A stable Re complex containing an imidazopyridine ligand with a high affinity for TSPO has been synthesized as a model for new 99mTc or 188/186Re-based radiopharmaceuticals to be used in SPECT diagnosis or in therapy, respectively. The new complex fac- [ReBr(CO)3(TZ6)], structurally characterized, showed high affinity (nanomolar concentration) for the target protein.

Geminal bisphosphonates (BPs), used in the clinic for the treatment of hypercalcaemia and skeletal metastases, have been also exploited for promoting the specific accumulation of platinum antitumor drugs in bone tissue. In this work, the platinum dinuclear complex [{Pt(en)}2(μ-AHBP-H2)]+ (1) (the carbon atom bridging the two phosphorous atoms carrying a 2-ammonioethyl and a hydroxyl group, AHBP-H2) has been used as scaffold for the synthesis of a Pt(II) trinuclear complex, [{Pt(en)}3(μ-AHBP)]+ (2), and a Pt(IV) adamantane-shaped dinuclear complex featuring an oxo-bridge, [{PtIV(en)Cl}2(μ-O)(μ-AHBP-H2)]+ (3) (X-ray structure). Compound 2 undergoes a reversible, pH dependent, rearrangement with a neat switch point around pH = 5.4. Compound 3 undergoes a one-step electrochemical reduction at Epc = −0.84 V affording compound 1. Such a potential is far lower than that of glutathione (−0.24 V), nevertheless compound 3 can undergo chemical reduction to 1 by GSH, most probably through a different (inner-sphere) mechanism. In vitro cytotoxicity of the new compounds, tested against murine glioma (C6) and human cervix (HeLa) and hepatoma (HepG2) cell lines, has shown that, while the PtIV dimer 3 is inactive up to a concentration of 50 μM, the two PtII polynuclear compounds 1 and 2 have a cytotoxicity comparable to that of cisplatin with the trinuclear complex 2 generally more active than the dinuclear complex 1.

The reactivity with acetylene of [PtX2(Me2phen)] (X = Cl, Br, I) complexes has been investigated. Whereas the chlorido species [PtCl2(Me2phen)] exhibits negligible reactivity at short reaction times, the bromido and iodido species [PtBr2(Me2phen)] and [PtI2(Me2phen)] lead initially to formation of Pt(II) five-coordinate complexes, [PtX2(η2-CHuCH)(Me2phen)], that evolve to four-coordinate alkenyl complexes of the type [PtX(η1-E-CHvCHX)(Me2phen)]. The alkenyl complexes, in the presence of excess acetylene, establish an equilibrium with the five-coordinate alkyne–alkenyl species [PtX(η1-E-CHvCHX)(η2-CHuCH)(Me2phen)] (X = Br, I). The π-bonded acetylene can be exchanged with free olefins or CuO, affording the new alkene–alkenyl or carbonyl–alkenyl complexes [PtX(η1-E-CHvCHX)(η2-olefin)(Me2phen)] and [PtX(η1- E-CHvCHX)(CuO)(Me2phen)]. The five-coordinate geometry of the alkyne–alkenyl and alkene–alkenyl complexes was assessed from NMR data and is fully consistent with that of a previously determined X-ray structure of [PtBr(η1-E-CHvCHBr)(η2-CH2vCH2)(Me2phen)].

The reactivity of [PtX2(Me2phen)] complexes (X = Cl, Br, I; Me2phen = 2,9-dimethyl-1,10-phenanthroline) with terminal alkynes has been investigated. Although the dichlorido species [PtCl2(Me2phen)] exhibits negligible reactivity, the bromido and iodido derivatives lead in short time to the formation of five-coordinate Pt(ii) complexes of the type [PtX2(Me2phen)(η(2)-CH[triple bond, length as m-dash]CR)] (X = Br, I; R = Ph, n-Bu), in equilibrium with the starting reagents. Similar to analogous complexes with simple acetylene, the five coordinate species can also undergo dissociation of an halido ligand and formation of the transient square-planar cationic species [PtX(Me2phen)(η(2)-CH[triple bond, length as m-dash]CR)](+). This latter can further evolve to give an unusual, sparingly soluble square planar product where the former terminal alkyne is converted into a :C[double bond, length as m-dash]C(H)(R) moiety with the α-carbon bridging the Pt(ii) core with one of the two N-donors of coordinated Me2phen. The final product [PtX2κ(2)-N,C-(Z)-N[combining low line]1-N10-C[combining low line][double bond, length as m-dash]C(H)(R)] (N1-N10 = 2,9-dimethyl-1,10-phenanthroline; X = Br, I) contains a Pt-N-C-C-N-C six-membered chelate ring in a square planar Pt(ii) coordination environment.

Iminoether derivatives of the formula trans-[PtCl2{HN=C(R)OR'}(2)] proved to be endowed with remarkable antitumor activity in vivo. Moreover, these trans compounds were more cytotoxic than their cis congeners, a trend opposite to that generally observed for corresponding platinum complexes with ammines. The imino ligands can have either E or Z configuration about the C=N double bond, and in the case of R = R' = Me, the E configuration is by far thermodynamically preferred. However, substitution of chloride anions with neutral ligands (L) alters the relative stability of the E and Z isomers. Upon investigation of the derivatives with L = PPh3, AsPh3, Me2S=O, and (H2N)(2)C=S, it has been concluded that an electrostatic interaction between the oxygen lone pair of the iminoether and the platinum center, fostered by the net positive charge of the complex and the low dielectric constant around the metal core provided by the hydrophobic L ligands, stabilizes the Z configuration. The same factors can favor iminoether isomerization. These conclusions are fully supported by X-ray crystal data. In the case of a reaction with thiourea, an aminic group of thiourea can substitute the methoxy group of a cis-iminoether, leading to the formation of a cyclic compound in a process reminiscent of the McLafferty rearrangement. Such a rearrangement could play a role in the interaction of the platinum-iminoether compounds with target DNA and proteins.