Inorganic (carbon-free) chelate rings

http://projects.itn.pt/P%20Campello/A%20short%20ride%20on%20scorpionates%20from%20d%20to%20felements%20Polyhedron%202004.pdf

A short ride on scorpionates: from d- to f-elements

30 – Technetium and Rhenium

The building blocks fac-[99mTc{κ3-HB(timMe)3}(CO)3] and fac-[99mTc{κ3-R(μ-H)B(timMe)2}(CO)3] [R is H (4a), Ph (5a); timMe is 2-mercapto-1-methylimidazolyl] were obtained almost quantitatively by reacting fac-[99mTc(CO)3(H2O)3]+ with the corresponding scorpionate. These compounds cross the intact blood–brain barrier in mice, with significant retention in the case of 4a and 5a. Using 4a as the lead structure, we have synthesized the functionalized complexes fac-[M{κ3-H(μ-H)B(timBu-pip)2}(CO)3] [M is Re (8), 99mTc (8a); timBu-pip is methyl[4-((2-methoxyphenyl)-1-piperazinyl)butyl](2-mercapto-1-methylimidazol-5-yl)methanamide] and fac-[M{κ
 3-H(μ-H)B(timMe)(timBu-pip)}(CO)3] [M is Re (9), 99mTc (9a)] and evaluated their potential as radioactive probes for the targeting of brain 5-HT1A serotonergic receptors. The Re complexes exhibit excellent affinity [IC50=0.172 ± 0.003 nM (8); IC50=0.65 ± 0.01 nM (9)] for the 5-HT1A receptor. The radioactive congeners (99mTc) have shown an initial brain uptake of 1.38 ± 0.46%ID g−1 (8a) and 0.43 ± 0.12%ID g−1 (9a), but suffer from a relatively fast washout.

Synthesis and biological evaluation of tricarbonyl Re(I) and Tc(I) complexes anchored by poly(azolyl)borates: application on the design of radiopharmaceuticals for the targeting of 5-HT1A receptors.

Publisher Summary This chapter reviews the chemistry observed with Group 7 (Mn, Tc, and Re) poly(pyrazolyl)borate complexes. The redox flexibility of these transition metals and the variability of poly(pyrazolyl) borate ligands have resulted in a wide range of chemistry. Poly(pyrazolyl)borate ligands support numerous complexes involving Group 7 transition metals. The flexibility of these ligands has allowed access to a range of oxidation states and geometries as well as provided Mn, Tc, and Re complexes with a diversity of reactivity. As a result of these attractive features, poly(pyrazolyl)borate ligands support a diversity of complexes, including coordination to all elements of groups 1 through 13 as well as some lanthanides and actinides. Transition metal complexes containing imido ligands are of interest due to their possible role in olefin aziridinations, metal-mediated metathesis of multiple bonds, ammoxidation reactions, C–H activation sequences as well as catalytic hydroamination of C–C multiple bonds. In addition, the chapter discusses about Rhenium, Manganese, and Technetium chemistry with respect to high oxidation as well as low oxidation state complexes.

Chemistry Surrounding Group 7 Complexes that Possess Poly(pyrazolyl)borate Ligands

Reaction of BrM(CO)5 or M2(CO)10(M = Mn or Re) with potassium dihydrobis(pyrazolylato)borate affords the crystallline complexes [{H2B(N2C3H3)2}M(CO)3(pyrazole)]. Reaction with phosphines or phosphites (L) leads to the rapid formation of the disubstitued compounds [{H2B(N2C3H3)2}M(CO)2L2]; in the case of the phosphines the ligands (L) have a relative cis-configuration, whereas, with phosphites the corresponding trans-complexes are obtained. The lability of the co-ordinated pyrazole is attributed to the effect of the ‘hard’ co-ordinated pyrazole nitrogen atoms. Tetra-alkylammonium halides react with [{H2B(N2C3H3)2}M(CO)3(prazole)] to form the stable anions [{H2B(N2C3H3)2}M(CO)3X]–(X = Br or l).

M. Green

Papers

Manganese and rhenium dihydrobis(pyrazolylato)borate-complexes