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

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)(3)Br-3] giving [Re{kappa(3)-H(mu-H) B(tim(Me,pip))(2)}(CO)(3)] 8, [Re{kappa(3)-H(mu-H) B(tim(Me,CH2-pip))(2)}(CO)(3)] 9, [Re{kappa(3)-Ph(mu-H)B(tim(Me))(tim(Me,pip))}( CO)(3)] 10 and [Re{kappa(3)-Ph(mu-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 H-1 NMR spectroscopies), and by X-ray diffraction analysis in the case of 8.