Abstract
Diazaphospholidine-sulfonato Pd(II) complexes [{kappa(2)-P,O-(N-Ar2C2H4N2P)C6H4SO3}PdMe(L)] 1-L (L = dmso, pyridine, lutidine, or mu-LiCl(solvent); 1a: Ar = Ph, 1b: Ar = 2-MeC6H4, 1c: Ar = 2-MeOC6H4, 1d: Ar = 2,4,6-Me3C6H2, 1e: Ar = 2,6-iPr(2)C(6)H(3), 1f: Ar = 2,6-(p-tolyl)(2)C6H3) were prepared and structurally characterized. The regioselectivity of methyl acrylate (MA) insertion into the Pd-Me bond is entirely inverted from >93% 1,2-insertion for bulky substituents (1d-f, yielding the insertion products [((PO)-O-boolean AND)Pd{kappa(2)-C,O-CH2CHMeC(O)OMe], 12) to the usual electronically controlled 2,1-insertion (>95%) for the less bulky Ar = Ph (1a, yielding the insertion product [((PO)-O-boolean AND)Pd{kappa(2)-C,O-CHEtC(O)OMe], 11, and beta-H elimination product methyl crotonate). DFT studies underline that this is due to a more favorable insertion transition state (2,1- favored by 12 kJ mol(-1) over 1,2- for 1a) vs destabilization of the 2,1-insertion transition state in 1d,e. By contrast, MA insertion into the novel isolated and structurally characterized hydride and deuteride complexes [{kappa(2)-P,O-(N-Ar2C2H4N2P)C6H4SO3}PdR(lutidine)) (Ar = 2,6-iPr(2)C(6)H(3); 9e: R = H, 10e: R = D) occurs 2,1-selectively. This is due to the insertion occurring from the isomer with the P-donor and the olefin in trans arrangement, rather than the insertion into the alkyl from the cis isomer in which the olefin is in proximity to the bulky diazaphospholidine. 1a-f are precursors to active catalysts for ethylene polymerization to highly linear polyethylene with M-n up to 35 000 g mol(-1). In copolymerization experiments, norbornene was incorporated in up to 6.1 mol % into the polyethylene backbone.