Synthesis, molecular structure, and reactivity of neutral and cationic areneosmium(II) complexes with diarylcarbenes as ligands

Birgit Weberndörfer*, Gerhard Henig, D. C.R. Hockless, Martin A. Bennett, Helmut Werner

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    30 Citations (Scopus)

    Abstract

    While the dinuclear compounds [(η6-mes)Os{κ1-OC(O)CF3} (μ-Cl)]2 (2) and [(η6-mes)Os{κ1-OS(O)2 CF3}(μ-Cl)]2 (3), prepared from [(η6-mes)OsCl(η3-C3H5)] (1) and CF3CO2H or CF3SO3H by elimination of propene, are not suitable precursors for the synthesis of osmium carbenes, the bis(trifluoroacetato) derivatives [(η6-arene)Os{κ1-OC(O)CF3} (κ2-O2CCF3)] (4, 9, 10) are useful starting materials. They react with diaryldiazomethanes R2CN2 to give the half-sandwich-type complexes [(η6-arene)Os{κ-OC(O)CF3}2 (=CR2)] (11-17) in good to excellent yields. The bis(tosylato)osmium(II)compounds [(η6-arene) Os{κ1-OS(O)2R} {κ2-O2 S(O)R}] (20, 21; R = p-C6H4CH3) behave differently and upon treatment with Ph2CN2 and PhCHN2 afford tetraphenylethene and a mixture of (E)- and (Z)-stilbene. The reaction of 12-15 and 17 with either Me3SiX or NH4X (X = Cl, Br, I) leads to the replacement of the trifluoroacetato ligands and the formation of the corresponding carbene complexes [(η6-arene)OsX2(=CR2)] (22-31) in 67-91% yield. An exchange of trifluoroacetate for chloride or bromide by using HCl or HBr is also possible. Treatment of [(η6-mes)OsCl2(=CPh2)] (28) with M(acac-[Fn]) (M = Na, Tl; n = 0, 3, or 6) affords the chelate compounds [(η6-mes)OsCl(κ2-acac-[Fn])] (33-35) via elimination of the carbene ligand. Compounds 33-35 are also accessible from [(η6-mes)-OsCl2]2 (19) and Hacac/NEt3 or Na(acac-[Fn]) (n = 3 or 6), respectively. While 14 (arene = mes; R = Ph) and 28 react with C6H5MgBr and CH3MgI only by displacement of trifluoroacetate or chloride for bromide or iodide, the reaction of 14 with CH2=CHMgBr gives the η3-allyl complex [(η6-mes)OsBr(η3-CH2CHCPh2)] (36). A C-C coupling also takes place upon treatment of 14 with CH2=CHOEt, resulting in the formation of the metallacyclic compound [(η6-mes)Os{κ2(C,O)-Ph2CCH=CHOEt} {κ1-OC(O)CF3}] (38). The bis(trifluoroacetato) derivatives 14, 15, and 17 react in acetone with water to afford the diaryl(carbonyl)-osmium(II) complexes [(η6-mes)OsR2(CO)] (39-41). On the basis of a labeling experiment, a mechanism for this unusual C-C cleavage reaction is proposed. The reaction of the dichloro compounds 28 and 29 with PPh3 in the presence of AgPF6 gives the cationic carbene complexes [(η6-mes)OsCl(PPh3)(=CR2)]PF6 (45, 46) in nearly quantitative yields. The molecular structures of 2, 15, 28, 35, and 46 were determined crystallographically.

    Original languageEnglish
    Pages (from-to)744-758
    Number of pages15
    JournalOrganometallics
    Volume22
    Issue number4
    DOIs
    Publication statusPublished - 17 Feb 2003

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