BO基杂配位铁羰基化合物Fe_2(BO)_2(CO)_n(n=9,5)的配位特性研究

Study on the coordination characteristics of the binuclear iron boronyl carbonyl Fe_2(BO)_2(CO)_n(n=9, 5)

含硼的双原子配体(如BO、BF等)稳定性差,有关BO基配位取代金属羰基化合物的实验研究和理论研究均较少,对配位过饱和及高度不饱和过渡金属配位体系的配位研究还鲜见报道.本文采用两种密度泛函方法 B3LYP和BP86对BO基杂配位的过饱和及高度不饱和铁羰基化合物Fe2(BO)2(CO)n(n=9,5)的配位特性进行了研究.研究结果表明,在配位过饱和Fe2(BO)2(CO)9中,两个Fe原子间距较大,没有明显直接成键作用.其低能构型都是桥连结构且更倾向于CO桥而不是BO桥,BO基多以端配位的形式出现;由于其体系配位过饱和的特征,优化的低能构型中出现了BO基耦合于端位CO基的配位结构29-6S和29-8S.在配位高度不饱和Fe2(BO)2(CO)5体系中,所有低能构型也都是桥连结构但倾向于BO桥而不是CO桥,显现BO基中氧原子的碱性比CO基中氧原子的碱性更强;由于其配位高度不饱和,构型25-1S、25-4T和25-5T中存在两个3-电子给体桥?2-μ-BO配位;25-2T、25-3T和25-6T中存在两个"首尾相连"的3-电子给体"–B–O–"桥;结构25-1T中出现了由两个BO配体耦合形成的4-电子给体反式双硼双氧(B2O2)配体.无论从单羰基离解能还是单核离解能来看,Fe2(BO)2(CO)5的热力学稳定性都远比Fe2(BO)2(CO)9高,可望是一个潜在的合成目标.

The coordination characteristics of the binuclear iron boronyl carbonyl Fe2（BO）2（CO）n （n=9, 5） were studied by two density functional methods （B3LYP and BP86） in this paper. The results show that most of the low-energy structures prefer the bridging CO groups rather than the bridging BO groups for supersaturated system Fe2（BO）2（CO）9. The long Fe...Fe distances indicate a lack of direct iron-iron bonding. In structure of 29-6S and 29-8S, one BO group couples to one terminal CO group, and then the coupled OBCO group coordinates to one Fe atom as the terminal ligand. For superunsaturated system Fe2（BO）2（CO）5, all of the low-energy structures prefer the bridging BO groups other than the bridging CO groups. This may be related to the higher basicity of the oxygen atom in a BO ligand relative to a CO ligand. Three of the seven low-energy Fe2（BO）2（CO）5 structures, namely 25-1S, 25-4T and 25-5T, have two bridging η^2-η-BO groups as three-electron donors involving both the oxygen and the boron atoms bonded to the same iron atom. Two end-on bridging BO groups functioning as three-electron donor, involving both the oxygen and the boron atoms bonded to the different iron atoms, are observed in three Fee（BO）2（CO）5 derivatives, namely 25-2T, 25-3T and 25-6T. The bridging dioxodiborene ligand with trans-B202, which is coupled by the two BO groups, functioning as a four-electron donor to the pair of iron atoms, is found in Fe2（BO）2（CO）5 derivative 25-1T.