Hosoya Hiromu, Akiyama Takuya, Mashima Kazushi, Tsurugi Hayato
Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
Graduate School of Pharmaceutical Sciences, Osaka University, Suita, Osaka 565-0871, Japan.
Dalton Trans. 2023 Sep 26;52(37):13154-13160. doi: 10.1039/d3dt01828h.
We found that bis(neopentylglycolato)diboron (Bnep) served as a bidentate ligand and a one-electron reducing agent for early transition metal chlorides to afford MCl(Bnep). Treatment of Bnep with MCl (M = Nb and Mo) produced MCl(Bnep) two successive reactions, coordination of Bnep to the metal center and one-electron reduction from M(V) to M(IV), while coordination of Bnep to MCl (M = Zr, Ti) was observed without reduction of the central metals. DFT studies for the reduction of NbCl by Bnep clarified the initial formation of seven-coordinated and Bnep-ligated Nb(V) species, NbCl(Bnep), and one chloride on niobium(V) moves to the Lewis acidic boron center to generate NbCl[(Bnep)Cl]. The chloride on the boron atom of NbCl[(Bnep)Cl] is trapped by the second Bnep to give [NbCl(Bnep)][ClBnep]. After the formation of [ClBnep] as an anionic sp-sp diboron adduct, one-electron reduction of the niobium(V) center produces NbCl(Bnep) along with [ClBnep]˙ as a plausible diboron species, whose decomposition affords ClBnep and Bnep. The reduction of metal halides in the presence of Bnep was exemplified by green LED irradiation of TiCl(Bnep), producing chloride-bridged titanium(III) species, (Bnep)TiCl(μ-Cl)TiCl(Bnep).
我们发现双（新戊二醇）二硼（Bnep）可作为双齿配体和早期过渡金属氯化物的单电子还原剂，从而生成MCl（Bnep）。Bnep与MCl（M = Nb和Mo）反应会经过两个连续反应生成MCl（Bnep），即Bnep与金属中心配位以及从M（V）到M（IV）的单电子还原，而观察到Bnep与MCl（M = Zr、Ti）配位时中心金属未被还原。对Bnep还原NbCl的密度泛函理论（DFT）研究表明，最初形成七配位且由Bnep配位的Nb（V）物种NbCl（Bnep），铌（V）上的一个氯原子迁移至路易斯酸性硼中心生成NbCl[（Bnep）Cl]。NbCl[（Bnep）Cl]硼原子上的氯原子被第二个Bnep捕获，生成[NbCl（Bnep）][ClBnep]。在形成作为阴离子sp-sp二硼加合物的[ClBnep]后，铌（V）中心的单电子还原生成NbCl（Bnep）以及作为可能的二硼物种的[ClBnep]˙，其分解产生ClBnep和Bnep。在Bnep存在下金属卤化物的还原以TiCl（Bnep）的绿色发光二极管照射为例，生成氯桥连的钛（III）物种（Bnep）TiCl（μ-Cl）TiCl（Bnep）。
