Amidate-Ligated Complexes of Rhodium(I): A Showcase of Coordination Flexibility

Reaction of the amidate ligand salts Na­[N­(Dipp)­C­(O)­R] (R = Ph (1a), tBu (1b); Dipp = 2,6-diisopropylphenyl) with [Rh­(NBD)­Cl]2 (NBD = norbornadiene) proceeds to give the dirhodium­(I) complexes [Rh2{μ2-N,O-N­(Dipp)­C­(O)­R}2(NBD)2] (R = Ph (2a), tBu (2b)) with variable coordination behavior. For complex 2b, a monomer–dimer equilibrium with the mononuclear complex [Rh­{κ2-N,O-N­(Dipp)­C­(O)tBu}­(NBD)] (3b) was established for the first time. Precursors 2a,b were treated with PPh3 and PCy3, giving the distorted-square-planar κ2-N,O amidates [Rh­{κ2-N,O-N­(Dipp)­C­(O)­R}­(PPh3)2] (R = Ph (4a), tBu (4b)) or the κ1-O complexes [Rh­{κ1-O-N­(Dipp)­C­(O)­R}­(NBD)­(PCy3)] (R = Ph (5a), tBu (5b)). Initial reactivity screening showed that complex 4b undergoes O2 activation, providing Ph3PO; via the transient peroxo complex 6b, which was characterized in the solution phase. The κ2-N,O amidate coordination in 6b has been conclusively established by diagnostic 13C­{1H} NMR spectroscopy.