Synthesis of Polyynes Using Dicobalt Masking Groups

Extended triisopropylsilyl end-capped polyynes have been prepared from the corresponding tetracobalt complexes by removing the complexed dicobalt tetracarbonyldiphenylphosphinomethane (Co2(CO)4dppm) moieties. Unmasking of this “masked alkyne equivalent” was achieved under mild conditions with elemental iodine at room temperature, making it possible to obtain fragile polyynes with up to 20 contiguous sp-hybridized carbon atoms. The Co2(CO)4dppm moiety has a strong geometric and steric effect on the polyyne but does not have a marked electronic effect on the terminal alkyne, as indicated by NMR and IR spectroscopy, density functional theory calculations, and X-ray crystallography. An unusual “alkyne hopping” migration of the dicobalt group was noticed as a minor side reaction during copper-catalyzed Eglinton coupling.

本研究通过脱除络合态的四羰基二(二苯基膦甲烷)合二钴[Co₂(CO)₄dppm]基团，从相应四钴配合物中制备得到了扩展型三异丙基硅基封端聚炔。该“掩蔽炔烃等价体”的脱保护可在温和条件下以单质碘于室温实现，由此可获得含有多达20个连续sp杂化碳原子的脆弱聚炔。经核磁共振（NMR）、红外（IR）光谱、密度泛函理论（DFT）计算以及X射线晶体学表征验证，Co₂(CO)₄dppm基团对聚炔具有显著的几何与位阻效应，但对末端炔烃未表现出明显的电子效应。在铜催化的埃格林顿（Eglinton）偶联反应过程中，我们观测到二钴基团发生了罕见的“炔烃跳跃”迁移，该反应为次要副反应。