Stepwise Construction of Polynuclear Complexes of Rhodium and Iridium Assisted by Benzimidazole-2-thiol. NMR and X-ray Diffraction Studies

Abstract

Reactions of [M(2)(&mgr;-Cl)(2)(cod)(2)] (cod = 1,5-cyclooctadiene, M = Rh, Ir) with benzimidazole-2-thiol (H(2)Bzimt) afford the mononuclear complexes [MCl(H(2)Bzimt)(cod)] (M = Rh (1), Ir (2)) for which a S-coordination of the ligand is proposed based on their spectroscopic data. The dinuclear complexes [M(2)(&mgr;-HBzimt)(2)(cod)(2)] (M = Rh (3), Ir (4)) are isolated from the reaction of [M(acac)(cod)] and benzimidazole-2-thiol. They contain the monodeprotonated ligand (HBzimt(-)) bridging the two metals in a &mgr;(2)-(1kappaN,2kappaS) coordination mode and in a relative cis,cis-HT arrangement. Complexes 3 and 4 react with the appropriate species [M(cod)(Me(2)CO)(2)](+) to afford the trinuclear cationic aggregates [M(3)(&mgr;-HBzimt)(2)(cod)(3)](+) (M = Rh (5), Ir (6)) and with the [M'(2)(&mgr;-OMe)(2)(cod)(2)] compounds to give the homo- and heterotetranuclear complexes [MM'(&mgr;-Bzimt)(cod)(2)](2) (M = M' = Rh (7), Ir (8); M = Ir, M' = Rh (9)) containing the dideprotonated ligand (Bzimt(2)(-)). The trinuclear neutral complexes [M(3)(&mgr;-Bzimt)(&mgr;-HBzimt)(cod)(3)] are intermediates detected in the synthesis of the tetranuclear complexes. Protonation of 9 with HBF(4) gives the unsymmetrical complex [Ir(2)Rh(&mgr;-HBzimt)(2)(cod)(3)]BF(4) (10). This reaction involves the protonation of the bridging ligands followed by the removal of one "Rh(cod)" moiety to give a single isomer. The molecular structure of [Rh(2)(&mgr;-Bzimt)(cod)(2)](2) (7) has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P2(1)/n, a = 20.173(5) Å, b = 42.076(8) Å, c = 10.983(3) Å, beta = 93.32(2) degrees, Z = 8, 7145 reflections, R = 0.0622, and R(w) = 0.0779. The complete assignment of the resonances of the (1)H NMR spectra of the complexes 3, 4, and 7-9 was carried out by selective decoupling, NOE, and H,H-COSY experiments. The differences in the chemical shifts of the olefinic protons are discussed on the basis of steric and magnetic anisotropy effects.

Hydrogen Bonding and Isomerism Arising from the Coordination Modes of Bridging Benzimidazole-2-thiolate Ligands in Tetranuclear Rhodium Complexes

“…As part of our current investigations into the chemistry of polynuclear complexes containing anionic ligands of the N−C−X (X = N, O, S) type, we recently reported the stepwise construction of a new family of di-, tri-, and tetranuclear complexes using the deprotonated forms of 2-mercaptobenzimidazole (H 2 Bzimt) as backbones to hold M(cod) moieties (M = Rh, Ir; cod = 1,5-cyclooctadiene) in close proximity. All these polynuclear complexes, and most of those reported with pyridine-2-thiolate (Pyt), benzothiazole-2-thiolate (Bztzt), and related ligands, show a basic eight-membered M 2 (μ-(1κN,2κS) 2 ) ring with the two bridging ligands arranged in HT (head-to-tail) or HH (head-to-head) dispositions, as found for rhodium and iridium dinuclear complexes (A, Figure ).…”

The oxidative conversion of the N,S-bridged complexes [{RhLL′(μ-X)}2] to [(RhLL′)3(μ-X)2]+ (X = mt or taz): a comparison with the oxidation of N,N-bridged analogues

“…Thus, at -80 (for 1) or -60 • C (for 2) four peaks are observed for the alkene protons or carbons of the cod ligand, as seen for [{Rh(cod)(m-Hbzimt)} 2 ]. 12 (The 1 H signals for the cod ligands of 1 and 2 are very broad at room temperature, probably as a result of rotation of the cod ligand about the metal-cod axis. 5 )…”

Syntheses and crystal structures of mononuclear and dinuclear (pentamethylcyclopentadienyl)iridium(III) complexes containing 2-mercaptobenzimidazole

“…When H 2 bimt is deprotonated to form a monoanionic Hbimt À or a dianionic bimt 2À , the imidazolate nitrogen can also be bound to a metal ion. Therefore, a variety of coordination and bridging modes become possible for H n bimt (2Àn)À (n = 0, 1, or 2) [6][7][8][9][10][11]. Furthermore, because the coordinated H n bimt (2Àn)À can be incorporated into hydrogen-bonding network as a donor (via imidazole N-H) or an acceptor (via imidazolate N or thiolate S), and because the planar benzimidazole ring is possible to form a p-p stacking interaction in the crystal, H 2 bimt and the deprotonated ions are versatile ligands in construction of coordination polymers or metal-organic frameworks (MOFs).…”