Activation and deactivation by temperature: Behavior of Ph 2PN(iPr)P(Ph)N(iPr)H in the presence of alkylaluminum compounds relevant to catalytic selective ethene trimerization

Abstract

Coordination, deprotonation, rearrangement, and cleavage of Ph 2PN(iPr)P(Ph)N(iPr)H (1) by trialkylaluminum compounds R 3Al (R=Me, Et) are reported that are relevant to the selective ethene trimerization system consisting of the ligand 1, CrCl3(THF) 3 and Et3Al that produces 1-hexene in more than 90% yield and highest purity. With increasing temperature and residence time first the formation of an adduct [Ph2PN(iPr)P(Ph)N(iPr)H][AlR3] (2), second the aluminum amide [Ph2PN(iPr)P(Ph)(AlR3)N(iPr)] [AlR2] (3) and third its rearrangement to the cyclic compound [N(iPr)P(Ph)P(Ph2)N(iPr)][AlR2] (4) were observed. The cleavage of 3 by an excess of R3Al into an amidophosphane and an iminophosphane could be the reason for its rearrangement to complex 4, as well as to the cyclic dimer [R2AlN(iPr)P(Ph)2]2 (5). The chemistry of ligand 1 in the presence of alkylaluminum compounds gives hints on possible activation and deactivation mechanisms of 1 in trimerization catalysis. Chemical transformer: Coordination, deprotonation, rearrangement, and cleavage of Ph2PN(iPr)P(Ph)N(iPr)H (1) by R3Al (R=Me, Et) are all relevant for a selective ethene trimerization system consisting of 1, CrCl3(THF)3, and Et3Al that produces 1-hexene in more than 90% yield and high purity (see scheme). This chemistry gives an insight into possible activation and deactivation pathways, which have to be considered for a better understanding of the catalytic system and technical requirements of the trimerization process. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.