4571-HW3-F2008-Answers - Organometallic Chemistry 4571...

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Organometallic Chemistry - 4571ANSWER KEYHomework # 3(Due: Nov 11, 2008) Check the box to the right if you want your graded homework to be placed out in the public rack outside Prof. Stanley’s office. Otherwise you will have to pick up your homework from Prof. Stanley in person: 1. (40 pts)Identify the following reactions by their type (migratory insertion, elimination, oxidative addition, reductive elimination, substitution, ligand addition or dissociation, β-hydride elimination, ligand coordination change, etc.). Note that some reactions may have several steps. For reactions with several steps, if the order is important you must list the steps in the correct order. Ir(+1) going to Ir(+3) indicates an oxidative addition rxn. CH4is a non-polar substrate and needs an empty orbital on the metal to bind to prior to oxidative addition. a) Cp*Ir(CO)2+ CH4Cp*Ir(CO)(H)(CH3) + CO hν1) CO ligand dissociation (promoted by photolysis) 2) oxidative addition of methane C-H bond The first PPh3substitution probably occurs via a dissociative route due to the steric bulk of the 3 PPh3groups. The incoming order of CO or dppe is not important. b) RhCl(PPh3)3+ dppe + CORhCl(CO)(dppe) + 3PPh31) PPh3substitution with CO 2) twoPPh3substitutions by dppe (one arm at a time) c) H2RhCl(PPh3)2(CH2CH3) HRhCl(PPh3)2+ CH3CH31) reductive elimination Rh(+4) going to Rh(+2). One could also first have a ligand dissociation of PPh3or Cl- to help promote the reductive elimination rxn. But the dissociated ligand needs to recoordinate after the reductive elimination.

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