Metallacyclopentadienes: synthesis, structure and reactivity

Abstract

Metallacyclopentadienes, which possess two M-C(sp) bonds and feature the structure of M(C[upper bond 1 start]R[double bond, length as m-dash]CR-CR[double bond, length as m-dash]C[upper bond 1 end]R), are an important class of five-membered metallacycles. They are considered as both reactive intermediates in the stoichiometric and catalytic transformations of organic molecules and useful precursors to main group element compounds, and have received considerable attention in organometallic chemistry, coordination chemistry and synthetic organic chemistry over the past six decades because of their unique metallacyclic structure. This review comprehensively presents the synthesis, structure and reactivity of the s-, p-, d- and f-block metallacyclopentadienes distributed in the whole periodic table. In addition, their application in synthetic organic chemistry and polymer chemistry is summarized. This review aims to be beneficial for the design and synthesis of novel metallacyclopentadienes, and for promoting the rapid development of metallacyclic chemistry.

Group 9 Metallacyclopentadienes as Key Intermediates in [2+2+2] Alkyne Cyclotrimerizations. Insight from Activation Strain Analyses

“…For example, they form in olefin metathesis reactions, [1] and in alkyne cyclotrimerizations, [2][3][4][5] or they are unwanted products resulting from ortho-metalation reactions. [7] This reaction (oxidative coupling) is the first step in the process of [2 + 2 + 2] alkyne cycloaddition (Scheme S1), for which a class of well-known catalysts are the fragments CpM (M=Co, Rh, Ir; Cp = C 5 H 5 À ). Various metals are involved in their formation, among which, but not exclusively, Zr, Mn, Mo, Cr, Pt, Pd, Fe, Ru, Os, Re, Co, Rh, and Ir.…”

Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

“…Axial coordination of one molecule of Me 3 SiCCH to the less sterically encumbering Cr1 of 1 3 (CrÀCr = 1.75 )( Figure S6a) elicit ad ramatic change of the ligation mode of two amidinates from ab ridging to chelating fashion ( Figure S6b). Although dinuclear metallacyclopentadienes have been well documented, [22] only dinuclear Co, [23] Ta, [24] and Ni [25] complexes were involved in catalytic cyclotrimerization of alkynes.I t should be pointed out that subsequent reactions of these dinuclear Co,T a, and Ni metallacyclopentadienes with one molecule of alkyne uniformly afforded the arene-capped dinuclear complexes,w here their metal-metal bonds and coordination modes of ligands were retained during catalysis. Although dinuclear metallacyclopentadienes have been well documented, [22] only dinuclear Co, [23] Ta, [24] and Ni [25] complexes were involved in catalytic cyclotrimerization of alkynes.I t should be pointed out that subsequent reactions of these dinuclear Co,T a, and Ni metallacyclopentadienes with one molecule of alkyne uniformly afforded the arene-capped dinuclear complexes,w here their metal-metal bonds and coordination modes of ligands were retained during catalysis.…”

Alkenyl Magnesium Compounds: Generation and Synthetic Application

“…The magnesacarbocycles discussed above are all generated in situ without isolation. In recent decades, we have been working on the synthetic application of 1,4‐dilithio 1,3‐butadienes (dilithio reagents) and their transmetalation reactions to construct different metallacycles . A series of well‐defined magnesacarbocycles including types IIIa and IIIb can be synthesized from dilithio reagents by transmetalation.…”

“…This considerably extends their application in organic chemistry, organometallic chemistry and coordination chemistry . Scheme summarizes three types of representative alkenyl magnesium compounds, for example, functionalized alkenyl Grignard reagents (I), alkenyl magnesium carbenoids (II), magnesacarbocycles containing alkenyl magnesium bond (III) . There are some methods to prepare alkenyl magnesium compounds.…”