Transition metal complexes of a bis(carbene) ligand featuring 1,2,4-triazolin-5-ylidene donors: structural diversity and catalytic applications

Abstract

Dialkylation of the 1,3-bis(1,2,4-triazol-1-yl)benzene with ethyl bromide resulted in the formation of [L-H2]Br2 which upon salt metathesis with NH4PF6 readily yielded the bis(triazolium) salt [L-H2](PF6)2 with non-coordinating counterions. [L-H2](PF6)2 and...

[(PPh3)2NiCl2]-Catalyzed C–N Bond Formation Reaction via Borrowing Hydrogen Strategy: Access to Diverse Secondary Amines and Quinolines

“…6,148.4,135.6,129.5,129.1,127.6,125.5,119.6,84.1,70.5,69.8,68.1 ppm. 1,2,3,b Following the general procedure, the title compound was isolated as a yellow liquid using silica gel column chromatography and eluting with 5% ethyl acetate in hexane (59 mg, 64% yield): 1 H NMR (500 MHz, CDCl 3 ) δ 7.97 (d, 1H), 7.77 (s, 1H), 7.67 (d, 1H), 7.59 (t, 1H), 7.41 (t, 1H), 3.11 (t, 2H), 2.95 (t, 2H), 2.01−1.96 (m, 2H), 1.90−1.85 (m, 2H) ppm; 13 C{ 1 H} NMR (126 MHz, CDCl 3 ) δ 159. 4, 146.6, 135.1, 131.1, 128.6, 128.3, 127.3, 127.0, 125.6, 33.6, 29.3, 23.3, 23.0 ppm.…”

Recent Advances in the Syntheses and Catalytic Applications of Homonuclear Ru‐, Rh‐, and Ir‐Complexes of CNHC^C Cyclometalated Ligands

“…Later in 2018, Rit et al studied the effect of stereoelectronic tuning of diverse cyclometalated Ru II -NHC complexes in their catalytic activities. They have reported various phenyl based cyclometalated Ru II -NHC complexes featuring planar ruthenacycles either with imidazolylidene moiety having varying substituents at the para-position of the N-phenyl ring (32 a-c) or a bulky mesoionic carbene centre (33,Scheme 22). [30a] These variations impart considerable difference in the electronic nature at the Ru II -centre as suggested by the 13 C{ 1 H} NMR and electrochemical analyses.…”

“…examples of stable di-ortho-metalated Ir III /Ru II -dinuclear complexes supported by the 1,2,4-triazolylidene donors. [33] The wellcharacterized complexes were showcased to be effective in two different important functional group transformations: alkene/ alkyne hydrogenation and β-alkylation of secondary alcohols using primary alcohols via borrowing hydrogen strategy (Scheme 26). With a low catalyst loading of 0.3 mol%, the Irprecatalyst was found to be more effective for the alkene/ alkyne hydrogenation whereas the Ru-precatalyst with a very low loading of 0.01 mol% showed excellent activity towards the C-alkylation reaction with a broad substrate scope.…”

Heterobimetallic Complexes Bridged by an Unsymmetrical Bis(NHC) Ligand: Study of Enhanced Catalytic Activity in Tandem Transformations and Understanding of Cooperativity between the Metal Centers

“…These well-defined complexes were then evaluated as catalysts in three one-pot tandem catalytic reactions: hydrodechlorination (HDC)/dehydrogenation (DH) of secondary alcohols, and hydrodechlorination (HDC)/ hydrodefluorination (HDF) and transfer hydrogenation (TH) of ketones. Encouragingly, the heterobimetallic catalysts 5 and 7 exhibited clear advantages over the equivalent catalytic systems generated by combining either the homobimetallic Ir III and Pd II catalysts 8 and 9 or the monometallic analogues Pd II (10) and Ir III (11), respectively. These results support our hypothesis that some sort of cooperativity does exist between the two different metal centers (Ir and Pd) bridged by a single ligand framework, thereby enhancing the catalytic activity of the heterobimetallic complexes in complex organic transformations.…”

“…Additionally, we have also synthesized the monometallic analogues 10 (Pd II ) and 11 (Ir III ) from [L2/L3-H]Br (Figure 2), respectively using modified literature procedures. [11,15] The cooperation between the different metal centers in heterobimetallic complexes to enhance their catalytic activity has been correlated with the distance between them (either through bonding or spatial proximity) in literature. [4a,e] In this particular case, given the relatively rigid nature of our ligand, communication between the metal centers can only occur 16), C19-PdÀ N6 177.2( 7), C19-PdÀ Br 88.6(5)-88.9( 5), N6-PdÀ Br 89.7(4)-92.8( 4), Br2-PdÀ Br1 177.50 (12).…”