Versatile bonding and coordination modes of ditriazolylidene ligands in rhodium(iii) and iridium(iii) complexes

Abstract

Metalation of novel ditriazolium salts containing a trimethylene (-CHCHCH-) or dimethylether linker (-CHOCH-) was probed with different rhodium(iii) and iridium(iii) precursors. When using [MCp*Cl], a transmetalation protocol via a triazolylidene silver intermediate was effective, while base-assisted metalation with MClvia sequential deprotonation of the triazolium salt with KOtBu and addition of the metal precursor afforded homoleptic complexes. The N-substituent on the triazole heterocycle directed the metalation process and led to C,C,C-tridentate chelating ditriazolylidene complexes for N-phenyl substituents. With ethyl substituents, only C,C-bidentate complexes were formed, while metalation with mesityl substituents was unsuccessful, presumably due to steric constraints. Through modification of the reaction conditions for the metalation step, an intermediate species was isolated that contains a C,C-bidentate chelate en route to the formation of the tridentate ligand system. Accordingly, C-H bond activation occurs prior to formation of the second metal-triazolylidene bond. Stability studies with a C,C,C-tridentate chelating ditriazolylidene iridium complex towards DCl showed deuterium incorporation at both N-phenyl groups and indicate that C-H bond activation is reversible while the C-Ir bond is robust. The flexible linker between the two triazolylidene donor sites provides access to both facial and meridional coordination modes.

Mesoionic and Related Less Heteroatom-Stabilized N-Heterocyclic Carbene Complexes: Synthesis, Catalysis, and Other Applications

“…The silver carbene either reacts after isolation or more often just generated in situ with a variety of metal precursors and has been successfully applied for the synthesis of triazolylidene complexes with Pd(II), 48,50−64 Ir(I), 65−67 Ir(III), 35,65−90 Ru(II), 36,44,48,66,74,79−81,83,89,91−110 Rh(I), 48,58,66,111−114 Rh-(III), 70,83,90 Au(I), 47,49,62,76,112,115−122 Cu(I), 123−127 Pt-(II), 128,129 Os(II), 74,79,96,103 Mo(I), 48 and Co(III). 130 Many of the complexes also form when Ag 2 O and the appropriate metal precursor are added simultaneously to the triazolium salt rather than sequentially via formation of the triazolylidene silver intermediate.…”

“…118 The synthetic versatility of the copper-catalyzed click reaction has been widely exploited for the preparation of a variety of bi-and polydentate triazolylidene ligands. In particular, bis(triazolylidene) complexes have been extensively investigated during recent years, including complexes of Re, 177 Ir, 68,70,71,80 Ru, 46,80,95 Rh, 46,70,137,195 Fe, 154 Ag, 46 and Pd. 46,52,64,165 These species can be divided in C4-linked bis(triazolylidene) species M 64,68,70,71,80,95,137,154,165,177 and N3-linked bis(triazolylidene) complexes of type N (Figure 17).…”

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

“…In the year of 2016, the same group reported the synthesis of ditriazolylidene coordinated Ir III and Rh III complexes by changing the linkers between the triazolylidene donors (Scheme 4). [13] Specifically, the N-substituents on the triazole moiety dictate the binding mode of the ligands to metal centre. For example, the N-phenyl substituted triazolylidenes are prone to ortho-metalation and hence, provides the tridentate coordination to yield mono-/ bis-homoleptic iridium and rhodium complexes based on the employed metal source.…”

“…[32] The complex 38 a was formed via free radical polymerization of the monomer 37 with the DVB through cross linking whereas the complex 38 b was formed via free radical polymerization of the monomer complex 37 itself with the help of AIBN radical initiator in both the cases. The incorporation of the Ru II -NHC complex onto the polymer was supported by solid state 13 C NMR studies where the signal at 108 ppm for the vinyl carbon in 38 disappeared when compared to the 13 C NMR spectrum of the monomer 37. Both the complexes show surface area in the range of 300 m 2 /g À 1 and the N 2 -adsorptiondesorption isotherms with relative pressure (P/P 0 ) in the range of 0.35-0.98 revealed the mesoporous nature of the complexes.…”

Dipyrromethene‐Triazolylidene Silver Complexes: Synthesis, Structure and Opportunities

“…[28] They can be obtained by direct metalation, by free-carbene generation followed by metal complexation or by transmetalation of a silver complex. The most common metals used for the transmetalation are palladium, [29][30][31][32] iridium, [33][34][35] rhodium, [36][37][38][39] ruthenium, [40][41][42][43] or gold. [44][45][46] The corresponding complexes are commonly used as catalysts in various transformations such as cross-coupling, [47][48][49] α-arylation, [49] hydrogenation, [35,[40][41][42]50] or in the synthesis of oxazolines.…”