Synthesis and Reactivity of the Cationic Methylene Complex [Cp₂ReCH₂]⁺

Reaction of Cp 2 ReCH 2 R (R = H, CH 3 ) (Cp = η 5 -C 5 H 5 ) with [Ph 3 C]B(Ar‘) 4 (Ar‘ = 3,5-CF 3 ) 2 C 6 H 3 ) generates carbene complexes [Cp 2 Re CH 2 ]B(Ar‘) 4 ( 1 ) and [Cp 2 Re CH(CH 3 )]B(Ar‘) 4 ( 3 ). Complex 1 is thermally robust and is only observed to decompose to [Cp 2 Re(C 2 H 4 )] + and [Cp 2 Re(NCCD 3 )] + upon prolonged thermolysis in acetonitrile- d 3 or upon addition of BF 4 - or PF 6 - salts. The formation of 1 is also observed upon reaction of [Cp 2 Re(CH 3 )H]B(Ar‘) 4 with CH 2 Cl 2 at 0 °C to give [Cp 2 Re(CH 2 Cl)Cl]B(Ar‘) 4 ( 2 ) followed by treatment with Mg. The electrophilic nature of 1 is confirmed by adduct formation with PPh 3, pyridine, and CN t Bu. Complex 1 reacts with halogens by 1,2-addition across the Re−C double bond to form halomethyl halide complexes [Cp 2 Re(CH 2 X)X]B(Ar‘) 4 (X = Cl, Br, I). Reaction of 1 with pyridine N -oxide gives the formaldehyde complex [Cp 2 Re(η 2 -H 2 C O)]B(Ar‘) 4 . The formaldehyde ligand can be displaced in solution by reaction with PPh 3, acetonitrile, or methylene chloride. Complex 1 reacts with sulfur-atom donor reagents to give the thioformaldehyde complex [Cp 2 Re(η 2 -H 2 C S)]B(Ar‘) 4 . Reaction of 1 with N 2 CHSiMe 3 generates the olefin complex [Cp 2 Re(η 2 -H 2 C CHSiMe 3 )]B(Ar‘) 4 .