The development of catalysts that incorporate polar CH2=CHX monomers in olefin insertion polymerizations would enable the direct synthesis of functionalized plastics. (Ortho-phosphino-arenesulfonate)PdRL catalysts copolymerize ethylene with a variety of CH2=CHX monomers to generate linear functionalized polyethylenes (PEs), but generally exhibit moderate to low activities and produce (co)polymers with moderate to low molecular weights. The electronic asymmetry associated the phosphine-sulfonate ligands in (PO)PdR catalysts appears to be important for their function, and new families of catalysts with electronically unsymmetrical ligands are being explored. A series of phosphine-diethyl phosphonate (P-PO) and phosphine-bis(diethyl phosphonate) (P-(PO)2) ligands and the corresponding (P-PO)PdMe(2,6-lutidine)+ and (P-(PO)2)PdMe(2,6-lutidine)+ complexes were synthesized. (P-PO)PdMe(2,6-lutidine)+ complexes 1a-c are active for ethylene oligomerization/polymerization, with activities ranging up to 1500 (kg)(mol)-1(h)-1 for 1b. The PE is highly linear, with over 80 % terminal unsaturation and low (230-1890 Da) molecular weight in all cases. 1b copolymerizes ethylene with methyl acrylate, with 95 % in-chain (rather than chain end) acrylate incorporation. The P-(PO)2 catalyst 1d is more active for ethylene homopolymerization (2600 (kg)(mol)-1(h-1)), yielding linear, low-molecular-weight PE (1280-1430 Da) with predominantly internal unsaturation. The chemistry of the phosphine-phosphinate complex (κ2-1-PPh2-2-PO2Ph-Ph)PdMe(2,6-lutidine) (2) has also been investigated. 2 undergoes partial dissociation of lutidine in solution to generate the poorly soluble base-free dimer {(κ2-1-PPh2-2-PO2Ph-Ph)PdMe}2, and reacts with B(C6F5)3 to generate P-O-B adduct 3. The solid-state structure of 3 exhibits strong π-π stacking interactions. 3 polymerizes ethylene with an activity of 35 (kg)(mol)-1(h)-1 to linear PE with Mn = 7700 Da. Addition of 1 equiv of B(C6F5)3 to 3 increases the activity fivefold, with little effect on Mn. The polymerization and copolymerization behavior of related complexes will be discussed.

Electronically unsymmetrical Pd catalysts for the copolymerization of olefins with polar vinyl monomers

250th National Meeting (2015)

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