Bimetallic Paddlewheel-type Dirhodium(II,II) Acetate and Formamidinate Complexes: Synthesis, Structure, Electrochemistry, and Hydroformylation Activity

Abstract

Classical hydroformylation catalysts use mononuclear rhodium(I) complexes as precursors; however, very few examples of bimetallic systems have been reported. Herein, we report fully substituted dirhodium(II,II) complexes (C1−C6) containing acetate and diphenylformamidinate bridging ligands (L1−L4). The structure and geometry around these paddlewheeltype, bimetallic cores were confirmed by single-crystal X-ray diffraction. The complexes C3−C6 show electrochemical redox reactions, with the expected reduction (Rh 2 4+/3+ ) and two oxidation (Rh 2 4+/5+ and Rh 2 5+/6+ ) electron transfer processes. Furthermore, the bimetallic complexes were evaluated as catalyst precursors for the hydroformylation of 1-octene, with the acetate-containing complexes (C1 and C2) showing near quantitative conversion (>99%) of 1-octene, excellent activity and chemoselectivity toward aldehydes (>98%), with moderate regioselectivity toward linear products. Replacement of the acetate with diphenylformamidinate ligands (complexes C3−C6) yielded moderate-togood chemoselectivity and regioselectivity, favoring linear aldehydes.

Dirhodium(II,II) Paddlewheel Complexes

“…Heteroleptic dirhodium complexes for highly enantioselective processes start to appear [105] . Dirhodium compounds can be used as catalysts for hydrogenation of alkenes [106] (such reactions were proposed to proceed via heterolytic splitting of hydrogen by the dirhodium complex) or can be used as catalysts for transfer hydrogenations [107] , dynamic kinetic resolution of alcohols, DKR of homoallyl‐carboxylic acids [108] or as catalysts in other processes as hydroformylation of alkenes [109,274] or reduction of CO 2 with silanes [110] . Photochemical and thermal evolution of molecular hydrogen from water [111] can be catalyzed with dirhodium paddlewheel complexes with electron withdrawing carboxylate ligands [112] .…”

“… Dirhodium(II,II) complexes containing N , N' ‐bridging ligands: A1 , [124] A2 , [125] A3 , [125] A4 , [125] A5 : Ar=Ph, [126] A5 : Ar=C 6 H 4 ‐( p ‐CF 3 , p ‐Cl, p ‐OCH 3 , m ‐OCH 3 ), [127] A5 : Ar=C 6 H 3/4 ‐( p ‐Me, m ‐Me, m ‐Cl, m ‐CF 3 , 3,4‐Cl 2 , 3,5‐Cl 2 ), [25] A5: Ar=C 6 H 4 ‐( p ‐F, p ‐Me, o ‐F, o ‐Me), [109] A6 : Ar=C 6 H 4 ( p ‐Br, p ‐NH 2 , p ‐tethered Ru complex by amide bond), [40] A6 : Ar= p ‐Py, [128] A7 , [127] A8 , [129] A9 , [130] A10 [131] …”

Cytotoxicity Evaluation of Unmodified Paddlewheel Dirhodium(II,II)-Acetate/-Formamidinate Complexes and Their Axially Modified Low-Valent Metallodendrimers

“…The ligands ( 1 , 2 ) and bimetallic dirhodium(II,II) complexes ( 3 – 6 ) used in this study ( Figure 1 ), were synthesized following previously published methods [ 35 ].…”

“…All reactions were carried out using standard Schlenk techniques under an inert (N 2 ) atmosphere. The ligands ( 1 , 2 ) [ 1 ], complexes ( 3 – 6 ) [ 35 ], and tripyridyl scaffold ( 7 ) [ 36 ] were synthesized according to the published literature procedures.…”

Enhancing the Air Stability of Dimolybdenum Paddlewheel Complexes: Redox Tuning through Fluorine Substituents

“…Substituted formamidinates and benzoates have both been shown to effectively tune the properties of paddlewheel complexes , and clusters. , However, there has not yet been a systematic study employing fluorinated formamidinates to control the properties of Mo 2 PWCs. Fluorine is the ideal substituent to tune Mo 2 PWCs for several reasons.…”