| 20017482 |
Shen Z, Jordan RF: Self-assembled tetranuclear palladium catalysts that produce high molecular weight linear polyethylene. J Am Chem Soc. 2010 Jan 13;132(1):52-3.
The phosphine-bis-arenesulfonate ligand PPh (2-SO (3) Li-4-Me-Ph)(2) (Li (2)[OPO]) coordinates as a kappa (2)-P,O chelator in Li [(Li-OPO) PdMe (Cl)] (2a) and (Li-OPO) PdMe (L) (L = pyridine (2b); MeOH (2d); 4-(5-nonyl) pyridine) (py', 3)). 2a reacts with AgPF (6) to form {(Li-OPO) PdMe}(n) (2c). Photolysis of 2d yields {(OPO) Pd}(2) (5) in which the [OPO](2-) ligand coordinates as a kappa (3)-O,P,O pincer. 3 self-assembles into a tetramer in which four (Li-OPO) PdMe (py') units are linked by Li-O bonds that form a central Li (4) S (4) O (12) cage. The Pd centers are equivalent but are spatially separated into two identical pairs. The Pd-Pd distance within each pair is 6.04 A. IR data (upsilon (ArSO (3)(-)) region) suggest that the solid state structures of 2a-c are similar to that of 3. 3 reacts with the cryptand Krypt211 to form [Li (Krypt211)][(OPO) PdMe (py')] (4). 3 is in equilibrium with a monomeric (Li-OPO) PdMe (py') species (3') in solution. 2a-c and 3 produce polyethylene (PE) with high molecular weight and a broad molecular weight distribution, characteristic of multisite catalysis. Under conditions where the tetrameric structure remains substantially intact, the PE contains a substantial high molecular weight fraction, while, under conditions where fragmentation is more extensive, the PE contains a large low molecular weight fraction. These results suggest that the tetrameric assembly gives rise to the high molecular weight polymer. In contrast, the monomeric complex 4, which contains a free pendant sulfonate group that can bind to Pd, oligomerizes ethylene to a Schultz-Flory distribution of C (4)-C (18) oligomers. |
81(1,1,1,1) |