While fluorine forms the strongest single bond to carbon, it is well established that transition metals can lengthen and weaken ligated C-F bonds. Described here are studies on the activation of C-F bonds on iridium (III) compounds induced by acids and reducing agents.
New methods towards the preparation of Cp*Ir(PMe3)(R F)(R) (R = Me, Ph) compounds using ZnR2 (R = Me, Ph) are reviewed and extended to the secondary butyl compound, Cp*Ir(PMe3)[CF(CF 3)(CF2CF3)](Me). X-ray crystallographic and variable temperature NMR studies were performed on Cp*Ir(PMe3)[CF(CF 3)(CF2CF3)](H) and Cp*Ir(PMe3)(CF 2CF2CF3)(Ph) in an effort to determine the ground state conformation and the origin of restricted rotation about some of the bonds.
Oxidative addition of I-CF2CF2CF3 to CpIr(CO)(PMe3) gave a mixture of four major products: [CpIr(CO)(PMe 3)(CF2CF2CF3)]I, CpIr(PMe3)(CF 2CF2CF3)(I), CpIr(PMe3)(COCF2 CF2CF3)(I), and CpIr(PMe3)(COCF 2CF2CF3)(CF2CF2CF3 ). A mechanism to the formation of these compounds has been proposed beginning with a single electron transfer from CpIr(CO)(PMe3) to I-CF2CF2CF3.
A novel class of perfluoroalkylidene compounds, (C5R 5)Ir(L)(=CFRF) (R = H, Me; L = CO, PMe3; R F = F, CF3, CF2CF3) has been prepared by reduction of the corresponding (perfluoroalkyl)(iodide) compounds, (C 5R5)Ir(L)(CF2RF)(I), with potassium or magnesium graphite. HCl addition to the iridium carbon double bond is shown to occur in a regio- and stereospecific cis fashion to yield (C5Me 5)Ir(L)(CFHRF)(Cl).
Iridium fluoroolefin compounds of the class, Cp*Ir(L)(CH2=CFR F) (L = CO, PMe3; RF = F, CF3, CF 2CF3), have been prepared by the reduction of Cp*Ir(L)(CH 2CF2RF)(I) with potassium or magnesium graphite. Addition of HCl resulted in formation of the methyl compounds, Cp*Ir(L)[CF(CH 3)(RF)](Cl), from a regio- and stereospecific addition of HCl. Addition of acids with more weakly coordinating anions (HOTf, HO 2CCF3) ultimately formed the rearranged product, Cp*Ir(L)(CH 2CHFRF)(X), which resulted from a β-hydride elimination from the methyl group.
The reaction of HX in ether with Cp*Ir(PMe3)[CF(CF3)(CF 2RF)](H) (RF = F, CF3) yielded Cp*Ir(PMe 3)[CH(CF3)(CF2RF)](Cl) and Cp*Ir(PMe 3)[CF(CF3)(CF2RF)](Cl) while the same reaction in toluene resulted in Cp*Ir(PMe3)(X)2 and CF3CH2CF2RF. However, no reaction of Cp*Ir(PMe3)[CF(CF3)(CF2RF)](Me) was observed with HX in toluene or ether.