Synthesis, crystal structure, and reactions of the 17-valence-electron rhenium methyl complex [(η5-C5Me5)Re(NO)(P(4-C6H4CH3)3)(CH3)]+ B(3,5-C6H3(CF3)2)4−: experimental and computational bonding comparisons with 18-electron methyl and methylidene complexes

Reactions of methyl complex (η5-C5Me5)Re(NO)(P(4-C6H4CH3)3)(CH3) (2b) and the ferrocenium salt (η5-C5H5)2Fe + BArF− (BArF−=B(3,5-C6H3(CF3)2)4−) or the trityl salt Ph3C+ BArF− give the very air sensitive title radical cation 2b + BArF− or the robust methylidene complex [(η5-C5Me5)Re(NO)(P(4-C6H4CH3)3)(CH2)]+ BArF− (3b+ BArF−) as analytically pure powders in 80% yields. The crystal structures of 2b and 2b + BArF− are determined. With the aid of high level density functional calculations on model complexes, key structural, bonding, and dynamic properties are compared. Similar quantities are calculated for 3b+ BArF−, which could not be crystallized, and the ReCH2 rotational barrier is bounded by NMR (ΔG‡383 K>17.5 kcal mol−1). Special attention is given to structural manifestations of backbonding, particularly with the phosphine ligands. Cobaltocene and 2b + BArF− react to give 2b. However, no phosphine exchange or well-defined thermal decomposition products of 2b + BArF− are detected.