Organokovinska kemija: Difference between revisions

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Večina organokovinskih spojin je trdnih pri sobni temperaturi, vendar so nekateri tekoči (npr.[[Wikipedia: Methylcyclopentadienyl manganese tricarbonyl|metilciklopentadienil mangan trikarbonil]] ali celo [[Wikipedia: Volatility (chemistry)|hlapni]] ali celo hlapni [[Wikipedia: Nickel tetracarbonyl|nikljev tetrakarbonil]].<ref>{{sfn|Crabtree|2009|p={{pn|date=October 2021}}}}</ref> Veliko organokovinskih spojin je [[Wikipedia: Air sensitivity|občutljivih na zrak]] (reagirajo s kisikom in vlago), zato se z njimi dela v [[Wikipedia: Inert Gas|inertni atmosferi]].<ref>{{sfn|Crabtree|2009|p={{pn|date=October 2021}}}}</ref> Nekatere organokovinske spojine, kot je [[Wikipedia: Triethylaluminium| trietilaluminij]] so [[Wikipedia: Pyrophoricity|piroforne]], kar pomeni, da pri njih lahko pride do [[Wikipedia: Combustion|vžiga]] že ob stiku z zrakom.<ref>{{Cite web|last=|first=|date=2016-05-24|title=Triethylaluminium - SDS|url=https://www.chemblink.com/MSDS/MSDSFiles/97-93-8_Sigma-Aldrich.pdf|url-status=live|archive-url=|archive-date=|access-date=2021-01-03|website=chemBlink}}</ref>
Večina organokovinskih spojin je trdnih pri sobni temperaturi, vendar so nekateri tekoči (npr.[[Wikipedia: Methylcyclopentadienyl manganese tricarbonyl|metilciklopentadienil mangan trikarbonil]] ali celo [[Wikipedia: Volatility (chemistry)|hlapni]] ali celo hlapni [[Wikipedia: Nickel tetracarbonyl|nikljev tetrakarbonil]].<ref>{{sfn|Crabtree|2009|p={{pn|date=October 2021}}}}</ref> Veliko organokovinskih spojin je [[Wikipedia: Air sensitivity|občutljivih na zrak]] (reagirajo s kisikom in vlago), zato se z njimi dela v [[Wikipedia: Inert Gas|inertni atmosferi]].<ref>{{sfn|Crabtree|2009|p={{pn|date=October 2021}}}}</ref> Nekatere organokovinske spojine, kot je [[Wikipedia: Triethylaluminium| trietilaluminij]] so [[Wikipedia: Pyrophoricity|piroforne]], kar pomeni, da pri njih lahko pride do [[Wikipedia: Combustion|vžiga]] že ob stiku z zrakom.<ref>{{Cite web|last=|first=|date=2016-05-24|title=Triethylaluminium - SDS|url=https://www.chemblink.com/MSDS/MSDSFiles/97-93-8_Sigma-Aldrich.pdf|url-status=live|archive-url=|archive-date=|access-date=2021-01-03|website=chemBlink}}</ref>


==Concepts and techniques==
==Ideje in tehnike==
As in other areas of chemistry, [[electron counting]] is useful for organizing organometallic chemistry. The [[18-electron rule]] is helpful in predicting the stabilities of organometallic complexes, for example [[Metal carbonyl|metal carbonyls]] and [[Transition metal hydride|metal hydrides]]. The 18e rule has two representative electron counting models, ionic and neutral (also known as covalent) ligand models, respectively.<ref name=":02">{{Cite book |last=Crabtree |first=Robert H. |url=https://www.worldcat.org/oclc/863383849 |title=The organometallic chemistry of the transition metals |date=2014 |isbn=978-1-118-78824-0 |edition=6 |location=Hoboken, New Jersey |pages=43, 44, 205 |oclc=863383849}}</ref> The hapticity of a metal-ligand complex, can influence the electron count.<ref name=":02" /> [[Hapticity]] (η, lowercase Greek eta), describes the number of contiguous ligands coordinated to a metal.<ref name=":02" /> For example, [[ferrocene]], [(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>Fe], has two [[Cyclopentadienyl ligand|cyclopentadienyl ligands]] giving a hapticity of 5, where all five carbon atoms of the C<sub>5</sub>H<sub>5</sub> ligand bond equally and contribute one electron to the iron center. Ligands that bind non-contiguous atoms are denoted the Greek letter kappa, κ.<ref name=":02" /> [[Chelation|Chelating]] κ2-acetate is an example. The [[covalent bond classification method]] identifies three classes of ligands, X,L, and Z; which are based on the electron donating interactions of the ligand. Many organometallic compounds do not follow the 18e rule. The metal atoms in organometallic compounds are frequently described by their [[d electron count]] and [[oxidation state]]. These concepts can be used to help predict their reactivity and preferred [[Molecular geometry|geometry]]. Chemical bonding and reactivity in organometallic compounds is often discussed from the perspective of the [[isolobal principle]].  
As in other areas of chemistry, [[electron counting]] is useful for organizing organometallic chemistry. The [[18-electron rule]] is helpful in predicting the stabilities of organometallic complexes, for example [[Metal carbonyl|metal carbonyls]] and [[Transition metal hydride|metal hydrides]]. The 18e rule has two representative electron counting models, ionic and neutral (also known as covalent) ligand models, respectively.<ref name=":02">{{Cite book |last=Crabtree |first=Robert H. |url=https://www.worldcat.org/oclc/863383849 |title=The organometallic chemistry of the transition metals |date=2014 |isbn=978-1-118-78824-0 |edition=6 |location=Hoboken, New Jersey |pages=43, 44, 205 |oclc=863383849}}</ref> The hapticity of a metal-ligand complex, can influence the electron count.<ref name=":02" /> [[Hapticity]] (η, lowercase Greek eta), describes the number of contiguous ligands coordinated to a metal.<ref name=":02" /> For example, [[ferrocene]], [(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>Fe], has two [[Cyclopentadienyl ligand|cyclopentadienyl ligands]] giving a hapticity of 5, where all five carbon atoms of the C<sub>5</sub>H<sub>5</sub> ligand bond equally and contribute one electron to the iron center. Ligands that bind non-contiguous atoms are denoted the Greek letter kappa, κ.<ref name=":02" /> [[Chelation|Chelating]] κ2-acetate is an example. The [[covalent bond classification method]] identifies three classes of ligands, X,L, and Z; which are based on the electron donating interactions of the ligand. Many organometallic compounds do not follow the 18e rule. The metal atoms in organometallic compounds are frequently described by their [[d electron count]] and [[oxidation state]]. These concepts can be used to help predict their reactivity and preferred [[Molecular geometry|geometry]]. Chemical bonding and reactivity in organometallic compounds is often discussed from the perspective of the [[isolobal principle]].  



Revision as of 14:18, 1 January 2023

n-butillitij, organokovinska spojina. Štirje atomi litija (v vijolični barvi) tvorijo tetraeder s štirimi butilnimi skupinami pritrjenimi na ploskve (ogljik je črn, vodik je bel).

Organokovinska kemija se ukvarja s preučevanjem organokovinskih spojin. To so kemijske spojine, ki vsebujejo vsaj eno kemijsko vez med ogljikovim atomom organske spojine in kovino. Ta kovina je lahko alkalijska, zemljoalkalijska ali prehodna, včasih je lahko tudi polkovina (npr. bor, silicij in selen). Template:Sfn<ref name=":0">Template:GoldBookRef</ref> Med organokovinske spojine prav tako spadajo vezi z organskimi fragmenti ali molekulami, vezi z "anorganskim" ogljikom, kot je ogljikov monoksid (kovinski karbonili), cianid ali karbid. Kljub temu, da nekatere sorodne spojine, kot so hidridi prehodnih kovin in kovinsko-fosfinski kompleksi strogo gledano niso nujno organokovinski, so le-ti pogosto vključeni v razprave. Soroden, vendar ločen izraz "kovinoorganska spojina" se nanaša na spojine, ki vsebujejo kovino in nimajo neposrednih vezi kovina-ogljik, vendar vsebujejo organske ligande. Reprezentativni predstavniki tega razreda so kovinski β-diketonati, alkoksidi, dialkilamidi in kovino-fosfinski kompleksi. Področje organokovinske kemije združuje vidike tradicionalne anorganske in organske kemije.Template:Sfn


Organokovinske spojine se široko uporabljajo tako stehiometrično v raziskovalnih in industrijskih kemijskih reakcijah, kot tudi v vlogi katalizatorjev za povečanje hitrosti nekaterih reakcij (npr. pri uporabi [[Wikipedia:homogeneous catalysis|homogene katalize), kjer med ciljne molekule spadajo polimeri, farmacevtski izdelki in številne druge vrste praktičnih produktov.

Organokovinske spojine

File:Magnesium bis-cyclopentadienyl bottle.jpg
Nerjaveča steklenica, ki vsebuje MgCp2 (magnezijev bis- ciklopentadienil), nevarno snov kot večina drugih organokovinskih spojin. Besedilo navaja "Zvezni zakon prepoveduje prevoz, če se ponovno napolni, in pri tem je denarna kazen do 25.000 dolarjev in 5 let zaporne kazni."

Organokovinske spojine se razlikujejo po predponi "organo-" (npr. organopaladijeve spojine) in vključujejo vse spojine, ki vsebujejo vez med atomom kovine in atomom ogljika organilne spojine.<ref name=":0" /> Poleg tradicionalnih kovin ( alkalijske kovine, zemljoalkalijske kovine, prehodne kovine in po-prehodne kovine) velja, da lantanoidi, aktinoidi, polkovine in elementi, kot so bor, silicij, arzen ter selen, tvorijo organokovinske spojine. <ref name=":0" /> Primeri organokovinskih spojin vključujejo Gilmanove reagente, ki vsebujejo litij in baker, ter Grignardove reagente, ki vsebujejo magnezij. Tetrakarbonil nikelj in ferocen sta primera organokovinskih spojin, ki vsebujeta prehodne kovine. Drugi primeri organokovinskih spojin vključujejo organolitijeve spojine, kot je n-butillitij (n-BuLi), organocinkove spojine, kot je dietilcink (Et2Zn), organokositrove spojine, kot je tributilkositrov hidrid (Bu3SnH), organoborove spojine, kot je [[Wikipedia:triethylborane|trietilboran] (Et3B), in organoaluminijeve spojine kot je trimetilaluminij (Me3Al).

Naravni organokovinski kompleks je metilkobalamin (oblika Vitamin B12), ki vsebuje kobalt-metilno vez. O tem kompleksu se skupaj z drugimi biološko pomembnimi kompleksi pogosto razpravlja na področju bioorganokovinske kemije.Template:Sfn

Razlika od koordinacijskih spojin z organskimi ligandi

Veliko kompleksov vsebuje koordinacijsko vez med kovino in organskimi ligandi. Komplekse, kjer se organski ligand veže na heteroatom kot sta kisik ali dušik, uvrščamo med koordinacijske spojine (npr. heme A in Fe(acac)3). V primeru, da kateri izmed ligandov tvori vez kovina-ogljik (M-C), potem tak kompleks uvrščamo med organokovinske spojine. Čeprav IUPAC uradno še ni definiral terminologije, nekateri kemiki uporabljajo pojem “organokovinski”, da opišejo katerokoli koordinacijsko spojino, ki vsebuje organski ligand, ne glede na odsotnost direktne vezi M-C.<ref>Template:Cite book</ref>

Položaj spojin v katerih ima kanonični anion negativen naboj, ki se porazdeli med (delokaliziran) ogljikov atom in atom, ki je bolj elektronegativen od ogljika (npr. enolati) ), se lahko razlikuje glede na lastnosti anionskega dela, kovinskega iona ali medija. V primeru, da direktna vez ogljik-kovina v spojini ni dokazana, se te spojine ne uvršča med organokovinske.<ref name=":0" /> Kot primer, litijevi enolati pogosto vsebujejo le Li-O vezi in niso organokovinski, medtem ko cinkovi enolati (Reformatsky reagenti) vsebujejo tako Zn-O vezi kot tudi Zn-C vezi in jih, zato uvrščamo med organokovinske.

Struktura in lastnosti

Vez kovina-ogljik v organokovinskih spojinah je močno kovaletna.Template:Sfn . Za močno elektropozitivne elemente, kot sta litij in natrij, ima ogljikov ligand karbanionski značaj značaj, vendar so prosti ogljikovi anioni zelo redki, takšen primer je cianid cianid.

Večina organokovinskih spojin je trdnih pri sobni temperaturi, vendar so nekateri tekoči (npr.metilciklopentadienil mangan trikarbonil ali celo hlapni ali celo hlapni nikljev tetrakarbonil.<ref>Template:Sfn</ref> Veliko organokovinskih spojin je občutljivih na zrak (reagirajo s kisikom in vlago), zato se z njimi dela v inertni atmosferi.<ref>Template:Sfn</ref> Nekatere organokovinske spojine, kot je trietilaluminij so piroforne, kar pomeni, da pri njih lahko pride do vžiga že ob stiku z zrakom.<ref></ref>

Ideje in tehnike

As in other areas of chemistry, electron counting is useful for organizing organometallic chemistry. The 18-electron rule is helpful in predicting the stabilities of organometallic complexes, for example metal carbonyls and metal hydrides. The 18e rule has two representative electron counting models, ionic and neutral (also known as covalent) ligand models, respectively.<ref name=":02">Template:Cite book</ref> The hapticity of a metal-ligand complex, can influence the electron count.<ref name=":02" /> Hapticity (η, lowercase Greek eta), describes the number of contiguous ligands coordinated to a metal.<ref name=":02" /> For example, ferrocene, [(η5-C5H5)2Fe], has two cyclopentadienyl ligands giving a hapticity of 5, where all five carbon atoms of the C5H5 ligand bond equally and contribute one electron to the iron center. Ligands that bind non-contiguous atoms are denoted the Greek letter kappa, κ.<ref name=":02" /> Chelating κ2-acetate is an example. The covalent bond classification method identifies three classes of ligands, X,L, and Z; which are based on the electron donating interactions of the ligand. Many organometallic compounds do not follow the 18e rule. The metal atoms in organometallic compounds are frequently described by their d electron count and oxidation state. These concepts can be used to help predict their reactivity and preferred geometry. Chemical bonding and reactivity in organometallic compounds is often discussed from the perspective of the isolobal principle.

A wide variety of physical techniques are used to determine the structure, composition, and properties of organometallic compounds. X-ray diffraction is a particularly important technique that can locate the positions of atoms within a solid compound, providing a detailed description of its structure.Template:SfnTemplate:Sfn Other techniques like infrared spectroscopy and nuclear magnetic resonance spectroscopy are also frequently used to obtain information on the structure and bonding of organometallic compounds.Template:SfnTemplate:Sfn Ultraviolet-visible spectroscopy is a common technique used to obtain information on the electronic structure of organometallic compounds. It is also used monitor the progress of organometallic reactions, as well as determine their kinetics.Template:Sfn The dynamics of organometallic compounds can be studied using dynamic NMR spectroscopy.Template:Sfn Other notable techniques include X-ray absorption spectroscopy,<ref>Template:Cite journal</ref> electron paramagnetic resonance spectroscopy, and elemental analysis.Template:SfnTemplate:Sfn

Due to their high reactivity towards oxygen and moisture, organometallic compounds often must be handled using air-free techniques. Air-free handling of organometallic compounds typically requires the use of laboratory apparatuses such as a glovebox or Schlenk line.Template:Sfn

History

Early developments in organometallic chemistry include Louis Claude Cadet's synthesis of methyl arsenic compounds related to cacodyl, William Christopher Zeise's<ref>Template:Cite journal</ref> platinum-ethylene complex,<ref>Template:Cite journal</ref> Edward Frankland's discovery of diethyl- and dimethylzinc, Ludwig Mond's discovery of Ni(CO)4,Template:Sfn and Victor Grignard's organomagnesium compounds. (Though not always acknowledged as an organometallic compound, Prussian blue, a mixed-valence iron-cyanide complex, was first prepared in 1706 by paint maker Johann Jacob Diesbach as the first coordination polymer and synthetic material containing a metal-carbon bond.Template:Sfn) The abundant and diverse products from coal and petroleum led to Ziegler–Natta, Fischer–Tropsch, hydroformylation catalysis which employ CO, H2, and alkenes as feedstocks and ligands.

Recognition of organometallic chemistry as a distinct subfield culminated in the Nobel Prizes to Ernst Fischer and Geoffrey Wilkinson for work on metallocenes. In 2005, Yves Chauvin, Robert H. Grubbs and Richard R. Schrock shared the Nobel Prize for metal-catalyzed olefin metathesis.<ref>Template:Cite journal</ref>

Organometallic chemistry timeline

Obseg

Podpodročja organokovinske kemije obsegajo:

Industrial applications

Organometallic compounds find wide use in commercial reactions, both as homogenous catalysts and as stoichiometric reagents. For instance, organolithium, organomagnesium, and organoaluminium compounds, examples of which are highly basic and highly reducing, are useful stoichiometrically but also catalyze many polymerization reactions.Template:Sfn

Almost all processes involving carbon monoxide rely on catalysts, notable examples being described as carbonylations.<ref name=Ullmann>Template:Ullmann</ref> The production of acetic acid from methanol and carbon monoxide is catalyzed via metal carbonyl complexes in the Monsanto process and Cativa process. Most synthetic aldehydes are produced via hydroformylation. The bulk of the synthetic alcohols, at least those larger than ethanol, are produced by hydrogenation of hydroformylation-derived aldehydes. Similarly, the Wacker process is used in the oxidation of ethylene to acetaldehyde.Template:Sfn

File:ConstrainedGeomCmpx.png
A constrained geometry organotitanium complex is a precatalyst for olefin polymerization.

Almost all industrial processes involving alkene-derived polymers rely on organometallic catalysts. The world's polyethylene and polypropylene are produced via both heterogeneously via Ziegler–Natta catalysis and homogeneously, e.g., via constrained geometry catalysts.<ref>Template:Cite journal</ref>

Most processes involving hydrogen rely on metal-based catalysts. Whereas bulk hydrogenations (e.g., margarine production) rely on heterogeneous catalysts, for the production of fine chemicals such hydrogenations rely on soluble (homogenous) organometallic complexes or involve organometallic intermediates.<ref name=Rylander>Template:Ullmann</ref> Organometallic complexes allow these hydrogenations to be effected asymmetrically.

Many semiconductors are produced from trimethylgallium, trimethylindium, trimethylaluminium, and trimethylantimony. These volatile compounds are decomposed along with ammonia, arsine, phosphine and related hydrides on a heated substrate via metalorganic vapor phase epitaxy (MOVPE) process in the production of light-emitting diodes (LEDs).

Organokovinske reakcije

Organokovinske spojine so podvržene številnim pomembnim reakcijam:


Organokovinski kompleksi olajšajo sintezo mnogih organskih spojin. Metateza sigma vezi je način tvorjenja novih ogljik-ogljik sigma vezi. Običajno se uporablja pri kompleksih prehodnih kovin leve polovice d-bloka, ki so v svojem najvišjem oksidacijskem stanju.<ref>Template:Cite journal</ref> Uporaba prehodnih kovin, ki so v najvišjih možnih oksidacijskih stanjih prepreči, da potečejo druge reakcije, kot je recimo oksidativna adicija. Poleg metateze sigma vezi, se metateza alkenov oz. olefinska metateza uporablja za tvorbo raznih ogljik-ogljik pi vezi. Nobena od teh metatez ne spremeni oksidacijskega stanja kovine.<ref></ref><ref></ref> Za tvorbo novih ogljik-ogljik vezi se uporabljajo tudi številne druge metode, kot sta beta-hidrid eliminacija in reakcija vstavljanja (ang. insertion reaction).

Kataliza

Organokovinski kompleksi se običajno uporabljajo za katalize. Glavni industrijski procesi vključujejohidrogenacijo, hidrosililacijo, hidrocianacijo, olefinsko metatezo, alkensko polimerizacijo, alkensko oligomerizacijo, hidrokarboksilacijo, karbonilacijo metanola in hidroformilacijo.Template:Sfn Organokovinski intermediati so tudi vključeni v številne heterogene katalize, analogne tem, ki so zgoraj naštete. Prav tako predvidevajo, da so uporabni za Fischer-Tropschev proces.

Organokovinski kompleksi se pogosto uporabljajo pri finih kemijskih sintezah v mikromerilu, posebej v "cross-coupling" reakcijahs<ref>Template:Cite journal</ref> , ki tvorijo vezi ogljik-ogljik, npr. Suzuki-Miyaura spajanje,<ref>Template:Cite journal</ref> Buchwald-Hartwigova aminacija za tvorbo aril aminov iz aril halidov,<ref>Template:Cite journal</ref> and Sonogashira spajanje, itd.

Tveganje za okolje

File:Roxarsone.png
Roxarson je organoarzenova spojine, ki se uporablja kot krma za živali.

V okolju najdemo organokovinske spojine, ki so naravne in nevarne za okolje. Nekatere organokovinske spojine v okolju so posledica človeške rabe. To so na primer organosvinčeve in organoživosrebrove spojine, ki so toksične. Tetraetilsvinec je bil pripravljen kot dodatek k bencinu, a se zaradi svinčeve toksičnosti ne uporablja več. Njegov nadomestek so druge organokovinske spojine, kot je npr. ferocen in metilciklopentadienil manganov trikarbonil (MMT).<ref name="Seyferth">Template:Cite journal</ref> Organoarzenova spojina roxarson je sporen dodatek h krmi za živali. Leta 2006 bi se ga naj samo v ZDA proizvedlo približno milijon kilogramov.<ref>Template:Cite journal</ref> Organokositrove spojine so se široko uporabljale v barvah proti obraščanju, ampak so jih zaradi tveganja za okolje prepovedali.<ref>Template:Cite journal</ref>

See also

References

<references/>

Sources

External links

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