Low-valent homobimetallic Rh complexes: influence of ligands on the structure and the intramolecular reactivity of Rh–H intermediates

Abstract

Supporting two metal binding sites by a tailored polydentate trop-based (trop = 5H-dibenzo[a,d]cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(i) complexes. These were studied as models for Rh/C hydrogenation catalysts.

Metal–Ligand Cooperative Proton Transfer as an Efficient Trigger for Rhodium-NHC-Pyridonato Catalyzed gem-Specific Alkyne Dimerization

“…In contrast, addition of the bulky trimethyl­phenyl­acetylene to 2 afforded Rh­{κ 2 - O , N -(Opy)}­{η 2 -H 2 CC­(Mes)­CC­(Mes)}­(IPr) ( 7 ), that results from the η 2 -CC coordination of the enyne reaction product formed by fast dimerization of the alkyne. This uncommon coordination mode for an enyne is reflected in the appearance in the 13 C­{ 1 H}-APT NMR spectrum of two doublets at δ 50.3 and 41.0 ppm with J C–Rh around 18.8 Hz, corresponding to the coordinated olefin. Most likely, the presence of the bulky substituents in the proximity of the alkynyl moiety hinders the coordination of the triple bond.…”

Mechanism of Heterogenization of Dirhodium Catalysts: Insights from DFT Calculations

“…32−34 These studies include but are by no means limited to the aforementioned fields of research of catalytic activity for C−Hinsertion or O−H-insertion reactions. Here a recent study by Jurt et al 35 on the H 2 formation on bimetallic rhodium complexes clearly illustrated the capability of DFT to account for intricate changes in reactivity depending on the types of ligands bound to the investigated dirhodium complex. Furthermore, a computational study of the reactivity using DFT can be reliably and accessibly extended to include aspects of solvation or dispersion interactions, 36,37 whose importance should not to be underestimated in any conclusive evaluation of structural or thermodynamic data.…”

Reduction of Nitrogen Oxides by Hydrogen with Rhodium(I)–Platinum(II) Olefin Complexes as Catalysts

“…The multidentate ligand 1 (Figure 2 a) was synthesized by adapting a recently published protocol (Supporting Information, Figure S1) [23] . The ligand is designed in such a way that two transition metals can bind in close proximity within the concave pocket formed by the diphenylphosphino group, Ph 2 P, the alkene unit of the central seven‐membered ring, and the two alkynyl units.…”

“…On the contrary, the addition of a complexing agent such as PPh 3 inhibits the hydrogenation of N 2 O (Table 1, entry 8) which also indicates that the catalysis proceeds in homogeneous solution [27] . Finally, the mononuclear rhodium complex in which the two‐electron donating PtMe 2 fragment is replaced by PPh 3 , [Rh( tropPPh 2 )(PPh 3 )](OTf) 10 , [23] has low activity (TON=10, Table 1, entry 10). This result indicates that the PtMe 2 fragment is important as structural and electronic modulator as well as cooperative metal center in substrate binding and activation (vide infra).…”

“…Themultidentate ligand 1 (Figure 2a)was synthesized by adapting arecently published protocol (Supporting Information, Figure S1). [23] Thel igand is designed in such aw ay that two transition metals can bind in close proximity within the concave pocket formed by the diphenylphosphino group, Ph 2 P, the alkene unit of the central seven-membered ring, and the two alkynyl units.The first metal is introduced by reacting 1 with [Rh 2 (m 2 -Cl) 2 (C 2 H 4 ) 4 ]inbenzene which gives the chlorobridged dimeric rhodium complex 2 in good yield (Figure 2a). Subsequent reaction with [Pt 2 Me 4 (m 2 -SMe 2 ) 2 ]i nd ichloromethane cleanly gives the heterobimetallic complex 3 in 85 % isolated yield.…”