周四金屬有機chapter

1、Chapter 6 Insertion and EliminationA. IntroductionB. CO insertion reactionsC. Insertion reactions involving alkene and alkyneD. a, b, g and d elimination reactionsOutlineA. Introduction1) 1,1-insertion2) 1,2-insertion3) 1,3-insertion4) 1,4-insertionTypes of insertion reactions:As the name suggests,

2、an insertion reaction involves the formal insertion of one ligand (usually unsaturated) into another metal-ligand bond on the same complex. 1) 1,1-insertione.g. U = CO, C2H4, C2R2, NO, CR2, CNR, RCN, O2, CO22) 1,2-insertione.g. Proposed mechanism:3) 1,3-insertion4) 1,4-insertionElimination (or de-in

3、sertion or extrusion) reactions are just reverse of insertion reactions.e.g. Elimination reaction:B. CO Insertion reactionsMain features of CO insertion reactionsThermodynamics of CO insertions Factors influencing the insertion reaction ratesDecarbonylation reactions There are many examples of CO in

4、sertions. e.g.1) Main features of CO insertion reactionsa). CO and R must be cis.b). It can be described as R migrationc). The configuration of R is unchanged.d). The feasibility and rate depend on M-R bond strength. ExamplesExercise. propose a mechanism for the reaction:2) Thermodynamics of CO inse

5、rtions Bond strength of M-R is a determining factor.The weaker the M-R bond, the easier to undergo an insertion reaction and the more favorable thermodynamically.Explain the following observations.(weak)(strong)(strong)3) Factors influencing the insertion reaction rates Factors enhancing reaction ra

6、te: More positive charge on C atom; Weak M-R bond strength. Which of the following reaction is faster?Answer : (a)(stronger)Which of the following reaction is faster?Answer : (b)Similarly, cations such as Na+, Mg2+ can also enhance the insertion reaction rate.Explanation: 4) Decarbonylation reaction

7、s.* The complexes must be unsaturated coordinatively.* The CO and R are cis to each other in the products. * The rate is dependent on R. e.g.(One CO ligand leaves from metal center firstly.) Insertion reactions involving alkenes and alkynes 1) Examples of alkene and alkyne insertion reactions2) Some

8、 features of alkene and alkyne insertion reactions Very important in catalysis 1) Examples of alkene and alkyne insertion reactions (adduct)2) Some features of alkene and alkyne insertion reactionsa) Need an intermediate in which the olefin or alkyne is cis to R.e.g.cisb) The transition state has a

9、coplanar geometry.Example:c) The stereochemistry is syn for the two substituents of CC. e.g.d) For substituted olefins, there are two possible structure. e.g. Which one is major ? Answer : A (less steric hindrance)D. a, b, g and d elimination reactions. 1) a elimination2) b elimination3) g eliminati

10、on4) d elimination1) a-elimination2) b-eliminationa) b-elimination.The most common position pathway for alkyls is b-H elimination, which converts a metal-alkyl into a hydrido-olefin complex.hydrido-olefin complexWhat is the condition for b-H elimination to occur ?A. There must be a b-H.B. The comple

11、x should be able to form four-membered co-planar transition state. (see (A) C. There is a vacant site cis to the alkyl (e.g. (B). but not (C). (need an empty orbital to accept C-H electron.)D. The olefin formed is stable.E. The metal has e- to go to s*(C-H).3) g-elimination4) d-eliminationMurai, S.; Kakiuchi, F.; Sekin