Magnesium Complexes Containing η1- and η3-Pyrrolyl or Ketiminato Ligands: Synthesis, Structural Investigation and ϵ-Caprolactone Ring-Opening Polymerisation

Aluminium complexes containing indolyl-phenolate ligands as catalysts for ring-opening polymerization of cyclic esters

A family of aluminium complexes supported by mono-anionic indolyl-phenolate ligands are described. Reactions of indolyl-phenolate based ligand precursors, IndHPhROH, with 1.0 or 0.5 equivalents of AlMe2Cl in toluene afforded aluminium indolyl-phenolate complexes 1-4 and aluminium bis-indolyl-phenolate complexes 5-8 respectively. The molecular structure is reported for 5. Based on the NMR spectroscopic and X-ray crystallographic studies, a 1,3-hydrogen shift could happen from nitrogen to carbon on the five-membered ring of the indolyl group upon reacting with aluminium reagents. These novel aluminium complexes demonstrate catalytic activities toward the ring-opening polymerization of cyclic esters in the presence of alcohol.

Ring-Opening Polymerization of ε-Caprolactone and Styrene Oxide-CO2 Coupling Reactions Catalyzed by Chelated Dehydroacetic Acid-Imine Aluminum Complexes

A series of chelated dehydroacetic acid-imine-based ligands L1H~L4H was synthesized by reacting dehydroacetic acid with 2-t-butylaniline, (S)-1-phenyl-ethylamine, 4-methoxylbenzylamine, and 2-(aminoethyl)pyridine, respectively, in moderate yields. Ligands L1H~L4H reacted with AlMe3 in toluene to afford corresponding compounds AlMe2L1 (1), AlMe2L2 (2), AlMe2L3 (3), and AlMe2L4 (4). All the ligands and aluminum compounds were characterized by IR spectra, 1H and 13C NMR spectroscopy. Additionally, the ligands L1H~L4H and corresponding aluminum derivatives 1, 3, and 4 were characterized by single-crystal X-ray diffractometry. The catalytic activities using these aluminum compounds as catalysts for the ε-caprolactone ring-opening polymerization (ROP) and styrene oxide-CO2 coupling reactions were studied. The results show that increases in the reaction temperature and selective solvent intensify the conversions of ε-caprolactone to polycaprolactone. Regarding the coupling reactions of styrene oxide and CO2, the conversion rate is over 90% for a period of 12 h at 90 °C. This strategy dispenses the origination of cyclic styrene carbonates, which is an appealing concern because of the transformation of CO2 into an inexpensive, renewable and easy excess carbon feedstock.

Effect of Substituents of Cerium Pyrazolates and Pyrrolates on Carbon Dioxide Activation

Homoleptic ceric pyrazolates (pz) Ce(RR’pz)₄ (R = R’ = tBu; R = R’ = Ph; R = tBu, R’ = Me) were synthesized by the protonolysis reaction of Ce[N(SiHMe₂)₂]₄ with the corresponding pyrazole derivative. The resulting complexes were investigated in their reactivity toward CO₂, revealing a significant influence of the bulkiness of the substituents on the pyrazolato ligands. The efficiency of the CO₂ insertion was found to increase in the order of tBu₂pz < Ph₂pz < tBuMepz < Me₂pz. For comparison, the pyrrole-based ate complexes [Ce₂(pyr)₆(µ-pyr)₂(thf)₂][Li(thf)₄]₂ (pyr = pyrrolato) and [Ce(cbz)₄(thf)₂][Li(thf)₄] (cbz = carbazolato) were obtained via protonolysis of the cerous ate complex Ce[N(SiHMe₂)₂]₄Li(thf) with pyrrole and carbazole, respectively. Treatment of the pyrrolate/carbazolate complexes with CO₂ seemed promising, but any reversibility could not be observed.

A Tale of Biphenyl and Terphenyl Substituents for Structurally Diverse Ketiminato Magnesium, Calcium and Germanium Complexes

In this paper, we have used two N,O-ketiminato ligands (L1 and L2) with biphenyl and terphenyl substituent on the nitrogen atom. Deprotonation of L1 with KN(SiMe₃ )₂ and subsequent reaction with MgI₂ led to a homoleptic dinuclear magnesium complex (1) with a Mg₂ O₂ four-membered ring. Deprotonation with nBuLi and subsequent reaction with MgI₂ afforded a unusual dinuclear magnesium complex (2) with a Mg₂ O₂ ring. Extension of the ligand for calcium resulted in a trinuclear calcium complex (3) with six four-membered Ca₂ O₂ rings. We could not isolate any chelating complex when L2 was used as a ligand, and only oxygen bound magnesium (4) and calcium (5) adducts were isolated. DFT studies were performed to understand this dissimilar behavior. More diverse results were obtained when lithiated L1 and L2 were treated with germanium dichloride. We were able to stabilize a monomeric germylene monochloride (7) with L1. However, with L2, an unusual ligand scrambling, and a C-C coupling take place, leading to the formation of a secondary carbocation with GeCl₃ - as a counter-anion (8). Besides, a germanium dichloride adduct (9) bound to the oxygen center of the ligand was obtained as the minor product.

Potassium complexes containing bidentate pyrrole ligands: synthesis, structures, and catalytic activity for the cyclotrimerization of isocyanates

Bidentate pyrrolyl ligands, 2-(t-butyliminomethyl)pyrrole and 2-(t-butylaminomethyl)pyrrole, reacted with KH to give complexes [C₄H₃N(2-CH[double bond, length as m-dash]N^tBu)K(THF)]_n (1) and [C₄H₃N(2-CH₂NH^tBu)K]_n (2), respectively. Each has been characterized by C, H and N microanalysis, NMR spectroscopy, and single crystal X-ray structural analysis. The X-ray structure of complex 1 (n≥ 1) demonstrated that it exists as a 1D zig-zag coordination polymer in the solid state. Conversely, the structure of complex 2 (n≥ 1) showed that it is a 2D supramolecular network. They proved to be an effective class of catalysts for cyclotrimerization of isocyanate in excellent yield under mild conditions.

1,8-Bis(silylamido)naphthalene complexes of magnesium and zinc synthesised through alkane elimination reactions

The reactions between magnesium or zinc alkyls and 1,8-bis(triorganosilyl)diaminonaphthalenes afford the 1,8-bis(triorganosilyl)diamidonaphthalene complexes with elimination of alkanes. The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and one or two equivalents of MgⁿBu₂ affords two complexes with differing coordination environments for the magnesium; the reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and MgⁿBu₂ in a 1 : 1 ratio affords 1,8-C₁₀H₆(NSiMePh₂)₂{Mg(THF)₂} (1), which features a single magnesium centre bridging both ligand nitrogen donors, whilst treatment of 1,8-C₁₀H₆(NSiR₃H)₂ (R₃ = MePh₂, ⁱPr₃) with two equivalents of MgⁿBu₂ affords the bimetallic complexes 1,8-C₁₀H₆(NSiR₃)₂{ⁿBuMg(THF)}₂ (R₃ = MePh₂2, R₃ = ⁱPr₃3), which feature four-membered Mg₂N₂ rings. Similarly, 1,8-C₁₀H₆(NSiⁱPr₃)₂{MeMg(THF)}₂ (4) and 1,8-C₁₀H₆(NSiMePh₂)₂{ZnMe}₂ (5) are formed through reactions with the proligands and two equivalents of MMe₂ (M = Mg, Zn). The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and two equivalents of MeMgX affords the bimetallic complexes 1,8-C₁₀H₆(NSiMePh₂)₂(XMgOEt₂)₂ (X = Br 6; X = I 7). Very small amounts of [1,8-C₁₀H₆(NSiMePh₂)₂{IMg(OEt₂)}]₂ (8), formed through the coupling of two diamidonaphthalene ligands at the 4-position with concomitant dearomatisation of one of the naphthyl arene rings, were also isolated from a solution of 7.

Solvent dependence of the solid-state structures of salicylaldiminate magnesium amide complexes

There are challenges in using magnesium coordination complexes as reagents owing to their tendency to adopt varying aggregation states in solution and thus impacting the reactivity of the complexes. Many magnesium complexes are prone to ligand redistributionviaSchlenk equilibrium due to the ionic character within the metal–ligand interactions. The role of the supporting ligand is often crucial for providing stability to the heteroleptic complex. Strategies to minimize ligand redistribution in alkaline earth metal complexes could include using a supporting ligand with tunable sterics and electronics to influence the degree of association to the metal atom. Magnesium bis(hexamethyldisilazide) was reacted with salicylaldimines [1L=N-(2,6-diisopropylphenyl)salicylaldimine and2L= 3,5-di-tert-butyl-N-(2,6-diisopropylphenyl)salicylaldimine] in either nondonor (toluene) or donor solvents [tetrahydrofuran (THF) or pyridine]. The structures of the magnesium complexes were studied in the solid stateviaX-ray diffraction. In the nondonor solvent,i.e.toluene, the heteroleptic complex bis{μ-2-[(2,6-diisopropylphenyl)iminomethyl]phenolato}-κ3N,O:O;κ3O:N,O-bis[(hexamethyldisilazido-κN)magnesium(II)], [Mg2(C19H22NO)2(C6H18NSi2)2] or [1LMgN(SiMe3)2]2, (1), was favored, while in the donor solvent,i.e.pyridine (pyr), the formation of the homoleptic complex {2,4-di-tert-butyl-6-[(2,6-diisopropylphenyl)iminomethyl]phenolato-κ2N,O}bis(pyridine-κN)magnesium(II) toluene monosolvate, [Mg(C27H38NO)2(C5H5N)2]·C5H5N or [{2L2Mg2(pyr)2}·pyr], (2), predominated. Heteroleptic complex (1) was crystallized from toluene, while homoleptic complexes (2) and the previously reported [1L2Mg·THF] [Quinqueet al.(2011).Eur. J. Inorg. Chem.pp. 3321–3326] were crystallized from pyridine and THF, respectively. These studies support solvent-dependent ligand redistribution in solution.In-situ1H NMR experiments were carried out to further probe the solution behavior of these systems.

Synthesis and catalytic application of magnesium complexes bearing pendant indolyl ligands

Three novel indole-based ligand precursors [HIndPh(R), R = methoxy, HIndPh(OMe) (); thiomethoxy, HIndPh(SMe) (); and N,N'-dimethylamino, HIndPh(NMe2) ()] have been synthesized via Sonogashira and cyclization reactions with moderate to high yield. Reactions of these ligand precursors with 0.6 equivalent of Mg(n)Bu2 in THF afforded the magnesium bis-indolyl complexes , respectively. All the ligand precursors and related magnesium complexes have been characterized by NMR spectroscopy and elemental analyses. The molecular structures are reported for compounds and . Under optimized conditions, compound demonstrates efficient catalytic activities towards the ring opening polymerization of l-lactide and ε-caprolactone in the presence of BnOH.

Magnesium and aluminum complexes bearing bis(5,6,7-trihydro quinolyl)-fused benzodiazepines for ε-caprolactone polymerization

New bis(5,6,7-trihydroquinolyl)-fused benzodiazepine ligands were synthesized and used to form dinuclear magnesium and aluminum complexes which showed efficient catalytic activity toward the ROP of ε-CL.

Group 1 and group 2 metal complexes supported by a bidentate bulky iminopyrrolyl ligand: synthesis, structural diversity, and ε-caprolactone polymerization study

We report here a series of alkali and alkaline earth metal complexes, each with a bulky iminopyrrolyl ligand [2-(Ph3CN=CH)C4H3NH] (1-H) moiety in their coordination sphere, synthesized using either alkane elimination or silylamine elimination methods or the salt metathesis route. The lithium salt of molecular composition [Li(2-(Ph3CN=CH)C4H3N)(THF)2] (2) was prepared using the alkane elimination method, and the silylamine elimination method was used to synthesize the dimeric sodium and tetra-nuclear potassium salts of composition [(2-(Ph3CN=CH)C4H3N)Na(THF)]2 (3) and [(2-(Ph3CN=CH)C4H3N)K(THF)0.5]4 (4) respectively. The magnesium complex of composition [(THF)2Mg(CH2Ph){2-(Ph3CN=CH)C4H3N}] (5) was synthesized through the alkane elimination method, in which [Mg(CH2Ph)2(OEt2)2] was treated with the bulky iminopyrrole ligand 1-H in 1 : 1 molar ratio, whereas the bis(iminopyrrolyl)magnesium complex [(THF)2Mg{2-(Ph3CN=CH)C4H3N}2] (6) was isolated using the salt metathesis route. The heavier alkaline earth metal complexes of the general formula {(THF)nM(2-(Ph3CN=CH)C4H3N)2} [M = Ca (7), Sr (8), and n = 2; M = Ba (9), n = 3] were prepared in pure form using two synthetic methods: in the first method, the bulky iminopyrrole ligand 1-H was directly treated with the alkaline earth metal precursor [M{N(SiMe3)2}2(THF)n] (where M = Ca, Sr and Ba) in 2 : 1 molar ratio in THF solvent at ambient temperature. The complexes 7-9 were also obtained using the salt metathesis reaction, which involves the treatment of the potassium salt (4) with the corresponding metal diiodides MI2 (M = Ca, Sr and Ba) in 2 : 1 molar ratio in THF solvent. The molecular structures of all the metal complexes (1-H, 2-9) in the solid state were established through single-crystal X-ray diffraction analysis. The complexes 5-9 were tested as catalysts for the ring-opening polymerization of ε-caprolactone. High activity was observed in the heavier alkaline earth metal complexes 7-9, with a very narrow polydispersity index in comparison to that of magnesium complexes 5 and 6.

Synthesis, structure and reactivity study of magnesium amidinato complexes derived from carbodiimides and N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-butadiene ligands

We report an amidinato ligand-supported series of magnesium complexes obtained from the insertion of a magnesium-carbon bond into a carbon-nitrogen double bond of different carbodiimides and α-diimine ligands. The magnesium complexes [Mg(CH2Ph){CyN[double bond, length as m-dash]C(CH2Ph)NCy}]2 (), [Mg(CH2Ph){(i)PrN[double bond, length as m-dash]C(CH2Ph)N(i)Pr}]2 () and the homoleptic [Mg{(t)BuN[double bond, length as m-dash]C(CH2Ph)N(t)Bu}2] () (Cy = cyclohexyl, (i)Pr = isopropyl, (t)Bu = tert-butyl) were prepared by the reaction of dibenzyl magnesium [Mg(CH2Ph)2(Et2O)2] with the respective carbodiimides either in 1 : 1 or 1 : 2 molar ratio in toluene. The analogous reaction of [Mg(CH2Ph)2(Et2O)2] with the N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (Dipp2DAD) ligand afforded the corresponding homoleptic magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}2] () (Dipp = 2,6 diisopropylphenyl) in good yield. The solid-state structures of magnesium complexes were confirmed by single-crystal X-ray diffraction analysis. It was observed that in each case, a magnesium-carbon bond was inserted into the carbon-nitrogen double bond of either carbodiimides or Dipp2DAD resulting in a monoanionic amido-imino ligand. In a further reaction between and N-aryliminopyrrolyl ligand 2-(2,6-(i)Pr2C6H3N[double bond, length as m-dash]CH)C4H3NH (ImpDipp-H) in 1 : 2 molar ratio, a new magnesium complex [Mg(ImpDipp)2{CyN[double bond, length as m-dash]C(CH2Ph)NHCy}] (), with one amidinato and two aryliminopyrrolyl ligands in the coordination sphere, was obtained in good yield. In contrast, the homoleptic magnesium complex reacted with one equivalent of N-aryliminopyrrolyl ligand (ImpDipp-H) to produce another mixed ligated magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}(ImpDipp)] (), with a benzylated DAD ligand and aryliminopyrrolyl ligands in the coordination sphere. Further reaction of complex with benzyl alcohol (PhCH2OH) afforded the third mixed ligated magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}(OCH2Ph)2] () in very good yield. The magnesium complexes were characterised using standard analytical/spectroscopic techniques and their solid-state structures were established by single-crystal X-ray diffraction analysis.

Designing ancillary ligands for heteroleptic/homoleptic zinc complex formation: synthesis, structures and application in ROP of lactides

Synthesis and characterization of a series of new amino-phenol/naphthol ligands (L1,2-H) have been developed and their respective zinc complexes (1 and 2-Zn) have been synthesized.

Aluminum complexes incorporating symmetrical and asymmetrical tridentate pincer type pyrrolyl ligands: synthesis, characterization and reactivity study

A series of aluminum complexes incorporating substituted symmetrical and asymmetrical tridentate pyrrolyl ligands are synthesized conveniently and the treatment of the derivatives with small organic molecules are analyzed. The reaction of lithiated [C4H2NH(2-CH2NH(t)Bu)(5-CH2NR1R2)], where for 1, R1 = R2 = Me; 2, R1 = H, R2 = (t)Bu, with AlCl3 in diethyl ether affords Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)]Cl2 (3) and Al[C4H2N(2,5-CH2NH(t)Bu)2]Cl2 (4), respectively, in high yields. Furthermore, subjecting 3 and 4 to reaction with one equiv. of LiNMePh in diethyl ether generates Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)][NMePh]Cl (5) and Al[C4H2N(2,5-CH2NH(t)Bu)2][NMePh]Cl (6), respectively, while eliminating one equiv. of LiCl. The reaction between compound 4 with two equiv. of LiO-Ph-4-Me in diethyl ether yields the aluminum di-phenoxide compound Al[C4H2N(2,5-CH2NH(t)Bu)2](O-Ph-4-Me)2 (7) whereas the combination of 3 and two equiv. of LiNH(t)Bu, produces Al[C4H2N(2-CH2N(t)Bu)(5-CH2NMe2)](NH(t)Bu)(NH2(t)Bu) (8). Additionally, the mixing of 1 and one equiv. of AlMe3 renders Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)]Me2 (9). Adding one more equiv. of AlMe3 with 9 affords {Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)AlMe3]Me2} (10), which can also be obtained by treating 1 with two equiv. of AlMe3 directly. The treatment of 9 with one equiv. of 2,6-dimethylphenol in diethyl ether gives the aluminum alkoxide derivative, Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)](O-C6H3-2,6-Me2)Me (11). Furthermore, the reaction between 9 and one equiv. of 1-ethyl-1-phenyl ketene, initiates the aluminum dimethyl complex Al{C4H2N[2-CH2CEtPh-C(=O)-NH(t)Bu](5-CH2NMe2)}Me2 (12) with a C-N bond breakage and a C-C bond formation. All the Al-derivatives are characterized by (1)H and (13)C NMR spectroscopy and the molecular structures are determined by single crystal X-ray diffractometry in solid state.