Electron-Deficient Iron Alkyl Complexes Supported by Diimine Ligand (Ph₂CN)₂C₂H₄: Evidence for Reversible Ethylene Binding

Abstract

Reaction of diimine ligands (Ph 2 CN) 2 C n H 2n (n ) 2, a; n ) 3, b) with FeCl 2 or FeBr 2 results in formation of the corresponding high-spin ferrous complexes {(Ph 2 CN) 2 C 2 H 4 }FeX 2 (1a, X ) Cl; 2a, X ) Br) and {(Ph 2 CN) 2 C 3 H 6 }FeCl 2 (1b). Dialkyl {(Ph 2 CN) 2 C 2 H 4 }Fe(CH 2 SiMe 3 ) 2 (3a) was prepared by treatment of (py) 2 Fe(CH 2 SiMe 3 ) 2 with diimine ligand a. Addition of B(C 6 F 5 ) 3 to 3a at -30 °C resulted in Me 3 SiCH 2 abstraction, affording [{(Ph 2 CN) 2 C 2 H 4 }Fe(CH 2 SiMe 3 )][Me 3 SiCH 2 B(C 6 F 5 ) 3 ] (5a). 19 F NMR spectroscopy revealed that this compound exists as a contact ion-pair in toluene solution. Compound 5a decomposes at room temperature in bromobenzene-d 5 or toluene-d 8 , affording dication [{(Ph 2 CN) 2 C 2 H 4 } 2 Fe] 2+ (6a); at elevated temperatures in toluene-d 8 the formation of [{(Ph 2 CN) 2 C 2 H 4 }Fe(CH 2 SiMe 3 )C 6 F 5 ] (7a) was observed as well. Neither ferrous chloride {(Ph 2 CN) 2 C 2 H 4 }FeCl 2 activated with methylaluminoxane nor contact ion-pair 5a is active in the polymerization of ethylene. Instead we were able, for the first time, to observe reversible ethylene binding to a cationic iron alkyl complex.

Ethylene oligomerization using iron complexes: beyond the discovery of bis(imino)pyridine ligands

“…Bouwkamp et al have coordinated the diimine ligand (Ph 2 CQN) 2 C 2 H 4 46 to an iron(II) centre. 59 Treatment of ferrous chloride complexes with MAO in toluene under ethylene pressure (5 atm) did not lead to any ethylene uptake, while a-diimine iron(II) complexes bearing ligands 47 developed by Chirik polymerized ethylene with low activities. 60 The activity of the four-coordinated iron precatalysts was significantly diminished in comparison to the Brookhart-Gibson five coordinated iron(II) dichloride complexes.…”

Direct evidence for a coordination–insertion mechanism of ethylene oligomerization catalysed by neutral 2,6-bisiminopyridine iron monoalkyl complexes

“…† The room temperature spectrum is consistent with essentially full dissociation of 3•C 2 H 4 , but ethylene oligomerization indicates that the complex remains thermodynamically accessible as a reaction intermediate. Although evidence for the reversible binding of ethylene to a Fe(II) alkyl complex has been reported before, 12 this is the first time that such an interaction is observed with a catalytically active Fe-BIP complex.…”

Unexpected Selective Methyl Group Abstractions from SiMe3 Moieties of CH2SiMe3 Ligands To Give New Cationic Titanium Complexes

“…One year later, Mountford and co‐workers reported on both the syntheses of zirconium complexes with CH 2 SiMe 3 moieties and tetradentate ligand frameworks X and their reactivities towards B(C 6 F 5 ) 3 through formation of the corresponding cationic complexes XI with the Me 3 SiCH 2 B(C 6 F 5 ) 3 − anion (one example given in Scheme , bottom) . Later, the research groups of Okuda and Bouwkamp provided structural data for iron and lanthanide complexes with the Me 3 SiCH 2 B(C 6 F 5 ) 3 − and Me 3 SiCH 2 BPh 3 − borate anions, respectively –…”