Arylamido Ligands Research Articles

Reduction of Carboxamides Into Amines Catalyzed by La[NH‐2,6‐iPr2‐4‐FcC6H2]3/HBpin

ABSTRACTReduction of carboxamides is an efficient approach to obtain the corresponding amines, albeit it is one of the most problematic. In this work, by use of pinacolborane (HBpin) as a reductant, the rare‐earth metal tris (arylamido) complex supported by a ferrocenyl‐modified arylamido ligand La[NH‐2,6‐iPr2‐4‐FcC6H2]3 was employed as a precatalyst for primary and secondary amide reductions. This catalyst system exhibited high activity toward hydroborative reduction of amides to amines under mild conditions, as well good tolerance for heteroatoms and functional groups in the reduction. A lanthanide hydride was experimentally verified as the active species and the reduction mechanism was proposed.

Gallium Methylene in the Pocket

Adduct complexes Ga6(μ-CH2)9(DMAP)3(THF) and Ga8(μ-CH2)12(PEt3)x (x = 4 and 6) could be obtained upon crystallization of Ga8(CH2)12 from THF/DMAP (hard Lewis bases) and PEt3 (soft Lewis base), respectively. Mixed methyl/methylene {Ga4} species with either bridging aryloxy, thiophenolato, or arylamido ligands were accessible via the treatment of Ga8(CH2)12 with phenols (HOC6H2Me3-2,4,6 and HOC6H3Me2-2,6), thiophenol HSC6H2Me3-2,4,6, and anilines (H2NC6H2Me3-2,4,6 and H2NC6H3Me2-2,6). Such tetrametallic complexes Ga4(μ2-CH2)2(CH3)4(μ2-XAr)4 (X = O, S, NH) are isostructural, displaying an adamantane-like core structure. The sterically more demanding phenol HOC6H3tBu2-2,6 afforded the {Ga5} cluster Ga5(μ2-CH2)6(OC6H3tBu2-2,6)3(THF)2 with the gallium centers exclusively bridged by methylene groups. Treatment of Ga8(CH2)12 with other protic substrates HOR/H2NR′, including HOCH2tBu, HOSi(OtBu)3, H2NC6H3iPr2-2,6, and H2NSiPh3 point to a pronounced stereoelectronic dependency and intricacy of such transformations but provided helpful information about potential side products such as [(CH3)2Ga(μ-X)]2 (X = OR, HNR′) and reaction intermediates. Efficient methylene → imido transformations using Ga8(CH2)12/aniline mixtures could not be implemented.

Monomeric, Divalent Vanadium Bis(arylamido) Complexes: Linkage Isomerism and Reactivity

Divalent complexes of vanadium were synthesized employing bulky silyl(aryl)amido ligands −N(SiiPr3)DIPP and −N(SitBu2Me)DIPP (DIPP = 2,6-iPr2C6H3). Solid-state structural characterization revealed that although the ligand −N(SiiPr3)DIPP supports a monomeric, bis(amido) complex of vanadium, its constitutional isomer −N(SitBu2Me)DIPP affords a homoleptic complex in which the vanadium center is sandwiched between the arene rings, an unusual binding mode for arylamido ligands. Magnetometry studies indicate that V[N(SiiPr3)DIPP]2 and V[(η5-DIPP)N(SitBu2Me)]2 have similar high-spin d3 electron configurations. However, spectroscopic methods, including electron paramagnetic resonance, nuclear magnetic resonance, infrared, and UV–visible spectroscopies, in addition to cyclic voltammetry and reactivity studies, suggest that V[N(SiiPr3)DIPP]2 is stereochemically nonrigid in solution, while V[(η5-DIPP)N(SitBu2Me)]2 is not. This nonrigidity explicitly impacts the reactivity of V[N(SiiPr3)DIPP]2, which can be used to a...

Synthesis, characterization and l-lactide polymerization behavior of rare-earth metal bis(silylamide) complexes supported by arylamido ligand

Salt metathesis of LnCl3, [2,6-iPr2C6H3N(SiMe3)]Li and LiN(SiHMe2)2 in 1:1:2 molar ratio in THF produced the mono-arylamido-ligated rare-earth metal bis(silylamide) complexes [2,6-iPr2C6H3N(SiMe3)]Ln[N(SiHMe2)2]2(THF) (Ln = Y (1), Lu (2), La (3)) in good isolated yields. All these complexes were characterized by elemental analysis, NMR spectroscopy and FT-IR spectroscopy. 1 was further structurally authenticated by single crystal X-ray diffraction. These complexes alone could serve as highly active initiators for l-lactide polymerization in toluene at 50 °C. Employing 1 as the initiator, l-lactide polymerization proceeded in a controllable fashion via the coordination-insertion mechanism verified by end group analysis of the oligomer.

Rare-earth metal bis(silylamide) complexes supported by mono-dentate arylamido ligand: synthesis, reactivity, and catalyst precursors in living cis-1,4-selective polymerization of isoprene.

The salt metathesis reaction of LnCl3 with 1 equivalent of arylamido lithium [2,6-(i)Pr2C6H3N(SiMe3)]Li followed by addition of 2 equivalents of LiN(SiHMe2)2 in THF at room temperature obtained neutral mono-arylamido-ligated rare-earth metal bis(silylamide) complexes [2,6-(i)Pr2C6H3N(SiMe3)]Ln[N(SiHMe2)2]2(THF) (Ln = Y (), Lu (), La ()) in good isolated yields. Treatment of with excess AlMe3 produced the mono(arylamido) Ln/Al heterotrinuclear methyl complexes [2,6-(i)Pr2C6H3N(SiMe3)]Ln[(μ-Me)2AlMe2]2 (Ln = Y (), Lu (), La ()) via amide-alkyl exchange. All these complexes were well-characterized by elemental analysis, NMR spectroscopy and FT-IR spectroscopy. , and were further structurally authenticated by X-ray crystallography. In the presence of [Ph3C][B(C6F5)4] and Al(i)Bu3, were highly active for cis-1,4-selective polymerization of isoprene, whereas /[Ph3C][B(C6F5)4]/Al(i)Bu3 promoted the polymerization in a living fashion.

Cobalt(II) amido complexes derived from a monodentate arylamido ligand featuring a highly electron-withdrawing C6F5 substituent.

A series of cobalt(ii) complexes of a highly electron-withdrawing amido ligand, [N(C6F5)(C6H3Pr(i)2-2,6)](-) (L), were synthesized and structurally characterized. Mononuclear [CoL(Cl)(TMEDA)] (3) and heterobimetallic [CoL2(μ-Cl)Li(THF)3] (4) were obtained by direct metathetical reactions of anhydrous CoCl2 with one molar equivalent of [LiL(TMEDA)] (1) (TMEDA = Me2NCH2CH2NMe2) and [LiL(THF)3] (2), respectively. Complex 3 underwent facile ligand substitution reactions with LiMe and NaN3, yielding the corresponding mixed-ligand complexes [CoL(X)(TMEDA)] (X = Me 5, N36). Treatment of 3 with NaOMe led to the heterobimetallic complex [CoL2(μ-OMe)Na(TMEDA)] (7). The solid-state structures of complexes 1-7 were established by X-ray diffraction analysis.

Exploring the Variable Hapticity of the Arylamide Ligand: Access to σ-Amidophenyl and π-Cyclohexadienylimine Structures

A study of the preference for σ vs π coordination of the arylamido ligand to a late transition metal shows that LiNPh2 reacts with RuHCl(PPh3)3 (1) to yield the bent-seat piano-stool complex RuH[(η5-C6H5)NPh](PPh3)2 (2a) but with RuHCl(CO)(PPh3)3 (3) to yield the σ-amide RuH(η1-NPh2)(CO)(PPh3)2 (4). The stability of the σ-bound NPh2 ligand in 4 reflects the π acidity of the CO ligand, which inhibits PPh3 loss. Carbonylation of 2a at 50 °C affords Ru(CO)3(PPh3)2 (8) and HNPh2, suggesting sequential π → σ isomerization and reductive elimination. The phenoxide ligand behaves similarly: RuH(η5-C6H5O)(PPh3)2 (2b) is formed from 1 but RuH(η1-OPh)(CO)(PPh3)3 (5) is formed from 3, and carbonylation of 2b gives 8 and phenol, although more forcing conditions are required (90 °C). The crystal structure of 2a is reported.

Half-Sandwich Rare Earth Metal Complexes as Novel Catalysts for Olefin Polymerization and Other Chemical Transformations

Abstract This article describes our recent studies on the synthesis and chemistry of mono(cyclopentadienyl)-ligated rare earth metal alkyl and hydride complexes. The half-sandwich mono- and dialkyl rare earth metal complexes are prepared either by alkane elimination reactions between trialkyl rare earth complexes and the neutral cyclopentadiene derivatives or by metathetical reactions of rare earth trichlorides with the alkali metal salts of the corresponding ligands. The reaction of the dialkyl complexes with an equivalent of a borate compound such as [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5)4] generates easily the corresponding cationic monoalkyl species, which serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins to yield a new family of polymer materials that show novel properties but are difficult to prepare by other catalysts. The half-sandwich monoalkyl rare earth complexes bearing the silylene-linked cyclopentadienyl–arylamido ligands act as excellent catalysts for the catalytic dimerization of terminal alkynes, cross coupling of terminal alkynes with isocyanides, and the catalytic addition of terminal alkyne C–H, amine N–H, and phosphine P–H bonds to carbodiimides. The hydrogenolysis of the dialkyl rare earth complexes with H2 affords a new class of polynuclear rare earth metal polyhydride complexes, which show unique features in both structure and reactivity.

Aluminum Complexes with Bidentate N,N‐Dialkylaniline–arylamido Ligands: Synthesis, Structures, and Catalytic Properties for Efficient Ring‐Opening Polymerization of ϵ‐Caprolactone

AbstractA number of Al complexes bearing bidentate N,N‐dialkylaniline–arylamido ligands, ortho‐(ArNCH2)C6H4NR2AlMe2 (R = Me, Ar = 2,6‐iPr2C6H3, 3a; 2,6‐Et2C6H3, 3b; 2,6‐Me2C6H3, 3c; 4‐MeC6H4, 3d; Ph, 3e; and R = Et, Ar = 2,6‐iPr2C6H3, 3f; 2,6‐Me2C6H3, 3g; Ph, 3h), have been synthesized from the reaction of the corresponding free ligands, ortho‐(ArNHCH2)C6H4NR2 (R = Me, Ar = 2,6‐iPr2C6H3, 2a; 2,6‐Et2C6H3, 2b; 2,6‐Me2C6H3, 2c; 4‐MeC6H4, 2d; Ph, 2e; and R = Et, Ar = 2,6‐iPr2C6H3, 2f; 2,6‐Me2C6H3, 2g; Ph, 2h), with AlMe3 (1 equiv.). All complexes were characterized by 1H and 13C NMR spectroscopy and elemental analysis. Single‐crystal X‐ray diffraction analysis of complexes 3c and 3e revealed that these Al complexes have a distorted tetrahedral geometry around the metal center. All complexes were found to be efficient catalysts for the ring‐opening polymerization of ϵ‐caprolactone (CL) in the presence of benzyl alcohol, and complexes 3a–h catalyze the polymerization of CL in a living fashion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Unusual Iron(II) and Cobalt(II) Complexes Derived from Monodentate Arylamido Ligands

The coordination chemistry of the N-substituted arylamido ligands [N(R)(C6H3R'2-2,6)] [R = SiMe3, R' = Me (L1); R = CH2But, R' = Pri (L2)] toward FeII and CoII ions was studied. The monoamido complexes [M(L1)(Cl)(tmeda)] [M = Fe (1), Co (2)] react readily with MeLi, affording the mononuclear, paramagnetic iron(II) and cobalt(II) methyl-arylamido complexes [M(L1)(Me)(tmeda)] [M = Fe (3), Co (4)]. Treatment of 2:1 [Li(L2)(THF)2]/FeCl2 affords the unusual two-coordinate iron(II) bis(arylamide) [Fe(L2)2] (5).

Nucleophilic aromatic substitution on aryl-amido ligands promoted by oxidizing osmium(IV) centers.

Addition of amine nucleophiles to acetonitrile solutions of the OsIV anilido complex TpOs(NHPh)Cl2 (1) [Tp = hydrotris(1-pyrazolyl)borate] gives products with derivatized anilido ligands, i.e., TpOs[NH-p-C6H4(N(CH2)5)]Cl2 (2) from piperidine and TpOs[NH-p-C6H4N(CH2)4]Cl2 (3) from pyrrolidine. These materials are formed in approximately 30% yield under anaerobic conditions, together with approximately 60% yields of the OsIII aniline complex TpOs(NH2Ph)Cl2 (5). Formation of the para-substituted materials 2 or 3 from 1 involves oxidative removal of two hydrogen atoms (two H+ and two e-). The oxidation can be accomplished by 1, forming 5, or by O2. Related reactions have been observed with other amines and with the 2-naphthylamido derivative, which gives an ortho-substituted product. Kinetic studies indicate an addition-elimination mechanism involving initial attack of the amine nucleophile on the anilido ligand. These are unusual examples of nucleophilic aromatic substitution of hydrogen. Ab initio calculations on 1 show that the LUMO has significant density at the ortho and para positions of the anilido ligand, resembling the LUMO of nitrobenzene. By analogy with nucleophilic aromatic substitution, 2 is quantitatively formed from piperidine and the p-chloroanilide TpOs(NH-p-C6H4Cl)Cl2 (7). Binding the anilide ligands to an oxidizing OsIV center thus causes a remarkable umpolung or inversion of chemical character from a typically electron-rich anilido to an electron-deficient aromatic functionality. This occurs because of the coupling of redox changes at the TpOsIV center with bond formation at the coordinated ligand.

Non-cyclopentadienyl Titanium(III)−Magnesium Hydride Formation by Reduction of an Amidotitanium(IV) Complex

The reduction of an arylamido-based titanium(IV) chloride by magnesium has resulted in the formation of a unique, non-cyclopentadienyl titanium(III)-magnesium hydride with the concomitant intramolecular metalation of the arylamido ligands.

Synthesis and structure of four-coordinate dimethyl aluminium complexes incorporating new N,O-chelating arylamido ligands

A new type of arylamido ligands with an intramolecular coordinating ortho-ether-substituent (i.e. a O,N − chelating ligand) is introduced. The achiral and chiral 4-coordinate dimethyl aluminium complexes [2-ROC 6H 4NR′]AlMe 2 ( 4a: R=R′=Cy; 4b: R=(−)-menthyl, R′=Cy, 4c: R=(−)-menthyl, R′=CPh 3) have been prepared by reaction of the appropriate amido Li salt with ClAlMe 2. Complex 4a could also be obtained, via methane elimination, by reaction of AlMe 3 with the corresponding ligand. The presence of two rotamers in solution at room temperature for 4b and for 4c is most likely due to a restricted rotation of the (−)-menthyl group at this temperature due to severe steric interactions with the rest of the complex.

ChemInform Abstract: Molybdenum and Tungsten Nitrosyl Complexes Containing Bulky Alkoxy, Aryloxy, and Arylamido Ligands: Their Electrochemical Behaviour and the Structure of [Mo{HB(Me2pz)3}(NO)I(OCH2CH2CH2Br)] .

AbstractMolybdenum and Tungsten Nitrosyl Complexes Containing Bulky Alkoxy, Aryloxy, and Arylamido Ligands: Their Electrochemical Behaviour and the Structure of lMo HB(Me,pz)3 (NO)I(OCH2CH2CH2Br)I. ‐ The title complexes (III) and (V) have been prepared by reaction of (I) under different conditions.

Molybdenum and tungsten nitrosyl complexes containing bulky alkoxy, aryloxy, and arylamido ligands: their electrochemical behaviour and the structure of [Mo{HB(Me2pz)3}(NO)I(OCH2CH2CH2Br)

The complexes [Mo{HB(Me2pz)3}(NO)X(NHR′)](X = I, R′=o-C6H4Me, 2,5-Me2C6H3, CHPh2, p-C6H4CN, p-C6H4N2Ph, p-C6H4N2C6H4NO2-p; XCl, R′=p-C6H4I), [W{HB(Me2pz)3}(NO)Cl(NHR′)](R′= CHPh2 or p-C6H4I), [Mo{HB(Me2pz)3}(NO)I(OR)](R = CH2CH2CH2Br, p-CH2C6H4Br, or p-C6H4CN), and [W{HB(Me2pz)3}(NO)Cl(OR)](R = Ph, CH2CH2CH2Br, or p-CH2C6H4-Br)(Me2pz = 3,5- dimethylpyrazolyl) have been prepared and characterised spectroscopically. Electrochemical studies (cyclic voltammetry, coulometry) of these complexes in acetonitrile established that all underwent at least one one-electron reduction process, some of which were reversible. The E1/2 values for the reduction were dependent on the nature of the metal, the halide, and the NHR′ or OR group. The structure of [Mo{HB(Me2pz)3}(NO)I(OCH2CH2CH2Br)] was determined crystallographically. The six-co-ordinate nature of the complex was confirmed and the Mo–O bond distance was 1.89 A, comparable to that in other related compounds.