Microwave‐Assisted Synthesis and Transformations of Cationic CpRu(II)(naphthalene) and CpRu(II)(naphthoquinone) Complexes

Abstract

Details of the direct synthesis of cationic Ru(II)(η5‐Cp)(η6‐arene) complexes from ruthenocene using microwave heating are reported. Developed for the important catalyst precursor [Ru(II)(η5‐Cp)(η6‐1‐4,4a,8a‐naphthalene)][PF6] reaction time could be shortened from three days to 15 min. The method was extended to [Ru(II)(η6‐benzene)(η5‐Cp)][PF6], [Ru(II)(η5‐Cp)(η6‐toluene)][PF6], [Ru(II)(η5‐Cp)(η6‐mesitylene)][PF6], [Ru(II)(η5‐Cp)(η6‐hexamethylbenzene)][PF6], [Ru(II)(η5Cp)(η6‐indane)][PF6], [Ru(II)(η5‐Cp)(η6‐2,6‐dimethylnaphthalene)][PF6], and [Ru(II)(η5‐Cp)(η6‐pyrene)][PF6]. 1‐methylnaphthalene and 2,3‐dimethylnaphthalene afforded mixtures of regioisomeric complexes. [Ru(Cp)(CH3CN)3][PF6], derived from the naphthalene precursor provided access to the cationic RuCp complexes of naphthoquinone, tetralindione, 1,4‐dihydroxynaphthalene, and 1,4‐dimethoxynaphthalene. Reduction of the tetralindione complex afforded selectively the endo,endo diol derivative. X‐Ray structures of five complexes are reported.

Preparation and Structural Characterization of [CpRu(1,10‐phenanthroline)(CH3CN)][X] and Precursor Complexes (X=PF6, BArF, TRISPHAT‐N)

“…However and unfortunately, previous attempts to perform anion metathesis of chloride to BAr F − by a direct exchange of [CpRu(η 6 ‐naphthalene)][Cl] with NaBAr F , were not met with success [57] . This problem could be circumvented in our hands starting from the [CpRu(η 6 ‐naphthalene)][PF 6 ] salt instead which was prepared following microwave assisted protocols [57,58] . In practice, a simple mixing for 30 min of NaBAr F and [1][PF 6 ] in a homogenous dichloromethane/acetone solution (1.2 : 1) provided, after crystallization from dichloromethane and hexane at 4 °C, the desired [CpRu(η 6 ‐naphthalene)][BAr F ] complex namely [1][BAr F ] in good yield (72 %, Scheme 2).…”

“…[57] This problem could be circumvented in our hands starting from the [CpRu(η 6 -naphthalene)][PF 6 ] salt instead which was prepared following microwave assisted protocols. [57,58] In practice, a simple mixing for 30 netic profiles for carbene CÀ H insertions into THF or stereoselective epoxide openings, with a slight advantage for the BAr F derivative in the THF series. However, OTf and BF 4 complexes present quite lower reactivity.…”

Spirocyclic Amide Acetal Synthesis by [CpRu]‐Catalyzed Condensations of α‐Diazo‐β‐Ketoesters with γ‐Lactams

“…First, the nature of the metal catalyst was investigated, 2 switching from copper to dirhodium and cyclopentadienyl ruthenium complexes ( entries 3 and 4 ) while decreasing the temperature to 60 °C with these more reactive decomposition catalysts. Using Rh 2 (OAc) 4 (1 mol‐%), [45] a yield of 37 % was obtained, while decomposition with [CpRu(MeCN)] 3 PF 6 (2.5 mol‐%) [46,47] led to a drastic improvement and a corresponding yield of 80 %. Selecting the [CpRu] complex for further experiments, the influence of the negative counterion was investigated, switching from PF 6 − to the large, lipophilic and less coordinating BAr F − anion [42] .…”

Carbon–Carbon Bond Formation between N-Heterocyclic Carbene Ligand on Ruthenium Carbene Catalysts and 1,4-Naphthoquinone via Intramolecular Carbon(sp3)–Hydrogen Bond Activation

“…Actually, when we used an excess amount of NQ (10 equiv) and PhCl as the solvent (bp = 131 °C), the yield of 3a improved to 77% (entry 5). The yield was further improved to 84% under a highly diluted concentration (entry 6, 0.025 M) …”

“…These results might be attributed to the fact that the desired C–H bond activation pathway hardly proceeded. Regarding S1n ’s reactivity, there is a similar report on the o -tolyl group in the NHC . They investigated, by computational research, which activation, C–C or C–H bond, is thermodynamically preferred as the reaction product and concluded that the formation of the C–C bond activated complex was preferred.…”