Chapter 4,Complexes of p-bound Ligands,1. Alkene complexes 2. Butadiene complexes 3. Alkyne complexes 4. Enyl Complexes 5. Complexes of the cyclic p-perimeters CnHn Metal p-complexes of Unsaturated ligands with heteroatoms 7. Characterization of organometallic compounds,Outline,References and suggested readings: 1. The Organometallic Chemistry of the Transition Metals, Robert H. Crabtree, 3rd Edition, 2001, Chapters 5, 10. 2. Organometallic Chemistry, G. O. Spessard, G. L. G. L. Miessler, Prentice-Hall: New Jersey, 1997, Chapter 5. 3. Organometallics, C. Elschenbrouch, A. Salzer, 1989, Chapter 15. 4. Organotransition Metal Chemistry, Akio Yamamoto, 1986. Chapters 3.4-3.9, 6.1d.,B. Preparation of olefin complexes,1. Alkene complexes,A. Structure and bonding of monoolefin complexes,C. Reactivity of olefin complexes,A. Structure and bonding of monoolefin complexes,Examples:,Non-planar,Bonding:,Q1. Which interaction is dominant? High valent metal (e- poor) systems: -Donation is dominant. Low valent metal (e- rich) systems: -Backdonation is dominant.,Q2. What are the effects of complexation?,d(C-C) u(C=C) e- density on C,Q3. Consider the fragment Pt(PPh3)2. Which of the following olefins would you expect to form the most stable olefin adduct A?,(a) CH2=CH2 (b) CH3-CH=CH2 (c) CH2=CHCN,Answer: (c) more backdonation,Q4. Which of the following olefin complexes is more stable?,* Usual stability of olefin complexes:,Answer: (A) small steric hindrance,Q5. Which of the following olefin complexes is more stable?,Answer: (b) release ring strain,Strong ring strain,ring strain released,B. Preparation of olefin complexes,1. From Substitution reactions: LnM-L + olefin - L + LnM-(olefin) Examples:,precipitation,2. Metal salt + olefin + reducing agents. e.g.,Mechanism ?,3. From alkyl and related species:,1). Insertion reactions,Examples:,C. Reactivity of olefin complexes,Examples:,monomer,3). Nucleophilic attack on coordinated olefins.,Examples:,Summary: Reactions of olefin complexes.,2. Butadiene complexes,A. Most common structures of butadiene complexes,B. Synthesis of butadiene complexes,C. Reactions of butadiene complexes,A. Most common structures of butadiene complexes,B. Synthesis of butadiene complexes,1. by substitution reactions. e.g.,2. Reaction of coordinated ligands. e.g.,Correct your notes !,C. Reactions of butadiene complexes,Examples:,16e,18e,18e,18e,18e,3. Alkyne complexes,A. Structure and bonding of alkyne complexes,B. Preparation of alkyne complexes,C. Reactivity of alkyne complexes,A. Structure and bonding of alkyne complexes,R-CC-R can be simple h2-ligand or bridging ligand. As simple h2-ligand, they can be 2e or 4e donors. e.g.,18e,18e,Q1. How can they be 2e or 4e donors?,In terms of bonding:,Correct your notes !,As bridging ligands:,Q2. For each pair of the following complexes, which one is more stable?,B. Preparation of alkyne complexes,1. By substitution reactions: e.g.,2. By other methods: e.g.,C. Reactivity of alkyne complexes,Similar to olefins complexes, e.g.,Q1. Give the product for the following reaction.,4. Enyl Complexes,A. Allyl complexes,Examples of other enyl complexes and their preparation,Enyl: Organic ligands with odd number of carbon chains. Examples:,A. Allyl complexes,1. Structure of allyl complexes,2. Preparation of allyl complexes,a. Metal salt + main group organometallic reagents.,Examples:,Correct your notes !,b). Low valent metal complexes + allylhalide.,Correct your notes !,c) Metal salts + olefin + base.,A previously mentioned example:,Examples,3. Reactivity of allyl complexes,a). With Nucleophiles:,b). With electrophile (for h1-allyls):,c). Insertion reactions.,B. Examples of other enyl complexes and their preparation,They can be prepared similar to allyl complexes.,Examples: a). Metal salt + main group organometallic reagents.,b). Transfer of H+ or H-,h5,h7,5. Complexes of the cyclic p-perimeters CnHn,A. C3R3 as ligands,B. C4R4 as ligands,C. C5R5 as ligands,D. Arene complexes,E. C7H7 and C8H8 as ligands,Common complexes of cyclic p-perimeters CnHn:,Common structural types,a). Sandwich complexes, e.g.,Cr Mn Fe Co Ni,b) Half-sandwich complexes,c) Multidecker sandwich,d). Complexes with tilted sandwich structures.,A. C3R3 as ligands,Common starting materials for preparing h3-C3R3 complexes?,Examples and preparation.,B. C4R4 as ligands,Q1. What are the common starting materials for preparing M(h4-C4R4) complexes?,Example and preparation.,Important chemical properties:,a. Show aromatic properties. e.g.,b). Can be used as a source of C4R4.,C. C5R5 as ligands,Common C5R5,Binding mode of C5R5,A).How to prepare CpM complexes?,Common starting materials:,Examples. 1). From a source of Cp - : most common route Cp- reagents: NaCp, CpMgBr, TlCp, CpSnMe3,2). From C5H6 or related ligands. e.g.,c). From a source of Cp+. e.g.,B. What are the typical chemical properties of h5-Cp ligand?,- h5-Cp ligand is usually unreactive.,- The following reactions ma