Rhenium(i) tricarbonyl complexes with mercaptoimidazolylborate ligands bearing piperazine fragments

Abstract

Reaction of an adequate borohydride salt with the functionalized mercaptoimidazoles timH^Me,pip 1 or timH^Me,CH₂-pip 2 have led to Na[H₂B(tim^Me,pip)₂] 3, Na[H₂B(tim^Me,CH₂-pip)₂] 4, Li[H(Ph)B(tim^Me)(tim^Me,pip)₂] 6 and Li[H(Ph)B(tim^Me)(tim^Me,CH₂-pip)₂] 7 (timH^Me = 1-methyl-2-mercaptoimidazole; timH^Me,pip = 1-methyl-5-[(4-(2′-methoxyphenyl)-1-piperazinyl)carbonyl]-2-mercaptoimidazole; timH^Me,CH₂pip = 1-methyl-5-[(4-(2′-methoxyphenyl)-1-piperazinyl)methyl]-2-mercaptoimidazole). These symmetric and assymmetric functionalized bis(mercaptoimidazolyl)borates, carrying a piperazine fragment, react readily with (NEt)₄[Re(CO)₃Br₃] giving [Re{κ³-H(μ-H)B(tim^Me,pip)₂}(CO)₃] 8, [Re{κ³-H(μ-H)B(tim^Me,CH₂-pip)₂}(CO)₃] 9, [Re{κ³-Ph(μ-H)B(tim^Me)(tim^Me,pip)}(CO)₃] 10 and [Re{κ³-Ph(μ-H)B(tim^Me)(tim^Me,CH₂-pip)}(CO)₃] 11. The organometallic complexes 8–11 are valuable models for the development of specific radiopharmaceuticals for imaging serotonergic CNS receptors. The new compounds (1–11) have been characterized by the usual analytical techniques (C, H, N analysis; IR and ¹H NMR spectroscopies), and by X-ray diffraction analysis in the case of 8.