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 (eta (5)-C5Me5)Re(NO)(P(4-C6H4CH3)(3))(CH3) (2b) and the ferrocenium salt (eta (5)-C5H5)(2)Fe.+ 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 [(eta (5)-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 (DeltaG(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 defected. (C) 2000 Elsevier Science B.V. All rights reserved.