4571-HW3-2008-Answers - Organometallic Chemistry 4571...

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Organometallic Chemistry - 4571ANSWER KEYHW # 3 Due: April 10, 2008 1. (30 pts)Predict and sketch out the structure for the transition-metal containing product for the following substitution reactions using one equivalent of each the reactants. State whether the mechanism is most likely associativeor dissociativeand reason(s) for your choice. a)CpFe(CH3)(CO)(H2C=CHCH3) + PPh3Dissociative: The Fe complex is 18e-, so it needs to lose the weakest coordinated ligand to open up a coordination site to bind the new ligand. Propylene will definitely be the most labile ligand. b)ReCl(CO)3(PMe3)2+ CH3Dissociative: The Re complex is 18e-, so it needs to lose the weakest coordinated ligand to open up a coordination site to bind the new ligand. Chloride is the most likely candidate to dissociate first. c)RuCl2(dmpe)(CO) + BrAssociative: The Ru complex is 16e-, so it already has an empty orbital and has fairly small ligands to allow an associative substitution by bromide to replace one of the more weakly bound chloride ligands. Ru has a moderate tendency for 16e- d6complexes. d)W(CO)2(PEt3)4+ P(OMe)3Dissociative: The W complex is 18e-, so it needs to lose the weakest coordinated ligand to open up a coordination site to bind the new ligand. Since the CO’s are very strongly π-backbonding, one of the bulkier, electron-donating PEt3ligands should dissociate first. 4-strongly donating alkylated phosphine ligands makes the metal too electron-rich so this (and sterics) will favor PEt3dissociation to allow a poorer σ-donor, better π-acceptor, and smaller phosphite ligand to coordinate. e)[Rh(CO)2(PPhMe2)2]++ PEt3Associative or dissociative: The Rh complex is 16e-, so it has an empty orbital to allow an associative substitution by PEt3to replace one of the other ligands. But if you judge the PPhMe2

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