Synthesis, Structures, and Norbornene Polymerization Behavior of Aryloxide-N-Heterocyclic Carbene Ligated Palladacycles

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Treatment of the o -hydroxyaryl imidazolinium pro-ligands (2-OH-3,5- t Bu 2 C 6 H 2 )(R)(C 3 H 3 N 2 ) + Br − [R = Me ( 3a ), i Pr ( 3b ), t Bu ( 3c ), Ph ( 3d ), Mes ( 3e )] with the palladacycle [Pd(dmba)(μ-Cl)] 2 (dmba = Me 2 NCH 2 C 6 H 5 ) ( 2 ) afforded the corresponding aryloxide-NHC (NHC = N-heterocyclic carbene)-ligated palladacycles (2-O-3,5- t Bu 2 C 6 H 2 )(R)(NHC)Pd(dmba) [R = Me ( 4 ), i Pr ( 5 ), Ph ( 6 ), Mes ( 7 ), t Bu ( 8 )]. Notably, without isolating 2, complexes 4 − 8 could also be obtained by one-pot, three-component, sequential reaction of N, N -dimethylbenzylamine, PdCl 2, and the pro-ligands in refluxing acetonitrile in the presence of K 2 CO 3 . When the N-functional group on the NHCs is tert -butyl, the NHC in 8 adopts an abnormal binding (C4-bonding). All these complexes were fully characterized by 1 H and 13 C NMR, high-resolution mass spectrometry (HRMS), and elemental analysis. Single-crystal X-ray diffraction analysis results further confirmed the molecular structures of 4 − 8 and the abnormal binding of NHC in 8 . With methylaluminoxane (MAO) as cocatalyst these palladacycles showed excellent catalytic activities up to 10 7 g of PNB (mol of Pd) −1 h −1 in the addition polymerization of norbornene.