1 Bis-amides and Amine Bis-amides as Ligands for Olefin Polymerization Catalysts Based on V(IV), Cr(IV) and Mn(IV). A Density Functional Theory Study Timothy K. Firman and Tom Ziegler University of Calgary

2 Outline  RM(NH 2 ) 2 NH 3 + (M=V,Cr,Mn) : bonding and ethylene polymerization  Second row analogies (M=Mo, Ru, Pd)  Linking nitrogen ligands with ethyl bridges: effects on bonding mode and catalytic properties

3 Computational Details All structures and energetics were calculated with the Density Functional Theory (DFT) program ADF. All atoms were modeled using a frozen core approximation. V, Cr, and Mn were modeled with a triple-  basis of Slater type orbitals (STO) representing the 3s, 3p, 3d, and 4s orbitals with a single 4p polarization function added. Mo, Ru, and Pd were similarly modeled with a triple-  STO representation of the 4s, 4p, 4d, 5s, and a single 5p polarization function. Main group elements were described by a double-  STO orbitals with one polarization function (3d for C, N and 2p for H.) In each case, the local exchange-correlation potential was augmented with electron exchange functionals and correlation corrections in the method known as BP86. First-order scalar relativistic corrections were added to the total energy of all systems. In most cases, transition states were located by optimizing all internal coordinates except for a chosen fixed bond length, iterating until the local maximum was found, with a force along the fixed coordinate less than.001 a.u. For  -hydride transfer, transition states were found using a standard stationary point search to a Hessian with a single negative eigenvalue. All calculations were spin unrestricted and did not use symmetry. The Boys and Foster method was used for orbital localization, and the orbitals were displayed using the adfplt program written by Jochen Autschbach.

4 d 1 V, d 2 Cr, d 3 Mn: a Comparison  All three metals were high spin in compounds analyzed  As the number of SOMOs increases, the metal will have correspondingly fewer available bonding orbitals  Amides can bind with either single or double bonds, depending on the metal’s available orbitals  Metal bonding orbitals are often shared between ligands, e.g. trans- ligands share a single  -bonding metal orbital, and can also share a  -bond.

5 Shared Orbitals: trans-NH 2 H 2 N-Cr-NH 2  orbitals in  -hydride transfer TS Two of four phase-combinations of four Boys localized orbitals

6 NH 2  orbitals H 2 N-Cr-NH 2  orbitals in  -hydride transfer TS These two ligands only bind with a total of two metal orbitals

7 Metal Alkyl Structures  d 1 V is nearly tetrahedral NH 2 are flat, with  bonds not in the same plane a  -agostic hydride  d 2 Cr is nearly tetrahedral NH 2 are flat,  aligned(shared) no  -agostic hydride  d 3 Mn includes a 146 ˚ angle NH 2 are bent out of plane due to weakened  -interactions no  -agostic hydride

8 Olefin Adduct  d 1 V is trigonal bipyramidal NH 2 are flat,  bonds unshared  -agostic hydride  d 2 Cr is trigonal bipyramidal NH 2 are flat,  bonds aligned  -agostic hydride  d 3 Mn is trigonal bipyramidal l NH 2 are bent out of plane l NH 2 is apical instead of ethene  -agostic hydride

9 Energies of NH 2 Rotation  A 90  torsion directs the π to the plane of the other N  At 90  and 90 , the two π orbitals are in the same plane- both N share a single metal orbital.  V prefers two separate π orbitals  Cr prefers to share one π orbital between both ligands  The difference is due to the Cr’s additional unpaired electron Energies are in kcal/mol Relative to minimum

10 Insertion  Insertion barriers are similar  Geometries are quite different from one another  Each has a ligand trans to a forming or breaking bond  E (Barrier) +16.3kcal/mol kcal/mol kcal/mol

11 Localized Orbitals: insertion Olefin insertion of d 2 Cr

12 Termination (  -hydride transfer)  Each termination barrier is higher than insertion  No  -hydride elimination TS found lower in energy than this transfer  The amine is either trans to the hydride, or to one of the reacting M-C bonds EE kcal/mol kcal/mol kcal/mol

13 Localized Orbitals:  -hydride transfer Chain Termination Transition State

14 Enthalpies Summary  Insertion and termination numbers are promising, particularly for a system lacking steric bulk  Uptake energy is too low. l Entropy will be unfavorable by about kcal/mol l Displacement of counterion will also effect uptake energetic

15 The Second Row Transition Metals  Good second row olefin polymerization catalysts exist, including d 0 Zr and d 8 Pd  Olefin uptake energies are expected to increase due to generally stronger bonds  Model systems with d 2 Mo,d 4 Ru, and d 6 Pd were calculated  These compounds are found to be low spin  Compounds with a like number of occupied metal orbitals may be analogous

16 Second Row Results While the uptake energies are substantially improved, these combinations of ligand and metal do not result in good catalysts.

17 Tethered Nitrogen Ligands  Electronically similar to the previous systems  Chelation will keep the ligands bound  All three nitrogen will stay on one side; this will leave the other side vacant and may help uptake  Limited conformational flexibility  Sterically unhindered, as in the untethered case

18 Uptake Enthalpy of Linked System  The metal-ethylene bond energy would be about 20 kcal/mol in each case, but large differences in reorganization energy result in differences in uptake energies.  The shapes of the untethered ethylene adducts predict energetics l In the untethered Cr adduct, the two NH 2 groups are near the NH 3 group with a hydrogen pointing toward it. The tethers hold it in just this position. l V has the N ligands close together, but must twist one of the NH 2 groups. l Mn has an NH 2 trans to the NH 3, which cannot occur with a tether, so the uptake energy is actually worse with the tether than without.  E reorganization is the energy required to distort the alkyl minimum to the shape of the adduct (minus the ethylene)

19 Catalytic Properties with Tether  The tether has a large effect on the energetics, in a substantially different way for each metals l In the V system, The N ligands are held in a position close to both transition states; the energies of both are decreased. l In Cr, the insertion is close to the tethered case, but the untethered termination prefers trans NH 2 groups, which is impossible for the tethered case. E BHT is much higher as a result. l In Mn, the tether causes each shape a similar energy penalty. Energies are similar to the untethered case.

20 Conclusions  The occupation of metal orbitals by single electrons has a substantial chemical effect  NR 2 can vary its bonding orbitals to compensate for other bonding changes, such as during insertion  Tethering the ligands alters the energetics differently for each transition state  Matching tether types with metal is important Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and Novacor Research and Technology Corporation.