Kongprakaiwoot Natcharee, Noll Bruce C, Brown Seth N
Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, Indiana 46556-5670, USA.
Inorg Chem. 2008 Dec 15;47(24):11902-9. doi: 10.1021/ic8016479.
A 2,2'-bis(methylene)biphenyl-bridged bis(hydroxamic acid) (HoxH(2)) is prepared by reaction of 2,2'-biphenyldiacetyl chloride with 2 equiv of N-methylhydroxylamine. Use of 1 equiv of CH(3)NHOH gives the cyclic diacylhydroxylamine, which is selectively ring-opened to give a mixed monohydroxamate-monodiketonate ligand HobH(2). Both ligands are metalated by Ti(O(i)Pr)(4) to give the corresponding LTi(O(i)Pr)(2) complexes as exclusively the cis-alpha, (R)-Lambda/(S)-Delta isomers, similar to the previously prepared bis(diketonate) analogues (Bob)TiX(2). The carbonyl oxygens of the hydroxamates in the Hox ligand are constrained to be cis to each other, and the crystal structure of (Hob)Ti(O(i)Pr)(2) suggests that the carbonyl oxygen is a slightly weaker donor than the diketonate oxygen, based on a modest difference in their trans influences. A differential trans effect is also manifest in the observation of only a single geometric isomer of (Hob)Ti(O(i)Pr)(O(3)SCF(3)) and in a 15.6:1 preference for the isomer of (Hob)Ti(OCH(2)CMe(2)CO(2)) in which the alkoxide is trans to the hydroxamate ligand.
通过2,2'-联苯二乙酰氯与2当量的N-甲基羟胺反应制备了一种2,2'-双(亚甲基)联苯桥连的双异羟肟酸(HoxH₂)。使用1当量的CH₃NHOH得到环状二酰羟胺，其被选择性开环得到混合的单异羟肟酸酯-单二酮酸酯配体HobH₂。两种配体都被Ti(OⁱPr)₄金属化，得到相应的LTi(OⁱPr)₂配合物，且仅为顺式-α，(R)-Λ/(S)-Δ异构体，类似于先前制备的双(二酮酸酯)类似物(Bob)TiX₂。Hox配体中异羟肟酸酯的羰基氧被限制为彼此顺式，并且(Hob)Ti(OⁱPr)₂的晶体结构表明，基于它们反位影响的适度差异，羰基氧作为供体比二酮酸酯氧稍弱。在仅观察到(Hob)Ti(OⁱPr)(O₃SCF₃)的单一几何异构体以及在(Hob)Ti(OCH₂CMe₂CO₂)的异构体中醇盐与异羟肟酸酯配体反位的异构体具有15.6:1的偏好中，也体现了不同的反位效应。
