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

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Abstract
Reaction of an adequate borohydride salt with the functionalized mercaptoimidazoles timHMe,pip 1 or timHMe,CH2-pip 2 have led to Na[H2B(timMe,pip)2] 3, Na[H2B(timMe,CH2-pip)2] 4, Li[H(Ph)B(timMe)(timMe,pip)2] 6 and Li[H(Ph)B(timMe)(timMe,CH2-pip)2] 7 (timHMe = 1-methyl-2-mercaptoimidazole; timHMe,pip = 1-methyl-5-[(4-(2′-methoxyphenyl)-1-piperazinyl)carbonyl]-2-mercaptoimidazole; timHMe,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(timMe,pip)2}(CO)3] 8, [Re{κ3-H(μ-H)B(timMe,CH2-pip)2}(CO)3] 9, [Re{κ3-Ph(μ-H)B(timMe)(timMe,pip)}(CO)3] 10 and [Re{κ3-Ph(μ-H)B(timMe)(timMe,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.