Complexes of the fac-{Re(CO)3}+ core with tridentate ligands derived from arylpiperazines

Arylpiperazines, XC6H4N(CH2CH2)2NH, are readily alkylated to give the N-alkylpiperazines of the type XC6H4N(CH2CH2)2N(CH2)nNH2. The amine functions of these derivatives are in turn easily subjected to mono- or dialkylation to provide potentially tridentate ligands of the types XC6H4N(CH2CH2)2N(CH2)nN(H)(CH2Y) and XC6H4N(CH2CH2)2N(CH2)nN(CH2Y)(CH2Z), respectively. The latter class of dialkylated derivatives may be symmetrically (Y=Z) or unsymmetrically (Y ≠ Z) substituted. The donor groups Y and Z of this study include pyridine, imidazole, methyl-imidazole, thiazole, carboxylate and thiolate. The reactions of these ligands with [NEt4]2[Re(CO)3Br3] yield complexes of the type [Re(CO)3{(YCH2)N(H)(CH2)n(H)xN(CH2CH2)2N(H)yC6H4X}]n and [Re(CO)3{(ZCH2)(YCH2)N(CH2)n(H)xN(CH2CH2)2N(H)yC6H4X}]n where the molecular charge n (0, +1, or +2) depends on the nature of the donor groups Y and Z (whether neutral or anionic or a combination of neutral and anionic) and on the degree of protonation of the piperazine unit (x=0 or 1; y=0 or 1). This variety of tridentate chelators provides complexes with fac-{Re(CO)3N3}, {Re(CO)3N2O}, {Re(CO)3NO2}, {Re(CO)3N2S} and {Re(CO)3NS2} coordination geometries. The structures of the model compound [Re(CO)3{(CH3N2C3H2CH2)N(H)CH2CH2-piperidine}]Br · H2O, [Re(CO)3{(CH3N2C3H2CH2)N(H)CH2CH2-Fphenpip}]Br, [Re(CO)3{(NC5H4CH2)N(H)CH2CH2-Fphenpip}]Br, [Re(CO)3{(O2CCH2)2NCH2CH2CH2-CH3OphenpipH}] · xCH3OH (x≈0.875), [Re(CO)3{(NC5H4CH2)2NCH2CH2CH2-CH3OphenpipH}]Br2 · 2CH2Cl2 · H2O and [Re(CO)3{(CH3N2C3H2CH2)(O2CCH2)NCH2CH2CH2-CH3OphenpipH2}]BrCl · 1.5CH3OH · H2O are discussed (phenpip: phenylpiperazine, –C6H4N(CH2CH2)2N–).