Preparation, Structure Characterization, and Oxidation Activity of Ruthenium Complexes with Tripodal Ligands Bearing Noncovalent Interaction Sites

Ruthenium(II/III) complexes with tripodal tris(pyridylmethyl)amine ligands bearing one, two, or three pivalamide
groups (MPPA, BPPA, TPPA:  amide-series ligands) or neopentylamine ones (MNPA, BNPA, TNPA:  amine-series
ligands) at the 6-position of the pyridine ring have been synthesized and structurally characterized. The X-ray
structure analyses of the single crystals of these complexes reveal that they complete an octahedral geometry
with the tripodal ligand and some monodentate ligands. The amide-series ligands prefer to form a Ru(II) complex,
while the amine-series ones give a Ru(III) complex. In the presence of PhIO oxidant, the catalytic activities for
epoxidation of olefins, hydroxylation of alkane, and dehydrogenation of alcohol have been investigated using the
six ruthenium complexes [RuII(tppa)Cl2] (1), [RuIII(tnpa)Cl2]PF6 (2), [RuII(bppa)Cl]PF6 (3), [RuIII(bnpa)Cl2]PF6 (4),
[RuII(mppa)Cl]PF6 (5), and [RuIII(mnpa)Cl2]PF6 (6). Among them, the amide-series complexes, 1, 3, and 5, showed
a higher epoxidation activity in comparison with the amine-series ones, 2, 4, and 6. On the other hand, the latter
showed a higher reactivity for hydroxylation, allylic oxidation, and CC bond cleavage reactions compared with
the former. Such a complementary reactivity is interpreted by the character of the ruthenium−oxo species involving
electronically equivalent formulas, Ru(V)O and Ru(IV)−O•.

本研究合成并结构表征了一系列在吡啶环6位带有1、2或3个新戊酰胺（pivalamide）基团（MPPA、BPPA、TPPA：酰胺系列配体）或新戊胺（neopentylamine）基团（MNPA、BNPA、TNPA：胺系列配体）的三脚架型三(吡啶甲基)胺（tripodal tris(pyridylmethyl)amine）配体合钌(II/III)配合物。对这些配合物的单晶开展X射线结构分析后发现，它们与三脚架型配体及单齿配体共同形成八面体配位几何构型。酰胺系列配体更倾向于形成钌(II)配合物，而胺系列配体则易生成钌(III)配合物。以亚碘酰苯（PhIO）为氧化剂，针对6种钌配合物——[RuII(tppa)Cl₂]（1）、[RuIII(tnpa)Cl₂]PF₆（2）、[RuII(bppa)Cl]PF₆（3）、[RuIII(bnpa)Cl₂]PF₆（4）、[RuII(mppa)Cl]PF₆（5）与[RuIII(mnpa)Cl₂]PF₆（6）——探究了其在烯烃环氧化、烷烃羟化以及醇脱氢反应中的催化活性。其中，酰胺系列配合物1、3、5相较于胺系列配合物2、4、6展现出更高的烯烃环氧化催化活性；反之，胺系列配合物则在烷烃羟化、烯丙基氧化以及C=C键断裂反应中表现出更优的反应活性。这种反应活性的互补性可通过钌氧（ruthenium−oxo）物种的结构特性加以解释，该类物种存在电子等价的两种形式：Ru(V)=O与Ru(IV)-O•。