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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Oxo-molybdenum and oxo-tungsten complexes of Schiff bases relevant to molybdoenzymes
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Oxo-molybdenum and oxo-tungsten complexes of Schiff bases relevant to molybdoenzymes

机译：与钼酶相关的席夫碱的氧钼和氧钨钨配合物

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摘要

A series of octahedral dioxomolybdenum(VI) complexes of the type [MoO_2L_2] {L = 4-Ar-pent-2-en-ol; L_(i-Pr2Ph) with Ar = 2,6-diisopropylphenyl (1); L_(M2Ph), with Ar = 2,6-dimethylphenyl (2), L_(MePh) with Ar = 2-methylphenyl (3) and with Ar = phenyl (4)} and dioxotungsten(VI) compounds [WO_2L_2] {L_(i-Pr2ph) (5); L_(Me2Ph) (6) and L_(MePh) (7)} with Schiff bases have been synthesized as models for oxotransferases. Spectroscopic characterization in solution shows with the sterically encumbered ligands L_(i-Pr2Ph) and L_(Me2)Ph isomerically pure products whereas the ligand with only one substituent in ortho position at the aromatic ring L_(MePh) revealed a dynamic mixture of three isomers as confirmed by variable temperature NMR spectroscopy. Single crystal X-ray diffraction analyses of compounds 1, 2 and 4 showed them to be in the N,N-trans conformation consistent with the larger steric demand at nitrogen. Oxygen atom transfer (OAT) properties towards trimethylphosphine were investigated leading to the isolation of two mononuclear molybdenum(IV) compounds [MoO(PMe_3)(L_(Me2Ph))_2] (8) and [MoO(PMe_3)(L_(Meph))_2] (9) as confirmed by spectroscopic and crystallographic means. The kinetics of OAT between complex [MoO_2(L_(Me2Ph))_2] (2) and PMe_3 was investigated by UV/Vis spectroscopy under pseudo-first-order conditions revealing single-step reactions with Eyring values of ΔH~≠ = +60.79 kJ mol~(-1) and ΔS~≠ = -112 J mol~(-1) K~(-1) and a first-order dependence of phosphine consistent with a slow nucleophilic attack of the phosphine showing the octahedral geometries of this system to be unfavorable for OAT. Compound 1 showed no OAT reactivity towards PMe_3 emphasizing the influence of sterical properties. Furthermore, the reactivity of the reduced compounds [MoO(PMe_3)(L_(Me2Ph))_2] (8) and [MoO(PMe_3)(L_(MePh))_2] (9) towards molecular oxygen was investigated leading, in the case of 8, to the substitution of PMe_3 by O_2 under formation of the peroxo compound [MoO(O_2)(LM)_2] (10). In contrast, the analogous reaction employing 9 led to oxidation forming the dioxo compound [MoO_2(L_(MePh))_2] (3).
机译：[MoO_2L_2]类型的一系列八面体二氧钼钼（VI）络合物{L = 4-Ar-pent-2-en-ol;具有Ar = 2,6-二异丙基苯基（1）的L_（i-Pr2Ph）; L_（M2Ph），其中Ar = 2,6-二甲基苯基（2），L_（MePh），其中Ar = 2-甲基苯基（3），且Ar =苯基（4）}和二氧钨（VI）化合物[WO_2L_2] {L_ （i-Pr2ph）（5）;已经合成了具有席夫碱的L_（Me2Ph）（6）和L_（MePh）（7）}作为氧代转移酶的模型。溶液中的光谱表征表明，空间受限的配体L_（i-Pr2Ph）和L_（Me2）Ph是异构体纯的产物，而在芳环L_（MePh）的邻位仅有一个取代基的配体显示出三种异构体的动态混合物经可变温度NMR光谱证实。化合物1、2和4的单晶X射线衍射分析表明，它们呈N，N-反式构型，与氮的更大空间需求相一致。研究了向三甲基膦的氧原子转移（OAT）特性，从而导致分离出两种单核钼（IV）化合物[MoO（PMe_3）（L_（Me2Ph））_ 2]（8）和[MoO（PMe_3）（L_（Meph）） ）_2]（9），由光谱和晶体学方法证实。在伪一级反应条件下，通过紫外/可见光谱研究了复合物[MoO_2（L_（Me2Ph））_ 2]（2）和PMe_3之间的OAT动力学，揭示了一步反应，艾尔值ΔH〜≠= +60.79 kJ mol〜（-1）和ΔS〜≠= -112 J mol〜（-1）K〜（-1）以及与磷化氢的缓慢亲核攻击相一致的磷化氢的一阶依赖性，显示了该物质的八面体几何形状该系统不利于OAT。化合物1没有显示出对PMe_3的OAT反应性，强调了空间性质的影响。此外，研究了还原化合物[MoO（PMe_3）（L_（Me2Ph））_ 2]（8）和[MoO（PMe_3）（L_（MePh））_ 2]（9）对分子氧的反应性，导致在8的情况下，在过氧化合物[MoO（O_2）（LM）_2]的形成下，O_2将PMe_3取代（10）。相反，采用9的类似反应导致氧化，形成二氧杂环丁烷化合物[MoO_2（L_（MePh））_ 2]（3）。

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