Cationic Ni(II) Species and Their Application in Olefin Polymerizations

[(η3-Allyl-Me)­Ni­(mesitylene)]­[BArF4] (allyl-Me = C3H4-2-Me (η3-methallyl); BArF4 = B­(3,5-(F3C)2C6H3)4; 1) was treated with the phosphine ligands tBu3P, Ad3P (Ad = tri-1-adamantylphosphine), and TMPP (TMPP = tris­(2,4,6-trimethoxyphenyl)­phosphine). Although these phosphines display similar steric bulk and differ only moderately in their electronic properties, very different reaction products are isolated. For tBu3P, only the phosphonium salt [tBu3P-C3H4-2-Me]­[BArF4] (2) is formed; this contrasts with the reactivity with TMPP, in which the mesitylene ligand is readily displaced to yield [(η3-allyl-Me)­Ni­(tmpp)]­[BArF4] (3). With Ad3P, we observe the formation of an unusual C–H bond activation product [(toluene)­Ni­(κC:P-C10H14–PAd2]­[BArF4] (4). Nevertheless, Ad3P successfully stabilizes the two-coordinate Ni­(I) species [(Ad3P)2Ni]­[BArF4] (5). Complexes 3–5 have been evaluated in the homopolymerization of ethylene and norbornene after addition of the Lewis acid B­(C6F5)3.