Homo- and Heterodinuclear Complexes with Triazolyl-diylidene. An Easy Approach to Tandem Catalysts

Abstract

The reaction of 1,2,4-trimethyltriazolium tetrafluoroborate ([LH 2 ](BF 4 ) 2 ) with several metal precursors provides a series of homo-and heterodimetallic compounds of Rh and Ir. The reaction of [LH 2 ](BF 4 ) 2 with [Cp*IrCl 2 ] 2 in the presence of NaH in MeOH yields the monocarbene complex [Cp*Ir(LH)Cl 2 ](BF 4 ), which is a very convenient synthon to the preparation of heterodimetallic species through the deprotonation of the remaining NCHN group. Three crystal structures of dimetallic compounds of di-iridium(III), iridium(III)/iridium(I), and iridium(III)/rhodium(I) are described. The complexes obtained have been tested in a tandem catalytic reaction implying the consecutive oxidative cyclization of 2-aminophenyl ethyl alcohol and the alkylation of the resulting imidazole with a series of primary alcohols. The new catalysts show high activity in the overall reaction process, and the selectivity in the production of the bisindolylmethane or monoalkylated indole is tuned by changing the indole/alcohol molar ratio.⊥ This article is dedicated to Prof. Robert H. Crabtree on the occasion of his 60th birthday.

Quinobis(imidazolylidene): Synthesis and Study of an Electron‐Configurable Bis(N‐Heterocyclic Carbene) and Its Bimetallic Complexes

“…The Rh1 À C1 distance of 2.033(2) in 4 a is within the range of rhodium-NHC bond lengths observed in analogous BBI complexes (2.003-2.073 ) [20] and monometallic NHCsupported variants (2.00-2.09 ). [22,57,59,90,92,[94][95][96] In addition, the average cis and trans rhodium-olefin distances in 4 a (2.115 and 2.211 , respectively) are comparable to those observed in the BBI-based variants (2.128-2.190 and 2.110-2.207 for cis and trans positions, respectively) and consistent with the Rh-cod bond lengths in monometallic NHCsupported analogues (2.09-2.23 ). [22,57,59,90,92,[94][95][96] Furthermore, the bite angle of the cod ligand in 4 a (86.…”

“…[85][86][87][88][89] 2 Cl], enabling investigation of the electron density at the metal center by IR spectroscopic analysis of the CO stretching frequencies. [85,86] Reaction of 1 with [22,70,87,93,94] Crystals of 4 a suitable for X-ray diffraction enabled structural confirmation ( Figure 4). A structure of the Ir congener suitable for publication could not be obtained due to twinning.…”

Hydrodefluorination of carbon–fluorine bonds by the synergistic action of a ruthenium–palladium catalyst

“…Figure 2 shows the complexes under study in this work. All three complexes were obtained from 1,2,4-trimethyl-triazolium tetrafluoroborate, following similar synthetic procedures as those that we have previously reported [33][34][35][36][37][38][39] . The preparation of the Pd-Ru heterodimetallic complex 3 was achieved by the stepwise deprotonation of the triazolium salt, followed by the subsequent addition of the corresponding metal source, as schematically shown in Fig.…”

“…1) [33][34][35][36][37][38][39] . The preparation of such types of heterodimetallic complexes allowed us to study several catalytic processes in which each metal fragment facilitated a mechanistically different cycle 33,35,36,40 . We also confirmed that the presence of the two different metals furnish catalytic benefits compared with the cases in which mixtures of homodimetallic species are used.…”

Double CH Bond Activation of C(sp3)H2 Groups for the Preparation of Complexes with Back‐to‐Back Bisimidazolinylidenes

“…[3] The use of heterodimetallic complexes of Ir/Rh and Ir/Pd enabled us to study their activity in catalytic tandem processes in which each metal mediated a mechanistically distinct reaction. [4] Some related dimetallic systems in which the linker between the two metal fragments is a bis(benzimidazolylidene) ligand were also reported by Bielawski and co-workers, [5] although in their case only homometallic complexes were described. The bisylidene ligands described by Bielawski and co-workers and by us have in common their preparation from bisazolium salts that were readily accessed by known literature procedures.…”