Coordination capabilities of pyrazolyl containing ligands towards the fac-[Re(CO)3]+ moiety

Abstract

The coordination capabilities of the pyrazolyl containing ligands pz*(CH₂)₂NH(CH₂)₂pz*, pz*(CH₂)₂NH(CH₂)₂NH₂, pz*(CH₂)₂S(CH₂)₂pz* and pz*(CH₂)₂S(CH₂)₂NH₂ (pz* = 3,5-Me₂pz) towards the synthon (NEt₄)₂[ReBr₃(CO)₃] (1) were studied. Depending on the reaction conditions, neutral or cationic Re(I) tricarbonyl complexes have been isolated: [ReBr(CO)₃(κ²-pz*(CH₂)₂NH(CH₂)₂pz*)] (2), [ReBr(CO)₃(κ²-pz*(CH₂)₂S(CH₂)₂pz*)] (3) [Re(CO)₃(κ³-pz*(CH₂)₂NH(CH₂)₂pz*)]Br (4), [Re(CO)₃(κ²-pz*(CH₂)₂S(CH₂)₂pz*)MeOH]Br (5), [Re(CO)₃(κ³-pz*(CH₂)₂NH(CH₂)₂NH₂)]Br (6) and [Re(CO)₃(κ³-pz*(CH₂)₂S(CH₂)₂NH₂)]Br (7). Complexes 2–7 have been characterized by the normal techniques, including X-ray crystallographic analysis in the case of 3, 4, 6 and 7. In these complexes the Re atom adopts a distorted octahedral coordination, being one of the triangular faces defined by the three carbonyl groups and the other three remaining coordination positions by the bidentate and the bromide ligands (3), or by the tridentate and neutral pyrazolyl containing ligands (4, 6, 7). Complexes 2–4, 6 and 7 are static in solution and the ¹H NMR data indicate clearly a κ²-coordination mode of the ligand in 2 and 3 and a κ³-coordination in 4, 6 and 7, which agrees with the coordination mode found in the solid state. Compound 5 displays a fluxional behaviour in solution as shown by variable temperature ¹H NMR studies. No X-ray data exists for this complex but the pattern obtained for the NMR spectrum at 215 K indicates a κ²-coordination mode for the pyrazolyl containing ligand.