SHOP-type nickel complexes with alkyl substituents on phosphorus, synthesis and catalyticethylene oligomerization

Abstract

The β-keto phosphorus ylides (n-Bu)₃PCHC(O)Ph 6, (t-Bu)₂PhPCHC(O)Ph 7, (t-Bu)Ph₂PCHC(O)Ph 8, (n-Bu)₂PhPCHC(O)Ph 9, (n-Bu)Ph₂PCHC(O)Ph 10, Me₂PhPCHC(O)Ph 11 and Ph₃PCHC(O)(o-OMe-C₆H₄) 12 have been synthesized in 80–96% yields. The Ni(II) complexes [NiPh{Ph₂PCHC(O)(o-OMeC₆H₄)}(PPh₃)] 13, [NiPh{Ph(t-Bu)PCHC(O)Ph}(PPh₃)] 15, [NiPh{(n-Bu)₂PCHC(O)Ph}(PPh₃)] 16 and [NiPh{Ph(n-Bu)PCHC(O)Ph}(PPh₃)] 17 have been prepared by reaction of equimolar amounts of [Ni(COD)₂] and PPh₃ with the β-keto phosphorus ylides 12 or 8–10, respectively, and characterized by ¹H and ³¹P{¹H} NMR spectroscopy. NMR studies and the crystal structure determination of 13 indicated an interaction between the hydrogen atom of the C–H group α to phosphorus and the ether function. The complexes [NiPh{Ph₂PCHC(O)Ph}(Py)] 18, [NiPh{Ph(t-Bu)PCHC(O)Ph}(Py)] 19, [NiPh{(n-Bu)₂PCHC(O)Ph}(Py)] 20, [NiPh{Ph(n-Bu)PCHC(O)Ph}(Py)] 21 and [NiPh{Me₂PCHC(O)Ph}(Py)] 22 have been isolated from the reactions of [Ni(COD)₂] and an excess of pyridine with the β-keto phosphorus ylides Ph₃PCHC(O)Ph 3 or 8–11, respectively, and characterized by ¹H and ³¹P{¹H} NMR spectroscopy. Ligands 3, 8, 10 and 12 have been used to prepare in situ oligomerization catalysts by reaction with one equiv. of [Ni(COD)₂] and PPh₃ under an ethylene pressure of 30 or 60 bar. The catalyst prepared in situ from 12, [Ni(COD)₂] and PPh₃ was the most active of the series with a TON of 12 700 mol C₂H₄ (mol Ni)⁻¹ under 30 bar ethylene. When the β-keto phosphorus ylide 8 was reacted in situ with three equiv. of [Ni(COD)₂] and one equiv. of PPh₃ under 30 bar of ethylene, ethylene polymerization was observed with a TON of 5500 mol C₂H₄ (mol Ni)⁻¹.