The unique reactivity of metal hydrides has encouraged considerable advances in both synthesis and catalysis. In this arena, ligand optimization has played a significant role, wherein metal–ligand cooperativity can be employed to guide reactivity. Of the organometallic hydride donors, rhodium(I) bis(diphosphine) compounds are known to be among the strongest with hydricity (ΔG_H^–) values near that of conventionally used reducing agents: e.g., trialkyl-substituted borohydrides (ΔG_H^– ≈ 26 kcal mol^–1 for [HBEt₃]^—). Herein, we assess the thermodynamic site of hydride transfer using a rhodium(I) compound bearing a boron-rich diphosphine ligand: [Rh^I(P₂B^Cy₄)₂]BPh₄ (P₂B^Cy₄ = 1,2-bis(di(3-dicyclohexylboraneyl)propylphosphino)ethane). The divergent reactivity of [Rh^I(P₂B^Cy₄)₂]BPh₄ and its all-alkyl relative [Rh^I(dnppe)₂]BPh₄ (dnppe = 1,2-bis(di-n-propylphosphino)ethane) toward hydride donors is underscored, where for the former the preferred site of hydride transfer is the ligand scaffold and not rhodium. This result is contrasted by facile generation of [Rh^I(dnppe)₂(H)]—a species having a value of ΔG_H^– ostensibly similar to that of [Rh^I(P₂B^Cy₄)₂(H)] (which is not observed), underscoring a noninnocent and cooperative role for the boron-rich secondary coordination sphere of the P₂B^Cy₄ scaffold. The use of the ligand to serve as a hydride source was accordingly examined.

中文翻译：

---

将铑包裹在硼烷树冠中：对氢化物形成和转移的影响

金属氢化物的独特反应性促进了合成和催化方面的巨大进步。在这个领域，配体优化发挥了重要作用，其中金属-配体协同作用可用于指导反应性。在有机金属氢化物供体中，众所周知，铑（I）双（二膦）化合物是最强的，其氢值 (Δ G _{H ^–} ) 值接近常规使用的还原剂：例如，三烷基取代的硼氢化物 (Δ G _{H ^–} ≈ 26 kcal mol ^–1 [HBEt ₃ ] ^— )。在此，我们使用带有富硼二膦配体的铑 (I) 化合物评估氢化物转移的热力学位点：[Rh ^I(P ₂ B ^Cy ₄ ) ₂ ]BPh ₄ (P ₂ B ^Cy ₄ = 1,2-双(二(3-二环己基硼烷基)丙基膦基)乙烷)。的[Rh的发散反应^我（P ₂乙^赛扬₄）₂ ] BPH ₄及其所有烷基相对的[Rh^我（d Ñ PPE）₂ ] BPH ₄（d Ñ PPE = 1,2-双（二- Ñ -丙基膦基）乙烷）向氢化物供体突出显示，对于前者，氢化物转移的首选位点是配体支架，而不是铑。该结果与 [Rh ^I (d n ppe) ₂ (H)]的轻松生成形成鲜明对比- 一种具有 Δ G _H值的物种_^-表面上类似于 [Rh ^I (P ₂ B ^Cy ₄ ) ₂ (H )]（未观察到），强调了 P ₂ B ^Cy ₄支架的富硼二级配位球的非无辜和合作作用。相应地检查了使用配体作为氢化物源。