1 / 4

Lecture 31 Structure and reactivity of organometallic compounds 1) Bonding and reactivity of transition metal carbonyl

Lecture 31 Structure and reactivity of organometallic compounds 1) Bonding and reactivity of transition metal carbonyl complexes.

bozica
Télécharger la présentation

Lecture 31 Structure and reactivity of organometallic compounds 1) Bonding and reactivity of transition metal carbonyl

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 31 Structure and reactivity of organometallic compounds 1) Bonding and reactivity of transition metal carbonyl complexes • Transition metal carbonyl complexes (metal carbonyls) are among the most well studies organometallic compounds (compounds with M-C bonds). Almost all transition metals form carbonyls. Many of them comply with the 18 electron rule. V(CO)6, Cr(CO)6, Mn2(CO)10, Fe(CO)5, Co2(CO)8, Ni(CO)4 • Carbonyl ligand is considered as a week 2-electron donor (s-donor) and very strong p-acceptor. • Because of the p-acceptor ability of CO a number of stable anionic metal carbonyls exists: Ti(CO)62-, V(CO)6-, Cr(CO)42-, Mn(CO)5-, Fe(CO)42-, Co(CO)4- • Some of them can be protonated to form metal carbonyl hydrides (HCo(CO)4, H2Fe(CO)4, HMn(CO)5 etc.) which often behave as strong protic acids in aqueous solutions. • Since CO is a weak s-donor, cationic metal carbonyls are rare and very electrophilic: Mn(CO)6+, Fe(CO)62+, Co(CO)5+, Ir(CO)63+, Hg(CO)22+ • There is a variety of polynuclear cluster carbonyl compounds containing M-M bonds. Analysis of the structure of CO helps understand the structure and reactivity of metal carbonyls

  2. 2) MO diagram of carbon(II) oxide CO (C∞v) HOMO LUMO 5s 4s

  3. 3) Bonding and IR spectroscopy of transition metal carbonyls • Electrons of HOMO of CO ligand are donated to an empty orbital of the metal (M-C s-bonding) • Electrons from one of the filled d-orbitals of the metal are back-donated to the LUMO of CO (M-C p-backbonding) • A good measure of the balance of the s-donation and p-back-donation is the IR stretching frequency of coordinated CO. • In free CO, n(CO)=2143 cm‑1 ; l(C-O) = 1.128Å • In terminal carbonylsn(CO) ranges from 1750 to 2278 cm-1 and l(C-O) from 1.12 to 1.18 Å C O C O

  4. 4) Coordination can make CO electron-poor or electron-rich • Donation to the metal or back-bonding: what dominates? The p-backbonding between CO and a very electron-rich metal center makes the ligand also electron-rich: • Vice versa, at electron-poor metal centers CO is electron-poor: or: Co2(CO)8 + NaOH NaCo(CO)4 + Na2CO3

More Related