Insertion and elimination olefin polymerization 1,1-insertion of CO, isonitriles, SO2, ... Migratory insertion! 4/16/2017 Insertion and Elimination

Insertion van CO en isonitriles CO insertion is hardly exothermic. An additional ligand may be needed to trap the acyl and so force the reaction to completion. In the absence of extra ligands often fast equilibrium. CO insertion in M-H, M-CF3, M-COR endothermic Þ no CO polymerization. Isonitriles do polymerize! 4/16/2017 Insertion and Elimination

Insertion van CO en isonitriles Double CO insertion ? 4/16/2017 Insertion and Elimination

Insertion van CO and isonitriles No double CO insertion ! 4/16/2017 Insertion and Elimination

Insertion van CO and isonitriles Increase rate of insertion: "Bulky" ligands Lewis acids Coordinate to O, stabilize product 4/16/2017 Insertion and Elimination

Insertion van CO and isonitriles Insertion is not always "real": 4/16/2017 Insertion and Elimination

Insertion and Elimination 1,2-insertion of olefins Standard Cossee mechanism 4/16/2017 Insertion and Elimination

Insertion and Elimination 1,2-insertion of olefins Insertion in M-H bonds is nearly always fast and reversible. Þ Hydrides catalyze olefin isomerization. Regiochemistry corresponds to Md+-Hd- To shift the equilibrium to the alkyl: Electron-withdrawing groups at metal Early transition metals Alkynes instead of olefins 4/16/2017 Insertion and Elimination

Insertion and Elimination 1,2-insertion of olefins Metals have a preference for primary alkyls. But substituted olefins are more stable! 4/16/2017 Insertion and Elimination

Insertion and Elimination 1,2-insertion of olefins Insertion in M-C bonds is slower than in M-H. Barrier usually 5-10 kcal/mol higher (factor 105-1010 in rate!) Reason: shape of orbitals (s vs. sp3) 4/16/2017 Insertion and Elimination

Insertion and Elimination 1,2-insertion of olefins a-agostic interaction facilitates tilting of alkyl and accelerates insertion ("Green-Rooney") 4/16/2017 Insertion and Elimination

Insertion and Elimination 1,2-insertion of olefins Repeated insertion: dimerization, oligomerization, polymerization Key factor: kCT / kprop = k k » 1: dimerization k » 1: oligomerization (always mixtures) k « 1: polymerization k » 0: "living" polymerization 4/16/2017 Insertion and Elimination

Insertion and Elimination 1,2-insertion of olefins Dimerization rarely desired Oligomers: surfactants, comonomers Polymers: plastics, construction materials, foils and films 4/16/2017 Insertion and Elimination

Insertion and Elimination 1,2-insertion of olefins Selective trimerization is possible but follows a complicated mechanism 4/16/2017 Insertion and Elimination

CO/olefin copolymerization M = L2Pd, L2Ni 4/16/2017 Insertion and Elimination

CO/olefin copolymerization No double CO insertion uphill No double olefin insertion CO binds more strongly, inserts more quickly Slow b-elimination from alkyl 5-membered ring hinders elimination 4/16/2017 Insertion and Elimination

Insertion and Elimination Hydroformylation 4/16/2017 Insertion and Elimination

1,n insertions/additions Attack on an h-polyene is always at a terminal carbon Þ Usually a,w-insertion A diene can be h2 bound Þ 1,2-insertion 4/16/2017 Insertion and Elimination

1,n insertions/additions Diene rubbers: Can be influenced by choice of catalyst. 4/16/2017 Insertion and Elimination

1,n insertions/additions Addition to enones: RLi, Grignards: usually 1,2 OrganoCu compounds often 1,4 4/16/2017 Insertion and Elimination

Less common elimination reactions a-elimination 4/16/2017 Insertion and Elimination

Less common elimination reactions Other ligand metallation reactions Via s-bond metathesis or oxidative addition/ reductive elimination 4/16/2017 Insertion and Elimination

Less common elimination reactions s-bond metathesis "H+" transfer from alkane to alkyl 4/16/2017 Insertion and Elimination

Less common elimination reactions b-elimination from alkoxides of late transition metals is easy 4/16/2017 Insertion and Elimination