Exploring the Variable Hapticity of the Arylamide Ligand: Access to σ-Amidophenyl and π-Cyclohexadienylimine Structures
摘要:
A study of the preference for sigma vs pi 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[(eta(5)-C6H5)NPh](PPh3)(2) (2a) but with RuHCl(CO)(PPh3)(3) (3) to yield the sigma-amide RuH(eta(1)-NPh2)(CO)(PPh3)(2) (4). The stability of the sigma-bound NPh2 ligand in 4 reflects the pi acidity of the CO ligand, which inhibits PPh3 loss. Carbonylation of 2a at 50 degrees C affords Ru(CO)(3)(PPh3)(2) (8) and HNPh2, suggesting sequential pi -> sigma a isomerization and reductive elimination. The phenoxide ligand behaves similarly: RuH(eta(5)-C6H5O)(PPh3)(2) (2b) is formed from 1 but RuH(eta(1)-OPh)(CO)(PPh3)(3) (5) is formed from 3, and carbonylation of 2b gives 8 and phenol, although more forcing conditions are required (90 degrees C). The crystal structure of 2a is reported.