1. 1 A Density Functional Study of the Competing Processes Occuring in Solution during Ethylene Polymerisation by the Catalyst (1,2Me 2 Cp) 2 ZrMe + Kumar Vanka and Tom Ziegler University of Calgary

2. 2 Introduction The vacant site in the cationic catalyst (1,2Me 2 Cp) 2 ZrMe +, in our case) can be attacked by several species in solution - the co-catalyst, the solvent, the pre- catalyst and the monomer. Apart from the monomer, all the other species would form dormant complexes in solution and hinder catalysis. The purpose of this study was to investigate the relative possibilities of such reactions occuring in solution and how well the monomer complexation could compete with the other inhibitive reactions.

3. 3 Computational Details The density functional theory calculations were carried out using the Amsterdam Density Functional (ADF) program version 2.3.3. 1 Geometry optimizations were carried out using the local exchange-correlation potential of Vosko et al. 2 A triple-zeta basis set was used to describe the outermost valence orbitals for the titanium and zirconium atoms, whereas a double-zeta basis set was used for the non-metals. The frozen core approximation was used to treat the core orbitals of all atoms. The gas phase energy differences between stationary points were calculated by augmenting the LDA energy with Perdew and Wang’s non-local correlations and exchange corrections. 3 The energy differences in solution was corrected from the gas phase energies by accounting for the solvation calculated by the Conductor-like Screening Model (COSMO). 4 The solvation energy calculations were carried out with a dielectric constant of 2.38 to represent toluene as the solvent. 1. (a) Baerends, E. J.; Ellis,D.E.; Ros, P. Chem. Phys. 1973, 2, 41. (b) Baerends, E. J.; Ros, P. Chem. Phys. 1973, 2,52. 1. (a) Baerends, E. J.; Ellis,D.E.; Ros, P. Chem. Phys. 1973, 2, 41. (b) Baerends, E. J.; Ros, P. Chem. Phys. 1973, 2,52. 2. Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980,58, 1200. 2. Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980,58, 1200. 3. Perdew, J. P. Phys. Rev. B 1992, 46, 6671. 3. Perdew, J. P. Phys. Rev. B 1992, 46, 6671. 4. Pye, C. C.; Ziegler, T. Theor. Chem. Acc. 1999 V 101, 396-408. 4. Pye, C. C.; Ziegler, T. Theor. Chem. Acc. 1999 V 101, 396-408.

4. 4 Dormant Product Formation *Li,L.; Marks, T.J.Organomettallics 1998, 17, 3996-4003 (1,2Me 2 Cp) 2 ZrMe + + [D]  (1,2Me 2 Cp) 2 ZrMe + ] [D] +  H dp The formation of dormant complexes of the type The formation of dormant complexes of the type (1,2Me 2 Cp) 2 ZrMe + ] [D] shown above, with D in this case being the pre-catalyst, has been experimentally observed by Marks et al.* Calculations were done to obtain optimized structures for the dormant complexes. The enthalpy of Dormant Product formation for the complexes was calculated and termed as shown above, with D in this case being the pre-catalyst, has been experimentally observed by Marks et al.* Calculations were done to obtain optimized structures for the dormant complexes. The enthalpy of Dormant Product formation for the complexes was calculated and termed as  H dp

5. 5 Relative Stabilities of Dormant Complexes Species  H dp Species  H dp kcal/mol kcal/mol (1,2-Me 2 Cp) 2 ZrMe + - -B(C 6 F 5 ) 3 -9.9 (1,2-Me 2 Cp) 2 ZrMe + - -C 6 H 5 CH 3 -10.2 (1,2-Me 2 Cp) 2 ZrMe + - -AlMe 3 -25.4 (1,2-Me 2 Cp) 2 ZrMe + - -(1,2Me 2 Cp) 2 ZrMe 2 -25.8 Results showed that the species AlMe 3 (TMA) and the pre-catalyst, (1,2Me 2 Cp) 2 ZrMe 2 would form the most stable dormant complexes.

6. 6 Increasing the Alkyl Chain 0.0 kcal/mol 8.4 kcal/mol The possibility of forming dormant complexes after insertion of one ethylene monomer unit into the Zr-C bond, was investigated for the pre-catalyst and TMA. The most stable conformer for the dormant complex was determined for each case. conformer for the dormant complex was determined for each case. 0.0 kcal/mol -3.9 kcal/mol

7. 7 Increasing the Alkyl Chain      H dp kcal/mol kcal/mol (1,2-Me 2 Cp) 2 ZrPr + - -AlMe 3 -15.4 (1,2-Me 2 Cp) 2 ZrPr + - -(1,2Me 2 Cp) 2 ZrMe 2 -15.6 The  H dp was calculated for the most stable dormant complexes of the extended chain cation (1,2-Me 2 Cp) 2 ZrPr + (Pr - Propyl) with the pre-catalyst and TMA. The value of  H dp was found to decrease by about 10 kcal/mol from the earlier corresponding complexes with the cation (1,2-Me 2 Cp) 2 ZrMe +, indicating that the possibility of forming dormant complexes decreases with increasing chain length.

8. 8 Formation of Sandwiched Complexes  H sp = 4.4 kcal/mol  H sp = -23.5 kcal/mol The possibility of a species like TMA inserting into an ion-pair between the cation and counterion and forming a sandwiched complex, with an enthalpy of  H sp, was investigated for two different ion-pairs [ and The possibility of a species like TMA inserting into an ion-pair between the cation and counterion and forming a sandwiched complex, with an enthalpy of  H sp, was investigated for two different ion-pairs [(1,2Me 2 Cp) 2 ZrMe + ][B(C 6 F 5 ) 3 Me - ], and [  H sp indicate that the possibility of such dormant, sandwiched complexes is a distinct possibility in solution. [(1,2Me 2 Cp) 2 ZrMe + ][B(C 6 F 5 ) 4 - ], the species inserting being TMA. The values of  H sp indicate that the possibility of such dormant, sandwiched complexes is a distinct possibility in solution.

9. 9 Monomer Separated Ion-pairs It is clear that if the monomer has to compete with the other species in solution, it has to successfully insert and form stable sandwiched complexes. The formation of such complexes was investigated for four different ion-pair complexes. The sandwich complex formed in one of the cases : for the ion-pair [ is shown above. The enthalpy of forming the monomer separated ion-pair was labelled as  H ms It is clear that if the monomer has to compete with the other species in solution, it has to successfully insert and form stable sandwiched complexes. The formation of such complexes was investigated for four different ion-pair complexes. The sandwich complex formed in one of the cases : for the ion-pair [(1,2Me 2 Cp) 2 ZrMe + ][B(C 6 F 5 ) 3 Me - ], is shown above. The enthalpy of forming the monomer separated ion-pair was labelled as  H ms

10. 10 Competition between Monomer and Solvent Counterion  H ss  H ms B(C 6 F 5 ) 3 Me - 18.7 14.4 B(C 10 F 7 ) 3 Me - 18.9 11.9 [(C 2 B 9 H 11 ) 2 Co] - 7.5 2.3 B(C 6 F 5 ) 4 - -4.2 -11.0 A comparison between the enthalpies of solvent (toluene) separated ( and monomer (ethylene) separated ( [ A comparison between the enthalpies of solvent (toluene) separated (  H ss ) and monomer (ethylene) separated (  H ms ) ion-pairs for four cases with the cation [(1,2Me 2 Cp) 2 ZrMe + ] and different counterions, showed that the monomer would “win” in the competition for the vacant coordinate site, against the solvent.

11. 11 Approach of the Monomer Approach 1 Approach 2 Approach 3 The low values of The low values of  H ms obtained makes it clear that the presence of the counterion in the vicinity of the catalytic cation has to be taken into account when considering the attack of the monomer at the vacant cationic site. The approach of the ethylene monomer towards the [ ion-pair [(1,2Me 2 Cp) 2 ZrEt + ][B(C 6 F 5 ) 4 - ], was considered from three different directions.

12. 12  - Complexes Formed Approaches 1 and 2 would lead to the sandwiched  complex I, while Approach 3 would lead to the  complex II above. Calculations showed that II was more stable than I by about 3.5 kcal/mol. This indicates that, for the ion-pair [ Approaches 1 and 2 would lead to the sandwiched  complex I, while Approach 3 would lead to the  complex II above. Calculations showed that II was more stable than I by about 3.5 kcal/mol. This indicates that, for the ion-pair [(1,2Me 2 Cp) 2 ZrEt + ][B(C 6 F 5 ) 4 - ], the attack of the monomer to thet cation from opposite to the counterion is the preferred approach to complexation and subsequent insertion into the metal alkyl bond. 0.0 kcal/mol -3.5 kcal/mol I II

13. 13 Total Separation of Counterion from  -Complex To further investigate the influence and presence of the counterion near the cation during insertion, the enthalpy of total separation of counterion from the  complex ( was calculated in three separate solvents. cation during insertion, the enthalpy of total separation of counterion from the  complex (  H ts ) was calculated in three separate solvents.

14. 14 Separation of Counterion from  -Complex Solvent  H ts for I  H ts for II C 6 H 5 CH 3 14.3 16.1 C 6 D 5 Cl 3.2 6.7 1,2-C 6 D 4 Cl 2 0.3 3.8 The enthalpy of total separation ( The enthalpy of total separation (  H ts ) was calculated for the  complexes I and II (refer to slide 12) in three different solvents. From the results obtained, it is clear that for solvents of low dielectric constant (  like toluene, C 6 H 5 CH 3 (        ),     likely to remain in the vicinity of the cation during insertion. The possibility of the counterion dissociating and being removed increases in more polar solvents like 1,2-C 6 D 4 Cl 2 (      .

15. 15 Conclusions The pre-catalyst, solvent and TMA can form dormant complexes with the cation in contact ion-pair systems. The stability of the dormant complexes is reduced with the increase of the alkyl chain length. The monomer (ethylene) can compete successfully with the solvent (toluene) in forming sandwiched complexes with the ion-pair. The total separation of the counterion from the ion-pair during monomer complexation and insertion is unlikely in non-polar solvents like toluene. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and Novacor Research and Technology Corporation.