Exploring the Variable Hapticity of the Arylamide Ligand: Access to σ‑Amidophenyl and π‑Cyclohexadienylimine Structures

A study
of the preference for σ vs π coordination of
the arylamido ligand to a late transition metal shows that LiNPh2 reacts with RuHCl­(PPh3)3 (1) to yield the bent-seat piano-stool complex RuH­[(η5-C6H5)­NPh]­(PPh3)2 (2a) but with RuHCl­(CO)­(PPh3)3 (3) to yield the σ-amide RuH­(η1-NPh2)­(CO)­(PPh3)2 (4). The stability
of the σ-bound NPh2 ligand in 4 reflects
the π acidity of the CO ligand, which inhibits PPh3 loss. Carbonylation of 2a at 50 °C affords Ru­(CO)3(PPh3)2 (8) and HNPh2, suggesting sequential π → σ isomerization
and reductive elimination. The phenoxide ligand behaves similarly:
RuH­(η5-C6H5O)­(PPh3)2 (2b) is formed from 1 but
RuH­(η1-OPh)­(CO)­(PPh3)3 (5) is formed from 3, and carbonylation of 2b gives 8 and phenol, although more forcing
conditions are required (90 °C). The crystal structure of 2a is reported.