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  • Title: Intramolecular metal-fluorocarbon coordination, C-F bond activation and lanthanoid-fluoride clusters with tethered polyfluorophenylamide ligands.
    Author: Deacon GB, Forsyth CM, Junk PC, Wang J.
    Journal: Chemistry; 2009; 15(13):3082-92. PubMed ID: 19222064.
    Abstract:
    Activating C--F bonds: Strong metal-fluorocarbon coordination in complexes of electropositive metals (e.g., Na, K, Yb) with chelating polyfluorophenyl-substituted amide ligands is a precursor to C--F bond activation and fluoride abstraction when M=Yb(II), giving heteroleptic Yb(III) fluoride clusters (see scheme).Metalation of either N,N-diethyl- or N,N-dimethyl-N'-2,3,5,6-tetrafluorophenylethane-1,2-diamines (HL 1 a, 1 b respectively) with [M{N(SiMe(3))(2)}] (M=Na, K) or [Yb{N(SiMe(3))(2)}(2)(thf)(2)] yielded the metal-amido compounds [Na(L)] (2 a), [K(L)] (3 a) and [Yb(L)(2)(thf)(2)] (4 a, 4 b). The Yb complexes were also synthesised by redox transmetalation/ligand exchange from Yb, Hg(C(6)F(5))(2) and HL in THF or 4 a from a reaction of 3 a with YbI(2) in THF. In the presence of N,N,N',N'- tetramethyl-1,2-ethanediamine (TMEDA) the complexes 2 a and 3 a yielded [Na(L)(2)Na(tmeda)] (5 a) and [K(2)(L)(2)(tmeda)(2)] (6 a), respectively, as crystalline compounds, whilst crystallisation of 4 a from DME gave [Yb(L)(2)(dme)] (7 a). Their structures have chelating metal-amide and NR(2) donors and additional intramolecular M-F-C connectivity with relatively short bond lengths (Na--F 2.65-3.00 A; K--F 2.70-3.00 A; Yb--F 2.56 A). The Yb complexes undergo C--F activation in solution forming [Yb(4)(L)(6)F(6)] (8 a, 8 b). The connectivity of [Yb(4)(L)(6)F(6)], as shown by the X-ray structures, comprised a circular Yb(4)(mu-F)(4) periphery with two opposing Yb centres having either one L ligand and a Yb(2)(mu-F)(2) bridge or two L ligands. Each polyfluorophenylamide exhibits additional intramolecular Yb-F-C coordination from one of the ortho-F atoms resulting in seven or eight coordinate Yb centres. An attempt to synthesise 4 a by redox transmetalation/ligand exchange using Hg(C[triple chemical bond]CPh)(2) as the mercury reagent gave [Yb(4)(O)(2)(L)(4)(C[triple chemical bond]CPh)(4)(thf)(2)]THF (9 aTHF), most likely as a result of oxidation of the initially formed product.
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