Synthesis, reactivity, and crystal structures of ferrocene-substituted amidinate derivatives

Reaction of FcLi (Fc=ferrocenyl) with DCC (DCC=l,3-dicyclohexylcarbodiimide), followed by the addition of water, yields the ferrocene-containing amidine Fc(NCy)NHCy in 50% yield. The amidine is readily deprotonated by LiN(SiMe3)2 or NaN(SiMe3)2 to yield alkali metal amidinates, [FcC(NCy)2]Li and [FcC(NCy)2]Na, in high yields. These serve as convenient sources of [FcC(NCy)2]− for a wide range of salt-metathesis reactions with transition metal halides. Reactions of [FcC(NCy)2]Li with 0.5 equivalents MX2 (M=Fe, Co; X=Cl, Br) form the paramagnetic 4-coordinate derivatives [FcC(NCy)2]2M. Reaction of [FcC(NCy)2]Na with CpFe(CO)2I affords the carbamoyl derivative CpFe(CO)[FcC(NCy)N(Cy)C(O)]. Although not thermally labile, a CO ligand is readily lost upon UV irradiation to give the amidinate derivative CpFe(CO)[FcC(NCy)2]. The addition of 13CO (50 psig) to a solution of CpFe(CO)[FcC(NCy)2] results in the rapid exchange of CO at 25 °C. Heating this solution to 80 °C results in the partial formation of the carbamoyl species by a formal CO insertion into an FeN bond. Reaction of [FcC(NCy)2]Li with 0.5 equivalents [Rh(CO)2(μ-Cl)]2 forms orange [FcC(NCy)2]Rh(CO)2 in good yield. Cyclic voltammetry measurements in THF reveal a quasi-reversible oxidation at E1/2=+0.46 V followed by an irreversible oxidation at +1.49 V (vs. Cp2Fe). Chemical oxidation of [FcC(NCy)2]Rh(CO)2 with AgBF4 generates the amidine-containing product {[FcC(NCy)NHCy]Rh(CO)2}[BF4].