Platinum metal thioether macrocyclic complexes: synthesis, electrochemistry, and single-crystal X-ray structures of cis-[RhCl2L2]PF6 and trans-[RhCl2L3]PF6(L2= 1,4,8,11 -tetrathiacyclotetradecane, L3= 1,5,9,13-tetrathiacyciohexadecane)

Abstract

Reaction of RhCl₃ with 1 mol equivalent of L[1,4,7,10-tetrathiacyclododecane (L¹), 1,4,8,11-tetrathiacyclotetradecane (L²), and 1,5,9,13-tetrathiacyclohexadecane (L³)] in refluxing MeOH affords the rhodium(III) complex cations [RhCl₂L]⁺. The complex cis-[RhCl₂L²]PF₆ crystallises in the monoclinic space group C2/c, with a= 10.746(8), b= 11.298(5), c= 15.708(8)Å, β= 92.00(5)°, and Z= 4. Å single-crystal X-ray structure shows the cation sitting on a crystallographically imposed C₂ axis with octahedral Rh^III bound to two mutually cis chloro ions [Rh–Cl 2.383 6(12)Å]. The tetrathia macrocycle adopts a folded conformation with S(1) and S(8)trans to chloride, Rh-S(1) 2.287 0(12) and Rh–S(4) 2.327 5(12)Å. The trans isomer has not been detected spectroscopically in reactions of Rh^III with L¹ and L²; the tendency of these ligands to co-ordinate to second- and third-row transition-metal ions to form cis complexes is ascribed to the large radii of these metal ions relative to the cavity size of the 12-and 14-membered rings. This is confirmed by structural analysis of [RhCl₂L³]PF₆ which shows mutually trans chloro ligands, Rh–Cl 2.339 1 (22)Å. The complex trans-[RhCl₂L³]PF₆ crystallises in the monoclinic space group C2/c, with a= 11.950 7(20), b= 11.1 055(15), c= 16.206 7(18)Å, β= 95.197(21)° and Z= 4. The single-crystal X-ray structure shows Rh^III on an inversion centre with the six-membered chelate rings of the macrocycle adopting alternate chair and twist-boat conformations, Rh–S(1) 2.348 3(25) and Rh–S(5) 2.348 3(27)Å.