Tunable zinc benzamidinate complexes: coordination modes and catalytic activity in the ring-opening polymerization of L-lactide.

Seven asymmetric zinc benzamidinate complexes featuring or lacking side-arm functionalities were synthesized. Using equimolar zinc reagent produced distinct dinuclear motifs [(C6H5-C = NC6H5)ZnEt]2 (R = tBu, 1; (CH2)2OMe, 2; (CH2)2NMe2, 3). Half the zinc reagent yielded dinuclear [(C6H5-C = NC6H5)2Zn]2 (R = tBu, 4) or mononuclear zinc bis(chelate) complexes (R = (CH2)2OMe, 5; (CH2)2NMe2, 6; CH2Py, 7). Molecular structures of 1-4 and 7 were determined via single-crystal X-ray diffraction. Altering benzamidinate substituents modifies both coordination modes and catalytic activities in ring-opening polymerization of L-lactide. Specifically, complex 7 exhibits enhanced catalytic activity at 25 °C using 100 equivalents of L-lactide with a turnover frequency of 1820 h-1.

Grignard reagents as deprotonation agents for oxazoline-amido-phenolate ligands: structural and catalytic implications with the role of halogen ions.

In this study, various halogen-substituted Grignard reagents were assessed as deprotonating agents for the oxazoline-amido-phenolate ligand, leading to the formation of magnesium complexes. The newly synthesized complexes with halogen substituents displayed three distinct coordinative modes, all extensively characterized through crystallographic methods. The introduction of halogen substituents induced changes in the Lewis acid properties of the complexes, thereby impacting their structural attributes and catalytic behavior during the initiation and propagation of ring polymerization of cyclic esters.

Zirconium and hafnium complexes containing N-alkyl-substituted amine biphenolate ligands: unexpected ligand degradation and divergent complex constitutions governed by N-alkyls.

The reactivity and thermal stability of zirconium and hafnium complexes containing the N-alkyl-substituted amine biphenolate ligands of the type [RN(CH2-2-O-3,5-C6H2(tBu)2)2](2-) ([R-ONO](2-); R = tBu (1a), iPr (1b), or nPr (1c)) were investigated. The reactions of either [1a]M(OiPr)2 (M = Zr or Hf) with equimolar H2[1a] or M(OiPr)4(HOiPr) (M = Zr or Hf) with 2 equiv of H2[1a] at 25 °C in diethyl ether or 80 °C in toluene afford moderate yields of colorless crystals of M[1a](OiPr)(iPrOCH2-2-O-3,5-C6H2(tBu)2) (M = Zr (4a) or Hf (5a)). Controlled experiments revealed that the production of 4a and 5a proceeds via unexpected thermal degradation of H2[1a] that produces a highly reactive, transient ortho-quinone methide intermediate. Similar reactions employing H2[1b] and H2[1c], however, led to the formation of homoleptic bis-ligand complexes Zr[1b]2 (8b) and M[1c]2 (M = Zr (8c) or Hf (9c)) as colorless crystals. Decisive factors governing these divergent reaction pathways and complex constitutions are discussed. The X-ray structures of 4a, 5a, 8b, 8c, and 9c are presented.

Well-defined (N-heterocyclic carbene)-Ag(I) complexes as catalysts for A3 reactions.

The use of well-defined (N-heterocyclic carbene)-Ag(I) complexes for the A(3) reaction allows for the coupling of unactivated aldehydes at room temperature and very short reaction times.

Preferential formation of homochiral helical sandwich-shaped architectures through the metal-mediated assembly of tris(imidazoline) ligands with a set of d(3)-d(10) transition-metal ions.

A novel type of chiral tris-monodentate imidazolinyl ligands ((S,S,S)-4 and (R,R,R)-4) has been achieved in good yields. The ligands show a strong tendency to induce the generation of the discrete sandwich-shaped M(3)L(2) architectures with programmed helicity through the edge-directed complexation with a series of d(3)-d(10) transition-metal ions, while taking advantage of the steric hindrance of the bulky substituents of the imidazoline rings to avoid the formation of extended metal-organic frameworks (MOFs). In spite of different coordination geometries, monovalent metal ions (e.g. Ag(+)), divalent metal ions (e.g. Pd(2+), Cu(2+), Cd(2+), Zn(2+), Co(2+), Mn(2+), and Ni(2+)), and even trivalent metal ions (e.g. Fe(3+) and Cr(3+)) exhibit isostructural coordination. Installation of stereocenters fused onto the imidazoline rings results in favored handedness of the self-assemblies through the expression of molecular chirality into supramolecular helicity. In the crystal structures of [M(3){(S,S,S)-4}(2)], the self-assembly has to adopt the M form to relax the van der Waals repulsions of the phenyl and isopropyl groups. The replacement of (S,S,S)-4 with (R,R,R)-4 exclusively affords the opposite helicity (P). These results should provide important insights for the design of chiral helical capsule-like assemblies.

Diverse Coordinative Zinc Complexes Containing Amido-Pyridinate Ligands: Structural and Catalytic Studies.

In this work, zinc complexes containing amidopyridinate ligands substituted with different pendant arms have been described. Treatment of ligand precursors with ZnEt2 at a 1:1 ratio in THF yields zinc ethyl complexes (PyN C 1 Py )2(ZnEt)2 (1) and (PyN C 2 NMe 2 )2(ZnEt)2 (2), respectively. Complexes 1 and 2 show the same geometry as a distorted tetrahedron, but adopt different coordination behaviors supported by the ligands. Complex 1 represents a rare and a non-centrosymmetric mode, which the amido group bridges two zinc centers to form a six-membered ring. However, complex 2 shows a centrosymmetric mode, which the pyridine group links to the zinc centers to form an eight-membered ring. Recrystallization of complex 2 gives an additional complex (PyN C 2 NMe 2 )4Zn3(µ3-O) (3). We attempted to prepare zinc benzyl oxide complexes but afforded only a self-assembly cubane complex Zn7Et6(OBn)8 (4). All molecular structures 1-4 are characterized depending on both single-crystal X-ray and spectroscopic data. Furthermore, their catalytic properties toward the ring opening polymerization of ε-caprolactone and L-lactide, using benzyl alcohol as the initiation reagent, are under investigation.

Effect on orthometallation of NHC palladium complexes toward the catalytic activity studies in Suzuki coupling reaction.

Herein, we report an approach to improve catalytic activity for cross-coupling reactions. N-Heterocyclic carbene (NHC) palladium complexes bearing a nitrogen-based ligand without orthometallation complexes show remarkable activities in Suzuki coupling reaction than orthometallation. Aryl chlorides examples employed in air and ambient temperature in Suzuki coupling reaction to reach completion within few minutes.

An unprecedented Zn10O4 heteroadamantane cage containing anilido-pyridinate ligand and its activity for ring opening polymerization of l-lactide and ε-caprolactone.

(NPyC2OMe)8Zn10Et4(µ4-O)4 (1) has been synthesized in situ by hydrolysis of ZnEt2 in a one pot process and it was proved by applying X-ray structure analysis that the organozinc anilido-pyridinate moiety encapsulated the zinc oxide cluster, which demonstrated one self-assembled coordinate mode "Zn10O4". Moreover, the catalytic activity was investigated and good activity for l-lactide and ε-caprolactone ring opening polymerization was observed with both living and controllable properties.

Sonogashira couplings catalyzed by collaborative (N-heterocyclic carbene)-copper and -palladium complexes.

A general protocol for the Sonogashira reaction using a 100:1 combination of (N-heterocyclic carbene)-Cu and (N-heterocyclic carbene)-Pd complexes is presented. Catalyst loadings of 1 mol % (NHC)-Cu and 0.01 mol % (NHC)-Pd allow for the coupling of aryl bromides and aryl alkynes, in air and in a non-anhydrous solvent, in high yields.

Zirconium and hafnium complexes containing N-alkyl substituted amine biphenolate ligands: coordination chemistry and living ring-opening polymerization catalysis.

The coordination chemistry of zirconium and hafnium complexes containing the tridentate amine biphenolate ligands [RN(CH2-2-O-3,5-C6H2(tBu)2)2](2-) ([R-ONO](2-); R = tBu (1a), iPr (1b), nPr (1c)) featuring distinct N-alkyl substituents is described. Alcoholysis of Zr(OiPr)4(HOiPr) or Hf(OiPr)4(HOiPr) with H2[1a] in diethyl ether solutions at -35 °C generates the corresponding five-coordinate [1a]M(OiPr)2 (M = Zr (2a), Hf (3a)) in high isolated yield. Similar reactions employing H2[1b] produce six-coordinate [1b]M(OiPr)2(HOiPr) (M = Zr (2b·HOiPr), Hf (3b·HOiPr)) as an isopropanol adduct. Repetitive trituration of 2b·HOiPr and 3b·HOiPr with diethyl ether gives five-coordinate 2b and 3b, respectively. Treatment of M(OiPr)4(HOiPr) with H2[1c] under similar conditions affords six-coordinate [1c]M(OiPr)2(HOiPr) (M = Zr (2c·HOiPr), Hf (3c·HOiPr)), subsequent recrystallization of which from acetonitrile-diethyl ether solutions leads to acetonitrile adducts 2c·MeCN and 3c·MeCN. Reactivity studies of these zirconium and hafnium complexes revealed that they are all active catalysts for ring-opening polymerization of ε-caprolactone. Among them, the N-isopropyl derived complexes are most reactive. Polymerizations catalyzed by 2b, 3b and 3c·MeCN were proved to be living. The X-ray structures of 2a·HOiPr, 2a·MeCN, 2c·HOiPr, 2c·MeCN, and 3c·MeCN are presented.

Palladacycles bearing tridentate CNS-type benzamidinate ligands as catalysts for cross-coupling reactions.

Three pendant benzamidines, [Ph-C(=NC(6)H(5))-{NH(E)}] [E = -(CH(2))(2)SMe (1); -(CH(2))(2)S(t)Bu (2); -o-C(6)H(4)SMe (3)], are described. Reactions of 1, 2 or 3 with one molar equivalent of Pd(OAc)(2) in CH(2)Cl(2) give the palladacyclic complexes, [Ph-C{-NH(η(1)-C(6)H(4))}{=N(E)}]Pd(OAc) [E = -(CH(2))(2)SMe (4); -(CH(2))(2)S(t)Bu (5); -o-C(6)H(4)SMe (6)], as mononuclear palladium complexes respectively. A minor product described as 5', {[Ph-C{-N(C(6)H(5))}{-N(CH(2))(2)S(t)Bu}]Pd(OAc)}(2), was isolated as benzamidinate-bridged dinuclear palladium complex upon recrystallizing from Et(2)O/hexane solution. Treatment of 1, 2 or 3 with one molar equivalent of PdCl(2) in the presence of NEt(3) in CH(2)Cl(2) gives the palladacyclic complexes, [Ph-C{-NH(η(1)-C(6)H(4))}{=N(E)}]PdCl [E = -(CH(2))(2)SMe (7); -(CH(2))(2)S(t)Bu (8); -o-C(6)H(4)SMe (9)], as mononuclear palladium complexes respectively. The crystal and molecular structures are reported for compounds 5, 5' and 6-8. The application of these palladacyclic complexes to the Suzuki and Heck coupling reactions was examined.

Structural and catalytic studies of zinc complexes containing amido-oxazolinate ligands.

Several zinc complexes bearing amido-oxazolinate ligands are described. Reactions of ligand precursors, HNC(2)(E)Oxa (HNC(2)(E)Oxa = HNC(2)(Me)Oxa, HNC(2)(OMe)Oxa, HNC(2)(StBu)Oxa and HNC(2)(NMe2)Oxa) or HNPh(SMe)Oxa, with half or one molar equivalent of ZnEt(2) afford bis(chelate) zinc complexes, (NC(2)(E)Oxa)(2)Zn [C(2)(E) = propyl, (1); C(2)(E) = 2-methoxyethyl, (2); C(2)(E) = 2-N,N'-dimethylethyl, (3)] or zinc ethyl complexes, (NC(2)(StBu)Oxa)ZnEt(4) and (NPh(SMe)Oxa)ZnEt(5), using tetrahydrofuran or hexane as solvents. The zinc benzyl oxide complexes, [(NC(2)(E)Oxa)Zn(µ-OBn)](2) [C(2)(E) = propyl, (6); C(2)(E) = 2-methoxyethyl, (7); C(2)(E) = 2-tert-butylthioethyl, (8)], are obtained from the reactions of ligand precursors, HNC(2)(E)Oxa, with one molar equivalent of ZnEt(OBn) (generated in situ on 1:1 ratio of ZnEt(2) and BnOH) in tetrahydrofuran. The molecular structures are reported for compounds 1, 3, 5, 6 and 7. All eight compounds were assessed as efficient catalyst precursors towards the ring-opening polymerization of L-lactide and ε-caprolactone.

Magnesium complexes containing bis-amido-oxazolinate ligands as efficient catalysts for ring opening polymerisation of L-lactide.

A series of magnesium bis(amido-oxazolinate) complexes have been described. Reactions of six amido-oxazolinate ligand precursors, HNC(2)(Me)Oxa, HNC(2)(OMe)Oxa, HNC(2)(StBu)Oxa, HNPhOxa, HNPh(OMe)Oxa or HNPh(SMe)Oxa, with half molar equivalent of Mg(n)Bu(2) in hexane yield the magnesium bis(amido-oxazolinate) complexes, (NC(2)(E)Oxa)(2)Mg [C(2)(E) = propyl, (NC(2)(Me)Oxa)(2)Mg (1); C(2)(E) = 2-methoxyethyl, (NC(2)(OMe)Oxa)(2)Mg (2); C(2)(E) = 2-tert-butylthioethyl, (NC(2)(StBu)Oxa)(2)Mg (3)], or magnesium bis(anilido-oxazolinate) complexes, (NArOxa)(2)Mg [Ar = phenyl, (NPhOxa)(2)Mg (4); Ar = 2-methoxyphenyl, (NPh(OMe)Oxa)(2)Mg (5); Ar = 2-methylthiophenyl, (NPh(SMe)Oxa)(2)Mg (6)], respectively. The molecular structures are reported for compounds 1, 2, 5 and 6. Their catalytic activities toward the ring opening polymerisation of L-lactide in the presence of benzyl alcohol are also under investigation.

Zinc anilido-oxazolinate complexes as initiators for ring opening polymerization.

Three new anilido-oxazolines, ortho-C(6)H(4)(NHAr')(4,4-dimethyl-2-oxazoline) [Ar'=2,4,6-trimethylphenyl, HNPh(TriMe)Oxa (1); 2,6-diisopropylphenyl, HNPh(DiiPr)Oxa (2); 2-methoxyphenyl, HNPh(OMe)Oxa (3)], have been prepared. Reactions of 1 or 2 with one molar equivalent of ZnEt(2) in tetrahydrofuran or hexane solution give the zinc ethyl complexes (NPh(TriMe)Oxa)ZnEt (4) and (NPh(DiiPr)Oxa)ZnEt (5). The dinuclear zinc benzyloxide complexes, [(NAr'Oxa)Zn(mu-OBn)](2), [Ar'=2,4,6-trimethylphenyl, (6); 2-methoxyphenyl, (7)], were synthesized by the reaction of 4 with one molar equivalent of benzyl alcohol in tetrahydrofuran solution (for 6) or by treatment of with 3 one molar equivalent of ZnEt(2) in tetrahydrofuran solution followed by the addition of one molar equivalent of benzyl alcohol (for 7). The molecular structures are reported for compounds 6 and 7. Their catalytic activities toward the ring opening polymerization reactions are under investigation.

Palladacyclic complexes bearing CNN-type ligands as catalysts in the Heck reaction.

Preparations of novel unsymmetrical, tridentate nitrogen ligand precursors, PhN=C(CMe2)(NPh)C=N(CH2)2NMe2(1) and PhN=C(CMe2)(NPh)C=N(CH2)Py (2), are described. Treatment of 1 with 1 molar equiv. (COD)PdCl2 in the presence of NEt3 or with 1 molar equiv. Pd(OAc)2 affords orthometallated palladium(II) complexes, [PhN=C(CMe2)(N-eta1-Ph)C=N(CH2)2NMe2]PdX (X=Cl (3); X=OAc (4)), respectively. Compound can be yielded via the reaction of with an excess of LiCl in methanol. Treatment of with 1 molar equiv. of (COD)PdCl2, Pd(OAc)2 or Pd(TFA)2 affords orthometallated palladium(II) complexes, [PhN=C(CMe2)(N-eta1-Ph)C=NCH2Py]PdX (X=Cl (5); X=OAc (6); X=TFA (7)), respectively. The crystal and molecular structures are reported for compounds 2, 3, 5 and 6. The application of these novel palladacyclic complexes to the Heck reaction with aryl halide substrates was examined.