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 (<b>1</b>) and Re (<b>2</b>)) and [M­(CO)₅­(CN­(CH₂)₁₀­COOMe)]­ClO₄ (M = Tc (<b>3</b>) and Re (<b>4</b>)), were prepared and characterized by IR, ¹H NMR, and ¹³C­{¹H} NMR spectroscopy. The crystal structures of <b>1</b> and <b>2</b> were determined using single-crystal X-ray diffraction. The kinetics of thermal decarbonylation of technetium complexes <b>1</b> and <b>3</b> 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 <b>2</b> and <b>4</b> were stable with respect to thermal decarbonylation. Histidine challenge reaction of complexes <b>1</b> and <b>2</b> 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 <b>1</b> is more stable under these conditions