Carboxylate-Functionalized Mesoionic Carbene Precursors: Decarboxylation, Ruthenium Bonding, and Catalytic Activity in Hydrogen Transfer Reactions

Abstract

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Aerobic dehydrogenation of amines to nitriles catalyzed by triazolylidene ruthenium complexes with O2 as terminal oxidant

“…The five-membered metallacycle features a typically acute C trz -Ru-N py bite angle of 77 (±1)° (Table 1). 41,42 The Ru-C trz bond length is 2.04(2) Å, and is thus in the expected range when compared to related triazolylidene complexes. 44,45 All four complexes show similar bond distances suggesting that variation of the ligand substitution pattern has only minor influences on the ligand bonding.…”

“…This frequency is in agreement with previously reported chelating triazolylidene ruthenium complexes. 40,41 The absence of the triazolylidene proton as well as the splitting of the aromatic p-cymene protons into four distinct doublets indicate chelation and therefore N,Cbidentate coordination of the pyridyl-triazolylidene ligand in complexes 4-6. Furthermore, the pyridyl α proton is considerably deshielded, e.g., a doublet at δ H = 8.81 for complex 6b, which is characteristic [41][42][43] for N-coordination of the pyridyl unit to the ruthenium center (cf.…”

“…In order to eliminate this potentially temperature-limiting step, the solvento complex 7 was prepared from the parent cymene analogue 5 upon reaction with AgOTf in refluxing MeCN (Scheme 3) via established procedures. 41,[46][47][48][49][50] In contrast to complex 5, the solvento complex 7 is moderately air-sensitive and gradually degrades over several days, as indicated by a color change from yellow to green. Successful ligand exchange was indicated by 1 H NMR spectroscopy, which showed the absence of the cymene resonances and the appearance of two singlets attributed to coordinated MeCN in 1 : 2 ratio (δ H = 2.54 and 2.07, respectively, CD 3 CN solution).…”

Relevance of Chemical vs. Electrochemical Oxidation of Tunable Carbene Iridium Complexes for Catalytic Water Oxidation

“…General: The metalation reactions were carried out under nitrogen atmosphere using standard Schlenk techniques, and all the reagents and solvents were used as obtained from commercial sources. The precursor compounds 2‐azidopyridine ( 1a ), 1‐(2‐pyridyl)‐1,2,3‐triazole ( 2a ), 5‐methoxy‐2‐(1 H ‐1,2,3‐triazol‐1‐yl)‐pyridine ( 2b ), 4‐methoxy‐2‐(1 H ‐1,2,3‐triazol‐1‐yl)‐pyridine ( 2c ), 4‐ N,N ‐dimethyl‐2‐(1 H ‐1,2,3‐triazol‐1‐yl)pyridinamine ( 2e ), ethyl 1‐(2‐pyridyl)‐1 H ‐1,2,3‐triazole‐4‐carboxylate ( 3a ), triazolium salts 5a , and 6a , as well as iridium complex 8a , and [IrCp*Cl2]2 were prepared according to literature procedures. All other ligand precursors are described in the supporting information.…”

“…The precursor compounds 2-azidopyridine (1a), [83] 1-(2-pyridyl)-1,2,3-triazole (2a), [84] 5-methoxy-2-(1H-1,2,3-triazol-1-yl)-pyridine (2b), [84] 4-methoxy-2-(1H-1,2,3-triazol-1-yl)-pyridine (2c), [84] 4-N,Ndimethyl-2-(1H-1,2,3-triazol-1-yl)pyridinamine (2e), [84] ethyl 1-(2pyridyl)-1H-1,2,3-triazole-4-carboxylate (3a), [85] triazolium salts 5a, [69] and 6a, [86] as well as iridium complex 8a, [69] and [IrCp*Cl2]2 [87] were prepared according to literature procedures. All other ligand precursors are described in the supporting information.…”