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. 2020 Mar 15:407:213118.
doi: 10.1016/j.ccr.2019.213118. Epub 2020 Jan 14.

Reactivity of terminal imido complexes of group 4-6 metals: stoichiometric and catalytic reactions involving cycloaddition with unsaturated organic molecules

Kento Kawakita  1 , Yuya Kakiuchi  1 , Hayato Tsurugi  1 , Kazushi Mashima  1 , Bernard F Parker  1   2 , John Arnold  2 , Ian A Tonks  3
Affiliations

Reactivity of terminal imido complexes of group 4-6 metals: stoichiometric and catalytic reactions involving cycloaddition with unsaturated organic molecules

Kento Kawakita et al. Coord Chem Rev. .

Abstract

Imido complexes of early transition metals are key intermediates in the synthesis of many nitrogen-containing organic compounds. The metal-nitrogen double bond of the imido moiety undergoes [2+2] cycloaddition reactions with various unsaturated organic molecules to form new nitrogen-carbon and nitrogen-heteroatom bonds. This review article focuses on reactivity of the terminal imido complexes of Group 4-6 metals, summarizing their stoichiometric reactions and catalytic applications for a variety of reactions including alkyne hydroamination, alkyne carboamination, pyrrole formation, imine metathesis, and condensation reactions of carbonyl compounds with isocyanates.

Keywords: Cycloaddition; Early transition metals; Group 4—6 metals; Nitrogen-containing organic compound; Terminal imido complex.

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Figures

Fig. 1.
Fig. 1.
Typical synthetic methods of terminal imido complexes
Fig. 2.
Fig. 2.
Examples of early transition metal catalysts and precatalysts for hydroamination of alkynes via cycloaddition.
Fig. 3.
Fig. 3.
Catalytic intermolecular hydroamination reactions of alkenes, allenes, and dienes.
Fig. 4.
Fig. 4.
Proposed transition states of alkyne insertion into titanacyclobutene
Scheme 1.
Scheme 1.
Representative Cycloaddition and Subsequent Organometallic Reactions of the Metal Imido Group
Scheme 2.
Scheme 2.
Cycloaddition Reactions of Cp2Zr(=NtBu) (2) with Alkynes, Alkenes, Imines, Carbonyls, Heterocumulenes, and Organic Azides
Scheme 3.
Scheme 3.
Cycloaddition Reactions of Titanium Imido Complex 24 with Phosphaalkyne and Nitrile
Scheme 4.
Scheme 4.
Reactivity of Fulvalene-Derived Titanium Imido Complexes 28–30
Scheme 5.
Scheme 5.
[2+2] Cycloaddition of Bis(imido)vanadium 35 with 2-Butyne and Ethylene
Scheme 6.
Scheme 6.
Cycloaddition Reactions of Bis(imido)niobium Complex 40 with Alkyne, Alkene, Aldehyde, Organic Azide, and α,β-Unsaturated Carbonyl Functional Groups.
Scheme 7.
Scheme 7.
Proposed Mechanism for Complex 41 Formation
Scheme 8.
Scheme 8.
Formation of 50 through Photolysis of Imido-azido Complex 49
Scheme 9.
Scheme 9.
Formation of a Niobium-Imine Complex 53 from Defluorination of α,α,α-trifluorotoluene
Scheme 10.
Scheme 10.
Insertion Reactions of Aldehydes, Imines, Carbodiimides, and Organic Azides into Azazirconacyclobutene 54
Scheme 11.
Scheme 11.
Insertion Reaction of Isobutyronitrile into Azatitanacyclobutene 62
Scheme 12.
Scheme 12.
Formation of Azametallacyclohexadiene Complexes through [2+2] Cycloaddition followed by Aryacetylene Insertion
Scheme 13.
Scheme 13.
Formation of Six-Membered Azametallacyclohexadienes 74 and 75 via Four-Membered Azametallacyclobutenes 76 and 77 and Reductive Elimination of Pyrrole Derivative
Scheme 14.
Scheme 14.
Proposed Mechanism for Zr-Catalyzed Hydroamination of Alkynes
Scheme 15.
Scheme 15.
Proposed Mechanism for Ta-Catalyzed Oxidative Amination
Scheme 16.
Scheme 16.
Proposed Reaction Mechanism for Ti-Catalyzed Guanylation of Amines
Scheme 17.
Scheme 17.
Proposed Mechanism for Carboamination of Alkynes with Aldimines
Scheme 18.
Scheme 18.
Proposed Mechanism for Ti-Catalyzed Carboamination of Alkynes with Alkenes and Azobenzenes
Scheme 19.
Scheme 19.
Proposed Mechanism for Titanium-Catalyzed Iminoamination of Alkynes
Scheme 20.
Scheme 20.
Proposed Mechanism for Ti-Catalyzed [2+2+1] Pyrrole Formation from Alkynes and Azobenzenes
Scheme 21.
Scheme 21.
Catalytic Pyrrole Formation from Diynes and Amines by Titanium Catalysts
Scheme 22.
Scheme 22.
Catalytic Pyrrole Formation by Hydroamination of Chloroenynes
Scheme 23.
Scheme 23.
Proposed Mechanism of the Ti-Catalyzed Four-Component Coupling Giving 2,3-Diamino Pyrroles
Scheme 24.
Scheme 24.
Catalytic Imine Metathesis by Early Transition Metal Catalysts
Scheme 25.
Scheme 25.
Two Proposed Mechanisms for Catalytic Imine Metathesis
Scheme 26.
Scheme 26.
Catalytic Carbodiimide Metathesis by Early Transition Metal Catalysts
Scheme 27.
Scheme 27.
Catalytic Isocyanate Condensation to Give Carbodiimides
Scheme 28.
Scheme 28.
Proposed Mechanism for Isocyanate Condensation to Give Carbodiimides
Scheme 29.
Scheme 29.
Catalytic Isocyanate or N-sulfonylimine Condensation with Aldehydes to Produce Imines
Scheme 30.
Scheme 30.
Catalytic Nitrene Metathesis to form Carbodiimides
Scheme 31.
Scheme 31.
Imine Metathesis Reactions of Niobium Bis(imido) Complexes
Scheme 32.
Scheme 32.
Catalytic Carbodiimide Formation Utilizing a Redox-active Ligand on Zirconium
Scheme 33.
Scheme 33.
Catalytic Isocyanate Formation by Direct Addition of CO to an Imido Group
Scheme 34.
Scheme 34.
Proposed Mechanism for Catalytic Z-Selective Semihydrogenation of Alkynes by the Cationic Vanadium Imido Catalyst [V(=NtBu)2(PMe3)3][Al(pftb)4] (pftb = perfluoro-tert-butoxide) (192).
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