Tailored RuNi heterobimetallic complexes as dual catalysts for ROMP of norbornene and ethylene oligomerization

Abstract

Abstract

A series of four novel Ru L -Ni L heterobimetallic complexes was synthesized via the in-situ condensation of primary amine Ru precursors with salicylaldehyde or 3- tert -butylsalicylaldehyde, generating an N,O-chelated iminic bridge that links the two metal centers. The reaction between [(Ph)Ni(PPh 3 ) 2 Cl], [RuCl 2 ( p -cymene)(4-(aminomethyl)pyridine)] or [RuCl 2 ( p -cymene)(4-(aminomethyl)piperidine)], and the aldehydes in a 1:1:1 M ratio afforded the complexes [Ph(PPh 3 )Ni( μ -N,O-Schiff)Ru( p -cymene)pip] ( Ru pip -Ni H ), [Ph(PPh 3 )Ni( μ -N,O- tert -butyl-Schiff)-Ru( p -cymene)pip] ( Ru pip -Ni t Bu ), [Ph(PPh 3 )Ni( μ -N,O-Schiff)Ru( p -cymene)pyridine] ( Ru py -Ni H ), and [Ph(PPh 3 )Ni( μ -N,O- tert -butyl-Schiff)Ru( p -cymene)pyridine] ( Ru py -Ni t Bu ). The complexes were fully characterized by FTIR, UV–vis, 1 H and 31 P{ 1 H} NMR spectroscopy, cyclic voltammetry, and DFT calculations. Structurally, the Schiff-base fragment functions as a rigid μ-(N,O) iminic bridge, coordinating the Ni II center while preserving the “piano-stool” Ru II geometry, thereby enforcing a well-defined Ru L -Ni L arrangement supported by DFT-optimized geometries. Electrochemical studies revealed two oxidation processes at ~1.05 V (Ni II/III , irreversible) and ~1.21 V (Ru II/III , quasi-reversible). The catalytic performance of the complexes was assessed in two benchmark transformations. In ROMP of norbornene using ethyldiazoacetate as carbene source, the complexes produced polyNBE in yields of 40–76% (1 h, 50 °C), with Ru pip -Ni t Bu showing superior activity. In ethylene oligomerization (EASC cocatalyst, 25 °C, 15 bar), all complexes displayed high turnover frequencies of ~150 s −1 and strong preference for C 4 oligomers (79–90%), with tert-butyl-containing systems offering enhanced α-C 4 selectivity.