Chiral Thiahelicene-Based Alkyl Phosphine–Borane Complexes: Synthesis, X‑ray Characterization, and Theoretical and Experimental Investigations of Optical Properties

Chiral helical-based
phosphanes are challenging and promising ligands,
with a great potential for the generation of both organic and organometallic
catalysts. We report here the preparation of novel chiral thiahelicene-based
alkyl phosphanes, isolated and characterized as air-stable borane
adducts, and the investigation of their experimental and theoretical
(chir)­optical properties. X-ray characterization of a mono- and a
disubstituted derivative as a racemic mixture has been performed,
which confirms the influence of the number and nature of substituents
on the flexibility of the helix. In addition, the absolute configuration
inferred from CD spectra of the two enantiomers of a diborane complex
has been established from X-ray analysis. State-of-the-art quantum
chemical calculations of vibrationally resolved spectra allow, for
the first time, for an unambiguous assignment of the experimentally
observed peaks in linear absorption and circular dichroism spectra
to excited electronic states of this class of thiahelicene phosphorus
derivatives.

以手性螺旋为基础的磷烷作为极具挑战性和发展潜力的配体，在生成有机金属催化剂方面展现出巨大的潜力。本研究报告了新型手性噻螺烷基烷基磷烷的制备，这些化合物作为空气稳定的硼烷加成物被分离并表征，同时对其实验及理论（手性）光学性质进行了研究。对一种单取代和一种二取代衍生物作为外消旋混合物的X射线表征，证实了取代基数量和性质对螺旋柔韧性的影响。此外，通过X射线分析确定了从二硼烷复合物的两个对映异构体的圆二色光谱推断出的绝对构型。基于振动分辨光谱的尖端量子化学计算，首次实现了对实验观察到的线性吸收和圆二色光谱峰的明确归属，这些峰对应于此类噻螺烷磷衍生物的激发电子态。