A Valence Bond Analysis of Olefin Polymerization Catalysts

Timothy K. Firman and Tom Ziegler

-Conjugated Ligands in d0 Systems

X X

X X

X= CR2, SiR2, NR, PR, O, S

X groups are isolobally analogous

Several good catalysts of this type are known

Resonance StructuresA localized bonding picture of these ligandsrequires multiple resonance structures, e.g.:

HC

HN NH

M+

- HC

HN NH

M

HC

HN NH

M

Main group elements require an octet of electronsBond order to metal is variable, which may facilitate bond breaking during olefin insertion

Model Compounds

X= CH2, SiH2, NH, PH, O, S

TiX

HC X X CHX

PTiX

X X

X

P

+ +