Tmeda Ligand Research Articles

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)-Centre: Labile Mono- and Bis(hydridogallyl)zinc Complexes.

In the presence of TMEDA (N,N,N',N'-tetramethylethylenediamine), partially deaggregated zinc dihydride as hydrocarbon suspensions react with the gallium(I) compound [(BDI)Ga] (I, BDI={HC(C(CH3 )N(2,6-iPr2 -C6 H3 ))2 }- ) by formal oxidative addition of a Zn-H bond to the gallium(I) centre. Dissociation of the labile TMEDA ligand in the resulting complex [(BDI)Ga(H)-(H)Zn(tmeda)] (1) facilitates insertion of a second equiv. of I into the remaining Zn-H to form a thermally sensitive trinuclear species [{(BDI)Ga(H)}2 Zn] (2). Compound 1 exchanges with polymeric zinc dideuteride [ZnD2 ]n in the presence of TMEDA, and with compounds I and 2 via sequential and reversible ligand dissociation and gallium(I) insertion. Spectroscopic and computational studies demonstrate the reversibility of oxidative addition of each Zn-H bond to the gallium(I) centres.

Syntheses, Structures, Magnetic Properties and Antibacterial Activities of Two Copper(II) Azido Complexes with Varied Nuclearities Containing Symmetrical 1,3-Diammine as Chelator

Two copper(II) azido complexes of the types mononuclear [Cu(TMEDA)2(N3)2] (1) and dinuclear [Cu(TMEDA)(μ1,1-N3)(N3)]2 (2) [TMEDA = trimethylenediamine; N3 – = azide ion] have been synthesized and characterized. X-ray structural analysis revealed that each copper(II) center in complex 1 adopts a distorted octahedron geometry with a CuN6 chromophore ligated through four N atoms of two different symmetrical TMEDA ligands as bidentate chelator and two N atoms of two terminal azides. In complex 2, each copper(II) center adopts a distorted square pyramidal geometry with a CuN5 chromophore ligated through two N atoms of TMEDA as bidentate chelator and two N atoms of two different azides as μ1,1-N3 bridging mode and one N atom of terminal azide ion. The two copper centers are connected through double μ1,1-N3 bridges affording a dinuclear structure with Cu···Cu separation 3.327(2) Å. In crystalline state, mononuclear units in complex 1 are associated through intermolecular N-H···N and C-H···N hydrogen bonds to form a 2D sheet structure viewed along crystallographic b-axis, whereas dinuclear entities in complex 2 are propagated through intermolecular N-H···N and C-H···N hydrogen bonds to form a 3D network structure viewed along crystallographic a-axis. The Variable-temperature magnetic susceptibility measurement evidenced a dominant antiferromagnetic interaction between the metal centers through μ1,1-azide bridges in complex 2 with J = − 0.40 cm-1. The antibacterial activities of the complexes have also been studied.

Catalytic and stoichiometric reactions of Arylpalladium(II) complexes bearing a trans-chelating dinitrogen ligand with arylboronic acids

Pd(II) complexes with 1,2-bis(2′-pyridylethylnyl)benzene (bpeb) ligand, PdCl2(bpep) and Pd(OAc)2(bpep), catalyze cross-coupling of arylboronic acids and aryl iodide, in spite of the trans-chelation of the ligand. Arylpalladium iodo and trifluoroacetate complexes with bpep ligand, Pd(C6H4X-4)(I)(bpep) (3a-3h, X = OMe, Me, H, COMe, CHO, COOEt, NO2, F), Pd(C6H3F2-2,4)(I)(bpep) (3i), Pd(C6H4X-4)(OCOCF3)(bpep) (4a-4e, X = OMe, Me, H, COMe, CHO) and Pd(C6F5)(OCOCF3)(bpep) (4j), were obtained by ligand exchange of the Pd complexes having tmeda ligand (tmeda = N,N,N′,N′-tetramethylethylenedi-amine). X-ray crystallographic results of arylpalladium(II) trifluoroacetate complex, Pd(C6H4OMe-4)(OCOCF3)(bpeb) (4a), and bis(trifluoroacetate)palladium(II) complex, Pd(OCOCF3)2(bpeb) (5) revealed the structures with two pyridyl groups of bpeb coordinated to Pd(II) in a trans-chelating bidentate mode. 2-Pyridyl hydrogens and an acetate oxygen of 5 are at close positions to each other (2.52 and 2.66 Å). The reaction of (4-MeC6H4)B(OH)2 (7b) with Pd(C6H4OMe-4)(OCOCF3)(bpeb) (4a) in the presence of Ag2O yields Pd(C6H4Me-4)(OCOCF3)(bpeb) (4b) via exchange of the aryl group between the palladium complex and arylboronic acid. The reaction of (4-CHOC6H4)B(OH)2 (7e) yields not only Pd(C6H4CHO-4)(OCOCF3)(bpeb) (4e) but also biaryls, 4-MeOC6H4-C6H4Y-4 (Y = OMe (8a), CHO (8e)). Hammett plots of the reaction exchange suggest higher reactivity of the Pd complex with more electron-donating aryl ligand.

Lithiation of N-Heterocyclic Olefins

Deprotonation of 1,3-dimethyl-2-methyleneimidazole (MeNHO) by nBuLi in hexane/benzene is fast and clean and gave a precipitate of the product in which the MeNHO ligand is cleanly lithiated in the alkene backbone (1). Lithiation of the much bulkier 1,3-bis(2,6-di-iso-propylphenyl)-2-methyleneimidazole (DIPPNHO) needs the presence of TMEDA as a cosolvent to give backbone lithiation (2). Depending on the cosolvent, the following products could be crystallized and fully characterized by X-ray diffraction and NMR: 1-THF, 1-TMEDA, 1-(TMEDA)0.5, and 2-TMEDA. The MeNHO ligand with a saturated backbone is less easily lithiated by nBuLi and does not even react at elevated temperatures. Addition of TMEDA, however, already gave decomposition at room temperature by ring opening to give a complex aggregate consisting of a dilithiated ligand fragment and two lithiated TMEDA ligands. DFT calculations shed light on a possible mechanism for cleavage of one of the cyclic C–N bonds. This process, which most likely goes throu...

Tri- (M = CuII) and hexanuclear (M = NiII, CoII) heterometallic coordination compounds with ferrocene monocarboxylate ligands: Solid-state structures and thermogravimetric, electrochemical and magnetic properties

The synthesis and characterization of the hexanuclear [M2(κO-O2CFc)2(µ-O2CFc)2(µ-H2O)(κ2N,N′-tmeda)2] (MII=Ni, 5; Co, 6; Fc=ferrocenyl, (η5-C5H4)(η5-C5H5)Fe; tmeda=N,N,N′,N′-tetramethylethylendiamine) and the trinuclear [Cu(κ2N,N′-tmeda)(κ2O,O′-O2CFc)2 2] (7) coordination compounds are described. Compounds 5–7 were prepared by the consecutive reaction of ferrocene carboxylic acid (FcCO2H; 1) with [nBu4N]OH followed by treatment of in situ formed [nBu4N][FcCO2] with the metal salts [M(tmeda)(NO3)2] (M=Ni, 2; Co, 3; Cu, 4). The structures of 5–7 in the solid state were determined by single crystal X-ray diffraction analysis. Isostructural 5 and 6 crystallise in the triclinic P1¯ (5) and in the monoclinic space group P21/n (6). The two MII(tmeda) entities of 5 and 6 with MII=Ni, Co, respectively, are syn, syn-bridged by two FcCO2− functionalities and one µ-bridging water molecule. Additionally, two FcCO2− ligands are κO-coordinated to each MII ion to form octahedral MN2O4 coordination setups. A related MN2O4 coordination setup is observed for 7 as well, whereby the CuII ion is coordinated by two O2CFc and one tmeda ligand. Electrochemical investigations reveal that all individual Fc units of 5–7 are oxidized separately. Thermogravimetric analysis showed that 5 and 6 start to decompose at 110 and 125°C and thus at significantly lower temperatures compared to 7 (200°C). The mass residues obtained after decomposition are composed of Fe2O3, FeNi3 and Fe0.64Ni=Ni0.36 (5), Fe and Co3O4 (6) and Cu2O and CuFeO2 (7), as determined by powder X-ray diffraction analysis (PXRD). Thermal susceptibility measurements of 5 and 6 determined a weak antiferromagnetic coupling in 5 and 6 with J=1.1K and J=1.9K, respectively.

Mixed-Ligand Approach to Palladium-Catalyzed Direct Arylation Polymerization: Effective Prevention of Structural Defects Using Diamines

This paper reports a novel mixed ligand catalyst for palladium-catalyzed direct arylation polymerization (DArP) of 2,6-diiododithienosilole (DTS-I2) and thienopyrroledione (TPD-H2) to give poly(DTS-alt-TPD). It has been documented that this monomer combination has a marked tendency to form homocoupling and branching defects in polymer chains, and the latter defects eventually lead to the formation of insoluble materials. This paper demonstrates that the combined use of P(o-MeOC6H4)3 and TMEDA ligands effectively prevents the defect formation. The side reactions that afford structural defects constitute a sequential process triggered by the reduction of DTS-I units. TMEDA as a simple diamine effectively inhibits the reduction of DTS-I units, giving poly(DTS-alt-TPD) (MnGPC = 20 000) in high cross-coupling selectivity (99%).

Exploring the reactivity of dimethylzinc with fluorine substituted 1-phenyl-4,5-dihydro-1H-pyrazol-5-ols

In the present study, different fluorine substituted 1-phenyl-4,5-dihydro-1H-pyrazol-5-ols have been synthesized in moderate yields and characterized by X-ray crystallography, revealing a high stability of the cyclic hemiaminal form in the solid state. Furthermore, NMR investigations confirmed this structural motif in solution. Interestingly, the formation of the corresponding pyrazoles by elimination of water was not observed under described reaction conditions, probably due to stabilization effects of the fluorine substitution. The ligands were treated with dimethylzinc and N,N,Ń,Ń-tetramethylethylenediamine (tmeda) in a 1:1:1 molar ratio to form tetrahedral monomeric complexes with a RO–Zn–Me motif. The additional coordination sites at the zinc are occupied by the tmeda ligand (η2-coordination). On the other hand, increasing the amount of ligands revealed the formation of complexes with a (RO)2–Zn–(tmeda) motif. Interestingly, with the highly fluorinated 1-phenyl-4,5-dihydro-1H-pyrazol-5-ols a new coordination mode (monodentate O-coordination) of pyrazoline ligands was observed.

Coordination Diversity in Mono- and Oligonuclear Copper(II) Complexes of Pyridine-2-Hydroxamic and Pyridine-2,6-Dihydroxamic Acids

Solution and solid state studies on Cu(II) complexes of pyridine-2-hydroxamic acid (HPicHA) and pyridine-2,6-dihydroxamic acid (H2PyDHA) were carried out. The use of methanol/water solvent allowed us to investigate the Cu(II)-HPicHA equilibria under homogeneous conditions between pH 1 and 11. In agreement with ESI-MS indication, the potentiometric data fitted very well with the model usually reported for copper(II) complexes of α-aminohydroxamate complexes ([CuL](+), [Cu5(LH-1)4](2+), [CuL2], [CuL2H-1](-)), however with much higher stability of the 12-MC-4 species. A series of copper(II) complexes has been isolated in the solid state and characterized by a variety of spectroscopic methods, X-ray structure analysis, and magnetic susceptibility measurements. The ligands show the tendency to form bi- and trinuclear species with copper(II) ions due to the {(N,N'); (O,O')} bis-(bidentate) chelating-and-bridging mode involving (O,O')-hydroxamate chelate formation combined with (N,N') chelating with participation of the pyridine and hydroxamic nitrogen atoms, so that the hydroxamate groups play a μ2-(N,O)-bridging role. Molecular and crystal structures of three synthesized complexes [Cu3(PicHA-H)2(dipy)2](ClO4)2·4/3DMSO·2/3H2O (1), [Cu2(PyDHA)(dipy)2(ClO4)2]·DMF·H2O (4), and [Cu3(PyDHA-2H)(tmeda)3](ClO4)2 (5) (dipy, 2,2'-dipyridyl; tmeda, N,N,N',N'-tetramethyl-1,2-diaminoethane) have been determined by single crystal X-ray analysis. In 1, two trans-situated doubly deprotonated hydroxamic ligands play a {(O,O')(N,N')}-(bis)bidentate-bridging function forming bridges between the medial, Cu(2) (CuN4), and the terminal, Cu(1) and Cu(3) (CuN2O2), copper(II) ions; the chelating dipy ligands are coordinated to the latter. In 4, the ligand is coordinated in a classical (O,O')-hydroxamate chelating mode with the help of two separate hydroxamic groups while the central tridentate donor compartment remains vacant. In 5, the hydroxamate ligand is coordinated by the {(O,O');(N,N',N″);(O″,O"')}-tridentate-(bis)bidentate mode, bridging three copper(II) ions, while the chelating tmeda ligands are coordinated to all three copper(II) ions. Magnetic susceptibility measurements (1.7-300 K) of powdered samples of the trinuclear complexes 1 and 5 revealed strong antiferromagnetic coupling between the copper(II) ions mediated by the hydroxamate bridges.

Heterobimetallic Coordination Polymers Based on the [Pt(SCN)4]2– and [Pt(SeCN)4]2– Building Blocks

New complexes and the first coordination polymers containing [Pt(SCN)4](2-) of the type [M(L)x][Pt(SCN)4] (where L = 2,2'-bipyridine (bipy), x = 2, M = Co(II), Ni(II), Cu(II); L = ethylenediamine (en), x = 2, M = Ni(II), Cu(II); L = N,N,N',N'-tetramethylethylenediamine (tmeda), x = 1, M = Cu(II); L = 2,2';6',2″-terpyridine (terpy), x = 1, M = Mn(II), Co(II); L = 1,10-phenanthroline (phen), x = 2, M = Pb(II)) were prepared by reacting the appropriate metal-ligand cations with K2[Pt(SCN)4] and structurally characterized. [M(bipy)2Pt(SCN)4]2·2MeOH (M = Co (1), Cu (4)) consist of supramolecular tetranuclear distorted squares containing two [M(bipy)2](2+) and two [Pt(SCN)4](2+) units. [Cu(bipy)2(NCS)]2[Pt(SCN)4] (6) is a double salt of the [Pt(SCN)4](2-) anion and two [Cu(bipy)(NCS)](+) cations. [Cu(en)2Pt(SCN)4] (7, 8) are 1-D coordination polymers that are coordinated in either cis or trans fashion at the [Pt(SCN)4](2-) unit, for 7 and 8, respectively. Complexes [Cu(en)2Pt(SeCN)4] (9) and [Ni(en)2Pt(SCN)4] (10) are similar to 8 and 7, respectively, but complex 9 (prepared using ((n)Bu4N)2[Pt(SeCN)4]) also presents intermolecular Se-Se interactions which resulted in an increased dimensionality. Compounds [M(terpy)Pt(SCN)4] (M = Mn (11), Co (13)) involve 2-D sheets of [M(terpy)](2+) and [Pt(SCN)4](2-) units, whereas [Mn(terpy)2][Pt(SCN)4] (12) is a double salt of one [Mn(terpy)2](2+) unit and one [Pt(SCN)4](2-). [Cu(tmeda)Pt(SCN)4] (14) contains a five-coordinate Cu(2+) metal center coordinated to one tmeda ligand and three different [Pt(SCN)4](2-) units, resulting in 2-D sheets. [Pb(phen)2Pt(SCN)4] (15) contains an 8-coordinate Pb(2+) metal center coordinated to two phen ligands and four [Pt(SCN)4](2-), generating a 3-D network in the solid state. Structural correlations were established between the ancillary ligand, the choice of metal, the structure of the [Pt(SCN)4](2-) building block, and the resulting dimensionality of the coordination polymers.

Pd(Fmes)2(tmeda)]: A Case of Intermittent CH⋅⋅⋅FC Hydrogen‐Bond Interaction in Solution

The X-ray structure of the title compound [Pd(Fmes)2 (tmeda)] (Fmes=2,4,6-tris(trifluoromethyl)phenyl; tmeda=N,N,N',N'-tetramethylethylenediamine) shows the existence of uncommon CH⋅⋅⋅FC hydrogen-bond interactions between methyl groups of the TMEDA ligand and ortho-CF3 groups of the Fmes ligand. The (19) F NMR spectra in CD2 Cl2 at very low temperature (157 K) detect restricted rotation for the two ortho-CF3 groups involved in hydrogen bonding, which might suggest that the hydrogen bond is responsible for this hindrance to rotation. However, a theoretical study of the hydrogen-bond energy shows that it is too weak (about 7 kJ mol(-1) ) to account for the rotational barrier observed (ΔH(≠) =26.8 kJ mol(-1) ), and it is the steric hindrance associated with the puckering of the TMEDA ligand that should be held responsible for most of the rotational barrier. At higher temperatures the rotation becomes fast, which requires that the hydrogen bond is continuously being split up and restored and exists only intermittently, following the pulse of the conformational changes of TMEDA.

Ligand Dynamics in the Solid: Lithium‐fluorenide and Lithium‐benzo[b]fluorenide N,N,N′,N′‐Tetramethylethylenediamine (tmeda) Complexes

AbstractThe dynamic behavior of the N,N,N′,N′‐tetramethylethylenediamine (tmeda) ligand has been studied in solid lithium‐fluorenide(tmeda) (3) and lithium‐benzo[b]fluorenide(tmeda) (4) using CP/MAS solid‐state 13C‐ and 15N‐NMR spectroscopy. It is shown that, in the ground state, the tmeda ligand is oriented parallel to the long molecular axis of the fluorenide and benzo[b]fluorenide systems. At low temperature (<250 K), the 13C‐NMR spectrum exhibits two MeN signals. A dynamic process, assigned to a 180° rotation of the five‐membered metallacycle (π‐flip), leads at elevated temperatures to coalescence of these signals. Line‐shape calculations yield ΔH‡=42.7 kJ mol−1, ΔS‡=−5.3 J mol−1 K−1, and $\rm{\Delta G_{298}^{\ddag}}$=44.3 kJ mol−1 for 3, and ΔH‡=36.8 kJ mol−1, ΔS‡=−17.7 J mol−1 K−1, and $\rm{\Delta G_{298}^{\ddag}}$=42.1 kJ mol−1 for 4, respectively. A second dynamic process, assigned to ring inversion of the tmeda ligand, was detected from the temperature dependence of T1ρ, the 13C spin‐lattice relaxation time in the rotating frame, and led to ΔH‡=24.8 kJ mol−1, ΔS‡=−49.2 J mol−1 K−1, and $\rm{\Delta G_{298}^{\ddag}}$=39.5 kJ mol−1 for 3, and ΔH‡=18.2 kJ mol−1, ΔS‡=−65.3 J mol−1 K−1, and $\rm{\Delta G_{298}^{\ddag}}$=37.7 kJ mol−1 for 4, respectively. For (D12)‐3, the rotation of the CD3 groups has also been studied, and a barrier Ea of 14.1 kJ mol−1 was found.

Mechanistic and Computational Studies of Oxidatively-Induced Aryl−CF3 Bond-Formation at Pd: Rational Design of Room Temperature Aryl Trifluoromethylation

This article describes the rational design of first generation systems for oxidatively induced Aryl-CF(3) bond-forming reductive elimination from Pd(II). Treatment of (dtbpy)Pd(II)(Aryl)(CF(3)) (dtbpy = di-tert-butylbipyridine) with NFTPT (N-fluoro-1,3,5-trimethylpyridinium triflate) afforded the isolable Pd(IV) intermediate (dtbpy)Pd(IV)(Aryl)(CF(3))(F)(OTf). Thermolysis of this complex at 80 °C resulted in Aryl-CF(3) bond-formation. Detailed experimental and computational mechanistic studies have been conducted to gain insights into the key reductive elimination step. Reductive elimination from this Pd(IV) species proceeds via pre-equilibrium dissociation of TfO(-) followed by Aryl-CF(3) coupling. DFT calculations reveal that the transition state for Aryl-CF(3) bond formation involves the CF(3) acting as an electrophile with the Aryl ligand serving as a nucleophilic coupling partner. These mechanistic considerations along with DFT calculations have facilitated the design of a second generation system utilizing the tmeda (N,N,N',N'-tetramethylethylenediamine) ligand in place of dtbpy. The tmeda complexes undergo oxidative trifluoromethylation at room temperature.

Tri-chlorido, 2-methylallyl and 2-butenyl tert-butylimido niobium and tantalum complexes: Synthesis, multinuclear NMR spectroscopy and reactivity

Pseudooctahedral complexes [MCl(3)(NtBu)L(2)] (M = Nb, L = py 1, ½ tmeda 3; M = Ta, L = py 2, ½ tmeda 4) have been studied by spectroscopic methods. By a VT (1)H NMR experiment a mutual exchange process between the py(ax) and py(free) in the complexes 1-2 was observed, whereas (13)C and (15)N NMR studies showed in the complexes 3-4 a tmeda ligand with an axial/equatorial coordination mode. The reaction of 2 with 3 equiv of Grignard reagent produces the methathesis products [TaR(3)(NtBu)] (R = CH(2)CMeCH(2)5, CH(2)CHCHCH(3)6) in which 2-methylallyl and 2-butenyl groups appear with a η(3)- and σ-coordination mode, respectively. When, toluene solutions of the compounds 5-6 were treated with 2 equiv of 2,6-dimethylphenylisocyanide the imido bisiminoacyl compounds [TaR(NtBu){C(R)NAr-κ(1)C}(2)] (Ar = 2,6-Me(2)C(6)H(3); R = CH(2)CMeCH(2)7, CH(2)CHCHCH(3)8) can be isolated, via an imido iminoacyl intermediate [TaR(2)(NtBu){C(R)NAr-κ(1)C}] (Ar = 2,6-Me(2)C(6)H(3); R = CH(2)CMeCH(2)9) as we have observed in the treatment of 5 with 1 equiv of isocyanide; however, the analogous reaction between 5 and COPh(2) leads to the formation of the trisalkoxo imido compound [Ta(OCPh(2)R)(3)(NtBu)] (R = CH(2)CMeCH(2)10). All new complexes were studied by IR and multinuclear NMR spectroscopy.

Homoleptic, heteroleptic and mixed-valent thallium and indium complexes of multidentate chalcogen-centred PCP-bridged ligands

The metathetical reaction of [Li(TMEDA)][HC(PPh(2)Se)(2)] ([Li(TMEDA)]1) with TlOEt in a 1:1 molar ratio afforded a homoleptic Tl(I) complex as an adduct with LiOEt, Tl[HC(PPh(2)Se)(2)]·LiOEt (7), which undergoes selenium-proton exchange upon mild heating (60 °C) to give the mixed-valent Tl(I)/Tl(III) complex {[Tl][Tl{(Se)C(PPh(2)Se)(2)}(2)]}(∞) (8). Treatment of TlOEt with [Li(TMEDA)](2)[(SPh(2)P)(2)CE'E'C(PPh(2)S)(2)] (3b, E' = S; 3c, E' = Se) in a 2:1 molar ratio produced the binuclear Tl(i)/Tl(i) complexes Tl(2)[(SPh(2)P)(2)CE'E'C(PPh(2)S)(2)] (9b, E' = S; 9c, E' = Se), respectively. Selenium-proton exchange also occurred upon addition of [Li(TMEDA)]1 to InCl(3) to yield the heteroleptic complex (TMEDA)InCl[(Se)C(PPh(2)Se)(2)] (10a). Other examples of this class of In(III) complex, (TMEDA)InCl[(E')C(PPh(2)E)(2)] (10b, E = E' = S; 10c, E = S, E' = Se) were obtained via metathesis of InCl(3) with [Li(TMEDA)](2)[(E')C(PPh(2)E)(2)] (2b, E = E' = S; 2c, E = S, E' = Se, respectively). All new compounds have been characterized in solution by (1)H and (31)P NMR spectroscopy and the solid-state structures have been determined for 8, 9c and 10a-c by single-crystal X-ray crystallography. Complex 8 is comprised of Tl(+) ions that are weakly coordinated to octahedral [Tl{(Se)C(PPh(2)Se)(2)}(2)](-) anions to give a one-dimensional polymer. The complex 9c is comprised of two four-coordinate Tl(+) ions that are each S,S',S'',Se bonded to the hexadentate [(SPh(2)P)(2)CSeSeC(PPh(2)S)(2)](2-) ligand in which d(Se-Se) = 2.531(2) Å. The six-coordinate In(III) centres in the distorted octahedral complexes 10a-c are connected to a tridentate [(E')C(PPh(2)E)(2)](2-) dianion, a chloride ion and a neutral bidentate TMEDA ligand.

Synergic Synthesis of Benzannulated Zincabicyclic Complexes, α-Zincated N Ylides, through Sodium-TMEDA-Mediated Zincation of a Haloarene

Double role for sodium: Within a synergic sodium TMP-zincate reagent, sodium mediates the direct ortho-zincation of chlorobenzene and delivers the TMEDA ligand to nucleophilically attack the benzene ring, thereby generating novel open and cyclic zinc zwitterions (example shown). TMP=2,2,6,6-tetramethylpiperidide; TMEDA=N,N,N,N-tetramethylethylenediamine.

Contacted Ion-Pair Lithium Alkylamidoaluminates: Intramolecular Alumination (Al−H Exchange) Traps for TMEDA and PMDETA

Exploring the reactivity of mixed-metal synergic bases, it is found that the lithium TMP aluminate iBu3Al(TMP)Li functions as a dual TMP/alkyl base, exhibiting 2-fold AMMAl (alkali-metal-mediated alumination) toward TMEDA to yield the heterobimetallic bis-(deprotonated TMEDA) derivative [Li{Me2NCH2CH2N(Me)CH2}2Al(iBu)2] (2). In contrast, the amide enriched aluminate iBu2Al(TMP)2Li acts as only a single-fold amido base toward TMEDA or PMDETA to afford the amine-deprotonated derivatives [Li{Me2NCH2CH2N(Me)CH2}(TMP)Al(iBu)2] (4) and [Li{Me2NCH2CH2N(Me)CH2CH2N(Me)CH2}(TMP)Al(iBu)2] (5), respectively. On their own, the aluminum compounds iBu3Al or iBu2Al(TMP) are not sufficiently strong bases to metalate TMEDA or PMDETA, so in 2, 4, and 5, the α-deprotonations of TMEDA and PMDETA are synergic in origin, as the intramolecular communication between Li and Al appears to activate the TMP and iBu bases. This special behavior can be attributed to intramolecular proximity effects between the active base component (TMP or iBu) and the ligating TMEDA or PMDETA molecule. X-ray crystallography studies reveal 2 is a contacted ion-pair ate containing two α-aluminated TMEDA ligands, which chelate the lithium cation which is linked to the distorted tetrahedral Al center by two N bridges from the metalated junction of the TMEDA molecules. In contrast, 4 and 5 have a mixed NCH2-TMP bridging ligand set, completed by two terminal iBu ligands on Al and a chelating metalated TMEDA or PMDETA ligand attached to Li, respectively. In addition, the 1H, 7Li, and 13C{1H} spectra of 2 (recorded in C6D6 solutions), 4, and 5 (recorded in cyclohexane solutions-d12) are disclosed.

Lithiated γ- O-functionalized propyl phenyl sulfides and sulfones of the type Li[CH(SO xPh)CH 2CH 2OR] ( x = 0, 2). [Li{CH(SPh)CH 2CH 2O t-Bu}(tmeda)] – A structurally characterized organolithium inner complex

Lithiation of O-functionalized alkyl phenyl sulfides PhSCH 2CH 2CH 2OR (R = Me, 1a; i-Pr, 1b; t-Bu, 1c; CPh 3, 1d) with n-BuLi/tmeda in n-pentane resulted in the formation of α- and ortho-lithiated compounds [Li{CH(SPh)CH 2CH 2OR}(tmeda)] (α- 2a– d) and [Li{ o-C 6H 4SCH 2CH 2CH 2OR)(tmeda)] ( o- 2a– d), respectively, which has been proved by subsequent reaction with n-Bu 3SnCl yielding the requisite stannylated γ-OR-functionalized propyl phenyl sulfides n-Bu 3SnCH(SPh)CH 2CH 2OR (α- 3a– d) and n-Bu 3Sn( o-C 6H 4SCH 2CH 2CH 2OR) ( o- 3a– d). The α/ ortho ratios were found to be dependent on the sterical demand of the substituent R. Stannylated alkyl phenyl sulfides α- 3a– c were found to react with n-BuLi/tmeda and n-BuLi yielding the pure α-lithiated compounds α- 2a– c and [Li{CH(SPh)CH 2CH 2OR}] (α- 4a– b), respectively, as white to yellowish powders. Single-crystal X-ray diffraction analysis of [Li{CH(SPh)CH 2CH 2O t-Bu}(tmeda)] (α- 2c) exhibited a distorted tetrahedral coordination of lithium having a chelating tmeda ligand and a C, O coordinated organyl ligand. Thus, α- 2c is a typical organolithium inner complex. Lithiation of O-functionalized alkyl phenyl sulfones PhSO 2CH 2CH 2CH 2OR (R = Me, 5a; i-Pr, 5b; CPh 3, 5c) with n-BuLi resulted in the exclusive formation of the α-lithiated products Li[CH(SO 2Ph)CH 2CH 2OR] ( 6a– c) that were found to react with n-Bu 3SnCl yielding the requisite α-stannylated compounds n-Bu 3SnCH(SO 2Ph)CH 2CH 2OR ( 7a– c). The identities of all lithium and tin compounds have been unambiguously proved by NMR spectroscopy ( 1H, 13C, 119Sn).

Unusual Reactivity of N,N,N′,N′-Tetramethylethylenediamine-Coordinated Neutral Nickel(II) Polymerization Catalysts

Tmeda-coordinated species [(N,O)NiCH3(tmeda)] (tmeda = N,N,N′,N′-tetramethylethylenediamine), obtained by reaction of [(tmeda)NiMe2] with salicylaldimines, (NO)H, are reactive and versatile intermediates for olefin polymerization catalysis. Solution NMR spectroscopic studies of 1-tmeda (N,O= 2,6-(3,5-(F3C)2C6H3)2C6H3-N═CH-(3,5-I2-2-OC6H2)) revealed two major binding modes of the tmeda ligand, open κ1- and, unexpectedly, chelating κ2-fashion, which interconvert slowly on the NMR chemical shift time scale, and form equilibria with solvent complexes 1-L (L= dmso, methanol). Binding of tmeda is favored by 2−3 orders of magnitude at the temperatures studied (25 to 80 °C) over binding of solvent. Chelating κ2-coordination of tmeda renders the monoanionic bidentate salicylaldiminato ligand κ1-coordinate. Exposure of dmso solutions of 1-tmeda to excess ethylene in an NMR tube at 55 °C resulted in the very minor formation of propylene and an equilibrium mixture of Ni(II)-ethyl complexes 2-dmso and [(κ1-N,O)Ni(αCH...

Intramolecular Carbolithiation Reactions for the Synthesis of 2,4-Disubstituted Tetrahydro-quinolines: Evaluation of TMEDA and (−)-Sparteine as Ligands in the Stereoselectivity † Dedicated to Prof. Josep Font on the occasion of his 70th birthday.

The preparation of 4-substituted 2-phenyltetrahydroquinolines from N-alkenylsubstituted 2-iodoanilines via intramolecular carbolithiation reactions has been investigated. The stereochemical outcome of the carbolithiation reactions depends on the nature of organolithium employed to perform the lithium-halogen exchange, the solvent, or the use of additives, for example, TMEDA or chiral bidentated ligands such as (-)-sparteine. Thus, the 2,4-disubstituted tetrahydroquinolines are obtained with moderate diastereoselectivities (up to 77:23) and with ee up to 94% when Weinreb amide derivatives are used (R = CONMe(OMe)).

Cyclic, trinuclear PdII complex of cytidine with pronounced double cone structure

Reaction of PdII(tmeda) (tmeda=N,N,N',N'-tetramethylethylenediamine) with the RNA nucleoside cytidine (Cytd) yields a cyclic nucleoside complex containing three metal entities and three cytidine anions, with metal cross-links involving N(3) and N(4)H(-) sites. [{Pd(Cytd(-)-N3,N4)(tmeda)}3](ClO4)3.6H2O has a characteristic double cone structure with the methyl groups of the tmeda ligands representing the lower rim and the ribose moieties forming the upper rim. The Pd3 triangle is equilateral (5.193(1)A). In the solid state structure, one of the ClO(4)(-) counter ions links the lower and the upper rims of adjacent cones, thereby leading to a 1D chain. No host-guest chemistry has been detected with a series of N-heterocyclic ligands in water.