Fluorine forms the strongest single bond to carbon, however, it is well established that transition metals can lengthen and weaken C-F bonds in fluorinated ligands. Described here are studies on the activation of C-F bonds in iridium compounds induced by reducing agents and the use of the perfluoroalkyl iridium complexes to activate C-H bonds.
The difluorocarbene complexes Cp*Ir(L)(=CF2) (L = CO, PMe 3), perfluoroalkylidene complexes Cp*Ir(L)(=CFRF) (L = CO, PMe3; RF = F, CF3, CF2CF 3), Cp*Ir(CO)[=C(CF3)2] and Cp*Ir(CO)[=C(CF 3)(C2F5)] were prepared by reduction of the Cp*Ir(L)(R F)(I) precursors with potassium or magnesium graphite. Addition of HCl to these perfluoroalkylidene complexes took place in a regio- and stereospecific cis fashion across the double bond to form Cp*Ir(L)(CHFRF)(Cl).
Reduction of Cp*Ir(CO)[=C(CF3)2] activated the β-C-F bonds to afford Cp*Ir(CO)(CF2=C=CF2). Reduction of Cp*Ir(CO)[=C(CF 3)(C2F5)] with different reducing agents selectively activated C-F bonds at β- or γ-carbons to form Cp*Ir(CO)(CF 3CCCF3), Cp*Ir(CO)[C(CF3)CFCF2] and Cp*Ir(CO)(CF2=C=C=CF2).
Iodide-bridged dimer compounds of the class [Cp*Ir(μ2-X)(R F)]2 (X=I, RF = CF3, CF2CF 3, CF2CF2CF3, iC 3F7 and secC4F9; X=Cl, Br, RF = CF2CF3) were prepared by the reaction of Cp*Ir(CO)(RF)(X) with N-methylmorpholine- N-oxide.
Addition of ethylene to [Cp*Ir(μ2-I)(C2F 5)]2 gave Cp*Ir(CH2=CH2)(C2F 5)I, which dissociated ethylene to reform the dimer complex under vacuum. Treatment with AgOTf gave Cp*Ir(CH2=CH2)(C2F 5)(OTf), which was transformed to Cp*Ir(CH2=CH2)(CFCF 3) by reduction. Addition of L (L = PMe3, PPh3 and CO) to the dimer gave Cp*Ir(L)(C2F5)I, which was converted to Cp*Ir(L)(CFCF3) (L = PMe3, PPh3 and CO) by reduction.
A novel class of iridium amido complexes Cp*Ir(RF)(NH tBu) [RF = CF2CF3, CF(CF 3)2] with an Ir=N double bond was prepared by reaction of [Cp*Ir(μ2-I)(RF)]2 with NH2 tBu and AgBF4. Reaction of the amido complexes with EtCOOH gave Cp*Ir(RF)(η2-OCOEt). Addition of HCl to Cp*Ir(CF2CF3)(NHtBu) gave Cp*Ir(CF2CF3)(NH2tBu)Cl, which dissociated the amine ligand and formed [Cp*Ir(μ2-Cl)(CF 2CF3)]2 under vacuum. The amido complex Cp*Ir(CF 2CF3)(NHtBu) could activate sp3 C-H bonds of CH3CN to form Cp*Ir(C2F 5){[NHC(Me)]2C(CN)}. Activation of a C-H bond of propene selectively formed the exo-allyl complex Cp*Ir(CF2CF 3)(η3-CH2CHCH2). Reaction with 1-butene afforded initially a 2:1 mixture of exo-syn- and exo-anti-methylallyl complexes Cp*Ir(CF2CF3)[η 3-CH(Me)CHCH2]. Over time this ratio slowly changed to 9:1.
Oxidative addition of Br-C6F11 to Cp*Ir(CO) 2 gave Cp*Ir(CO)(COC6F11)Br. Reduction of it with potassium graphite gave Cp*Ir(CO)2 and perfluorocyclohexene.
