Highly Efficient Nickel-Catalyzed 2-Methyl-3-butenenitrile Isomerization: Applications and Mechanistic Studies Employing the TTP Ligand Family

Abstract

A series of sterically and electronically fine-tuned, chelating diphosphine ligands were synthesized. The ligands are analogues of Triptyphos (TTP, 1), all based upon a variably 9,10-two-carbon-bridged 9,10-dihydroanthracene scaffold. These new TTP-type ligands were employed in the Ni(0)catalyzed isomerization of 2-methyl-3-butenenitrile (2M3BN), one of the key steps of industrial adiponitrile production by the DuPont process. The reaction showed a surprising preference for ligands bearing electron-donating substituents, such as methoxy or methyl groups, in the phenyl para position of the Ni-ligating PPh 2 units. Octyltriptyphos (3) afforded the highest 2M3BN-isomerization turnover rate yet reported. A series of deuterium-labeling experiments was performed to investigate the possibility of an isomerization mechanism consisting of a cascade of de-and rehydrocyanation steps, which could be excluded. Using the ethano-bridged ligand 4, complex 16a (4-κP:κP 0 )Ni(η 3 -C 4 H 7 )CN (supposedly an intermediate of the 2M3BN-isomerization reaction) was isolated, and its solid-state structure was determined by X-ray diffraction analysis. The complete catalytic cycle of 2M3BN isomerization with ligand 4, as suggested by the available experimental evidence, was modeled using DFT methods.

XL-Xantphos: Design and Synthesis of a Mechanistic Probe of Xantphos O-Coordination in Catalytic Reactions

“…The Triptyphos ligand was designed, like Xantphos, to adopt large P–M–P bite angles . Bidentate structures of Triptyphos, as well as tridentate, pincer complexes from C–H activation of the bicyclic bridge have been reported.…”

Organometallic chemistry

“…Postdocs from all over the world studied industrially important processes focusing on their fundamental principles [110,112,115,121,123,126–127]. The biennial “Heidelberg Forum of Molecular Catalysis” (HFMC), organized by Peter Hofmann until 2013, has been one of the most visible scientific events of Heidelberg’s chemical institutes.…”

Organometallic Chemistry

“…In 2006, he initiated the foundation of the "Catalysis Research Laboratory" (CaRLa), a cooperation of Ludwighafen's BASF and Heidelberg University, for which he acted as scientific head until October 2014. Postdocs from all over the world studied industrially important processes focusing on their fundamental principles [110,112,115,121,123,126,127] Peter Hofmann was an archetypical scientist and teacher, and in many respects a role model for colleagues and students. His scientific work revealed a high degree of intellectual creativity and deep chemical understanding, leading to modern and original research.…”