New reactive, divalent lanthanoid formamidinates [Yb(Form)(2)(thf)(2)] (Form=[RNCHNR]; R=o-MeC(6)H(4) (o-TolForm; 1), 2,6-Me(2)C(6)H(3) (XylForm; 2), 2,4,6-Me(3)C(6)H(2) (MesForm; 3), 2,6-Et(2)C(6)H(3) (EtForm; 4), o-PhC(6)H(4) (o-PhPhForm; 5), 2,6-iPr(2)C(6)H(3) (DippForm; 6), o-HC(6)F(4) (TFForm; 7)) and [Eu(DippForm)(2)(thf)(2)] (8) have been prepared by redox transmetallation/protolysis reactions between an excess of a lanthanoid metal, Hg(C(6)F(5))(2) and the corresponding formamidine (HForm). X-ray crystal structures of 2-6 and 8 show them to be monomeric with six-coordinate lanthanoid atoms, chelating N,N'-Form ligands and cis-thf donors. However, [Yb(TFForm)(2)(thf)(2)] (7) crystallizes from THF as [Yb(TFForm)(2)(thf)(3)] (7a), in which ytterbium is seven coordinate and the thf ligands are "pseudo-meridional". Representative complexes undergo C-X (X=F, Cl, Br) activation reactions with perfluorodecalin, hexachloroethane or 1,2-dichloroethane, and 1-bromo-2,3,4,5-tetrafluorobenzene, giving [Yb(EtForm)(2)F](2) (9), [Yb(o-PhPhForm)(2)F](2) (10), [Yb(o-PhPhForm)(2)Cl(thf)(2)] (11), [Yb(DippForm)(2)Cl(thf)] (12) and [Yb(DippForm)(2)Br(thf)] (16). X-ray crystallography has shown 9 to be a six-coordinate, fluoride-bridged dimer, 12 and 16 to be six-coordinate monomers with the halide and thf ligands cis to each other, and 11 to have a seven-coordinate Yb atom with "pseudo-meridional" unidentate ligands and thf donors cis to each other. The analogous terbium compound [Tb(DippForm)(2)Cl(thf)(2)] (13), prepared by metathesis, has a similar structure to 11. C-Br activation also accompanies the redox transmetallation/protolysis reactions between La, Nd or Yb metals, Hg(2-BrC(6)F(4))(2), and HDippForm, yielding [Ln(DippForm)(2)Br(thf)] complexes (Ln=La (14), Nd (15), Yb (16)).
Four new cerium(III) formamidinate complexes comprising [Ce(p-TolForm)3 ], [Ce(DFForm)3 (thf)2 ], [Ce(DFForm)3 ], and [Ce(EtForm)3 ] were synthesized by protonolysis reactions using [Ce{N(SiMe3 )2 }3 ] and formamidines of varying functionality, namely N,N'-bis(4-methylphenyl)formamidine (p-TolFormH), N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH), and the sterically more demanding N,N'-bis(2,6-diethylphenyl)formamidine (EtFormH). The bimetallic cerium lithium complex [LiCe(DFForm)4 ] was synthesized by treating a mixture of [Ce{N(SiHMe2 )2 }3 (thf)2 ] and [Li{N(SiHMe2 )2 }] with four equivalents of DFFormH in toluene. Oxidation of the trivalent cerium(III) formamidinate complexes by trityl chloride (Ph3 CCl) caused dramatic color changes, although the cerium(IV) species appeared transient and reformed cerium(III) complexes and N'-trityl-N,N'-diarylformamidines shortly after oxidation. The first structurally characterized homoleptic cerium(IV) formamidinate complex [Ce(p-TolForm)4 ] was obtained through a protonolysis reaction between [Ce{N(SiHMe2 )2 }4 ] and four equivalents of p-TolFormH. [Ce{N(SiHMe2 )2 }4 ] was also treated with DFFormH and EtFormH, but the resulting cerium(IV) complexes decomposed before isolation was possible. The new cerium(IV) silylamide complex [Ce{N(SiMe3 )2 }3 (bda)0.5 ]2 (bda=1,4-benzenediolato) was synthesized by treatment of [Ce{N(SiMe3 )2 }3 ] with half an equivalent of 1,4-benzoquinone, and showed remarkable resistance towards protonolysis or reduction.
The preparation of a new heterobimetallic samarium(II) formamidinate complex and selected reactions of samarium(II) complexes and one samarium(III) formamidinate complex with benzophenone or CS2 are discussed. Treatment of the tris(formamidinato)samarium(III) complex [Sm(DippForm)3] 1 (DippForm = N,N'-bis(2,6-diisopropylphenyl)formamidinate, (CH(NC6H3-(i)Pr2-2,6)2) with potassium graphite in toluene yielded the dark brown heterobimetallic formamidinatosamarium(II)/potassium complex [KSm(DippForm)3]n 2. Divalent 2, a Lewis base solvent free homoleptic species, differs significantly from the related heteroleptic formamidinatosamarium(II) complex [Sm(DippForm)2(thf)2] 3 with respect to its constitution, structure, and reactivity toward benzophenone. While 2 reacts giving complex 1, the reaction of 3 with benzophenone generates the highly unusual [Sm(DippForm)2(thf){μ-OC(Ph)═(C6H5)C(Ph)2O}Sm(DippForm)2] (C6H5 = 1,4-cyclohexadiene-3-yl-6-ylidene) 4. The formation of 4 highlights a rare C-C coupling between a carbonyl carbon and the carbon at the para position of a phenyl group of the OCPh2 fragment. An analogous reaction of [Yb(DippForm)2(thf)2] gives an isostructural complex 4Yb. 3 reacts with carbon disulfide forming a light green dinuclear formamidinatosamarium(III) complex [{Sm(DippForm)2(thf)}2(μ-η(2)(C,S):κ(S',S″)-SCSCS2)] 5 through an unusual C-S coupling induced by an amidinatolanthanoid species giving the thioformylcarbonotrithioate ligand. The trivalent organometallic [Sm(DippForm)2(CCPh)(thf)] complex activates the C═O bond of benzophenone by an insertion reaction, forming the light yellow [Sm(DippForm)2{OC(Ph)2C2Ph}(thf)] 6 as a major product and light yellow unsolvated [Sm(DippForm)2{OC(Ph)2C2Ph}] 7 as a minor product. Molecular structures of complexes (2, 4-7) show that κ(N,N') bonding between a DippForm and samarium atom exists in all compounds, but in 2, DippForm also bridges K and Sm by 1κ(N):2κ(N') bonding and two 2,6-diisopropylphenyl groups are η(6)-bonded to potassium.
The synthesis of the bulky divalent (polyphenylcyclopentadienyl)lanthanoid sandwich complexes [Ln(C 5 Ph 5 ) 2 ] (Ln = Sm, Eu) and [Ln(C 5 Ph 4 H) 2 (solv)] (Ln = Sm, solv = thf; Ln = Eu, solv = dme)], from redoxtransmetalation/protolysis (RTP) reactions, has been achieved. An analogous reaction with Yb afforded the solvent-separated ion pair [Yb(dme) 4 ][C 5 Ph 4 H] 2 . In addition, rare divalent samarium halide complexes [Sm(C 5 Ph 5 )(μ-Br)(thf) 2 ] 2 and [Sm(C 5 Ph 4 H)I(thf) 3 ], were also prepared, either by RTP or ligand rearrangement. X-ray studies showed that the [Ln(C 5 Ph 5 ) 2 ] complexes adopt highly symmetrical sandwich structures, whereas the [Ln(C 5 Ph 4 H) 2 (solv)] complexes have open sandwich structures. The unexpected, but limited, solubility of the [Ln(C 5 Ph 5 ) 2 ] complexes allowed for variabletemperature NMR spectra of [Sm(C 5 Ph 5 ) 2 ] to be obtained. Detailed 1D and 2D NMR studies were conducted on [Sm(C 5 Ph 4 H) 2 (thf)] to ascertain its structure in donor and nondonor solvents. During the course of these studies, the mixed tetraarylcyclopentadienyl sandwich complex [Sm{C 5 (2,5-Ph) 2 (3,4-p-tol 2 )H} 2 (thf)] was also prepared in order to fully assign the spectrum of [Sm(C 5 Ph 4 H) 2 (thf)]. The europium sandwich complexes [Eu(C 5 Ph 5 ) 2 ] and [Eu(C 5 Ph 4 H) 2 (dme)] exhibit remarkable luminescence properties with high quantum yields (45% and 41%, respectively) coupled w i th long emission lifetimes (approximately 800 and 1300 ns, respectively) in toluene.
The homoleptic pyrazolate complexes [CeIII4(Me2pz)12] and [CeIV(Me2pz)4]2 quantitatively insert CO2 to give [CeIII4(Me2pz⋅CO2)12] and [CeIV(Me2pz⋅CO2)4], respectively (Me2pz=3,5‐dimethylpyrazolato). This process is reversible for both complexes, as observed by in situ IR and NMR spectroscopy in solution and by TGA in the solid state. By adjusting the molar ratio, one molecule of CO2 per [CeIV(Me2pz)4] complex could be inserted to give trimetallic [Ce3(Me2pz)9(Me2pz⋅CO2)3(thf)]. Both the cerous and ceric insertion products catalyze the formation of cyclic carbonates from epoxides and CO2 under mild conditions. In the absence of epoxide, the ceric catalyst is prone to reduction by the co‐catalyst tetra‐n‐butylammonium bromide (TBAB).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.