FeB Double Bonds: Synthetic, Structural, and Reaction Chemistry of Cationic Terminal Borylene Complexes

Application of halide abstraction chemistry to asymmetric haloboryl complexes (η5-C5Me5)Fe(CO)2B(ERn)X leads to the first synthetic route to cationic multiply bonded group 13
diyl species, [(η5-C5Me5)Fe(CO)2B(ERn)]+. The roles of steric bulk and π electron release within
the ERn substituent in generating tractable borylene complexes have been probed, as has
the nature of the counterion. A combination of spectroscopic, structural, and computational
techniques leads to the conclusion that the bonding in complexes such as [(η5-C5Me5)Fe(CO)2B(Mes)]+ is best described as an FeB double bond composed of B→Fe σ donor and
Fe→B π back-bonding components. An extended study of the fundamental reactivity of
cationic borylene systems reveals that this is dominated not only by nucleophilic addition
at boron but also by iron-centered substitution chemistry leading to overall displacement of
the borylene ligand.

将卤离子提取化学应用于不对称卤代硼基配合物(η⁵-C₅Me₅)Fe(CO)₂B(ERₙ)X，首次开发出制备阳离子型多重键第13族二基物种[(η⁵-C₅Me₅)Fe(CO)₂B(ERₙ)]⁺的合成路径。本研究考察了ERₙ取代基的空间位阻与π电子释放能力对获得可分离硼烯配合物的影响，同时探究了抗衡离子的性质。通过光谱学、结构表征与计算技术的联用手段，得出如下结论：[(η⁵-C₅Me₅)Fe(CO)₂B(Mes)]⁺这类配合物中的成键模式，最优描述为Fe=B双键，其由B→Fe的σ给体作用与Fe→B的π反馈成键组分共同构成。针对阳离子硼烯体系基础反应性的拓展研究显示，该类体系的反应不仅以硼原子位点的亲核加成为主导，同时还会发生铁中心的取代反应，最终实现硼烯配体的整体置换。