Technetium and Rhenium Pentacarbonyl Complexes with C2 and C11 ω‑Isocyanocarboxylic Acid Esters

Technetium­(I) and rhenium­(I) pentacarbonyl complexes with ethyl 2-isocyanoacetate and methyl 11-isocyanoundecanoate, [M­(CO)5­(CNCH2­COOEt)]­ClO4 (M = Tc (1) and Re (2)) and [M­(CO)5­(CN­(CH2)10­COOMe)]­ClO4 (M = Tc (3) and Re (4)), were prepared and characterized by IR, 1H NMR, and 13C­{1H} NMR spectroscopy. The crystal structures of 1 and 2 were determined using single-crystal X-ray diffraction. The kinetics of thermal decarbonylation of technetium complexes 1 and 3 in ethylene glycol was studied by IR spectroscopy. The rate constants and activation parameters of this reaction were determined and compared with those for [Tc­(CO)6]+. It was found that rhenium complexes 2 and 4 were stable with respect to thermal decarbonylation. Histidine challenge reaction of complexes 1 and 2 in phosphate buffer was examined by IR spectroscopy. In the presence of histidine, the rhenium pentacarbonyl isocyanide complex partially decomposes to form an unidentified yellow precipitate. Technetium analogue 1 is more stable under these conditions.

锝(Tc)(I)与铼(Re)(I)的五羰基配合物，配体分别为2-异氰基乙酸乙酯和11-异氰基十一烷酸甲酯，对应配合物为[M(CO)₅(CNCH₂COOEt)]ClO₄（M=Tc，记为1；M=Re，记为2）以及[M(CO)₅(CN(CH₂)₁₀COOMe)]ClO₄（M=Tc，记为3；M=Re，记为4）。上述配合物均已合成，并通过红外(IR)光谱、氢核磁共振(¹H NMR)及碳-13{氢}核磁共振(¹³C{¹H} NMR)光谱进行了表征。配合物1和2的晶体结构通过单晶X射线衍射法得以解析。采用红外光谱法研究了锝配合物1与3在乙二醇中发生热脱羰基反应的动力学过程，测定了该反应的速率常数与活化参数，并将其与[Tc(CO)₆]⁺对应反应的相关参数进行了对比。研究发现，铼配合物2与4对热脱羰基反应具有优异的稳定性。通过红外光谱法考察了配合物1和2在磷酸盐缓冲液中的组氨酸竞争反应：在组氨酸存在的条件下，该五羰基异氰类铼配合物会发生部分分解，生成一种未鉴定的黄色沉淀物；而同族的锝配合物1在该条件下则表现出更高的稳定性。