Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare-Earth Complexes: Non-Redox Oxygen Atom Transfer

Rare-earth metal ethylene and ethyne complexes

Guanidinate homometallic rare-earth ethyl complexes [LLn(μ2-η1:η2-Et)(Et)]2 (Ln = Y(1-Y), Lu(1-Lu)) and heterobimetallic rare-earth ethyl complexes LLn(Et)(μ2-η1:η2-Et)(μ2-η1-Et)(AlEt2) (Ln = Y(2-Y), Lu(2-Lu)) have been synthesized by the treatment of LLn(CH2C6H4NMe2-o)2 (L = (PhCH2)2NC(NC6H3iPr2-2,6)2) with different equivalents of AlEt3 in toluene at ambient temperature. Interestingly, the unprecedented rare-earth ethyne complex [LY(μ2-η1-Et)2(AlEt)]2(μ4-η1:η1:η2:η2-C2H2) (3-Y) containing a [C2H2]4- unit was afforded from 2-Y. The formation mechanism study on 3-Y was carried out by DFT calculations. Furthermore, the nature of the bonding of 3-Y was also revealed by NBO analysis. The reactions of LLn(CH2 C6H4NMe2-o)2 (Ln = Y, Lu) with AlEt3 (4 equiv.) in toluene at 50 °C produced firstly the non-Cp rare-earth ethylene complex LY(μ3-η1:η1:η2-C2H4)[(μ2-η1-Et)(AlEt2)(μ2-η1-Et)2(AlEt)] (4-Y), and the Y/Al ethyl complex LY[(μ2-η1-Et)2(AlEt2)]2 (5-Y) as an intermediate of 4-Y was isolated from the reaction of LY(CH2C6H4NMe2-o)2 with AlEt3 (4 equiv.) in toluene at -10 °C.

Diversity of transformation of heteroallenes on acenaphthene-1,2-diimine aluminum oxide

The reactions of oxide [(dpp-bian)Al(μ2-O)2Al(dpp-bian)] (1) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with phenyl- or cyclohexylisocyanates result in the formation of carbonimidate derivatives [(dpp-bian)Al(μ-O)(μ-RNCO2)Al(dpp-bian)] (R = Ph, 2; Cy, 3). Addition of N,N'-dicyclohexylcarbodiimide to compound 1 leads to the formation of ureate complex [(dpp-bian)Al(μ-O)(μ-(CyN)2CO)Al(dpp-bian)] (4). The reactions of the oxide 1 with pinacolborane and catecholborane afford oxo-bridged hydride [{(dpp-bian)Al(H)}(μ-O){Al(OBpin)(dpp-bian)}] (5) and compound [{(dpp-bian)Al(OBCat)}2(μ-O)] (7), respectively. Insertion of cyclohexylisocyanate into the Al-H bond of compound 5 gives CO insertion product [{(dpp-bian)Al(OC(H)NCy)}(μ-O){Al(OBpin)(dpp-bian)}] (6). New compounds have been characterized by ESR and IR spectroscopy; their molecular structures have been established by single-crystal X-ray analysis. The oxide 1 serves as a catalyst for the hydroboration of heteroallenes (isocyanates, carbodiimides) with pinacolborane.

A binuclear guanidinate yttrium carbyne complex: unique reactivity toward unsaturated C-N, C-O and C-S bonds

A guanidinato-stabilized binuclear yttrium carbyne complex [(PhCH2)2NC(NC6H3iPr2-2,6)2]2Y2(μ2-Me)(AlMe3)2(μ4-CH) (1) was synthesized via C-H bond activation and its versatile reactivities were investigated. Complex 1 underwent σ-bond metathesis with PhSSPh and nucleophilic addition with PhCN to form the corresponding yttrium thiolate complex 3 and aza-allyl complex 4 respectively. Additionally, the rare yttrium carbide complex 5 was also prepared by treatment of complex 1 with S8. Interestingly, in the reaction with PhNCS, the C[double bond, length as m-dash]S double bond was cleaved, followed by C-H bond activation to give the yttrium sulfide complex 7 with a ketenimine dianion ligand. Unexpectedly, the reaction of complex 1 with CO (1 atm) resulted in deoxygenative coupling of CO, to afford mono- or dioxo-yttrium complexes at different temperatures. The mechanism of the possible formation processes of complexes 3 and 9 was elucidated by DFT calculations.

Controllable carbonyl-assisted C(sp3)–C(sp3) bond reduction and reorganization

Unprecedentedly preferential reduction of unstrained C(sp3)–C(sp3) bond over ketone, hydrogenative [2+2+2]-cycloreversion of 2,4-diacylcyclohexanols, and cyclizative degradation of poly(vinylketone) have been achieved by organolanthanide catalysis.

Rare-earth-metal half-sandwich complexes incorporating methyl, methylidene, and hydrido ligands

Complexes Cp*₃Ln₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ (Ln = Y, Dy; Cp* = C₅Me₅) are formed via elimination of CH₄ and C₂H₄ from the respective trinuclear polymethyl complexes [Cp*Ln(μ₂-CH₃)₂]₃, involving the methyl/methylidene complex Cp*₃Ln₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-CH₃)(thf)₂ as an intermediate. Compound Cp*₃Y₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ displays "Schrock-type" nucleophilic carbene reactivity, converting ketones into the corresponding terminal alkenes. Treatment of Cp*₃Y₃(μ₂-CH₃)₃(μ₃-CH₂)(μ₃-H)(thf)₃ with [D₄]methanol proved accessibility of all small-group functionalities as indicated by the simultaneous formation of deuterated HD and deuterated methanes CH₃D and CH₂D₂.

Trinuclear scandium methylidyne complexes stabilized by pentamethylcyclopentadienyl ligands

The first examples of scandium methylidyne complexes [(Cp*)Sc(μ2-X)]3(μ3-CH) (Cp* = C5Me5; X = Br, Me, OMe), free of Lewis acids, can be achieved in high yields from [(Cp*)ScMe2]2 through a facile route. The chemical and geometrical flexibility to incorporate organic substrates indicates a rich chemistry of complex [(Cp*)Sc(μ2-OMe)]3(μ3-CH).

Reactivity of Ce(iv) imido compounds with heteroallenes

The reactivity of alkali metal capped Ce(iv) imido compounds [M(DME)₂][CeNAr^F(TriNOx)] (1-M with M = K, Rb, Cs and Ar^F = 3,5-bis(trifluoromethyl)phenyl) with CO₂ and organic isocyanates has been evaluated.

Carbonyl group and carbon dioxide activation by rare-earth-metal complexes

The rare-earth elements (Ln = Sc, Y, La-Lu) are widely used in stoichiometric and catalytic carbonyl group transformations. Sufficient availability, non-toxicity, high oxophilicity, tunable ion size/Lewis acidity and enhanced ligand exchangeability have been major driving factors for their successful implementation. Routinely employed reagents for stoichiometric carbonyl group transformations are divalent ytterbium and samarium compounds (e.g., ketone reduction), bimetallic CeCl3/LiR (C-C coupling), or ceric ammonium nitrate CAN (cyclic ketone oxidation). Rare-earth-metal triflates, and in particular Sc(OTf)3, are prominent examples of Lewis acid catalysts for versatile use in organic synthesis (e.g., Aldol and Michael reactions). Moreover, Ln(ii) and Ln(iii) complexes efficiently catalyze the (co)polymerization of carbonyl group-containing monomers including lactones, lactides, acrylates, and carbon dioxide. Featuring the most notorious greenhouse gas, CO2 is currently assessed as a cheap, abundant, and non-toxic C1 building block. Ln(iii) complexes are not only capable of efficient CO2 capture via reversible insertion but also of CO2 activation for catalytic conversions (copolymerization/cycloaddition with epoxides). This perspective focuses on structurally elucidated Ln complexes resulting from ketone or carbonyl derivative activation/insertion as well as carbon dioxide insertion products. The respective compounds will be sorted by structural motifs and, if applicable, details on reactivity and feasibility of catalytic reactions are presented. The article is subdivided in three parts: (i) donor and insertion products of ketones and aldehydes, (ii) redox-enhanced activation of carbonyl derivatives, and (iii) CO2 insertion/redox products and homogeneous catalytic conversion.

A Combined Experimental and Theoretical Study of the Versatile Reactivity of an Oxocerium(IV) Complex: Concerted Versus Reductive Addition

A combined experimental and theoretical investigation on the cerium(IV) oxo complex [(L_OEt )₂ Ce(=O)(H₂ O)]⋅MeC(O)NH₂ (1; L_OEt ^- =[Co(η⁵ -C₅ H₅ ){P(O)(OEt)₂ }₃ ]^- ) demonstrates that the intermediate spin-state nature of the ground state of the cerium complex is responsible for the versatility of its reactivity towards small molecules such as CO, CO₂ , SO₂ , and NO. CASSCF calculations together with magnetic susceptibility measurements indicate that the ground state of the cerium complex is of multiconfigurational character and comprised of 74 % of Ce^IV and 26 % of Ce^III . The latter is found to be responsible for its reductive addition behavior towards CO, SO₂ , and NO. This is the first report to date on the influence of the multiconfigurational ground state on the reactivity of a metal-oxo complex.

Yttrium dialkyl supported by a silaamidinate ligand: synthesis, structure and catalysis on cyclotrimerization of isocyanates

A four-coordinate yttrium dialkyl complex with a sterically demanding silaamidinate ligand exhibited high activity and excellent functional group tolerance for the catalysis of isocyanate cyclotrimerization.