Nickel and Palladium Complexes with New Phosphinito-Imine Ligands and Their Application as Ethylene Oligomerization Catalysts

Abstract

Phosphinito-imines, a new class of P,N donors, are readily generated by reaction of bulky arylamide anions [R 2 CONAr]-(R 2 = Me or t-Bu; Ar = 2,6-i-Pr 2 C 6 H 4) with chlorophosphines ClP(R 1) 2. In solution, free phosphinito-imines exist in equilibrium with the corresponding amidophosphine tautomers, containing a nitrogen-bound P(R 1) 2 group. However, reacting the tautomer mixtures with metal precursor complexes, such as NiBr 2 (dme) or PdCl 2 (cod), selectively affords stable phosphinito-imine complexes MX 2 (P-N) (M = Ni, Pd) in excellent yields. These complexes are diamagnetic and exhibit square planar structures in the solid state, but in solution the Ni derivatives exchange with a small amount of the corresponding high-spin tetrahedral isomers. On treatment with MMAO or DEAC, NiX 2 (P-N) complexes become active ethylene oligomerization catalysts, affording mainly butenes along with smaller amounts of hexenes and octenes. The activity and the selectivity of these catalysts depend on the structure of the phosphinito-imine ligand and the co-catalyst used. When activated with DEAC, complexes containing the P(i-Pr) 2 moiety are extremely active, achieving TOFs over 10 6 mol C 2 H 4 /mol Ni •h and high selectivity for butenes.

Nickel Catalyzed Olefin Oligomerization and Dimerization

“…In addition, the molecular weight of the products may be tuned by varying the bulk of the N-alkyl substituents on the imino moiety. 93 Most nickel(II) bearing (P,N)-ligands are selective towards short-chain oligomers such as butenes and hexenes in the presence of ethylene and a cocatalyst. 86 15a R = tBu 15b R = iPr Phosphinito-imine ligands were investigated by Campora et al 93 Upon activation with AlEt 2 Cl, nickel complexes 15 are active.…”

Pyrazolyl‐phosphinoyl nickel (II) complexes: synthesis, characterization and ethylene dimerization studies

“…[36] To access the catalytic lifetime of Ni1, the activities and selectivities were also monitored at 10, 20, 30 and 40 min at 10°C with [Al]/[Ni] molar ratio of 300. Reducing the temperature from 10°C to 0°C leads to similar activity [TOF = 19.9 × 10 3 (mol ethylene) (mol Ni) −1 h −1 ] and selectivity (95.2%) for 1-butene.…”

“…When activated with MMAO, this nickel precatalyst displayed low thermal stability, since their activity was sensibly reduced when the temperature was raised from 0°C to 30°C. [36] To access the catalytic lifetime of Ni1, the activities and selectivities were also monitored at 10, 20, 30 and 40 min at 10°C with [Al]/[Ni] molar ratio of 300. As can be seen in Figure 4, the activities remained constant for 30 min [TOF = 16.5 × 10 3 (mol ethylene) (mol Ni) −1 h −1 ] and undergoes complete deactivation after this time [TOF = 12.3 × 10 3 (mol ethylene) (mol Ni) −1 h −1 at 40 min].…”

Ruthenium complexes of diphenylphosphino derivatives of carboxylic amides: Synthesis and characterization of bidentate P,N- and P,O-chelate ligands and their reactivity towards [RuCl2(PPh3)3]

“…Although N,O-ligands already comprise some hard-soft-ambidenticity, their functionalization with phosphines enlarges the hard-soft variation in the donor set by formation of neutral P,N-or P,O-ligands and generation of 1,4-bidentate ligands capable of forming fivemembered chelates. The diversity of products from phosphino-functionalization of carboxylic amides is attributed to the formation of phosphinoamides (N-PPh 2 derivatives) and phosphinitoimines (O-PPh 2 derivatives) as possible tautomers [3]. (Furthermore, carboxylic amides with phosphine functionalization in α-position [4,5] or other positions of the organic backbone [6], have been studied in transition metal coordination chemistry.)…”