Phosphinimide−Phosphinimide Ligands:  New Bulky Ligands for Ethylene Polymerization Catalysts

The phosphinimide−phosphines PPh<INF>2</INF>(NPR<INF>3</INF>) (R = i-Pr<BO> 1</BO>, t-Bu<BO> 2</BO>) were readily prepared in 80−98% yield. These species react with AlMe<INF>3</INF> or B(C<INF>6</INF>F<INF>5</INF>)<INF>3</INF> to form Me<INF>3</INF>AlPPh<INF>2</INF>(NPR<INF>3</INF>) (R = i-Pr<BO> 3</BO>, t-Bu<BO> 4</BO>) and (C<INF>6</INF>F<INF>5</INF>)<INF>3</INF>B(PPh<INF>2</INF>(NPi-Pr<INF>3</INF>)) (<BO>5</BO>), respectively. Oxidation of compounds <BO>1</BO> and <BO>2</BO> with Me<INF>3</INF>SiN<INF>3</INF> yields Me<INF>3</INF>SiNPPh<INF>2</INF>(NPR<INF>3</INF>) (R = i-Pr<BO> 6</BO>, t-Bu<BO> 7</BO>). These species react with CpTiCl<INF>3</INF> to give titanium(IV) complexes CpTiCl<INF>2</INF>(NPPh<INF>2</INF>(NPR<INF>3</INF>) (R = i-Pr <BO>8</BO>, t-Bu <BO>9</BO>) and subsequently the alkylated complexes CpTiMe<INF>2</INF>(NPPh<INF>2</INF>(NPR<INF>3</INF>)) (R = i-Pr <BO>10</BO>, t-Bu <BO>11</BO>). Compounds <BO>8</BO>−<BO>11</BO> were tested for activity in ethylene polymerization. In the presence of excess methylalumoxane, the species <BO>8 </BO>and <BO>9 </BO>gave rise to active single-site catalysts, generating 299 and 34 gPE mmol^-1 h^-1, respectively. In contrast, activation of <BO>10</BO> and <BO>11</BO> by [Ph<INF>3</INF>C][B(C<INF>6</INF>F<INF>5</INF>)<INF>4</INF>] showed negligible polymerization activity. Reaction of <BO>11 </BO>with B(C<INF>6</INF>F<INF>5</INF>)<INF>3</INF> was shown to give numerous products, one of which was the dicationic species [CpTi(μ-Cl)(NPPh<INF>2</INF>(NPt-Bu<INF>3</INF><INF></INF>)]<INF>2</INF>[BC<INF>6</INF>F<INF>5</INF>)<INF>4</INF>]<INF>2</INF>, <BO>12</BO>. The formation of this species and the implications of these results for catalyst and ancillary ligand design are considered and discussed. X-ray crystallographic data are reported for <BO>1</BO>, <BO>3</BO>, <BO>4</BO>, <BO>8</BO>, and <BO>12</BO>.