乙腈溶液中锇氮化合物电化学诱导桥氮偶联过程的原位FTIR反射光谱研究(英)

In situ FTIRS Studies of the Electrochemically Induced Coupling of Osmium Nitrido Species in Acetonitrile

采用原位 红外反射 光谱（ｉｎ＿ｓｉｔｕ Ｆ Ｔ Ｉ Ｒ Ｓ） 结合紫 外可见 光谱（ Ｕ Ｖ／ Ｖｉｓ） 和 电化学循 环伏安技术（ Ｃ Ｖ） ，研究了［ Ｏｓ Ｖ Ｉ（ Ｎ）（ Ｎ Ｈ３） ４］（ Ｃ Ｆ３ Ｓ Ｏ３） ３ 的 电化 学诱 导桥 氮偶 联过 程． 首次 在 Ｐｔ 电 极上检测到桥 氮 混 合 价 锇 物 种［ Ｏｓ＿ Ｎ ≡ Ｎ＿ Ｏｓ］ 及 其 随 电 位 的 变 化 过 程 ． 在 约 ２ ｍ ｍ ｏｌ／ Ｌ 〔 Ｏｓ Ｖ Ｉ（ Ｎ）（ Ｎ Ｈ３） ４〕（ Ｃ Ｆ３ Ｓ Ｏ３） ３ ＋ ０ ．１ ｍ ｏｌ／ Ｌ Ｔ Ｂ Ａ Ｈ 的乙腈溶 液中，选 取０ ．４ ～－ １ ．０ Ｖ 电位 区间 １００ ｍ Ｖ／ｓ 扫描速度 ，对 Ｐｔ 或 Ｇ Ｃ 电 极进行电 化学循环 伏安处 理，处 理 后的 电极 表 面均 可积 累 一层 深绿 色 的沉积物，表 明电化 学诱导 Ｎ＿ Ｎ 偶联效 应已在 电极上 发生， 并形 成了 混合 价 桥氮 络合 物． 同时 ，在 上述过程中 所生成 的混合价 锇氮物种 ，有可能 较强地 吸附在电 极表 面，且 形成 一定 厚度 的表 面层， 从而减缓了 体系中 Ｏｓ Ｖ Ｉ≡ Ｎ 物种在电 极上的 继续还 原．同 时可 以看 到，随 着 Ｃ Ｖ 的 不 断进 行，溶 液 颜色将逐渐 地由黄变 绿．经过 长时间（

he search for inorganic systems that can cleave N≡N triple bond under mild conditions is an important subject. It is well known that the metal nitrido (M≡N) complexes are possible intermediates in nitrogen fixation [1] and in the reduction of nitrite to ammonia [2,3] . Recently, these complexes have received considerable attention [4～9] for their intriguing photochemical and electrochemical properties. Among different high valence metal nitrido complexes, some osmium(VI) nitrido species are stable enough to be isolated [4～10] , demonstrating that the study on this class of complexes becomes feasible. Meyer and co_workers [4] have reported the electrochemical interconversion between [Os VI (N)(terpy)Cl 2] + and [Os II (NH 3)(terpy)Cl 2] (terpy=2,2':6', 2'_terpyridine). Recently, Che et al. have reported the isolation of an osmium(VI) nitrido complex [Os VI (N)(NH 3) 4Cl] 2+ through oxidation of [Os III (NH 3) 5Cl] 2+[8] . Photolysis of an acetonitrile solution of [Os VI (N)(NH 3) 4](CF 3SO 3) 3 in the presence of an organic electron donor resulted in the formation of the dinitrogen_bridged osmium(II,III) dimer {[Os(NH 3) 4(CH 3CN)] 2(N 2)} 5+[7,8] . It has been found that the one_electron reduced Os V≡N reacts with the starting Os VI ≡N to yield the μ_dinitrogen Os II _N≡N_Os III complex with a second order rate constant of (3.75±0.30)× 10 5 dm 3 mol -1 s -1 in acetonitrile at room temperature [8] . Recently, Taube and co_workers [11] reported that the electrochemical reduction of [Os VI (N)(NH 3) 4] 3+ in acetonitrile resulted also in similar N_N coupling reaction. To our knowledge there is no report, up to now, concerning the in situ FTIR spectroscopic studies of direct coupling of nitrogen atoms of metal nitrido compounds. In the present study, the potential cycling was used to induce the formation of a μ_dinitrogen complex through electrochemical reduction of [Os VI (N)(NH 3) 4](CF 3SO 3) 3 in acetonitrile (donor). The intermediates and products of the reaction on Pt electrode was investigate by means of in situ FTIRS and UV/Vis spectroscopy.