Alkene Hydrogenation Catalyzed by Nickel Hydride Complexes of an Aliphatic PNP Pincer Ligand

✍ Scribed by Kalyan V. Vasudevan; Brian L. Scott; Susan K. Hanson

• Book ID: 115555355
• Publisher: John Wiley and Sons
• Year: 2012
• Tongue: English
• Weight: 525 KB
• Volume: 2012
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/ejic.201200758

✦ Synopsis

Abstract

To investigate metal–ligand cooperativity as a strategy for promoting nickel‐catalyzed alkene hydrogenation, cationic and neutral nickel(II) hydride complexes of the aliphatic pincer ligand PNHP^Cy^ {PNHP^Cy^ = HN[CH~2~CH~2~P(Cy)~2~]~2~} have been synthesized and characterized. Cationic hydride complex [(PNHP^Cy^)Ni(H)]BPh~4~ (2) catalyzed the hydrogenation of styrene and 1‐octene under mild conditions. Only low conversion was observed in the hydrogenation of 3,5‐dimethoxybenzaldehyde using 2. The neutral hydride complex (PNP^Cy^)Ni(H) (3) was also found to be an alkene hydrogenation catalyst. Mechanistic experiments suggest that for catalyst 2, the hydrogenation reaction proceeds through a pathway involving initial insertion of the alkene into the Ni–H bond. Contrary to the initial hypothesis, reactivity comparisons with the methyl‐substituted hydride complex [(PNMeP^Cy^)Ni(H)]BPh~4~ {PNMeP^Cy^ = (CH~3~)N[CH~2~CH~2~P(Cy)~2~]~2~} suggest that metal–ligand cooperativity is not involved in these rare examples of mild and homogeneous nickel hydrogenation catalysis.