Exploring the Variable Hapticity of the Arylamide
Ligand: Access to σ‑Amidophenyl and π‑Cyclohexadienylimine
Structures
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Abstract
A study
of the preference for σ vs π coordination of
the arylamido ligand to a late transition metal shows that LiNPh<sub>2</sub> reacts with RuHCl(PPh<sub>3</sub>)<sub>3</sub> (<b>1</b>) to yield the bent-seat piano-stool complex RuH[(η<sup>5</sup>-C<sub>6</sub>H<sub>5</sub>)NPh](PPh<sub>3</sub>)<sub>2</sub> (<b>2a</b>) but with RuHCl(CO)(PPh<sub>3</sub>)<sub>3</sub> (<b>3</b>) to yield the σ-amide RuH(η<sup>1</sup>-NPh<sub>2</sub>)(CO)(PPh<sub>3</sub>)<sub>2</sub> (<b>4</b>). The stability
of the σ-bound NPh<sub>2</sub> ligand in <b>4</b> reflects
the π acidity of the CO ligand, which inhibits PPh<sub>3</sub> loss. Carbonylation of <b>2a</b> at 50 °C affords Ru(CO)<sub>3</sub>(PPh<sub>3</sub>)<sub>2</sub> (<b>8</b>) and HNPh<sub>2</sub>, suggesting sequential π → σ isomerization
and reductive elimination. The phenoxide ligand behaves similarly:
RuH(η<sup>5</sup>-C<sub>6</sub>H<sub>5</sub>O)(PPh<sub>3</sub>)<sub>2</sub> (<b>2b</b>) is formed from <b>1</b> but
RuH(η<sup>1</sup>-OPh)(CO)(PPh<sub>3</sub>)<sub>3</sub> (<b>5</b>) is formed from <b>3</b>, and carbonylation of <b>2b</b> gives <b>8</b> and phenol, although more forcing
conditions are required (90 °C). The crystal structure of <b>2a</b> is reported
