Dicarbonyl cis-[M(CO)₂(N,O)(C)(P)] (M = Re, ^99mTc) Complexes with a New [2 + 1 + 1] Donor Atom Combination

Abstract

The synthesis and characterization of the dicarbonyl mixed ligand cis-[Re(CO)(quin)(cisc)(PPh)] complex, 4, where quin is the deprotonated quinaldic acid, cisc is cyclohexyl isocyanide, and PPh is triphenylphosphine, is presented. The synthesis of 4 proceeds in three steps. In the first, the intermediate fac-[Re(CO)(quin)(HO)] aqua complex 2 is generated from the fac-[NEt][Re(CO)Br] precursor, together with the brominated products fac-[Re(CO)(quinH)(Br)] 1a and fac-[NEt][Re(CO)(quin)(Br)] 1b, in low yield. In the following step, replacement of the aqua ligand of complex 2 by the monodentate isocyanide ligand leads to the formation of fac-[Re(CO)(quin)(cisc)], 3. In the third step replacement of the species trans to the isocyanide carbonyl group of 3 by a phosphine generates complex 4. The Re complexes 2-4 were prepared in high yield and fully characterized by elemental analysis, spectroscopic methods, and X-ray crystallography. At the technetium-99m (Tc) tracer level, the analogous complexes 3' and 4' were produced in high radiochemical purity, characterized by comparative reverse phase high-performance liquid chromatography and showed high resistance to transchelation by histidine or cysteine. This new [N,O][C][P] donor atom combination with the cis-[M(CO)] core (M = Re, Tc) is a promising scaffold for the development of novel diagnostic and therapeutic targeted radiopharmaceuticals.

Synthesis and Characterization of Novel [2 + 1] Tricarbonyl Rhenium Complexes with the Hydrophilic Phosphine Ligands PTA and CAP

“…Comparing the Re-P bond length between the complexes synthesized, the following trends can be noted: (i) the Re-P bond length between PTA and CAP complexes that carry the same bidentate ligand ( 3a and 3b ) does not differ significantly, i.e., 2.4375 for 3a and 2.4584 for 3b ; (ii) the Re-P bond length of the PTA complex 3a is similar to other fac -[Re(CO) 3 (bid)PTA] complexes reported in the literature [ 6 , 30 ]; and (iii) the Re-P bond length of all PTA and CAP complexes synthesized herein is consistently shorter compared to other fac -[Re(CO) 3 (bid)P] reported in the literature where P is a phosphine other than PTA and CAP, e.g., PPh 3 , P(Cy) 3 , P(Cy) 2 Ph [ 6 , 30 , 43 ] which is possibly attributed to the better σ -donating properties of PTA and CAP.…”

“…Complex 1 was synthesized according to a published procedure [ 43 ]. Briefly, [NEt 4 ] 2 [ReBr 3 CO 3 ] (231 mg, 0.30 mmol) and quinaldic acid (quin) (51.9 mg, 0.30 mmol) were dissolved in H 2 O (15 mL).…”

Aerobically stable and substitutionally labile α-diimine rhenium dicarbonyl complexes

“…26 More recently Triantis reported the synthesis and characterization of the dicarbonyl mixed ligand cis-[Re(CO) 2 (quin)(CNR)(PPh 3 )] by reuxing a toluene solution of fac-[Re(CO) 3 (quin)(CNR)] with triphenylphosphine (quin ¼ quinaldic acid). 27 The vast majority of complexes of the cis-[Re I (CO) 2 ] core are those with PR 3 ligands (mono-, bi-or tridentate chelates) occupying coordination sites of the metal. Species of formula cis-trans-[…”

“… 26 More recently Triantis reported the synthesis and characterization of the dicarbonyl mixed ligand cis -[Re(CO) 2 (quin)(CNR)(PPh 3 )] by refluxing a toluene solution of fac -[Re(CO) 3 (quin)(CNR)] with triphenylphosphine (quin = quinaldic acid). 27 …”

Aerobically Stable and Substitutionally Labile α-Diimine Rhenium Dicarbonyl Complexes

“…26 More recently Triantis reported the synthesis and characterization of the dicarbonyl mixed ligand cis-[Re(CO) 2 (quin)(CNR)(PPh 3 )] by refluxing a toluene solution of fac-[Re(CO) 3 (quin)(CNR)] with triphenylphosphine (quin = quinaldic acid). 27 The vast majority of complexes of the cis-[Re I (CO) 2 ] core are those with PR 3 ligands (mono-, bi-or tridentate chelates) occupying coordination sites of the metal. Species of formula cis-trans-[Re I (CO) 2 (PR 3 ) 2 (N_N)] + have been known for fifty years, 28 but it was in the last two decades that their luminescent properties have been studied in details, particularly since the realization of linear and closed multicomponent systems bridged by R 2 P_PR 2 chelates.…”