Morris Louis J, Rajabi Nasir A, Hill Michael S, Manners Ian, McMullin Claire L, Mahon Mary F
Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.
Department of Chemistry, University of Victoria, Victoria, BC V8P 5C2, Canada.
Dalton Trans. 2020 Oct 27;49(41):14584-14591. doi: 10.1039/d0dt03415k.
Reactions of B(C6F5)3 with the β-diketiminato (BDI) alkaline-earth phosphidoborane complexes, 1a [(BDI)Ca(H3B·PPh2)] and 1b [(BDI)Mg(H3B·PPh2)]2 (BDI = [HC{C(CH3)N(2,6-iPr-C6H3)}2]-) result in the formation of phosphinodiboronate complexes 4a [(BDI)Ca(η6-toluene){H3B·PPh2·B(C6F5)3}] and 4b [(BDI)Mg{H3B·PPh2·B(C6F5)3}]. Calcium complex 4a is stable in aromatic solvents at room temperature and does not display well-defined onward reactivity at elevated temperatures. Magnesium complex 4b undergoes a room temperature transformation to provide the known hydridoborate derivative 3b [(BDI)Mg{HB(C6F5)3}] and an N,P,N'-ligated species, 5 [{HC(C(CH3)N(2,6-iPr-C6H3))2(H2BPPh2)}Mg{H3B·PPh2·B(C6F5)3}] that results from interception of the putative phosphinoborane, H2B = PPh2, by the BDI ligand backbone following B(C6F5)3-mediated hydride abstraction. NMR spectroscopic investigations were supported by DFT calculations, which suggested a mechanism involving B(C6F5)3 migration and hydride abstraction within the coordination sphere of magnesium. Interception of H2B = PPh2 by B(C6F5)3 is proposed to stabilise this species, whilst activating it towards ligand-centred nucleophilic attack. The significant stabilisation energy calculated for the Ca-π(toluene) interaction in 4a accounts for the contrasting outcomes between the two Ae-elements. The crystal structures of compounds 4a and 5 are presented and discussed.
三（五氟苯基）硼（B(C6F5)3）与β-二酮亚胺基（BDI）碱土金属磷硼烷配合物1a [（BDI）Ca(H3B·PPh2)] 和1b [（BDI）Mg(H3B·PPh2)]2（BDI = [HC{C(CH3)N(2,6-iPr-C6H3)}2]-）反应，生成膦二硼酸酯配合物4a [（BDI）Ca(η6-甲苯){H3B·PPh2·B(C6F5)3}] 和4b [（BDI）Mg{H3B·PPh2·B(C6F5)3}]。钙配合物4a在室温下于芳香族溶剂中稳定，在升高温度时未表现出明确的后续反应活性。镁配合物4b在室温下发生转变，生成已知的氢硼酸酯衍生物3b [（BDI）Mg{HB(C6F5)3}] 和一种N,P,N'-配位的物种5 [{HC(C(CH3)N(2,6-iPr-C6H3))2(H2BPPh2)}Mg{H3B·PPh2·B(C6F5)3}]，该物种是在B(C6F5)3介导的氢化物提取后，由BDI配体主链截获推定的膦硼烷H2B = PPh2形成的。核磁共振光谱研究得到了密度泛函理论计算的支持，该计算表明了一种涉及B(C6F5)3迁移和镁配位球内氢化物提取的机制。有人提出，B(C6F5)3对H2B = PPh2的截获可稳定该物种，同时使其易于发生以配体为中心的亲核攻击。计算得出的4a中Ca-π（甲苯）相互作用的显著稳定能解释了两种碱土金属元素之间截然不同的结果。给出并讨论了化合物4a和5的晶体结构。
