Metal carbido complex#carbido cluster
{{Short description|Coordination complex that contains a carbon atom as a ligand}}
A metal carbido complex is a coordination complex that contains a carbon atom as a ligand. They are analogous to metal nitrido complexes. Carbido complexes are a molecular subclass of carbides, which are prevalent in organometallic and inorganic chemistry. Carbido complexes represent models for intermediates in Fischer–Tropsch synthesis, olefin metathesis, and related catalytic industrial processes.{{Cite journal |last1=Reinholdt |first1=Anders |last2=Bendix |first2=Jesper |date=2022-01-12 |title=Transition Metal Carbide Complexes |url=https://pubs.acs.org/doi/10.1021/acs.chemrev.1c00404 |journal=Chemical Reviews |language=en |volume=122 |issue=1 |pages=830–902 |doi=10.1021/acs.chemrev.1c00404 |pmid=34797626 |s2cid=244428940 |issn=0009-2665}} Ruthenium-based carbido complexes are by far the most synthesized and characterized to date. Although, complexes containing chromium, gold, iron, nickel, molybdenum, osmium, rhenium, and tungsten cores are also known. Mixed-metal carbides are also known.{{Cite journal |last1=Zhao |first1=Lili |last2=Chai |first2=Chaoqun |last3=Petz |first3=Wolfgang |last4=Frenking |first4=Gernot |date=2020-10-26 |title=Carbones and Carbon Atom as Ligands in Transition Metal Complexes |journal=Molecules |language=en |volume=25 |issue=21 |page=4943 |doi=10.3390/molecules25214943 |issn=1420-3049 |pmc=7663554 |pmid=33114580|doi-access=free }}{{Cite journal |last1=Maitlis |first1=Peter M. |last2=Quyoum |first2=Ruhksana |last3=Long |first3=Helen C. |last4=Turner |first4=Michael L. |date=October 1999 |title=Towards a chemical understanding of the Fischer–Tropsch reaction: alkene formation |url=https://linkinghub.elsevier.com/retrieve/pii/S0926860X99001556 |journal=Applied Catalysis A: General |language=en |volume=186 |issue=1–2 |pages=363–374 |doi=10.1016/S0926-860X(99)00155-6}}
Carbido clusters
File:Fe5C(CO)15.png5C(CO)15}}.{{cite journal|title=The Preparation, Properties and Structure of the Iron Carbonyl Carbide Fe5(CO)15C|author=Emile H. Braye |author2=Lawrence F. Dahl |author3=Walter. Hubel |author4=Dale L. Wampler |journal=J. Am. Chem. Soc.|year=1962|volume=84|issue=24|pages=4633–4639|doi=10.1021/ja00883a004}}]]
Most molecular carbido complexes are clusters, usually featuring carbide as a six-fold bridging ligand. Examples include [
The iron carbonyl carbides exist not only in the encapsulated carbon ([
Bimetallic and exotic clusters such as metal carbide clusterfullerenes (MCCF's) have also been able to be prepared.{{Citation |last1=Hill |first1=Ernestine W. |title=Tetrairon Carbido Carbonyl Clusters |date=2007-01-05 |url=https://onlinelibrary.wiley.com/doi/10.1002/9780470132586.ch36 |work=Inorganic Syntheses |pages=182–188 |editor-last=Ginsberg |editor-first=Alvin P. |access-date=2023-03-25 |place=Hoboken, NJ, USA |publisher=John Wiley & Sons, Inc. |doi=10.1002/9780470132586.ch36 |isbn=978-0-470-13258-6 |last2=Bradley |first2=John S. |last3=Cassidy |first3=Juanita |last4=Whitmire |first4=Kenton H.}}{{Cite journal |last1=Saha |first1=Sumit |last2=Zhu |first2=Lei |last3=Captain |first3=Burjor |date=2013-03-04 |title=Bimetallic Octahedral Ruthenium–Nickel Carbido Cluster Complexes. Synthesis and Structural Characterization |url=https://pubs.acs.org/doi/10.1021/ic302470w |journal=Inorganic Chemistry |language=en |volume=52 |issue=5 |pages=2526–2532 |doi=10.1021/ic302470w |pmid=23421564 |issn=0020-1669}}Image:Au6C(PPh3)6.png6C(PPh3)6](2+)}}, containing a carbon-gold core.]]
Doubly bridging carbide ligands
Bridging carbido ligands can be subdivided into three classes:
- cumulenic {{chem2|L_{n}M\dC\dM'L_{n}|}},
- metallocarbyne {{chem2|L_{n}M\tC\sM'L_{n}|}}, and
- polar covalent {{chem2|L_{n}M\tC:→M'L_{n}|}}.{{cite journal|last=Hill|first=Anthony|author2=Sharma, Willis|title=Heterodinuclear Bridging Carbido and Phosphocarbyne Complexes|journal=Organometallics|year=2012|volume=31|pages=2538–2542|doi=10.1021/om201057c|issue=7}}
Cumulenic compounds generally bridge two metal atoms of the same element and are symmetrical.{{Cite journal |last=Mansuy |first=D. |date=1980-01-01 |title=New iron-porphyrin complexes with metal-carbon bond - biological implications |url=https://www.degruyter.com/document/doi/10.1351/pac198052030681/html |journal=Pure and Applied Chemistry |language=en |volume=52 |issue=3 |pages=681–690 |doi=10.1351/pac198052030681 |s2cid=98036930 |issn=1365-3075|doi-access=free }} However, there are exceptions to this.{{Cite journal |last1=Solari |first1=Euro |last2=Antonijevic |first2=Sasa |last3=Gauthier |first3=Sébastien |last4=Scopelliti |first4=Rosario |last5=Severin |first5=Kay |date=January 2007 |title=Formation of a Ruthenium μ‐Carbide Complex with Acetylene as the Carbon Source |url=https://onlinelibrary.wiley.com/doi/10.1002/ejic.200600991 |journal=European Journal of Inorganic Chemistry |language=en |volume=2007 |issue=3 |pages=367–371 |doi=10.1002/ejic.200600991 |issn=1434-1948}}
In contrast, metallocarbyne compounds are generally constitutionally heterobimetallic, with complexes containing varying coordination geometries being common. These moieties have been able to serve as precursors to elaborate molecular scaffolds such as porphyrin derivatives.{{Cite journal |last1=Frogley |first1=Benjamin J. |last2=Hill |first2=Anthony F. |date=2020 |title=Carbyne decorated porphyrins |url=http://xlink.rsc.org/?DOI=D0DT02809F |journal=Dalton Transactions |language=en |volume=49 |issue=35 |pages=12390–12400 |doi=10.1039/D0DT02809F |pmid=32852027 |hdl=1885/217011 |s2cid=221347588 |issn=1477-9226|hdl-access=free }}
The polar covalent class is distinguished from metallocarbynes by a very fine line. This carbide-metal interaction is considered labile in nature. Carbon here can be understood fundamentally as being similar to CO ligands, that is, dative (L-type). Although, this class has also been described to some extent being analogous to the behavior of Lewis acid adduct-forming terminal nitrido and oxo complexes e.g. (PMe2Ph)2Cl-Re≡N-BCl3 and tBu(CH2)3(Br)W=O-AlBr3.{{Cite journal |last1=Hejl |first1=Andrew |last2=Trnka |first2=Tina M. |last3=Day |first3=Michael W. |last4=Grubbs |first4=Robert H. |date=2002 |title=Terminal ruthenium carbido complexes as σ-donor ligands |url=http://xlink.rsc.org/?DOI=B207903H |journal=Chem. Commun. |language=en |issue=21 |pages=2524–2525 |doi=10.1039/B207903H |issn=1359-7345}}
Terminal carbides
In rare cases, carbido ligands are terminal. One example is {{chem2|RuC(PCy3)2Cl2}} with a Ru-C distance of 163 pm, typical for a triple bond.{{cite journal | last1 = Carlson | first1 = Robert G. | last2 = Gile | first2 = Melanie A. | last3 = Heppert | first3 = Joseph A. | last4 = Mason | first4 = Mark H. | last5 = Powell | first5 = Douglas R. | last6 = Vander Velde | first6 = David | last7 = Vilain | first7 = Joseph M. | year = 2002 | title = The Metathesis-Facilitated Synthesis of Terminal Ruthenium Carbide Complexes: A Unique Carbon Atom Transfer Reaction | journal = Journal of the American Chemical Society | volume = 124 | issue = 8| pages = 1580–1581 | doi = 10.1021/ja017088g | pmid = 11853424 }} The complex can be obtained by metathesis of vinyl acetate to give {{chem2|[Ru(CH\-p\-C6H4Me)(PCy3)2Cl2]}} results in a metastable {{chem2|Ru(Cl2)(PCy3)2C2HOAc}} complex, which eliminates acetic acid.{{cite journal|last=Caskey|first=Stephen|title=Two General Routes to Terminal Carbido Complexes|journal=J. Am. Chem. Soc.|date=11 November 2005|volume=127 | issue = 48| doi = 10.1021/ja0453735|pmid=16316197|pages=16750–16751}}
Such transition metal, one coordinate-carbon bonded complexes are comparable to carbon monoxide, cyanide, and isonitrile analogues. These carbides can be used as synthons to access a wide range of carbyne complexes, the most notable being Fischer carbynes.{{Cite journal |last1=Enriquez |first1=Alejandro E. |last2=White |first2=Peter S. |last3=Templeton |first3=Joseph L. |date=2001-05-01 |title=Reactions of an Amphoteric Terminal Tungsten Methylidyne Complex |url=https://pubs.acs.org/doi/10.1021/ja0035001 |journal=Journal of the American Chemical Society |language=en |volume=123 |issue=21 |pages=4992–5002 |doi=10.1021/ja0035001 |pmid=11457327 |issn=0002-7863}} American chemist Christopher C. Cummins is one of the pioneers of this area.
Preparative routes and characterization
= Carbido clusters =
Synthesis of carbido clusters can be accomplished by hydrolysis, thermolysis of labile ligands, thermal rearrangements, and photolysis. Their synthesis has historically been crudely achieved by serendipitous chance following apparent random molecular organization. One example is the following reaction:
= Doubly bridging carbide ligands =
== Cumulenic ==
Synthetic routes to cumulenic carbido complexes can be efficient and lead to rapid, near quantitative product formation with simple purifications.{{Cite journal |last1=Solari |first1=Euro |last2=Antonijevic |first2=Sasa |last3=Gauthier |first3=Sébastien |last4=Scopelliti |first4=Rosario |last5=Severin |first5=Kay |date=January 2007 |title=Formation of a Ruthenium μ‐Carbide Complex with Acetylene as the Carbon Source |url=https://onlinelibrary.wiley.com/doi/10.1002/ejic.200600991 |journal=European Journal of Inorganic Chemistry |language=en |volume=2007 |issue=3 |pages=367–371 |doi=10.1002/ejic.200600991 |issn=1434-1948}} This dimerization involves the formation of a vinylidene from an alkyne. Mechanistically, there are various proposed pathways, starting with oxidative addition of the alkyne to the metal core, followed by either intramolecular 1,2-H shifts or intermolecular 1,3-H shifts.{{Cite journal |last1=Grotjahn |first1=Douglas B. |last2=Zeng |first2=Xi |last3=Cooksy |first3=Andrew L. |date=2006-03-01 |title=Alkyne-to-Vinylidene Transformation on trans -(Cl)Rh(phosphine) 2: Acceleration by a Heterocyclic Ligand and Absence of Bimolecular Mechanism |url=https://pubs.acs.org/doi/10.1021/ja058736p |journal=Journal of the American Chemical Society |language=en |volume=128 |issue=9 |pages=2798–2799 |doi=10.1021/ja058736p |issn=0002-7863}} For Ruthenium coordination complexes, bridging Ru-Cl bond lengths have been observed to lie in the range of 1.76-1.8 Å. Ru-C bonds can vary significantly as a result of trans effect phenomena which is caused by the respective ethylene and vinylidene ligands.
== Metallocarbyne ==
The appropriate halocarbyne precursors of choice can be reacted with organolithium reagents to afford the respective lithiocarbyne derivate by virtue of lithium/halogen exchange.{{Cite journal |last1=Jamison |first1=G. M. |last2=White |first2=P. S. |last3=Templeton |first3=J. L. |date=June 1991 |title=Synthesis of Group 6 (aryloxy)carbyne and phosphoniocarbyne complexes from chlorocarbyne precursors |url=https://pubs.acs.org/doi/abs/10.1021/om00052a048 |journal=Organometallics |language=en |volume=10 |issue=6 |pages=1954–1959 |doi=10.1021/om00052a048 |issn=0276-7333}} This species can serve as a lynchpin for subsequent carbide linkage with an additional metal complex. Phosphine-based analogues were first introduced by Templeton and co.{{Cite journal |last1=Jamison |first1=G. M. |last2=White |first2=P. S. |last3=Templeton |first3=J. L. |date=June 1991 |title=Synthesis of Group 6 (aryloxy)carbyne and phosphoniocarbyne complexes from chlorocarbyne precursors |url=https://pubs.acs.org/doi/abs/10.1021/om00052a048 |journal=Organometallics |language=en |volume=10 |issue=6 |pages=1954–1959 |doi=10.1021/om00052a048 |issn=0276-7333}} These types of complexes can be characterized crystallographically and are distinguishable by their Cs symmetry.
== Polar covalent ==
Addition of tricyclohexylphosphine to the carbene complex (PPh3)2(Cl)2Ru=C(CHCO2Me)2 results in olefin extrusion and yields an air stable anionic carbido complex. This species displaces a dimethyl sulfide ligand from PdCl2(SMe)2 to give the μ-carbido bimetallic complex (PCy3)2Cl2Ru≡C-PdCl2(SMe2). Spark towards a novel type of bonding was proposed following empirical observations wherein the carbido-palladium interaction could be readily disturbed. Reversible coordination ensues upon exposure of the bimetallic complex to carbon monoxide. Additionally, no coordination occurs if the anionic carbido complex contains bulky ligands such as H2IMes. This indicates that the thermodynamic sink towards making the C-M bond is not very favorable, suggesting a weak interaction. Although not intuitive, characterization of this type of bonding can be inferred if 13C NMR shifts are observed to be far downfield, and C-M bond lengths are similar to those of complexes proven to contain carbon-based σ-donor ligands such as [(Et2H2Im)PdCl(μ-Cl)]2.{{Cite journal |last1=Liu |first1=Shiuh-Tzung |last2=Hsieh |first2=Tung-Ying |last3=Lee |first3=Gene-Hsiang |last4=Peng |first4=Shie-Ming |date=1998-03-01 |title=Carbene Transfer between Transition-Metal Ions |url=https://pubs.acs.org/doi/10.1021/om9709897 |journal=Organometallics |language=en |volume=17 |issue=6 |pages=993–995 |doi=10.1021/om9709897 |issn=0276-7333}}
= Terminal carbido ligands =
Metathesis using Grubbs-type alkylidene complexes can be used to synthesize terminal carbido-containing complexes. One example is RuC(PCy3)2Cl2 with a Ru-C distance of 163 pm, typical for a triple bond.{{Cite journal |last1=Liu |first1=Shiuh-Tzung |last2=Hsieh |first2=Tung-Ying |last3=Lee |first3=Gene-Hsiang |last4=Peng |first4=Shie-Ming |date=1998-03-01 |title=Carbene Transfer between Transition-Metal Ions |url=https://pubs.acs.org/doi/10.1021/om9709897 |journal=Organometallics |language=en |volume=17 |issue=6 |pages=993–995 |doi=10.1021/om9709897 |issn=0276-7333}} The complex can be obtained by metathesis of vinyl acetate to give [Ru(CH-p-C6H4Me)(PCy3)2Cl2] results in a metastable Ru(Cl2)(PCy3)2C2HOAc complex, which eliminates acetic acid.{{Cite journal |last1=Liu |first1=Shiuh-Tzung |last2=Hsieh |first2=Tung-Ying |last3=Lee |first3=Gene-Hsiang |last4=Peng |first4=Shie-Ming |date=1998-03-01 |title=Carbene Transfer between Transition-Metal Ions |url=https://pubs.acs.org/doi/10.1021/om9709897 |journal=Organometallics |language=en |volume=17 |issue=6 |pages=993–995 |doi=10.1021/om9709897 |issn=0276-7333}}
The "naked" carbido ligand is weakly basic, forming complexes with other metal centers. The C-M bond is typically found to be around 1.65 Å. The 13C NMR resonance values for the carbido carbons vary widely, but range from δ211-406.{{Cite journal |last1=Hejl |first1=Andrew |last2=Trnka |first2=Tina M. |last3=Day |first3=Michael W. |last4=Grubbs |first4=Robert H. |date=2002 |title=Terminal ruthenium carbido complexes as σ-donor ligands |url=http://xlink.rsc.org/?DOI=B207903H |journal=Chem. Commun. |language=en |issue=21 |pages=2524–2525 |doi=10.1039/B207903H |issn=1359-7345}} Another example of a terminal carbido complex is Li[MoC(NR2)3] (Mo-C distance of 172 pm), which forms upon deprotonation of the respective methylidyne precursor.{{Cite journal |last1=C. Peters |first1=Jonas |last2=L. Odom |first2=Aaron |last3=C. Cummins |first3=Christopher |date=1997 |title=A terminal molybdenum carbide prepared by methylidyne deprotonation |url=http://xlink.rsc.org/?DOI=a704251e |journal=Chemical Communications |language=en |issue=20 |pages=1995–1996 |doi=10.1039/a704251e |issn=1359-7345}}
See also
- Metallocarbohedryne ("met-car"), a stable cluster with formula {{chem2|M8C12}} (M = Ti, Zr, V, etc.{{which|date=September 2022}})
References
{{Reflist}}{{Organometallics}}{{Coordination complexes}}