The σ-alkane complexes of transition metals, which contain an essentially intact alkane molecule weakly bound to the metal, have been well established as crucial intermediates in the activation of the strong C–H σ-bonds found in alkanes. Methane, the simplest alkane, binds even more weakly than larger alkanes. Here we report an example of a long-lived methane complex formed by directly binding methane as an incoming ligand to a reactive organometallic complex. Photo-ejection of carbon monoxide from a cationic osmium–carbonyl complex dissolved in an inert hydrofluorocarbon solvent saturated with methane at −90 °C affords an osmium(II) complex, [η⁵-CpOs(CO)₂(CH₄)]⁺, containing methane bound to the metal centre. Nuclear magnetic resonance (NMR) spectroscopy confirms the identity of the σ-methane complex and shows that the four protons of the metal-bound methane are in rapid exchange with each other. The methane ligand has a characteristically shielded ¹H NMR resonance (δ –2.16), and the highly shielded carbon resonance (δ –56.3) shows coupling to the four attached protons (¹J_C–H = 127 Hz). The methane complex has an effective half-life of about 13 hours at –90 °C.

过渡金属的 σ-烷烃配合物含有与金属弱结合的基本完整的烷烃分子，已被确立为活化烷烃中发现的强 C-H σ-键的关键中间体。甲烷是最简单的烷烃，其结合力甚至比较大的烷烃更弱。在这里，我们报告了一个长寿命甲烷复合物的例子，该复合物是通过将甲烷作为进入配体直接结合到反应性有机金属络合物上而形成的。在 -90 °C 下，从溶解在甲烷饱和的惰性氢氟烃溶剂中的阳离子锇-羰基络合物中的一氧化碳光喷射得到锇(II) 络合物，[η ⁵ -CpOs(CO) ₂ (CH ₄ )] ⁺，含有与金属中心结合的甲烷。核磁共振 (NMR) 光谱证实了 σ-甲烷复合物的身份，并表明金属结合甲烷的四个质子彼此快速交换。甲烷配体具有特征性屏蔽的¹ H NMR 共振 ( δ –2.16)，高度屏蔽的碳共振 ( δ –56.3) 显示与四个连接的质子 ( ¹ J _C–H  = 127 Hz) 的耦合。甲烷复合物在 –90 °C 下的有效半衰期约为 13 小时。