Crowded Diphosphinomethane Ligands in Catalysis: [(R₂PCH₂PR′₂-κ²P)NiR″]⁺Cations for Ethylene Polymerization without Activators

Abstract

The preparation of a series of nickel dichloride complexes with bulky diphosphinomethane chelate ligands R2PCH2PR′2 is reported. Reaction with the appropriate Grignard reagent leads to the corresponding dimethyl and dibenzyl complexes. Cationic monomethyl and mono-η3-benzyl complexes are generated from these dialkyl complexes by protonation with [H­(OEt2)2]+[B­(3,5-(CF3)2C6H3)4]−, while the complex [(dtbpm-κ2 P)­Ni­(η3-CH­(CH2Ph)­Ph]+[B­(3,5-(CF3)2C6H3)4]− is obtained from protonation of the Ni(0) olefin complex (dtbpm-κ2 P)­Ni­(η2-trans-stilbene). Crystal structures of examples of dichlorides, dimethyl, dibenzyl, cationic methyl, and cationic η3-benzyl complexes are reported. Solutions of the cations polymerize ethylene under mild conditions and without the necessity of an activating agent, to form polyethylene having high molecular weights and low degrees of chain branching. In comparison to the Ni methyl cations, the η3-benzyl cation complexes are more stable and somewhat less active but still very efficient in C2H4 polymerization. The effect on the resulting polyethylene of varying the substituents R, R′ on the phosphine ligand has been examined, and a clear trend for longer chain PE with less branching in the presence of more bulky substituents on the diphosphine has been found. Density functional calculations have been used to examine the rapid suprafacial η3 to η3 haptotropic shift processes of the [(R2PCH2PR′2)­Ni] fragment and the η3–η1 change of the coordination mode of the benzyl group required for polymerization in those cations.

Coordination Behavior of a P4‐Butterfly Complex towards Transition Metal Lewis Acids: Preservation versus Rearrangement

“…However, this value is smaller compared to other tetrahedrally coordinated Ni II compounds that have magnetic moments within the range of μ eff =3.3–4.0 μ B [29] . On the other hand, complexes of [NiX 2 L] (X=Cl, Br, I; L=bis‐diphosphines) are mainly described to be diamagnetic caused by the square planar geometry [7, 8, 30] …”

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp3)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base

“…Single crystals of 7·PPh 3 and 7·P i Bu 3 were grown from a saturated THF and toluene solutions, respectively. The solid-state structures, depicted in Figure , indicate they are square planar and exhibit characteristic Ni–C bonds (1.929(3) Å for 7·PPh 3 and 1.935(3) Å for 7·P i Bu 3 ), similar to known complexes. ,,− The different steric profiles of phosphine ligands does not have a significant influence on the bond angles, with a N(2)–Ni(1)–C(1) angle of 168.5(1)° for 7·PPh 3 and 166.9(1)° for 7·P i Bu 3 ].…”

Organometallic chemistry

“…His research interests combined all three fields, with a focus on homogeneous catalysis with transition metal complexes. Bidentate donor ligands with a small bite angle such as bis(di- tert -butylphosphino)methane (dtbpm) were a unique feature of his work [61,67,70–72 80–81 84,86,93–94 97,100–101 103,107,124,128,148–149] that ultimately enabled C–Si activation of organosilanes and the C–C activation of oxiranes by coordinatively unsaturated platinum species [66,149]. In the mechanism of the Dötz reaction, he found that chromacyclobutene structures were unrealistic intermediates and instead proposed vinylcarbene complexes as much more stable isomers [64,68,88].…”