Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers

Abstract

Zwitterionic structure is necessary for Ni complexes to catalyze carbonylative polymerization (COP) of cyclic ethers. The cationic charge at the Ni center imparts sufficient electrophilicity to the Ni-acyl bond for it to react with cyclic ethers to give an acyl-cyclic ether oxonium intermediate, while the ligand-centered anionic charge ensures that the resultant oxonium cation is ion-paired with the Ni nucleophile. The current catalysts give non-alternating copolymers of carbon monoxide and cyclic ethers and are the most effective when both ethylene oxide and tetrahydrofuran are present as the cyclic ether monomers.

Electrostatic vs. inductive effects in phosphine ligand donor properties and reactivity

“…77 This result is consistent with the enhanced donation previously observed for phosphines with anionic borates. 68,83,86,[90][91][92]95,96,100,101,[109][110][111][112] In addition to metal carbonyl adducts, phosphine selenide compounds have also been used to quantify the donor strength and basicity of phosphines via their P-Se coupling constants (JP-Se). 113,114 The use of NMR coupling constants is advantageous due to greater instrumental resolution and sensitivity in the coupling value as compared to vibrational spectroscopy.…”

“…Figure 2.Correlation between the TEP of selected phosphine ligands and the JP-Se in CDCl3 of their respective phosphine selenides (black and grey squares, grey line is the linear fit) 75,92,93. The green square is the experimental TEP for 1 determined using compound2 and the calculated JP-Se.…”

Electrostatic vs. Inductive Effects in Phosphine Ligand Donor Properties, Reactivity, and Catalysis

“…[74] This result is consistent with the enhanced donation previously observed for phosphines with anionic borates. [75][76][77][78][79][80][81][82][83][84][85][86][87][88] To further study the basicity and electron donation of 1 the corresponding phosphine selenide, [PPh4][Se=PPh2CH2BF3] ([PPh4][1 Se ]), was prepared. Phosphorus-selenium coupling constants (JP-Se) have a linear correlation with the TEP of various phosphines, providing another measure of phosphine donor strength (black squares in Figure 2).…”

“…In order to prepare [PPh4][1 Se ], K1 was stirred overnight in THF with an excess of elemental Se and PPh4Br. The 31 P{ 1 H} NMR spectrum of [PPh4][1 Se ] contains a quartet peak at 33 ppm, with satellite quartets at 31 and 35 ppm from coupling to the 77 Se nucleus, and a singlet at 23 ppm corresponding to PPh4. The SXRD structure of [PPh4][1 Se ] shows the PPh4 at a distance of >6 Å from B, P, or Se, which suggests little to no interaction between the charged fragments in the solid state (Figure 1C and Figure S55).…”

“…[74] Indeed, cationic and anionic functional groups have previously been incorporated into phosphines, frequently leading to distinct properties or reactivity in comparison to neutral analogues. [31,[75][76][77][78][79][80][81][82][83][84][85][86][87][88] Still, how charged residues change phosphine properties, namely the relative contributions of through-space or through-bond effects, has not been investigated. This gap is noteworthy as a recent computational study into the impact of electric fields on the reactivity of a PMe3 supported Pd complex suggests that anions can accelerate oxidative addition through the application of a local electric field even without covalent bonding interactions.…”