cl, Br; L = tertiary phosphine, pyridine) have been isolated by reduction of the corresponding adducts [M(OAr)2(X)3(L)] in the presence of excess L. Crystallographic studies show an all-trans, octahedral arrangement of ligands about the metal center. The effect of the halide, donor ligand and aryloxide substituents upon the structural parameters is discussed. (C) 2000 Elsevier Science S.A.
Quinoline binding mode as a function of oxidation state in aryloxide-supported tantalum complexes: models for hydrodenitrogenation catalysis
Allen, Kevin D.,Bruck, Michael A.,Gray, Steven D.,Kingsborough, Richard P.,Smith, David P.,et al.
, p. 3315 - 3334 (2008/10/09)
The heterocyclic complexes [η1(N)-QUIN]Ta(OAr)3Cl2 (1) and [η1(N)-6MQ]Ta(OAr)3Cl2 (2) (where Ar=2,6-diisopropylphenyl, QUIN=quinoline, and 6MQ=6-methylqunoline) are prepared from Ta(OAr)3Cl2(OEt2) and QUIN or6-MQ in pentane. [η1(N)-6MQ]Ta(OAr)2Cl3 (4) is prepared similarly f rom Ta(OAr)2Cl3(OEt2). Upon rapid, two-electron reduction of these complexes, an η1(N) η2(N,C) bonding rearrangement is effected and the thermally sensitive, d(2) species [η2(N,C)-QUIN]Ta(OAr)3 (5), [η2(N,C)-6MQ]Ta(OAr)3 (6), and [η2(N,C)-6MQ]Ta(OAr)2Cl(OEt2)(9) can be isolated. Alternatively, [η2(N,C)-6MQ]Ta(OAr)2Cl(OEt2) ( 9) can be prepared in higher yield from (η6-C6Me6)Ta(OAr)2Cl and 6MQ. The trimethylphosphine adducts [η2(N,C)-QUIN]Ta(OAr)3(PMe3) (7) and [η2(N,C)-6MQ]Ta(OAr)3(PMe3) (8) can be prepared by simple coordination of PMe3 to the base-free compounds 5 and 6. When Ta(OAr)2Cl3(OEt2) is reduced by one electron in the presence of QUIN, 6MQ, or pyridine, the d(1) bis(ligand) complexes [η1(N)-QUIN]2Ta(OAr)2Cl2 (10), [η1(N)-6MQ]2Ta(OAr)2Cl2 (11), and [η1(N)-py]2Ta(OAr)2Cl2 (12) can be isolated. Complexes 10 and 11 are not readily converted to the η2(N,C) analogues 5 and 6 by further reduction. Under mild hydrogenation conditions, the only heterocyclic ligands which are hydrogenated are those in the η2(N,C) mode to a d(2) metal. Structural studies on [η2(N,C)-6MQ]Ta(OAr)3(PMe3) (8) and [η2(N,C)-6MQ]Ta(OAr)2Cl(OEt2) (9) have been undertaken. [η2(N,C)-6MQ]Ta(OAr)3(PMe3) (8) crystallizes in the monoclinic space group C21/C (No. 15) with a=32.849 (3) ?, b=19.579 (2) ?, c=23.822 (2) ?, β=135.69 (49)°, and V=10702 (2) ?**3 with Z=8 and ρ(calcd)=1.16 g cm**-3. [η2(N,C)-6MQ]Ta(OAr)2Cl(OEt2) (9) crystallizes in the monoclinic space group P21/N (No. 14) with a=12.059 (9) ?, b=17.975 (14) ?, c=17.949 (13) ?, β=100.29 (3)°, and V=3828 (9) ?**3 with Z=4 and ρ(calcd)=1.37 g cm**-3. Both structures indicate an interruption of aromaticity to the heterocyclic ring only when bound in this fashion, consistent with the observation of 1,2,3,4-tetrahydroquinoline as the principal hydrogenation product of [η2(N,C)-QUIN]Ta(OAr)3 (5) with no decahydroquinoline being observed.
