Intramolecular metal-fluorocarbon coordination, C-F bond activation and lanthanoid-fluoride clusters with tethered polyfluorophenylamide ligands

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=YbII, giving heteroleptic YbIII fluoride clusters. 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(SiMe3)2}] (M=Na, K) or [Yb{N(SiMe3)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(C6F5)2 and HL in THF or 4 a from a reaction of 3 a with YbI2 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)2Na(tmeda)] (5 a) and [K2(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 NR2 donors and additional intramolecular M-F-C connectivity with relatively short bond lengths (Na-F 2.65–3.00 Å; K-F 2.70–3.00 Å; Yb-F 2.56 Å). The Yb complexes undergo C[BOND]F activation in solution forming [Yb4(L)6F6] (8 a, 8 b). The connectivity of [Yb4(L)6F6], as shown by the X-ray structures, comprised a circular Yb4(µ-F)4 periphery with two opposing Yb centres having either one L ligand and a Yb2(µ-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≡CPh)2 as the mercury reagent gave [Yb4(O)2(L)4(C≡CPh)4(thf)2]⋅THF (9 a⋅THF), most likely as a result of oxidation of the initially formed product