CROWN THIOETHER CHEMISTRY - THE RHODIUM COMPLEXES OF 1,4,7-TRITHIACYCLONONANE (9S3) AND 1,5,9-TRITHIACYCLODODECANE (12S3) AND THE CONFORMATIONAL FACTORS THAT STABILIZE MONOMERIC RH(II) IONS

Reaction of the trithia ligands 9S3 (1,4,7-trithiacyclononane), 10S3 (1,4,7-trithiacyclodecane), 12S3 (1,5,9-trithiacyclododecane), and ttn (2,5,8-trithianonane) with rhodium(III) triflate in methanol yields the homoleptic thioether complexes [Rh(L)2]3+ (L = 9S3, 10S3, 12S3, and ttn). Average Rh-S distances in these cations increase from 2.34 angstrom in the 9S3 complex to 2.36 angstrom in the 12S3 analogue. Cyclic voltammetry in MeNO2 shows that [Rh(9S3)2]3+ undergoes two one-electron reductions. The first of these corresponds to a discrete mononuclear Rh(II) complex that has been characterized by EPR as well as electrochemical methods. The 10S3 analogue, [Rh(10S3)2]3+, behaves similarly. In the 12S3 analogue the quasi-reversible Rh(III/II) couple contrasts with the irreversibility of the Rh(II/I) process. In continuation of this trend, the acyclic complex [Rh(ttn)2]3+ shows no reversible electrochemistry. The conformational properties of the macrocyclic ligand play a crucial role in stabilizing [Rh(L)2]2+ complexes, as shown by their increasing stability to disproportionation in the order L = 9S3 > 10S3 > 12S3 >> ttn. Crystal data: [Rh(9S3)2](CF3SO3)3, RhC15H24S9F9O9, fw = 910.83, monoclinic, space group C2/c (no. 15), a = 18.638 (6) angstrom, b = 10.643 (3) angstrom, c = 16.075 (2) angstrom, beta = 105.93 (2)o, Z = 4; [Rh(12S3)2](BF4)3, RhC18H36S6B3F12, fw = 808.2, monoclinic, space group P2(1)/c (no. 14), a = 17.673 (5) angstrom, b = 10.874 (4) angstrom, c = 17.164 (3) angstrom, beta = 110.85 (1)o, Z = 4.