Synthesis And Catalysis Of Ni(Ⅱ) Complexes Bearing Imidazolium Or Corresponding N-Heterocyclic Carbene

A series of mixed imidazolium/phosphine ionic Ni（Ⅱ） complexes of formula[DRIM][Ni（PPh₃）X₃]（R=2,6-diisopropylphenyl, X=Cl,1; R=isopropyl, X=Cl,2;R=tertbutyl, X=Cl,3; R=2,6-diisopropylphenyl, X=Br,4; R=isopropyl, X=Br,5;R=tertbutyl, X=Br,6; R=2,6-diisopropylphenyl, X=I,7; R=isopropyl, X=I,8; R=tertbutyl, X=I,9）, bisimidazolium ionic Ni（Ⅱ） comples of formula [DRIM]₂[NiCl₄]（R=2,6-diisopropylphenyl,14; R=isopropyl,15; R=tertbutyl,16） and mixedNHC/phosphine Ni（Ⅱ） complexes of formula Ni（PPh₃）（NHC）Cl₂（NHC=IPr,18; NHC=ItBu,19） have been prepared. The structure/catalysis dependence of complexes1-9,14-16have been investigated in the model reaction of Kumada ross-coupling betweenaryl halides and aryl Grignard reagents.1. Reactions of Ni（PPh₃）₂Cl₂with one equivalent of imidazolium chloridesafforded mixed imidazolium/phosphine ionic Ni（Ⅱ） complexes1-3with the halide atomis Cl; Reaction of Ni（PPh₃）₂Cl₂with one equivalent of imidazolium chlorides in thepresence of NaBr or NaI afforded the corresponding bromides4-6or iodides7-9,respectively. All of them have been characterized by elemental analysis and1H NMRspectra. The structures of complexes1,2,4-8have been determined by X-ray singlecrystal diffraction.2. Reactions of Ni（DME）Cl₂with two equivalents of imidazolium chloridesafforded bisimidazolium ionic Ni（Ⅱ） complexes （14-16）. All of them have beencharacterized by elemental analysis and1H NMR spectra.3. The structural variations of the mixed imidazolium/phosphine ionic Ni（Ⅱ）complexes1-9showed significant effects on their catalytic activivies in Kumadaross-coupling between aryl halides and aryl Grignard reagents. It has been revealed thatthe catalytic activities of these complexes were strongly influenced by the kind ofN-substituent in the imidazolium ring, whereas, were independent of the nature of X. Among them, complexes3,6and9, which had a bulky N-substituent, showed the higestcatalytic activities, whereas, complexes2,5and8, which had a relatively smallerN-substituent, had the lowest catalytic activities.4The divisities of catalytic activities among the mixed imidazolium/phosphineionic Ni（Ⅱ） complexes1-3, the bisimidazolium ionic Ni（Ⅱ） complexes14-16andbisphosphine Ni（Ⅱ） complex Ni（PPh₃）2Cl2had been investigated. It has been found thecatalytic activity of the mixed imidazolium/phosphine ionic Ni（Ⅱ） complexes are muchhigher than those of the corresponding bisimidazolium Ni（Ⅱ） complexes, whereas,bisphhosphine Ni（Ⅱ） complex had the lowest catalytic activity.5. Reactions of mixed imidazolium/phosphine ionic Ni（Ⅱ） complexes1and3withIPr and ItBu, respectively, afforded mixed NHC/phosphine ionic Ni（Ⅱ） complexes18and19. Both of them have been characterized by elemental analysis. Between them,complex18have been characterized by1H NMR, and new complex19have beendetermined by X-ray single crystal diffraction. Reactions of complexes1and3withItBu and IPr, respectively, both afforded complex18.