A DFT computational study and a structural analysis of the coordination of arenes to transition metals in low -hapticity (η1 and η2) modes have been developed, including a pseudosymmetry analysis of ...the molecular orbitals and the introduction of a hapticity map that makes evident the different degrees of intermediate hapticities. Calculations on PtIIL3(C6H6) model complexes reveal a preference for the η2 mode, while the η1 coordination is found to be a low-energy transition state for a haptotropic shift. The attachment of the arene to a side group that is coordinated to the metal introduces geometrical constraints, which result in hapticities intermediate between one and two. Comparison of the η1 arene complexes with benzonium cations shows that in the former case the bonding to the metal involves essentially the π system of the arene, affecting only slightly the delocalized nature of the carbon–carbon bonds. This behavior is in sharp contrast with the frequently found η1 coordination of Cp that involves σ bonding and full dearomatization of the ring.
Methyl Complexes of the Transition Metals Campos, Jesús; López-Serrano, Joaquín; Peloso, Riccardo ...
Chemistry,
May 4, 2016, Letnik:
22, Številka:
19
Journal Article
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Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, 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 five 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.
A new transition: This review offers a concise overview of the synthetic, reactivity, and bonding aspects of the chemistry of transition‐metal methyl compounds. After a systematic look at d‐block elements, two further sections are specifically devoted to methyl‐bridged complexes and reactivity. Citing more than 500 references, this contribution is mainly focused on the last five years.
We report the synthesis and structural characterization of five-coordinate complexes of rhodium and iridium of the type (η5-C5Me5)M(N^N)+ (3-M + ), where N^N represents the aminopyridinate ligand ...derived from 2-NH(Ph)-6-(Xyl)C5H3N (Xyl = 2,6-Me2C6H3). The two complexes were isolated as salts of the BArF anion (BArF = B3,5-(CF3)2C6H34). The M–Namido bond of complexes 3-M + readily activated CO, C2H4, and H2. Thus, compounds 3-M + reacted with CO under ambient conditions, but whereas for 3-Rh + , CO migratory insertion was fast, yielding a carbamoyl carbonyl species, 4-Rh + , the stronger Ir–Namido bond of complex 3-Ir + caused the reaction to stop at the CO coordination stage. In contrast, 3-Ir + reacted reversibly with C2H4, forming adduct 5-Ir + , which subsequently rearranged irreversibly to Ir(H)(C(Me)N(Ph)−) complex 6-Ir + , which contains an N-stabilized carbene ligand. Computational studies supported a migratory insertion mechanism, giving first a β-stabilized linear alkyl unit, IrCH2CH2N(Ph)–, followed by a multistep rearrangement that led to the final product 6-Ir + . Both β- and α-H eliminations, as well as their microscopic reverse migratory insertion reactions, were implicated in the alkyl-to-hydride–carbene reorganization. The analogous reaction of 3-Rh + with C2H4 originated a complex mixture of products from which only a branched alkyl RhC(H)(Me)N(Ph)– (5-Rh + ) could be isolated, featuring a β-agostic methyl interaction. Reactions of 3-M + with H2 promoted a catalytic isomerization of the Ap ligand from classical κ2-N,N′ binding to κ-N plus η3-pseudoallyl coordination mode.
A cationic rhodium compound which is an active catalyst for both the hydrogen isotope exchange in hydrosilanes and the hydrosilylation of carbonyl compounds permits, in a one-flask, two-step ...procedure, efficient deutero- and tritiosilylations using SiEt3H under D2 (0.5 bar) or T2, at low catalyst loadings (0.1–0.5 mol %).
In My Element: Molybdenum Carmona, Ernesto
Chemistry,
January 2, 2019, Letnik:
25, Številka:
1
Journal Article
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The In My Element series celebrates the personal accounts from Chemistry – A European Journal Editorial Board members for the 2019 International Year of the Periodic Table. In this contribution, ...Ernesto Carmona gives his story on molybdenum.
Five plus H2 gives four: UV irradiation of a bis(amidinate) complex with a (H)MoMo(H) core induces reductive elimination of H2 and formation of a known quintuply bonded MoMo species (see scheme) ...that reacts back with H2 to restore (H)MoMo(H). UV irradiation of the bis(hydride) species in benzene and toluene gives arene complexes in which the aromatic hydrocarbon bridges the molybdenum atoms. Dipp=2,6‐diisopropylphenyl.
More than 1 g of the dizinc compound Zn2(η5‐C5Me5)2 can be readily obtained in a single preparation. Density functional calculations reveal that the ZnZn bond is relatively strong and derives mainly ...from interaction between the Zn 4 s orbitals (see picture).
The bis(hydride) dimolybdenum complex, Mo2(H)2{HC(N‐2,6‐iPr2C6H3)2}2(thf)2, 2, which possesses a quadruply bonded Mo2II core, undergoes light‐induced (365 nm) reductive elimination of H2 and arene ...coordination in benzene and toluene solutions, with formation of the MoI2 complexes Mo2{HC(N‐2,6‐iPr2C6H3)2}2(arene), 3⋅C6H6 and 3⋅C6H5Me, respectively. The analogous C6H5OMe, p‐C6H4Me2, C6H5F, and p‐C6H4F2 derivatives have also been prepared by thermal or photochemical methods, which nevertheless employ different Mo2 complex precursors. X‐ray crystallography and solution NMR studies demonstrate that the molecule of the arene bridges the molybdenum atoms of the MoI2 core, coordinating to each in an η2 fashion. In solution, the arene rotates fast on the NMR timescale around the Mo2‐arene axis. For the substituted aromatic hydrocarbons, the NMR data are consistent with the existence of a major rotamer in which the metal atoms are coordinated to the more electron‐rich CC bonds.
Quintuply bound Mo2{HC(N‐2,6‐iPr2C6H3)2}2(arene) complexes (arene=C6H6, C6H5Me, C6H5OMe, p‐C6H4Me2, C6H5F, and p‐C6H4F2 and Dipp=2,6‐iPr2C6H3) have been prepared and structurally characterized by experimental and theoretical methods (see figure). Coordination of the arene to the quintuple MoI–MoI bond results in an effective metal–metal bond order substantially lower than five as a consequence of a strong electronic interaction between δ and δ* dimetal orbitals and the π and π* orbitals of the arene.
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•Use of terms “carbene” and “alkylidene” in organometallic chemistry is discussed.•Unusual species included are cationic Ni(III), Pd(II), Pt(IV) and Ag(I) alkylidenes.•Group 10 and 11 ...alkylidene complexes with no heteroatom stabilization are reviewed.
This review aims to offer a detailed summary of the discoveries regarding non-heteroatom-substituted alkylidenes of group 10 and 11 metals that have appeared in the literature since the first isolable representative of this class was reported in 2002. Special attention is focused on synthetic and bonding aspects of well-defined species. The importance of this family of compounds in catalytic organic transformations is often mentioned and a number of references are provided. We stress, however, that it is not the main issue of this review, as this topic has received considerable attention in the current literature.
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