No abstract

The reaction of L′2PdR2 (L′ = pyridine (py), pyridazine; L′2 = cyclooctadiene, TMEDA) with 2-{(2-OMe-Ph)2P}-4-Me-benzenesulfonic acid ([PO-OMe]H, [1a]H) or 2-{(2-Et-Ph)2P}-4-Me-benzenesulfonic acid ([PO-Et]H, [1b]H) yields [PO-OMe]Pd(R)(L) (L = py, R = CH2SiMe3 (2a), CH2 tBu (3a), CH2Ph (4a); R = Me, L = pyridazine (5a), py (6a), PPh3 (7a)) or [PO-Et]Pd(Me)(py) (6b). 2a and 6b have square-planar structures in which the alkyl group is cis to the phosphine and the [PO]Pd chelate rings are puckered. The reaction of 2a and 3a with B(C6F5)3 yields {[PO-OMe]Pd(R)}2 (R = CH2SiMe3 (8a), CH2 tBu (9a)). 8a is a sulfonate-bridged dimer in the solid state. 2a, 6a, and 6b polymerize ethylene to linear polyethylene that contains low levels of Me branches, one CC unit per chain (mostly 1- or 2-olefins), and M n in the range 6000 to 19 000. 6a is slightly more active but produces polymers with similar molecular weight and structure compared to 6b. 6a copolymerizes ethylene and hexene at low ethylene pressure (5 atm), but no α-olefin incorporation is observed at high pressure (30 atm). An ethylene polymerization mechanism is proposed, which involves insertion and chain transfer of [PO]Pd(R)(ethylene) species (II) and ethylene trapping and much slower chain-walking of the [PO]Pd(CH2CH2R) species (III) formed by insertion of II.

The synthesis of the 2,4-bis(amino)cyclodiphosph(V)azane cis-[tBu(H)N(OPNtBu)2N(H)tBu] (3) and the syntheses and solid-state structures of cis-[Ph(H)N(EPNtBu)2N(H)Ph] (E = S (6), Se (7)) are reported. When 6 was treated with nBuLi, the dilithio salt {[(2THF·LiPhN)(SPNtBu)2(NPhLi·2THF)]·THF} (10) was isolated. The reactions of cis-[tBu(H)N(E=PNtBu)2N(H)tBu (E = O (3), S (4), Se (5)) and cis-[R(H)N(ArPNtBu)2N(H)R] (R = tBu, Ar = Ph (8), Ar = p-Tol (9)) with 2 equiv of trimethylaluminum afforded the bis(dimethylaluminum) complexes {(Me2Al)[RN(EPNtBu)2NR](AlMe2)} (R = tBu, E = O (11), E = S (12), E = Se (13); R = Ph, E = S (14), Se (15), and R = tBu, E = N-p-Tol (16), E = N−Ph (17)). Compounds 11, 12, and 16 were characterized by single-crystal X-ray studies and shown to be trispirocyclic complexes in which the ligands coordinate both dimethylaluminum moieties in an η2-fashion, as dimeric aminophosphoranates.

Heterogeneous derivatives of catalysts discovered by Ziegler and Natta are important for the industrial production of polyolefin plastics. However, the interaction between precatalysts, alkylaluminum activators, and oxide supports to form catalytically active materials is poorly understood. This is in contrast to homogeneous or model heterogeneous catalysts that contain resolved molecular structures that relate to activity and selectivity in polymerization reactions. This study describes the reactivity of triisobutylaluminum with high surface area aluminum oxide and a zirconocene precatalyst. Triisobutylaluminum reacts with the zirconocene precatalyst to form hydrides and passivates −OH sites on the alumina surface. The combination of passivated alumina and zirconium hydrides formed in this mixture generates ion pairs that polymerize ethylene.