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

Abstract

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.