This reaction also affords (C5H5)2ZrH2, which is treated withmethylene chloride to give Schwartz's reagent[3]
An alternative procedure that generated Schwartz's reagent from dihydride has also been reported.[4] Moreover, it's possible to perform anin situ preparation of (C5H5)2ZrHCl from zirconocene dichloride by using LiH. This method can also be used to synthesize isotope-labeled molecules, like olefines by employing Li2H or Li3H as reducing agents.[5]
Schwartz's reagent has a low solubility in common organic solvents.[6] The trifluoromethanesulfonate (C5H5)2ZrH(OTf) is soluble in THF.[7]
The complex adopts the usual "clam-shell" structure seen for other Cp2MXn complexes.[8] The dimetallic structure has been confirmed byMicrocrystal electron diffraction.[9] The results are consistent withFT-IR spectroscopy, which established that the hydrides are bridging.Solid state NMR spectroscopy also indicates a dimeric structure. The X-ray crystallographic structure for the methyl compound (C5H5)4Zr2H2(CH3)2 compound is analogous.[10]
Computational studies indicate that hydrozirconation occurs from the interior portion.[19][20]When treated with one equivalent of Cp2ZrClH,diphenylacetylene gives the corresponding alkenylzirconium as a mixture ofcis and trans isomers. With two equivalents of hydride, the endproduct was a mixture oferythro andthreo zircono alkanes:
The correspondingorganoboron andorganoaluminum compounds were already known, but these are air-sensitive and/orpyrophoric whereas organozirconium compounds are not.
One example of aone-pot hydrozirconation - carbonylation - coupling is depicted below:[24][25]
With certainallyl alcohols, thealcohol group is replaced by nucleophilic carbon forming acyclopropane ring:[26] The selectivity of the hydrozirconation of alkynes has been studied in detail.[27][28] Generally, the addition of the Zr–H proceeds via thesyn-addition. The rate of addition to unsaturated carbon-carbon bonds is terminal alkyne >terminal alkene ≈ internal alkyne > disubstituted alkene[29]Acyl complexes can be generated by insertion ofCO into the C–Zr bond resulting from hydrozirconation.[30] Upon alkene insertion into the zirconium hydride bond, the resulting zirconium alkyl undergoes facile rearrangement to the terminal alkyl and therefore only terminal acyl compounds can be synthesized in this way. The rearrangement most likely proceeds via β-hydride elimination followed by reinsertion.
Hart, D. W.; Schwartz, J. (1974). "Hydrozirconation. Organic Synthesis via Organozirconium Intermediates. Synthesis and Rearrangement of Alkylzirconium(IV) Complexes and Their Reaction with Electrophiles".J. Am. Chem. Soc.96 (26):8115–8116.Bibcode:1974JAChS..96.8115H.doi:10.1021/ja00833a048.
Hart, Donald W.; Blackburn, Thomas F.; Schwartz, Jeffrey (1975). "Hydrozirconation. III. Stereospecific and regioselective functionalization of alkylacetylenes via vinylzirconium(IV) intermediates".J. Am. Chem. Soc.97 (3):679–680.Bibcode:1975JAChS..97..679H.doi:10.1021/ja00836a056.
^Pinheiro, Danielle L. J.; De Castro, Pedro P.; Amarante, Giovanni W. (2018). "Recent Developments and Synthetic Applications of Nucleophilic Zirconocene Complexes from Schwartz's Reagent".European Journal of Organic Chemistry.2018 (35):4828–4844.doi:10.1002/ejoc.201800852.S2CID102770378.
^Buchwald, Stephen L.; LaMaire, Susan J.; Nielsen, Ralph B.; Watson, Brett T.; King, Susan M. (1993). "Schwartz's Reagent".Org. Syntheses.71: 77.doi:10.15227/orgsyn.071.0077.
^Rossini, A. J.; Mills, R. W.; Briscoe, G. A.; Norton, E. L.; Geier, S. J.; Hung, I.; Zheng, S.; Autschbach, J.; Schurko, R. W. (2009). "Solid-State Chlorine NMR of Group IV Transition Metal Organometallic Complexes".Journal of the American Chemical Society.131 (9):3317–3330.Bibcode:2009JAChS.131.3317R.doi:10.1021/ja808390a.PMID19256569.
^Wu, J.; Panek, J. S. (2011). "Total Synthesis of (−)-Virginiamycin M2: Application of Crotylsilanes Accessed by Enantioselective Rh(II) or Cu(I) Promoted Carbenoid Si–H Insertion".J. Org. Chem.76 (24):9900–9918.doi:10.1021/jo202119p.PMID22070230.
^Pankratyev, E. Y.; Tyumkina, T. V.; Parfenova, L. V.; Khursan, S. L.; Khalilov, L. M.; Dzhemilev, U. M. (2011). "DFT and Ab Initio Study on Mechanism of Olefin Hydroalumination by XAlBui2 in the Presence of Cp2ZrCl2 Catalyst. II.(1) Olefin Interaction with Catalytically Active Centers".Organometallics.30 (22):6078–6089.doi:10.1021/om200518h.
^Wang, Juping; Xu, Huiying; Gao, Hui; Su, Cheng-Yong; Zhao, Cunyuan; Phillips, David Lee (2010). "DFT Study on the Mechanism of Amides to Aldehydes Using Cp2Zr(H)Cl".Organometallics.29 (1):42–51.doi:10.1021/om900371u.
^Hart, D. W.; Schwartz, J. (1974). "Hydrozirconation. Organic Synthesis via Organozirconium Intermediates. Synthesis and Rearrangement of Alkylzirconium(1V) Complexes and Their Reaction with Electrophiles".Journal of the American Chemical Society.96 (26):8115–8116.Bibcode:1974JAChS..96.8115H.doi:10.1021/ja00833a048.
^Kang, Suk-Ku (2002). "Palladium-catalyzed coupling reaction of acylzirconocene chlorides with hypervalent iodonium salts: synthesis of aryl-substituted ketones".Journal of the Chemical Society, Perkin Transactions 1 (4):459–461.doi:10.1039/b110983a.
^Gandon, Vincent (2002). "A one-pot access to cyclopropanes from allylic ethers via hydrozirconation–deoxygenative ring formation".Chemical Communications (12):1308–1309.doi:10.1039/b203762a.PMID12109129.
^Panek, J. S.; Hu, T. (1997). "Stereo- and Regiocontrolled Synthesis of Branched Trisubstituted Conjugated Dienes by Palladium(0)-Catalyzed Cross-Coupling Reaction".J. Org. Chem.62 (15):4912–4913.doi:10.1021/jo970647a.
