Synthesis and Alkyne Metathesis Activity of Pincer Rhenium Carbyne Complexes
Long Yiu Tsang, Wei Bai, Lam Cheung Kong, Herman H. Y. Sung, Ian D. Williams, Guochen Jia
Abstract
While alkyne metathesis reactions involving d 0 carbynes (alkylidynes) are well documented, those involving well-defined non-d 0 carbynes are still rare. This work reports the synthesis and alkyne metathesis activity of d 2 Re(V) carbyne complexes supported by a [LXL]-type monoanionic [PNP]-pincer ligand, a [LLX]-type monoanionic [PNO]-pincer ligand, and a [ON OH ]-bidentate ligand derived from the Schiff base 2-[(2-hydroxyphenyl)iminomethyl]phenol. Treatment of Re(≡CCH 2 Ph)Cl 2 (PMePh 2 ) 3 ( 1 ) with bis(2-diphenylphosphino-4-tolyl)amine (PNHP) and 2-{(2-diphenylphosphino-phenyl)iminomethyl}phenol (PNOH) in the presence of NEt 3 produced the pincer complexes Re(≡CCH 2 Ph)Cl(PMePh 2 )(PNP) ( 2 ) and Re(≡CCH 2 Ph)Cl(PMePh 2 )(PNO) ( 3 ), respectively. The Schiff base 2-[(2-hydroxyphenyl)iminomethyl]phenol (HON OH ) reacted with Re(≡CCH 2 Ph)Cl 2 (PMePh 2 ) 3 ( 1 ) to give Schiff base complex Re(≡CCH 2 Ph)Cl(PMePh 2 )(ON OH ) ( 4 ) (ON OH = o -O-C 6 H 4 –CH═ N -( o -C 6 H 4 OH)) bearing a [ON OH ]-bidentate ligand. The [PNP]- and [PNO]-pincer complexes are catalytically active for homometathesis of neat 1-methoxy-4-(1-propyn-1-yl)benzene at 150 °C, while the complex bearing the [ON OH ]-bidentate Schiff base ligand is catalytically inactive under similar conditions. The energy profiles for metathesis reactions of model pincer rhenium alkyne-carbyne complexes have been calculated with DFT methods.