Ceylan Yavuz S, Cundari Thomas R
Department of Chemistry and Center of Advanced Scientific Computing and Modeling, University of North Texas , 115 Union Circle, No. 305070, Denton, Texas 76203-5017, United States.
J Phys Chem A. 2017 Dec 7;121(48):9358-9368. doi: 10.1021/acs.jpca.7b09103. Epub 2017 Nov 21.
A computational analysis of model transition-metal terminal boride [MB(PNP)] complexes is reported. A combination of density functional theory methods, natural bond orbital analysis, and multiconfiguration self-consistent field calculations were employed to investigate the structure and bonding of terminal boride complexes, in particular, the extent of metal dπ-boron pπ bonding. Comparison of metal-boride, -borylene, and-boryl bond lengths confirms the presence of metal-boron π bonds, albeit the modest shortening (∼3%) of the metal-boron bond suggests that the π-bonding is very weak in terminal borides. Calculated free energies of H addition to the boride complexes to yield the corresponding boryl complexes indicate that metal-boride π-bond strengths are 22 kcal/mol or less as compared to 44 kcal/mol for an analogous nitride complex. It is concluded that, for the boride complexes studied, covering a range of different 4d and 5d metals, that the metal-boride bond consists of a reasonably covalent σ but two very polarized metal-boron π bonds. The high polarization of the boron-to-metal π bonds indicates that the terminal boride is an acceptor or Z-type ligand.
报道了对模型过渡金属末端硼化物[MB(PNP)]配合物的计算分析。采用密度泛函理论方法、自然键轨道分析和多组态自洽场计算相结合的方式，研究末端硼化物配合物的结构和键合，特别是金属dπ-硼pπ键合的程度。金属-硼化物、-硼烯和-硼基键长的比较证实了金属-硼π键的存在，尽管金属-硼键适度缩短（约3%）表明末端硼化物中的π键合非常弱。计算得到的氢加成到硼化物配合物以生成相应硼基配合物的自由能表明，与类似氮化物配合物的44 kcal/mol相比，金属-硼化物π键强度为22 kcal/mol或更低。得出的结论是，对于所研究的涵盖一系列不同4d和5d金属的硼化物配合物，金属-硼化物键由一个相当共价的σ键和两个非常极化的金属-硼π键组成。硼到金属的π键的高极化表明末端硼化物是一种受体或Z型配体。
