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|verifiedrevid = 406870808 |
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|ImageFileL1=Zirconocene-dichloride-2D-skeletal.png |
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|ImageFileL1=Zirconocene-dichloride-2D-skeletal.png |
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|ImageFileR1=Zirconocene-dichloride-from-xtal-3D-balls.png |
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|ImageFileR1=Zirconocene-dichloride-from-xtal-3D-balls.png |
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|Section1={{Chembox Identifiers |
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|Section1={{Chembox Identifiers |
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| CASNo_Ref = {{cascite|correct|CAS}} |
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|CASNo_Ref = {{cascite|correct|CAS}} |
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| CASNo=1291-32-3 |
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|CASNo=1291-32-3 |
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|UNII_Ref = {{fdacite|correct|FDA}} |
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| PubChem=10891641 |
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|UNII = SQE0U3LG60 |
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|PubChem=10891641 |
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|ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}} |
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|ChemSpiderID = 29081433 |
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|SMILES = 1cccc1.1cccc1... |
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|InChI = 1/2C5H5.2ClH.Zr/c2*1-2-4-5-3-1;;;/h2*1-5H;2*1H;/q2*-1;;;+4/p-2 |
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|InChIKey = QMBQEXOLIRBNPN-NUQVWONBAX |
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|StdInChI_Ref = {{stdinchicite|changed|chemspider}} |
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|StdInChI = 1S/2C5H5.2ClH.Zr/c2*1-2-4-5-3-1;;;/h2*1-5H;2*1H;/q2*-1;;;+4/p-2 |
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|StdInChIKey_Ref = {{stdinchicite|changed|chemspider}} |
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|StdInChIKey = QMBQEXOLIRBNPN-UHFFFAOYSA-L |
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|Section2={{Chembox Properties |
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|Section2={{Chembox Properties |
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| C=10 | H=10 | Zr = 1 | Cl = 2 |
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|C=10 | H=10 | Zr=1 | Cl=2 |
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| Appearance= white solid |
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|Appearance= white solid |
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|Solubility= Soluble (Hydrolysis) |
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| Solubility= Soluble (Hydrolysis) |
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| OtherCpds = ]</br> ]</br> ]</br> ]</br> ]</br> ]</br> ]</br>}} |
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|OtherCompounds = ]<br> ]<br> ]<br> ]<br> ]<br> ]}} |
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'''Zirconocene dichloride''' is an ] composed of a ] central atom, with two ] and two ] ligands. |
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'''Zirconocene dichloride''' is an ] composed of a ] central atom, with two ] and two ] ligands. It is a colourless ] solid that is somewhat stable in air. |
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==Preparation== |
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Zirconocene dichloride may be prepared from ]-] complex and ]:<ref>{{cite journal | author = ] and J.G. Birmingham | year = 1954 | title = Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta | journal = ] | volume = 76 | issue = 17 | pages = 4281–4284 | doi = 10.1021/ja01646a008}}</ref> |
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==Preparation and structure== |
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:ZrCl<sub>4</sub>(THF)<sub>2</sub> + 2 NaCp → Cp<sub>2</sub>ZrCl<sub>2</sub> + 2 NaCl + 2 THF |
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Zirconocene dichloride may be prepared from ]-] complex and ]: |
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:ZrCl<sub>4</sub>(THF)<sub>2</sub> + 2 NaCp → Cp<sub>2</sub>ZrCl<sub>2</sub> + 2 NaCl + 2 THF |
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The closely related compound Cp<sub>2</sub>ZrBr<sub>2</sub> was first described by Birmingham and Wilkinson.<ref>{{cite journal | author = ] and J. M. Birmingham | year = 1954 | title = Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta | journal = ] | volume = 76 | issue = 17 | pages = 4281–4284 | doi = 10.1021/ja01646a008}}</ref> |
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The compound is a ]: the Cp rings are not parallel, the average Cp(centroid)-M-Cp angle being 128°. The Cl-Zr-Cl angle of 97.1° is wider than in ] (85.6°) and ] (82°). This trend helped to establish the orientation of the ] in this class of complex.<ref>K. Prout, T. S. Cameron, R. A. Forder, and in parts S. R. Critchley, B. Denton and G. V. Rees "The crystal and molecular structures of bent bis-π-cyclopentadienyl-metal complexes: (a) bis-π-cyclopentadienyldibromorhenium(V) tetrafluoroborate, (b) bis-π-cyclopentadienyldichloromolybdenum(IV), (c) bis-π-cyclopentadienylhydroxomethylaminomolybdenum(IV) hexafluorophosphate, (d) bis-π-cyclopentadienylethylchloromolybdenum(IV), (e) bis-π-cyclopentadienyldichloroniobium(IV), (f) bis-π-cyclopentadienyldichloromolybdenum(V) tetrafluoroborate, (g) μ-oxo-bis tetrafluoroborate, (h) bis-π-cyclopentadienyldichlorozirconium" ''Acta Crystallogr.'' 1974, volume B30, pp. 2290–2304. {{doi|10.1107/S0567740874007011}}</ref> |
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==Reactions== |
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==Reactions== |
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===Schwartz's reagent=== |
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In the laboratory, zirconocene dichloride is easily reacted with ] to give Cp<sub>2</sub>ZrHCl ]: |
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Zirconocene dichloride reacts with ] to give Cp<sub>2</sub>ZrHCl ]: |
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:(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>ZrCl<sub>2</sub> + <sup>1</sup>/<sub>4</sub> LiAlH<sub>4</sub> → (C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>ZrHCl + <sup>1</sup>/<sub>4</sub> ] |
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Since lithium aluminium hydride is a strong reductant, some over-reduction occurs to give the dihydrido complex, Cp<sub>2</sub>ZrH<sub>2</sub>; treatment of the product mixture with methylene chloride converts it to Schwartz's reagent.<ref name=buchwald>{{OrgSynth | author1=S. L. Buchwald |author2= S. J. LaMaire |author3= R. B. |author4= Nielsen |author5= B. T. Watson |author6= S. M. King| title=Schwartz's Reagent| collvol = 9| collvolpages=162 | prep = CV9P0162}}</ref> |
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:(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>ZrCl<sub>2</sub> + <sup>1</sup>/<sub>4</sub> LiAlH<sub>4</sub> → (C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>ZrHCl + <sup>1</sup>/<sub>4</sub> "LiAlCl<sub>4</sub>" |
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===Negishi reagent=== |
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As lithium aluminium hydride is a strong reductant, some over-reduction occurs to give the dihydrido complex, Cp<sub>2</sub>ZrH<sub>2</sub>; treatment of the product mixture converts it to Schwartz's reagent.<ref name=buchwald>{{OrgSynth | author=S. L. Buchwald, S. J. LaMaire, R. B. Nielsen, B. T. Watson, and S. M. King| title=Schwartz's Reagent| collvol = 9| collvolpages=162 | prep = CV9P0162}}</ref> |
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Zirconocene dichloride can also be used to prepare the '''] reagent''', Cp<sub>2</sub>Zr(]-]), which can be used as a source of Cp<sub>2</sub>Zr in oxidative cyclisation reactions. The Negishi reagent is prepared by treating zirconocene dichloride with ], leading to replacement of the two chloride ligands with ]s. The dibutyl compound subsequently undergoes ] to give one η<sup>2</sup>-butene ligand, with the other butyl ligand promptly lost as ] via ].<ref>{{Cite journal | last1 = Negishi | first1 = E. | last2 = Takashi | first2 = T. | doi = 10.1021/ar00041a002 | title = Patterns of Stoichiometric and Catalytic Reactions of Organozirconium and Related Complexes of Synthetic Interest | journal = Accounts of Chemical Research | volume = 27 | issue = 5 | pages = 124–130 | year = 1994 }}</ref> |
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=== Carboalumination === |
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Zirconocene dichloride catalyzes the carboalumination of alkynes by ] to give a (alkenyl)dimethylalane, a versatile intermediate for further cross coupling reactions for the synthesis of stereodefined trisubstituted olefins. For example, ] can be prepared as a single stereoisomer by carboalumination of 1-buten-3-yne with trimethylaluminium, followed by palladium-catalyzed coupling of the resultant vinylaluminium reagent with geranyl chloride.<ref>{{Cite web|url=http://www.orgsyn.org/demo.aspx?prep=cv7p0245|title=Palladium-Catalyzed Synthesis of 1,4-Dienes by Allylation of Alkenylalanes: α-Farnesene|website=www.orgsyn.org|language=en|access-date=2019-11-27}}</ref> |
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The use of trimethylaluminium for this reaction results in exclusive formation of the ''syn''-addition product and, for terminal alkynes, the anti-Markovnikov addition with high selectivity (generally > 10:1). Unfortunately, the use of higher alkylaluminium reagents results in lowered yield, due to the formation of the hydroalumination product (via β-hydrogen elimination of the alkylzirconium intermediate) as side product, and only moderate regioselectivities.<ref>{{Citation|last=Huo|first=Shouquan|title=Carboalumination Reactions|date=2016-09-19|url=http://doi.wiley.com/10.1002/9780470682531.pat0834|work=PATAI'S Chemistry of Functional Groups|pages=1–64|editor-last=Rappoport|editor-first=Zvi|place=Chichester, UK|publisher=John Wiley & Sons, Ltd|language=en|doi=10.1002/9780470682531.pat0834|isbn=978-0-470-68253-1|access-date=2021-01-19}}</ref> Thus, practical applications of the carboalumination reaction are generally confined to the case of methylalumination. Although this is a major limitation, the synthetic utility of this process remains significant, due to the frequent appearance of methyl-substituted alkenes in natural products. |
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=== Zr-walk === |
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Zirconocene dichloride together with a reducing reagent can form the zirconocene hydride catalyst in situ, which allows a positional isomerization (so-called "Zr-walk"<ref>{{Cite journal |last1=Sommer |first1=Heiko |last2=Juliá-Hernández |first2=Francisco |last3=Martin |first3=Ruben |last4=Marek |first4=Ilan |date=2018-02-08 |title=Walking Metals for Remote Functionalization |journal=ACS Central Science |volume=4 |issue=2 |pages=153–165 |doi=10.1021/acscentsci.8b00005 |pmid=29532015 |pmc=5833012 |s2cid=4389888 |issn=2374-7943|doi-access=free }}</ref>), and ends up with a cleavage of allylic bonds. Not only individual steps under stoichiometric conditions were described with Schwartz reagent,<ref>{{Cite journal |last1=Cénac |first1=Nathalie |last2=Zablocka |first2=Maria |last3=Igau |first3=Alain |last4=Commenges |first4=Gérard |last5=Majoral |first5=Jean-Pierre |last6=Skowronska |first6=Aleksandra |date=1996-02-20 |title=Zirconium-Promoted Ring Opening. Scope and Limitations |url=http://dx.doi.org/10.1021/om950491+ |journal=Organometallics |volume=15 |issue=4 |pages=1208–1217 |doi=10.1021/om950491+ |issn=0276-7333}}</ref> and Negishi reagent,<ref>{{Cite journal |last1=Masarwa |first1=Ahmad |last2=Didier |first2=Dorian |last3=Zabrodski |first3=Tamar |last4=Schinkel |first4=Marvin |last5=Ackermann |first5=Lutz |last6=Marek |first6=Ilan |date=2013-12-08 |title=Merging allylic carbon–hydrogen and selective carbon–carbon bond activation |url=http://dx.doi.org/10.1038/nature12761 |journal=Nature |volume=505 |issue=7482 |pages=199–203 |doi=10.1038/nature12761 |pmid=24317692 |s2cid=205236414 |issn=0028-0836}}</ref> but also catalytic applications on alkene hydroaluminations,<ref>{{Cite journal |last1=Negishi |last2=Yoshida |year=1980 |title=A novel zirconium- catalyzed hydroalumination of olefins |journal=Tetrahedron Lett. |volume=21 |issue=16 |pages=1501–1504|doi=10.1016/S0040-4039(00)92757-6 }}</ref> radical cyclisation,<ref>{{Cite journal |last1=Fujita |last2=Nakamura |last3=Oshima |title=Triethylborane-Induced Radical Reaction with Schwartz Reagent. |journal=J. Am. Chem. Soc. |year=2001 |publication-date=2001 |volume=123 |issue=13 |pages=3137–3138|doi=10.1021/ja0032428 }}</ref> polybutadiene cleavage,<ref>{{Cite journal |last1=Zheng |first1=Jun |last2=Lin |first2=Yichao |last3=Liu |first3=Feng |last4=Tan |first4=Haiying |last5=Wang |first5=Yanhui |last6=Tang |first6=Tao |date=2012-11-08 |title=Controlled Chain-Scission of Polybutadiene by the Schwartz Hydrozirconation |url=http://dx.doi.org/10.1002/chem.201202942 |journal=Chemistry - A European Journal |volume=19 |issue=2 |pages=541–548 |doi=10.1002/chem.201202942 |pmid=23139199 |issn=0947-6539}}</ref> and reductive removal of functional groups<ref>{{Cite journal |last1=Matt |first1=Christof |last2=Kölblin |first2=Frederic |last3=Streuff |first3=Jan |date=2019-09-06 |title=Reductive C–O, C–N, and C–S Cleavage by a Zirconium Catalyzed Hydrometalation/β-Elimination Approach |url=https://pubs.acs.org/doi/10.1021/acs.orglett.9b02572 |journal=Organic Letters |language=en |volume=21 |issue=17 |pages=6983–6988 |doi=10.1021/acs.orglett.9b02572 |pmid=31403304 |s2cid=199539801 |issn=1523-7060}}</ref> were reported. |
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==References== |
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==Further reading== |
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*{{cite journal | author = A. Maureen Rouhi | title=Organozirconium Chemistry Arrives| journal=]| volume=82 | issue= 16 | year=1998 | pages=162 | url = http://pubs.acs.org/cen/nlw/8216sci1.html}} |
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*{{cite journal | author = A. Maureen Rouhi | title=Organozirconium Chemistry Arrives| journal=]| volume=82 | issue= 16 | year=1998 | pages=162 | url = http://pubs.acs.org/cen/nlw/8216sci1.html | doi = 10.1021/cen-v082n015.p035}} |
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{{Zirconium compounds}} |
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{{Cyclopentadienide complexes}} |
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{{DEFAULTSORT:Zirconocene Dichloride}} |
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{{DEFAULTSORT:Zirconocene Dichloride}} |
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