Diastereoselective Synthesis of Arene Ruthenium(II) Complexes Containing Chiral Phosphetane-Based Tethers,1

Synthesis of Phosphet-2-one Derivatives via Phosphinidene Transfer to Cyclopropenones

We report the first synthesis and structural characterization of free, uncomplexed phosphet-2-ones. These unsaturated four-membered phosphacycles were prepared by phosphinidene transfer from dibenzo-7-phosphanorbornadiene compounds, RPA (A = C14H10, anthracene), to cyclopropenones in yields of up to 89%. Theoretical studies suggest that the reaction proceeds through ketene-ylide and ketene-phosphaalkene intermediates. Further transformations of the phosphet-2-ones led to the isolation of more phosphet-2-ones and 1,2-dihydrophosphetes, including two furanone derivatives which are postulated to be produced by intramolecular phosphine-catalyzed [3 + 2] annulations.

Chiral Arene Ligand as Stereocontroller for Asymmetric C-H Activation

Development of chiral ligands is the most fundamental task in metal-catalyzed asymmetric synthesis. In the last 60 years, various kinds of ligands have been sophisticatedly developed. However, it remains a long-standing challenge to develop practically useful chiral η⁶ -arene ligands, thereby seriously hampering the asymmetric synthesis promoted by arene-metal catalysts. Herein, we report the design and synthesis of a class of readily tunable, C₂ -symmetric chiral arene ligands derived from [2.2]paracyclophane. Its ruthenium(II) complexes have been prepared and successfully applied in the enantioselective C-H activation to afford a series of axially chiral isoquinolones (up to 99 % yield and 96 % ee). This study not only lays chemists' longstanding doubts about whether it is possible to use chiral arene ligands to stereocontrol ruthenium(II)-catalyzed asymmetric C-H activation, but also opens up a new avenue to achieve asymmetric C-H activation.

Half-sandwich ruthenium(ii) complexes with tethered arene-phosphinite ligands: synthesis, structure and application in catalytic cross dehydrogenative coupling reactions of silanes and alcohols

The preparation of the tethered arene-ruthenium(ii) complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (R = Ph, n = 1 (9a), 2 (9b), 3 (9c); R = ⁱPr, n = 1 (10a), 2 (10b), 3 (10c)) from the corresponding phosphinite ligands R₂PO(CH₂)_nPh (R = Ph, n = 1 (1a), 2 (1b), 3 (1c); R = ⁱPr, n = 1 (2a), 2 (2b), 3 (2c)) is presented. Thus, in a first step, the treatment at room temperature of tetrahydrofuran solutions of dimers [{RuCl(μ-Cl)(η⁶-arene)}₂] (arene = p-cymene (3), benzene (4)) with 1-2a-c led to the clean formation of the corresponding mononuclear derivatives [RuCl₂(η⁶-p-cymene){R₂PO(CH₂)_nPh}] (5-6a-c) and [RuCl₂(η⁶-benzene){R₂PO(CH₂)_nPh}] (7-8a-c), which were isolated in 66-99% yield. The subsequent heating of 1,2-dichloroethane solutions of these compounds at 120 °C allowed the exchange of the coordinated arene. The substitution process proceeded faster with the benzene derivatives 7-8a-c, from which complexes 9-10a-c were generated in 61-82% yield after 0.5-10 h of heating. The molecular structures of [RuCl₂(η⁶-p-cymene){ⁱPr₂PO(CH₂)₃Ph}] (6c) and [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPⁱPr₂}] (n = 1 (10a), 2 (10b), 3 (10c)) were unequivocally confirmed by X-ray diffraction methods. In addition, complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (9-10a-c) proved to be active catalysts for the dehydrogenative coupling of hydrosilanes and alcohols under mild conditions (r.t.). The best results were obtained with [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}] (10c), which reached TOF and TON values up to 117 600 h^-1 and 57 000, respectively.

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

Two routes to the title compounds are evaluated. First, a ca. 0.01 M CH₂Cl₂ solution of H₃B·P((CH₂)₆CH=CH₂)₃ (1·BH₃) is treated with 5 mol % of Grubbs' first generation catalyst (0 °C to reflux), followed by H₂ (5 bar) and Wilkinson's catalyst (55 °C). Column chromatography affords H₃B·P(n-C₈H₁₇)₃ (1%), H₃B·P((CH₂)₁₃CH₂)(n-C₈H₁₇) (8%; see text for tie bars that indicate additional phosphorus–carbon linkages, which are coded in the abstract with italics), H₃B·P((CH₂)₁₃CH₂)((CH₂)₁₄)P((CH₂)₁₃CH₂)·BH₃ (6·2BH₃, 10%), in,out-H₃B·P((CH₂)₁₄)₃P·BH₃ (in,out-2·2BH₃, 4%) and the stereoisomer (in,in/out,out)-2·2BH₃ (2%). Four of these structures are verified by independent syntheses. Second, 1,14-tetradecanedioic acid is converted (reduction, bromination, Arbuzov reaction, LiAlH₄) to H₂P((CH₂)₁₄)PH₂ (10; 76% overall yield). The reaction with H₃B·SMe₂ gives 10·2BH₃, which is treated with n-BuLi (4.4 equiv) and Br(CH₂)₆CH=CH₂ (4.0 equiv) to afford the tetraalkenyl precursor (H₂C=CH(CH₂)₆)₂(H₃B)P((CH₂)₁₄)P(BH₃)((CH₂)₆CH=CH₂)₂ (11·2BH₃; 18%). Alternative approaches to 11·2BH₃ (e.g., via 11) were unsuccessful. An analogous metathesis/hydrogenation/chromatography sequence with 11·2BH₃ (0.0010 M in CH₂Cl₂) gives 6·2BH₃ (5%), in,out-2·2BH₃ (6%), and (in,in/out,out)-2·2BH₃ (7%). Despite the doubled yield of 2·2BH₃, the longer synthesis of 11·2BH₃ vs 1·BH₃ renders the two routes a toss-up; neither compares favorably with precious metal templated syntheses.

Half-sandwich arene ruthenium complexes: synthetic strategies and relevance in catalysis

Half-sandwich arene ruthenium complexes exhibit versatile chemistry, serve as excellent precursors and find potential applications in many organic transformations. This review mainly focuses on the chemistry of piano-stool ruthenium complexes with special emphasis on the achiral or chiral-at-ruthenium center. Also, it deals with the synthesis, nomenclature and stereochemistry of arene ruthenium complexes along with mechanistic insights into the epimerization reactions and their applications in catalytic organic transformations with some selected examples.

Functionalized arene-ruthenium(II) complexes: dangling vs. tethering side chain

The reactivity of compounds [RuCl2(η(6)-C6H5OCH2CH2OH)(L)] (L = phosphine or phosphite) towards the chloride abstractor AgSbF6 has been investigated. Thus, the treatment of the triphenylphosphite complex [RuCl2(η(6)-C6H5OCH2CH2OH){P(OPh)3}] with one equivalent of AgSbF6 gave rise to the formation of the dinuclear dichloro-bridged species [{Ru(μ-Cl)(η(6)-C6H5OCH2CH2OH){P(OPh)3}}2](2+) as the hexafluoroantimonate salt. On the other hand, the triphenylphosphine analog [RuCl2(η(6)-C6H5OCH2CH2OH)(PPh3)] led, under the same experimental conditions, to the di-ruthenium derivative [{RuCl(η(6)-C6H5OCH2CH2OH)(PPh3)}2(μ-Cl)][SbF6] containing only one Cl-bridge. In sharp contrast, treatment of precursors [RuCl2(η(6)-C6H5CH2CH2CH2OH)(L)] (L = P(OPh)3, PPh3, P(OEt)3) with AgSbF6 resulted in the clean formation of the tethered compounds [RuCl{η(6):κ(1)(O)-C6H5CH2CH2CH2OH}(L)][SbF6]. The differences in reactivity observed have been rationalized by theoretical calculations.