Metal Alkyl Research Articles

Superior Alkylating Agents for Bulky Esters/Ketones via Strontium‐Mediated Barbier‐Type Reaction

AbstractAn efficient method has been developed for the Barbier‐type alkylation reaction of bulky esters or ketones in the presence of metallic strontium and alkyl iodides. The reaction proceeded smoothly at ambient temperature to afford the fully alkylated corresponding alcohols in better yield than those obtained when using the corresponding Grignard reagents. The method is especially effective for introducing isobutyl or neopentyl groups into phenyl or adamantyl skeletons.

Sulfone–Metal Exchange and Alkylation of Sulfonylnitriles

AbstractThe first general sulfone–metal exchange is described. Treating substituted 2‐pyridylsulfonylacetonitriles with either BuLi or Bu3MgLi generates metalated nitriles that efficiently intercept a variety of electrophiles to afford quaternary nitriles. The 2‐pyridylsulfone is critical for the sulfone–metal exchange because chelation anchors the organometallic proximal to the electrophilic, tetrasubstituted sulfone to override complex‐induced deprotonation. Alkylating commercial 2‐pyridinesulfonylacetonitrile with mild bases, either K2CO3 or DBU, and subsequent sulfone–metal exchange and alkylation rapidly assembles quaternary nitriles by three alkylations, only one of which requires an organometallic reagent.

Ceric Cyclopentadienides Bearing Alkoxy, Aryloxy, Chlorido, or Iodido Co-Ligands.

A series of heteroleptic tris(cyclopentadienyl) CeIV complexes has been isolated and crystallographically characterized, revealing the broad accessibility of such organocerium(IV) compounds. The oxidation of complexes CpMe3 Ce(thf) and Cp'3 Ce(thf) (CpMe =C5 H4 Me, Cp'=C5 H4 SiMe3 ), bearing monosubstituted electron-poor cyclopentadienyl ligands, with 0.5 equivalents of 1,4-benzoquinone or C2 Cl6 gave the cerium(IV) hydroquinolate complexes CpMe3 Ce(OC6 H4 O)CeCpMe3 and Cp'3 Ce(OC6 H4 O)CeCp'3 , or the chloride complexes CpMe3 CeCl and Cp'3 CeCl, respectively; the iodide complex Cp'3 CeI was obtained from the reaction of Cp'3 Ce(thf) with elemental iodine. The behavior of Cp'3 CeCl in salt metathesis protocols employing alkali metal amides or alkyl, alkoxide, and aryloxide reagents was investigated, which gave rise to the robust and isolable cerium(IV) alkoxide Cp'3 Ce(OtBu). Trivalent [Cp'2 CeCl]2 was synthesized by AlMe4 →Cl exchange utilizing Cp'2 Ce(AlMe4 ) and AlMe2 Cl. The reactivity of [Cp'2 CeCl]2 towards the oxidants Ph3 CCl, C2 Cl6 , 1,4-benzoquinone, and I2 has been assessed, and has provided useful information on CeIII /CeIV redox deactivation pathways. In addition to X-ray structure analysis, all the complexes were characterized by NMR, DRIFT (diffuse reflectance IR Fourier transform), and UV/Vis spectroscopy as well as elemental analysis. The tetravalent compounds were further analyzed for their magnetic susceptibility by using Evans' method.

Novel cationic rare earth metal alkyl catalysts for precise olefin polymerization

ABSTRACTThis mini‐review provides recent progress in the synthesis of rare earth metal dialkyl complexes and their application as highly efficient and regio‐/stereoselective catalysts in the coordination‐insertion (co)polymerization of olefins such as styrene, isoprene, 1,3‐cyclohexadiene, and ocimene. Through modifying the coordination atom, the ligand skeleton, and the substitutent on the skeleton of the chelating ligand, tuning the electron density and the steric environment around the rare earth metal center, the precise control of the activity and regio‐/stereoselectivity of the (co)polymerization as well as the comonomer incorporation and sequence distribution of the resulting copolymers are achieved. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2271–2280

George A. Olah (1927-2017).

George A. Olah (1927-2017).

Aminophenolates of aluminium, gallium and zinc: Synthesis, characterization and polymerization activity

Complexes containing aminophenolate ligands are considered as very efficient initiators of ring‐opening polymerization (ROP). Our systematic studies of the reactions of two selected aminophenols, 2‐[(p‐tolylamino)methyl]‐4‐(2,4,4‐trimethylpentan‐2‐yl)phenol (L'H2) and 2‐cyclohexylaminomethyl‐4‐methylphenol (L″H2), with alkyl compounds of aluminium, gallium and zinc resulted in the formation of a variety of products depending on the type of metallic centre and alkyl groups bonded to metal atoms. New trinuclear aluminium complexes (Me5Al3(L′)2 (1) and Me5Al3(L″)2 (2)), monomeric aluminium (tBu2Al(L'H) (3) and tBu2Al(L″H) (5)) and gallium (tBu2Ga(L'H) (4) and tBu2Ga(L″H) (6)) compounds, and dinuclear gallium (Et2Ga(L″H)·Et3Ga (7)) and zinc (tBuZn(L″H)]2 (8)) complexes were isolated and characterized. The molecular and crystal structures of 7 and 8 were determined on the basis of an X‐ray diffraction study. Polymerization tests showed that only three complexes (6–8) had activity in the ROP of ε‐caprolactone, whereas 1–5 were inactive in ROP.

Photolysis of Pincer-Ligated PdII–Me Complexes in the Presence of Molecular Oxygen

The reactions of t-BuPNP and t-BuPCP PdII–Me complexes (t-BuPNP = 2,6-bis[(di-tert-butylphosphino)methyl]pyridine and t-BuPCP = 2,6-bis[(di-tert-butylphosphino)methyl]phenyl) with O2 are described and compared with the reported O2 reactivity of related PdII–Me complexes. [(t-BuPNP)PdMe]Cl was found to react with O2 upon photolysis resulting in oxidation of the pincer ligand backbone to produce a (t-BuPNO)PdCl complex. In contrast, photolysis of (t-BuPCP)PdMe with O2 resulted in oxidation of the Pd–Me group to form (t-BuPCP)PdOCO2H. Isotopic labeling, radical initiators, and solvent studies were used to gain insight into the mechanisms of these unusual reactions of late metal alkyls with molecular oxygen.

1,4-Specific copolymerization of 1,3-cyclohexadiene with isoprene and their terpolymerization with styrene by cationic half-sandwich fluorenyl rare-earth metal alkyl catalysts

1,4-Copolymerization of 1,3-cyclohexadiene with isoprene and terpolymerization with styrene have been achieved by cationic half-sandwich fluorenyl rare-earth metal species.

A fluorinated dialkoxide-based magnesium-ion electrolyte

A magnesium-ion battery electrolyte that results in high conductivity, 100% coulombic efficiency, and low overpotentials is presented. The fluorinated dialkoxide-based electrolyte is synthesized via a green route without the use of any metal alkyls.

Dispersion Forces, Disproportionation, and Stable High‐Valent Late Transition Metal Alkyls

AbstractThe transition metal tetra‐ and trinorbornyl bromide complexes, M(nor)4 (M=Fe, Co, Ni) and Ni(nor)3Br (nor=1‐bicyclo[2.2.1]hept‐1‐yl) and their homolytic fragmentations were studied computationally using hybrid density functional theory (DFT) at the B3PW91 and B3PW91‐D3 dispersion‐corrected levels. Experimental structures were well replicated; the dispersion correction resulted in shortened M−C bond lengths for the stable complexes, and it was found that Fe(nor)4 receives a remarkable 45.9 kcal mol−1 stabilization from the dispersion effects whereas the tetragonalized Co(nor)4 shows stabilization of 38.3 kcal mol−1. Ni(nor)4 was calculated to be highly tetragonalized with long Ni−C bonds, providing a rationale for its current synthetic inaccessibility. Isodesmic exchange evaluation for Fe(nor)4 confirmed that dispersion force attraction between norbornyl substituents is fundamental to the stability of these species.

Dispersion Forces, Disproportionation, and Stable High-Valent Late Transition Metal Alkyls.

The transition metal tetra- and trinorbornyl bromide complexes, M(nor)4 (M=Fe, Co, Ni) and Ni(nor)3 Br (nor=1-bicyclo[2.2.1]hept-1-yl) and their homolytic fragmentations were studied computationally using hybrid density functional theory (DFT) at the B3PW91 and B3PW91-D3 dispersion-corrected levels. Experimental structures were well replicated; the dispersion correction resulted in shortened M-C bond lengths for the stable complexes, and it was found that Fe(nor)4 receives a remarkable 45.9 kcal mol-1 stabilization from the dispersion effects whereas the tetragonalized Co(nor)4 shows stabilization of 38.3 kcal mol-1 . Ni(nor)4 was calculated to be highly tetragonalized with long Ni-C bonds, providing a rationale for its current synthetic inaccessibility. Isodesmic exchange evaluation for Fe(nor)4 confirmed that dispersion force attraction between norbornyl substituents is fundamental to the stability of these species.

Activation and Deactivation of Phillips Catalyst for Ethylene Polymerization Using Various Activators

The present article reveals important roles of metal alkyl activators in tuning the performance of the Phillips catalyst in ethylene polymerization. The addition of aluminum alkyl aids the activation of the catalyst, while excess addition leads to the loss of the activity. The balance between the activation and deactivation depends on the type of employed aluminum alkyl, and tri‐n‐octylaluminum offers the most efficient catalyst usage by preferentially suppressing the deactivation. The passivation of aluminum trialkyl with a hindered phenol mildens not only the deactivation but also chain transfer reactions, leading to an increment of high molecular weight fractions.image

Kinetic Isotope Effects as a Probe for the Protonolysis Mechanism of Alkylmetal Complexes: VTST/MT Calculations Based on DFT Potential Energy Surfaces

Protonolysis by platinum or palladium complexes has been extensively studied because it is the microscopic reverse of the C-H bond activation reaction. The protonolysis of (COD)PtIIMe2, which exhibits abnormally large kinetic isotope effects (KIEs), is proposed to occur via a concerted pathway (SE2 mechanism) with large tunneling. However, further investigation of KIEs for the protonolysis of ZnMe2 and others led to a conclusion that there is no noticeable correlation between the mechanism and magnitude of KIE. In this study, we demonstrated that variational transition state theory including multidimensional tunneling (VTST/MT) could accurately predict KIEs and Arrhenius parameters of the protonolysis of alkylmetal complexes based on the potential energy surfaces generated by density functional theory. The predicted KIEs, EaD - EaH values, and AH/AD ratios for the protonolysis of (COD)PtIIMe2 and ZnIIMe2 by TFA agreed very well with experimental values. The protonolysis of ZnMe2 with the concerted pathway has a very flat potential energy surface, which produces a very small tunneling effect and therefore a small KIE. The predicted KIE for the stepwise protonolysis (SE(ox) mechanism) of (COD)PtIIMe2 was much smaller than that of the concerted pathway, but greater than the KIE of the concerted protonolysis of ZnMe2. A large KIE, which entails a significant tunneling effect, could be used as an experimental probe of the concerted pathway. However, a normal or small KIE should not be used as an indicator of the stepwise mechanism, and the interplay between experiments and reliable theory including tunneling would be essential to uncover the mechanism correctly.

ChemInform Abstract: Lanthanides and Actinides: Annual Survey of Their Organometallic Chemistry Covering the Year 2015

AbstractReview: 176 refs.

Group 13 metal (Al, Ga, In) alkyls supported by N-heterocyclic carbenes for use in lactide ring-opening polymerization catalysis

The synthesis of several N-heterocyclic carbene (NHC) group 13 metal adducts of the type (NHC)MR3 [NHC=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IDipp); M=Al, Ga, In; R=Me, Et] is described. In the case of the In adduct (IMes)InMe3, characterization data include its X-ray crystallographic determined molecular structure. The prepared compounds act as efficient ring-opening polymerization (ROP) initiators of rac-lactide, allowing access to either linear poly(lactic acid) (PLA) or cyclic PLA depending on the nature of the initiator and the reaction conditions. For these NHC-MMe3 systems, the addition of benzyl alcohol (acting as a chain transfer agent) was found to be beneficial both to ROP activity and control. In particular, the Al and In systems (IMes)MMe3 (M=Al, In) in combination with BnOH are highly effective ROP initiators of rac-lactide at room temperature (TOF=600h−1).

Activation and selective oxy-functionalization of alkanes with metal complexes: Shilov reaction and some new aspects

The quest of selective catalytic reactions for direct conversion of alkanes into valued products remains to be the most important task objective of modern chemistry and metal complex catalysis. Nowadays it is adopted that the formation of metal–alkyl intermediates (MR) is a necessary condition for activation and functionalization of alkanes on metal complexes but the mechanism of subsequent reactions of metal alkyls remain obscure, so that effective catalytic systems of this kind are still rare and uncommon. Although it is widely adopted that alkane σ-complexes (M·RH) most frequently are primary hydrocarbon intermediates in these processes, low profile in the literature is given to their reactivity and these are often considered simply just as some ‘collision complexes’. Nevertheless, theoretical and experimental studies provide more and more evidence that the СН bonds in such complexes may be markedly weakened and/or polarized, thus opening wide horizons for occurrence of subsequent direct homolytic or heterolytic reactions of alkanes. This review addresses the discussion of new routes for activation and oxygenation of saturated hydrocarbons, including those via alkane σ-complexes, without formation of metal–alkyl intermediates.

Synthesis and structural characterization of NHC-stabilized Al(III) and Ga(III) alkyl cations and use in the ring-opening polymerization of lactide

Group 13 metal (Al, Ga) alkyls supported by N-heterocyclic carbenes (NHCs), (NHC)MMe3 (NHC = IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, IDipp = 1,3-di-diisopropylphenylimidazol-2-ylidene; M = Al, Ga), were successfully ionized via a methide abstraction route with B(C6F5)3 in the presence of an external Lewis base (THF, Et2O) to afford the corresponding cations of the type (NHC)MMe2(L)+ (L labile) as CH3B(C6F5)3- salts. Such cations, which are the first examples of NHC-stabilized Al and Ga cationic alkyls, are stable in solution (CH2Cl2) and the molecular structure of cation (IMes)AlMe2(Et2O)+ was determined by X-ray crystallographic diffraction studies. All cationic compounds were also tested as initiators of the ring-opening polymerization (ROP) of rac-lactide (rac-LA). The Al cation (IMes)AlMe2(THF)+ effectively polymerizes rac-LA at room temperature in the presence of BnOH to produce chain-length-controlled and narrow disperse polylactide (TOF = 160 h−1).

ChemInform Abstract: Palladium‐Catalyzed C(sp3)—C(sp2) Cross‐Coupling of Homoleptic Rare‐Earth Metal Trialkyl Complexes with Aryl Bromides: Efficient Synthesis of Functionalized Benzyltrimethylsilanes.

The first C(sp3)–C(sp2) cross-coupling of rare-earth metal alkyl complexes with aryl bromides has been developed. This reaction was conducted at low catalyst loading (0.5 mol%) and exhibited a broad substrate scope, thus providing a facile method for the synthesis of benzyltrimethylsilanes with diverse functional groups.

Promoting non-transition metal alkylation with organic halides in the presence of binary systems based on an organometallic compound and a transition metal compound: VIII. Selectivity of the binary systems action

Selectivity of action of binary systems based on an organometallic compound and a transition metal compound in a direct synthesis of organometallic compounds via alkylation of metals with organic halides has been considered. Study of the side reactions in the course of zinc and cadmium powders alkylation (gaseous hydrocarbons evolution) taken as an example has demonstrated that the increase in activity of the binary system components is accompanied by decrease in its selectivity. The intensity of the side reactions is steeply increased above certain temperature determined by the nature of the reactants and components of the binary system. The surface of the alkylated metal containing adatoms and small clusters of the transition metal promotes the side processes.

Promoting non-transition metal alkylation with organic halides in the presence of binary systems based on an organometallic compound and a transition metal compound: IX. Alkylation of aluminum and concluding remarks

Study of aluminum powder alkylation with ethyl bromide in the presence of ethylaluminum sesquibromide and copper(I) iodide has revealed that binary systems based on an organometallic compound and a transition metal compound are efficient promotors of direct synthesis of organoaluminum compounds as well. Major conclusions drawn in a series of studies on non-transition metals (Zn, Cd, and Al) alkylation with organic halides in the presence of the binary systems are summarized.