Methyl Complexes of the Transition Metals

Abstract

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, i.e. based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition metal complexes containing M-CH3 fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last 5 years. After a panoramic overview on M-CH3 compounds of groups 3 to 11 which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.

Metal–metal cooperative bond activation by heterobimetallic alkyl, aryl, and acetylide PtII/CuIcomplexes

“…Thus, complexes 3[X] are the examples of a solution-stable heterobimetallic complex with an unsymmetrical bridging Me group. 19 Interestingly, the dearomatized complex 4, characterized by three molecules in the asymmetric cell, features a noticeably longer interaction between Cu I and Pt II , 2.6890(5)-2.7459(6)Å, which is not much larger than the sum of the covalent radii. 18 The distances from C of the proximal Me group to Cu I are longer (2.518(5)-2.559(5)Å) compared to that of complexes 3 [X].…”

Dehydrogenation, Methyl Elimination and Insertion Reactions of the Agostic Methyl‐Bridged Complex [Mo2Cp2(μ‐κ1:η2‐CH3)(μ‐PtBu2)(μ‐CO)]

“…Alkyl complexes are a most important class of compounds within organometallic chemistry, and the reactivity of the corresponding σ M−C bonds is a central matter of the discipline, extensively studied in the case of mononuclear complexes . The chemistry of binuclear complexes featuring bridging alkyl ligands, however, is comparatively less developed, even if such complexes might serve as models for the intermediate species involved in several processes of interest, these including olefin oligomerization and polymerization, alkyl transfer reactions, and heterogeneously catalyzed CO hydrogenation . When compared to electron‐precise analogues, it is expected that the reactivity of alkyl‐bridged complexes might be further increased in molecules bearing metal‐metal multiple bonds, because of the coordinative and electronic unsaturation of the dimetal centre in such species.…”

“…When compared to electron‐precise analogues, it is expected that the reactivity of alkyl‐bridged complexes might be further increased in molecules bearing metal‐metal multiple bonds, because of the coordinative and electronic unsaturation of the dimetal centre in such species. However, complexes displaying alkyl ligands bridging over metal‐metal multiple bonds are scarce, and their reactivity has been little explored . This situation changed upon our synthesis of the dimolybdenum complexes [Mo 2 Cp 2 (μ‐κ 1 :η 2 ‐CH 2 R)(μ‐PCy 2 )(CO) 2 ] (R=H, Ph), which feature agostic alkyl ligands over shortened Mo‐Mo double bonds, and turned out to be highly reactive, being able to undergo coupling reactions to CO, CNR and Cp ligands, as well as photochemical dehydrogenation and more complex processes .…”

“…[1] The chemistry of binuclear complexes featuring bridging alkyl ligands, however,i sc omparativelyl ess developed, even if such complexes might serve as modelsf or the intermediate species involved in severalp rocesses of interest, thesei ncluding olefin oligomerization and polymerization, alkyl transfer reactions, and heterogeneously catalyzed CO hydrogenation. [2,3] When compared to electron-precise analogues, it is expected that the reactivityo fa lkyl-bridged complexes might be further increasedi nm olecules bearing metal-metal multiple bonds, because of the coordinativea nd electronic unsaturation of the dimetal centre in such species. However,c omplexes displaying alkyl ligands bridging over metal-metalm ultiple bondsa re scarce,a nd their reactivity hasb een little explored.…”

“…However,c omplexes displaying alkyl ligands bridging over metal-metalm ultiple bondsa re scarce,a nd their reactivity hasb een little explored. [3][4][5] This situation changed upon our synthesis of the dimolybdenum complexes [Mo 2 Cp 2 (m-k 1 :h 2 -CH 2 R)(m-PCy 2 )(CO) 2 ]( R = H, Ph), which feature agostic alkyl ligands over shortened Mo-Mo double bonds, [6] and turned out to be highly reactive, being able to undergo coupling reactions to CO, CNR and Cp ligands, as well as photochemical dehydrogenation and more complex processes. [7,8] It was then of interestt oe xaminet he reactivity of relateda gosticc omplexes at even more unsaturated centres, as in the case of the monocarbonyl derivative [Mo 2 Cp 2 (mk 1 :h 2 -CH 3 )(m-PCy 2 )(m-CO)],w hichf eatures an agostic methyl ligand bridging over an intermetallic triple bond, [8d] but these studies wereh amperedb yt he high air-sensitivityo ft his molecule.…”