lecture 14 - Lecture 14 - Organometallic Ligands and...

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Lecture 14 — Organometallic Ligands and Bonding I. Organometallic Basics A. An Organometallic Complex contains at least one M—C bond 1) Includes ligands: CO, NO, N 2 , PR 3 , H 2 2) Both σ and π bonding between M and C occur B. History 1) Zeise s Salt synthesized in 1827 = K[Pt(C 2 H 4 )Cl 3 ] • H 2 O a) Confirmed to have H 2 C=CH 2 as a ligand in 1868 b) Structure not fully known until 1975 2) Ni(CO) 4 3) Grignard Reagents (XMgR) synthesized about 1900 a) Accidentally produced while trying to make other compounds b) Utility to organic synthesis recognized early on
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4) Ferrocene synthesized in 1951 (several researchers) a) Modern organometallic chemistry begins with this discovery b) Many new ligands and reactions produced ever since 5) Organometallic chemistry has really been around for millions of years a) Naturally occurring cobalimins contain Co—C bonds b) Vitamin B 12
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Geometric isomers of octahedral complexes MX 3 Y 3 fac -[CoCl 3 F 3 ] 3– mer -[CoCl 3 F 3 ] 3–
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Geometric isomers of octahedral complexes MX 2 Y 4 cis -[CoCl 3 F 3 ] 3– trans -[CoCl 3 F 3 ] 3– Also holds true for square planar complexes MX 2 Y 2
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Naming Coordination Compounds A complex is a substance in which a metal atom or ion is associated with a group of neutral molecules or anions called ligands . Coordination compounds are neutral substances (i.e., uncharged) in which at least one ion is present as a complex. A. To name a coordination compound, no matter whether the complex ion is the cation or the anion, always name the cation before the anion . (This is just like naming an ionic compound.) B . In naming the complex ion: I.Name the ligands first, in alphabetical order, then the metal atom or ion . Note: The metal atom or ion is written before the ligands in the chemical formula . 2. The names of some common ligands are listed in Table 1.
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Table 1. Names of Some Common Ligands Anionic Ligands Names Neutral Ligands Names Br - bromo NH 3 ammine F - fluoro H 2 O aqua O 2- oxo NO nitrosyl OH - hydroxo CO carbonyl CN - cyano O 2 dioxygen C 2 O 4 2- oxalato N 2 dinitrogen CO 3 2- carbonato C 5 H 5 N pyridine CH 3 COO - acetato H 2 NCH 2 CH 2 NH 2 ethylenediamine
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More Nomenclature 3. Greek prefixes are used to designate the number of each type of ligand in the complex ion, e.g. di-, tri- and tetra-. If the ligand already contains a Greek prefix (e.g. ethylene di amine) or if it is polydentate ligands (ie. can attach at more than one binding site) the prefixes bis-, tris-, tetrakis-, pentakis-, are used instead. The numerical prefixes are listed in Table 2. Table 2. Numerical Prefixes Number Prefix Number Prefix Number Prefix 1 mono 5 penta (pentakis) 9 nona (ennea) 2 di (bis) 6 hexa (hexakis) 10 deca 3 tri (tris) 7 hepta 11 undeca 4 tetra (tetrakis) 8 octa 12 dodeca
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More nomenclature 4 . After naming the ligands, name the central metal. If the complex ion is a cation, the metal is named same as the element. For example, Co in a complex
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lecture 14 - Lecture 14 - Organometallic Ligands and...

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