Synthesis, characterisation and structural studies of amidinate and guanidinate alkaline earth–transition metal bonded complexes

Low-Valent Transition Metalate Anions in Synthesis, Small Molecule Activation, and Catalysis

This review surveys the synthesis and reactivity of low-oxidation state metalate anions of the d-block elements, with an emphasis on contributions reported between 2006 and 2022. Although the field has a long and rich history, the chemistry of transition metalate anions has been greatly enhanced in the last 15 years by the application of advanced concepts in complex synthesis and ligand design. In recent years, the potential of highly reactive metalate complexes in the fields of small molecule activation and homogeneous catalysis has become increasingly evident. Consequently, exciting applications in small molecule activation have been developed, including in catalytic transformations. This article intends to guide the reader through the fascinating world of low-valent transition metalates. The first part of the review describes the synthesis and reactivity of d-block metalates stabilized by an assortment of ligand frameworks, including carbonyls, isocyanides, alkenes and polyarenes, phosphines and phosphorus heterocycles, amides, and redox-active nitrogen-based ligands. Thereby, the reader will be familiarized with the impact of different ligand types on the physical and chemical properties of metalates. In addition, ion-pairing interactions and metal-metal bonding may have a dramatic influence on metalate structures and reactivities. The complex ramifications of these effects are examined in a separate section. The second part of the review is devoted to the reactivity of the metalates toward small inorganic molecules such as H2, N2, CO, CO2, P4 and related species. It is shown that the use of highly electron-rich and reactive metalates in small molecule activation translates into impressive catalytic properties in the hydrogenation of organic molecules and the reduction of N2, CO, and CO2. The results discussed in this review illustrate that the potential of transition metalate anions is increasingly being tapped for challenging catalytic processes with relevance to organic synthesis and energy conversion. Therefore, it is hoped that this review will serve as a useful resource to inspire further developments in this dynamic research field.

Mg(I)-Fe(-II) and Mg(0)-Mg(I) covalent bonding in the MgnFe(CO)4- (n = 1, 2) anion complexes: an infrared photodissociation spectroscopic and theoretical study

Heteronuclear magnesium-iron carbonyl anion complexes MgFe(CO)₄^- and Mg₂Fe(CO)₄^- are produced in the gas phase and are detected by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The geometric structures and the metal-metal bonding are discussed with the aid of quantum chemical calculations. Both complexes are characterized to have a doublet electronic ground state with C_3v symmetry containing a Mg-Fe bond or a Mg-Mg-Fe bonding unit. Bonding analyses indicate that each complex involves an electron-sharing Mg(I)-Fe(-II) σ bond. The Mg₂Fe(CO)₄^- complex involves a relatively weak covalent Mg(0)-Mg(I) σ bond.

Low-oxidation state cobalt-magnesium complexes: ion-pairing and reactivity

Magnesium cobaltates (Arnacnac)MgCo(COD)2 (1-3) were synthesised by reacting (Arnacnac)MgI(OEt2) with K[Co(η4-COD)2] (COD = 1,5-cyclooctadiene) [Arnacnac = CH(ArNCMe)2; Ar = 2,4,6-Me3-C6H2 (Mes), 2,6-Et2-C6H3 (Dep), 2,6-iPr2-C6H3Mes (Dipp)]. Compounds 1-3 form contact ion-pairs in toluene, while solvent separated ion-pairs are formed in THF. The effect of ion-pairing on the reactivity is illustrated by reaction of 2 with tert-butylphosphaalkyne, which affords distinct 1,3-diphosphacyclobutadiene complexes. The heteroleptic sandwich complex [(Depnacnac)MgCo(P2C2tBu2)]2 (4) is selectively formed in toluene, while the homoleptic bis(1,3-diphosphacyclobutadiene) complex [(Depnacnac)Mg(THF)3][Co(P2C2tBu2)2] (5) is obtained in THF. Complex 4 is a precursor to further unusual phosphaorganometallic compounds. Substitution of the labile COD ligand in 4 by white phosphorus (P4) enabled the synthesis of the phosphorus-rich sandwich compound [(Depnacnac)MgCoP4(P2C2tBu2)]2 (6). The heterobimetallic complex (Cp*NiP2C2tBu2)Co(COD) (7) was isolated after treatment of 4 with Cp*Ni(acac) (Cp* = C5Me5, acac = acetylacetonate).

Nature of the Short Rh-Li Contact between Lithium and the Rhodium ω-Alkenyl Complex [Rh(CH2CMe2CH2CH═CH2)2]. Inorg Chem 2021;60:8790-8801. [PMID: 34097392 DOI: 10.1021/acs.inorgchem.1c00737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

We describe the preparation of the cis-bis(η¹,η²-2,2-dimethylpent-4-en-1-yl)rhodate(I) anion, cis-[Rh(CH₂CMe₂CH₂CH═CH₂)₂]^-, and the interaction of this species with Li⁺ both in solution and in the solid state. For the lithium(diethyl ether) salt [Li(Et₂O)][Rh(CH₂CMe₂CH₂CH═CH₂)₂], VT-NMR and ¹H{⁷Li} NOE NMR studies in toluene-d₈ show that the Li⁺ cation is in close proximity to the d_z² orbital of rhodium. In the solid-state structure of the lithium(12-crown-4) salt [Li(12-crown-4)₂][Li{Rh(CH₂CMe₂CH₂CH═CH₂)₂}₂], one lithium atom is surrounded by two [Rh(CH₂CMe₂CH₂CH═CH₂)₂]^- anions, and in this assembly there are two unusually short Rh-Li distances of 2.48 Å. DFT calculations, natural energy decomposition, and ETS-NOCV analysis suggest that there is a weak dative interaction between the 4d_z² orbitals on the Rh centers and the 2p_z orbital of the Li⁺ cation. The charge-transfer term between Rh and Li⁺ contributes only about the 1/5 of the total interaction energy, however, and the principal driving force for the proximity of Rh and Li in compounds 1 and 2 is that Li⁺ is electrostatically attracted to negative charges on the dialkylrhodiate anions.

N,N'-Bis[2,6-bis-(1-methyl-eth-yl)phen-yl]pyridine-4-carboximidamide toluene hemisolvate

The title compound, C30H39N3·0.5C7H8, is a symmetrically N,N'-disubstituted aryl-amidine containing a 4-pyridyl substituent on the carbon atom of the N-C-N linkage and bulky 2,6-diiso-propyl-phenyl groups on the nitro-gen atoms. It crystallizes in the Z-anti configuration and its amidine C-N bonds present amine [1.368 (1) Å] and imine [1.286 (1) Å] features. Intra-molecular hydrogen bonds are present in the structure together with inter-molecular N-H⋯N and C-H⋯N inter-actions linking the mol-ecules in chains along the a- and c-axis directions.

3d–4f heterometallic complexes by the reduction of transition metal carbonyls with bulky LnII amidinates

Heterometallic lanthanide-transition metal carbonyl complexes [Sm₂–Co₂], [Yb–Co], and [Sm₂–Fe₃] have been synthesized by redox reactions between bulky amidinate stabilized divalent Ln and TM carbonyl complexes.

The addition of Grignard reagents to carbodiimides. The synthesis, structure and potential utilization of magnesium amidinates

Direct synthesis of magnesium amidinates of the general formula [RNC(R1)NR]MgR2 has been performed from appropriate carbodimide and Grignard reagents (R = iPr, Cy, pTol; R1 = Me, nBu; R2 = nBu, Cl, I). Magnesium bisamidinates of the composition [RNC(R1)NR]2Mg(solvent)2 are accessible from [RNC(R1)NR]MgR2 and via the Schlenk-like equilibrium in coordinating solvents. The only isolated amidinatomagnesium halide, preserved in the dinuclear form of {[pTolNC(Me)N-pTol]Mg(THF)}2-μ-(THF)-μ-(Cl)2, has been obtained from the reaction of pTol-N[double bond, length as m-dash]C[double bond, length as m-dash]N-pTol with MeMgCl(THF)n in hexane. The reaction of pTol-N[double bond, length as m-dash]C[double bond, length as m-dash]N-pTol with two equivalents of MeMgI gives an unprecedented dinuclear cyclic adduct {μ-[pTolNC(Me)N-pTol][MgI(OEt2)]2-μ-Me}. The structures of these complexes have been investigated by NMR spectroscopy, sc-XRD and theoretical methods. Selected complexes have been tested as initiators of ring-opening polymerization reactions with various substrates, the copolymerization of oxiranes and CO2 as well as the esterification of lactides.

Synthesis of copper(i) cyclic (alkyl)(amino)carbene complexes with potentially bidentate N^N, N^S and S^S ligands for efficient white photoluminescence

Copper(i) complexes of cyclic (alkyl)(amino)carbenes coordinated to monodentate or hemilabile guanidinato and formamidinato complexes show intense photoluminescence including white emissions.

Unravelling nucleophilic aromatic substitution pathways with bimetallic nucleophiles

Reaction of nucleophiles containing polar (Fe–Mg) and apolar (Mg–Mg) bonds with 2-(pentafluorophenyl)pyridine are calculated to proceed by stepwise and concerted S_NAr pathways respectively.