Effects of the Heterocycle and Its Substituents on Structure and Fluxionality in Rhodium(I) and Iridium(I) Complexes with the Hindered Thiolates 6-tert-Butylpyridine-2-thiolate and 1-Alkyl-4-tert-butylimidazole-2-thiolate (alkyl = methyl andtert-butyl)

Abstract

Three new sterically hindered heterocyclic thiolate ligands are studied (HetS = 6-tert-butylpyridine-2-thiolate, tBu-PyS; 1-methyl-4-tert-butylimidazole-2-thiolate, Me-tBu-ImS; 1,4-di-tert-butylimidazole-2-thiolate, tBu2-ImS). Related Rh(I) and Ir(I) metal complexes with molecular formulas [M(HetS)(COD)] n , [M(HetS)(CO)2] n , and [M(HetS)(CO)(PPh3)] n (where n = 1 or 2) were made to assess the steric and electronic effects of heterocycle (pyridine vs imidazole) and bulky substituents on the ring. A combination of solution-phase molecular weight determination, infrared spectroscopy, variable-temperature NMR, and solid-state X-ray diffraction studies were used to determine the molecularity of the complexes (value of n) and the coordination modes of the ligands. In the pyridine series, no evidence was found for nitrogen coordination; the presence of the tert-butyl group makes the heterocyclic thiolate behave like a nonheterocyclic derivative. In the imidazole series, three coordination modes were found, all of them including complexation through both the thiolate sulfur and the basic ring nitrogen. Evidence for fluxional and dimer−monomer interconversions was found for several of the imidazole derivatives, and the size of the 1-alkyl group played a significant role in determining the structures of the complexes.

Structural evolution of a recoverable rhodium hydrogenation catalyst

“…data was consistent with two equivalent COs found in a bridged structure, modeled best by one-S, one-Cl, one-Rh and two-CO ligands (Fig. 4b), similar to structures observed by others previously [20][21][22]. Based on the less complex NMR at early times, the thioether ligand (Rh-methionine) appears to react with rhodium and rearranges more rapidly than the terminal sulfur in cysteamine.…”

Dinuclear Pyridine-4-thiolate-Bridged Rhodium and Iridium Complexes as Ditopic Building Blocks in Molecular Architecture

“…In considering the goal of connecting dinuclear and mononuclear units, and given our experience in the synthesis and characterization of thiolate-bridged rhodium and iridium dinuclear complexes [43][44][45][46][47] and related hydrosulfide-bridged counterparts, 48 properties, 45,[49][50][51][52][53][54][55] and its catalytic activity in the hydroformylation of olefins under mild conditions. [56][57][58][59][60] Monodentate thiolato bridging ligands provided flexible structures that support a wide range of bonding and non-bonding metal distances by modification of the hinge angle 5 between the rhodium coordination planes.…”

“…43,45,[85][86][87] Interestingly, a number of thiolate-bridged dinuclear rhodium and iridium complexes containing cyclooctadiene ligands display a synendo conformation in the solid state and exhibit a dynamic behavior similar to that found in complex 1. 45,[86][87][88][89] Unfortunately, the 1 Most probably, the thiolato ligands display an anti conformation with the endo substituent at the side of the molecule with the small carbonyl ligands as is usually found in related complexes. 45 General strategy for self-assembly reactions.…”

Efficient Organocatalytic Dehydrogenation of Ammonia Borane

“…It is tempting to attribute the higher activity of the tert ‐butyl derivatives 2 and 4 to the destabilization of their respective dimers. The synthesis of 4 has been described previously, but its SCXRD structure has not been reported yet . Single crystals suitable for X‐ray analysis were obtained in the course of this study .…”

“…This corroborates the importance of catalyst bifunctionality,t hat is,t he presence of the basic pyridine ring for the catalytic activity of 4.I ti st empting to attribute the higher activity of the tert-butyl derivatives 2 and 4 to the destabilization of their respective dimers.T he synthesis of 4 has been described previously,b ut its SCXRD structure has not been reported yet. [13] Single crystals suitable for X-ray analysis were obtained in the course of this study. [14] TheSCXRD structure is that of the thiopyridone dimer 4 2 (Figure 1).…”