Reaction Of CrCl3 Research Articles

Syntheses, Characterizations, Crystal Structures, and Protonation Reactions of Dinitrogen Chromium Complexes Supported with Triamidoamine Ligands

A novel dinitrogen-dichromium complex, [{Cr(LBn)}2(μ-N2)] (1), has been prepared from reaction of CrCl3 with a lithiated triamidoamine ligand (Li3LBn) under dinitrogen. The X-ray crystal structure analysis of 1 revealed that it is composed of two independent dimeric Cr complexes bridged by N2 in the unit cell. The bridged N-N bond lengths (1.188(4) and 1.185(7) Å) were longer than the free dinitrogen molecule. The elongations of N-N bonds in 1 were also supported by the fact that the ν(N-N) stretching vibration at 1772 cm-1 observed in toluene is smaller than the free N2. Complex 1 was identified to be a 5-coordinated high spin Cr(IV) complex by Cr K-edge XANES measurement. The 1H NMR spectrum and temperature dependent magnetic susceptibility of 1 indicated that complex 1 is in the S = 1 ground state, in which two Cr(IV) ions and unpaired electron spins of the bridging N22- ligand are strongly antiferromagnetically coupled. Reaction of complex 1 with 2.3 equiv of Na or K gave chromium complexes with N2 between the Cr ion and the respective alkali metal ion, [{CrNa(LBn)(N2)(Et2O)}2] (2) and [{CrK(LBn)(N2)}4(Et2O)2] (3), respectively. Furthermore, the complexes 2 and 3 reacted with 15-crown-5 and 18-crown-6 to form the respective crown-ether adducts, [CrNa(LBn)(N2)(15-crown-5)] (4) and [CrK(LBn)(N2)(18-crown-6)] (5). The XANES measurements of complexes 2, 3, 4, and 5 revealed that they are high spin Cr(IV) complexes like complex 1. All complexes reacted with a reducing agent and a proton source to form NH3 and/or N2H4. The yields of these products in the presence of K+ were higher than those in the presence of Na+. The electronic structures and binding properties of 1, 2, 3, 4, and 5 were evaluated and discussed based on their DFT calculations.

Penta-coordinated Cr(II) and Cu(II) complexes appended with 4′-(4-quinolyl)-2,2′:6′,2″-terpyridine: Crystal structure, Hirshfeld surface analysis, luminescence and thermal properties

Two new chromium and copper complexes containing 4′-(4-quinolyl)-2,2′:6′,2′'-terpyridine (qtpy) have been synthesized and characterized using elemental analysis, IR and X-ray crystal structure determination. The reaction of CrCl3.6H2O with qtpy in presence of granulated zinc as a reducing agent has been resulted in the formation of the new terpyridine chromium(II) complex [Cr(qtpy)Cl2] (1). Moreover, the reaction of CuBr2 with qtpy affords the new complex [Cu(qtpy)Br2] (2). Recrystallization of 1 from DMF and recrystallization of 2 from DMSO yield the respective solvates, [Cr(qtpy)Cl2].DMF (1.DMF) and [Cu(qtpy)Br2].2DMSO (2.2DMSO), confirmed by X-ray single crystal analysis. The crystal structures of isostructural complexes [Cr(qtpy)Cl2].DMF (1.DMF) and [Cu(qtpy)Br2].2DMSO (2.2DMSO) reveal that chromium(II) and copper(II) adopt the penta-coordinated square pyramidal geometry in which Cr and Cu are coordinated by three nitrogen atoms of qtpy and two Cl- for 1.DMF, and two Br- for 2.2DMSO. As well, the crystal packings of complex 1.DMF, and 2.2DMSO clearly show the formation of supramolecular structures through C-H…X (X = N, O, halide) hydrogen bond interactions. The 3D Hirshfeld surface analysis and 2D fingerprint maps were used for quantitative mapping out of the intermolecular interactions for 1.DMF, and 2.2DMSO. Luminescence properties of 1 and 2 displayed the ligand-based π–π* emission bands in solution. Thermal properties of 1 and 2 show that they undergo thermal decomposition and the corresponding metal oxide formed in each case.

Synthesis and Characterization of Two "Tied-Back" Lithium Ketimides and Isolation of a Ketimide-Bridged [Cr2]6+ Dimer with Strong Antiferromagnetic Coupling.

Reaction of 1 equiv of KN(SiMe3)2 with 9-fluorenone results in the formation of (Me3Si)N═C13H8 (1) in high yield after work-up. Addition of 1 equiv of phenol to 1 results in rapid desilylation and formation of 9-fluorenone imine, HN═C13H8 (2). Subsequent reaction of 2 with 1 equiv of LiNiPr2 results in deprotonation and formation of [Li(Et2O)]4[N═C13H8]4 (3) in good yield. Reaction of 1 equiv of KN(SiMe3)2 with 2-adamantanone for 7 days at room temperature results in the formation of (Me3Si)N═C10H14 (4) in good yield. Dissolution of 4 in neat MeOH results in rapid desilylation concomitant with formation of 2-adamantanone imine, HN═C10H14 (5). Subsequent reaction of 5 with 1 equiv of LiNiPr2 results in formation of [Li(THF)]4[N═C10H14]4 (6). Both 3 and 6 were characterized by X-ray crystallography. Finally, reaction of CrCl3 with 3.5 equiv of 6 results in formation of the [Cr2]6+ dimer, [Li][Cr2(N═C10H14)7] (7), which can be isolated in modest yield after work-up. Complex 7 features a Cr-Cr bond length of 2.653(2) Å. Additionally, solid-state magnetic susceptibility measurements reveal strong antiferromagnetic coupling between the two Cr centers, with J = -200 cm-1.

Extremely Active Ethylene Tetramerization Catalyst Avoiding the Use of Methylaluminoxane: [iPrN{P(C6H4‐p‐SiR3)2}2CrCl2]+[B(C6F5)4]−

AbstractSasol's original ethylene tetramerization catalyst requires the use of expensive MMAO, a low working temperature (∼60 °C), and generates polyethylene (PE) as a side product. In this study, we developed an upgraded catalytic system that successfully avoids the need for MMAO. [(PNP)CrCl2]+[B(C6F5)4]−‐type species was obtained from the reaction of CrCl3(THF)3, [PhN(H)Me2]+[B(C6F5)4]−, and iPrN[P(C6H4‐p‐Si(nBu)3)2]2 (2) as well as from simply reacting 2 with [CrCl2(NCCH3)4]+[B(C6F5)4]−. The bulky (nBu)3Si‐substituents play the crucial role of preventing the formation of the inactive [(PNP)2CrCl2]+[B(C6F5)4]−. The prepared [2‐CrCl2]+[B(C6F5)4]− combined with iBu3Al was extremely active (>4000 kg/g‐Cr/h), performed well at a high temperature of up to 90 °C, and generated a negligible amount of PE (0.03 wt%). Screening the performance with a series of iPrN[P(C6H4‐p‐SiR3)2]2 further supported that bulky R3Si‐substituents are crucial not only to achieve extremely high activities but also to minimize the generation of PE. Structure of a [(PNP)CrCl2]+[B(C6F5)4]− species was elucidated by X‐ray crystallography.

Producing highly linear polyethylenes by using t‐butyl‐functionalized 2,6‐bis(imino)pyridylchromium(III) chlorides

ABSTRACTA new family of t‐butyl substituted chromium(III) chloride complexes (Cr1–Cr6), bearing 2‐(1‐(2,6‐dibenzhydryl‐4‐t‐butylphenylimino)ethyl)‐6‐(1‐(arylimino)ethyl)pyridine (aryl = 2,6‐Me2C6H3 Cr1, 2,6‐Et2C6H3 Cr2, 2,6‐i‐Pr2C6H3 Cr3, 2,4,6‐Me3C6H2 Cr4 and 2,6‐Et2‐4‐MeC6H2 Cr5) or 2,6‐bis(1‐(2,6‐dibenzhydryl‐4‐t‐butylphenylimino)ethyl)pyridine (Cr6), has been synthesized by the reaction of CrCl3·6H2O in good yield with the corresponding ligands (L1–L6), respectively. The molecular structures of Cr2 and Cr6 were characterized by X‐ray diffraction highlighted a distorted octahedral geometry with the coordinated N,N,N ligand and three bonded chlorides around the metal center. On activation with modified methylaluminoxane or triisobutyl aluminum, most of the chromium precatalysts exhibit good activities toward ethylene polymerization and produce linear polyethylenes with high‐molecular weight. In addition, an in‐depth catalytic evaluation of Cr2 was conducted to investigate how cocatalyst type and amount, reaction temperature, and run time affect the catalytic activities and polymer properties. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1049–1058

Synthesis and characterization of chromium complexes 2-Me4CpC6H4CH2(R)NHCrCl2 and their catalytic properties in ethylene homo- and co-polymerization.

A series of new half-sandwich secondary amine-coordinated dichlorochromium complexes chelated by 2-(tetramethylcyclopentadienyl)benzylamine ligands, 2-Me4CpC6H4CH2(R)NHCrCl2 [R = iPr (1), Cy (2), Ph (3), 4-MePh (4), 2,6-Me2Ph (5), 2,6-Et2Ph (6)], have been synthesized from the reactions of CrCl3(THF)3 with the dilithium salts of the corresponding ligands in THF, followed by the addition of 1/2 eq. of H2O to the reaction mixtures. The isolated yields of the chromium complexes were found to increase with the increase in the amount of H2O introduced and reach the highest values (66-76%) when 1/2 eq. of H2O is added. Attempts to isolate the 2-(tetramethylcyclopentadienyl)benzylamidochromium complexes, 2-Me4CpC6H4CH2(R)NCrCl, were not successful. The new dichlorochromium complexes were characterized by IR, 1H NMR, EPR, and UV/Vis spectroscopy and elemental analyses, and the molecular structures of complexes 1, 5 and 6 were determined by X-ray crystallography. The X-ray crystallographic analysis reveals that these chromium complexes possess a three-legged piano-stool geometry with the amine N atom in a mitered six-membered chelating ring and the two chloride atoms as the legs. Upon activation with AlR3 and Ph3CB(C6F5)4, complexes 1-6 exhibit reasonable catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing polyethylenes with moderate to high molecular weights and poly(ethylene-co-1-hexene)s with moderate comonomer incorporation which are typical linear low-density polyethylenes (LLDPE). Complex 4 was found to show higher catalytic activity for ethylene homo- and co-polymerization than other complexes under similar conditions, while complex 3 produced poly(ethylene-co-1-hexene)s with the highest comonomer incorporation.

Chromium-catalyzed para-selective formation of quaternary carbon centers by alkylation of benzamide derivatives

Selective creation of quaternary carbon centers has been a long-standing challenge in synthetic chemistry. We report here the chromium-catalyzed, para-selective formation of arylated quaternary carbon centers by alkylative reactions of benzamide derivatives with tertiary alkylmagnesium bromides at room temperature. The reaction, which was enabled by a low-cost chromium(III) salt combined with trimethylsilyl bromide, introduces a sterically bulky tertiary alkyl scaffold on the para-position of benzamide derivatives in a highly selective fashion without either isomerization of the tertiary alkyl group or formation of ortho-alkylated byproducts. Forming low-valent Cr species in situ by reaction of CrCl3 with t-BuMgBr accompanied by evolution of hydrogen can be considered, which serves as reactive species to promote the reaction. The para-alkylation likely occurs via a radical-type nucleophilic substitution of imino-coordination benzimidate intermediate.

Formation of the layered conductive magnet CrCl2(pyrazine)2 through redox-active coordination chemistry.

The unique properties of graphene, transition-metal dichalcogenides and other two-dimensional (2D) materials have boosted interest in layered coordination solids. In particular, 2D materials that behave as both conductors and magnets could find applications in quantum magnetoelectronics and spintronics. Here, we report the synthesis of CrCl2(pyrazine)2, an air-stable layered solid, by reaction of CrCl2 with pyrazine (pyz). This compound displays a ferrimagnetic order below ∼55 K, reflecting the presence of strong magnetic interactions. Electrical conductivity measurements demonstrate that CrCl2(pyz)2 reaches a conductivity of 32 mS cm-1 at room temperature, which operates through a 2D hopping-based transport mechanism. These properties are induced by the redox-activity of the pyrazine ligand, which leads to a smearing of the Cr 3d and pyrazine π states. We suggest that the combination of redox-active ligands and reducing paramagnetic metal ions represents a general approach towards tuneable 2D materials that consist of charge-neutral layers and exhibit both long-range magnetic order and high electronic conductivity.

From 4'-Hydroxy-2,2':6',2''-Terpyridine Complex of Chromium(III) towards Cr2O3 Nanoparticles: Effects of the Calcination Temperature on the Particle Size and Morphology

A new chromium(III) complex containing 4ʹ-hydroxy-2,2ʹ:6ʹ,2ʺ-terpyridine (tpyOH) has been prepared by the reaction of CrCl3. 6H2O with tpyOH in the presence of metallic zinc to afford the new complex [CrCl3(tpyOH)] (1). The complex 1 was used as a suitable precursor for the preparation of Cr2O3 nanoparticles by the simple calcination method at three different annealed temperatures of 400, 600, and 800 ˚C. The structures of the products have been fully characterized by IR, powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX). The average particle size using Scherrer’s equation is calculated to be about 27-36 nm. The results suggest that temperature is an effective way to tailor the morphology and crystallinity of the prepared nanoparticles. The photophysical properties and thermal gravimetric analysis (TGA) of the complex 1 have also been investigated. The emission of 1 exhibits the high-energy intense π→π* intraligand and low-energy MLCT transitions in DMSO solution. The TGA results show the stability of the complex up to 400 ˚C after stepwise decomposition of the coordinated ligands.

Tricoordinate Organochromium(III) Complexes Supported by a Bulky Silylamido Ligand Produce Ultra‐High‐Molecular Weight Polyethylene in the Absence of Activators

Low‐coordinate organoCr(III) complexes supported by the silylamido ligand –N(SiMe3)DIPP (DIPP = 2,6‐diisopropylphenyl) are ethylene polymerization catalyst precursors without the need of additional cocatalyst. The reaction of CrCl3(THF)3 with 3 or 2 equiv. of LiN(SiMe3)DIPP yields either a four‐membered cyclometalated Cr complex or Cr[N(SiMe3)DIPP]2Cl, respectively, with no trace of Cr[N(SiMe3)DIPP]3. Addition of 1 equiv. of LiN(SiMe3)DIPP to Cr[N(SiMe3)DIPP]2Cl also leads to the four‐membered metallacycle, which upon heating transforms to a new six‐membered Cr metallacycle, likely via a σ‐bond metathesis step. Cr[N(SiMe3)DIPP]2Cl can be readily converted to bis(amido)Cr(III) vinyl and alkyl complexes Cr[N(SiMe3)DIPP]2R (R = vinyl, Bn, and Me). All of these structurally characterized low‐coordinate Cr(III) complexes with a Cr–C bond initiate the polymerization of ethylene in the absence of activators or cocatalysts, producing ultra‐high‐molecular weight polyethylene.

Siloxide Complexes of Chromium(II), Manganese(II), Cobalt(II), and Chromium(III) Incorporating Potassium(I)

Abstract Heteroleptic ate complexes of the type K[M{N(SiMe3)2}2{OSi(OtBu)3}] (M = Cr, Mn, Co) were synthesized by adding one equivalent of the potassium salt KOSi(OtBu)3 to the bis(trimethylsilyl)amide precursors [Cr{N(SiMe3)2}2(thf)2], [Mn{N(SiMe3)2}2(thf)] and [Co{N(SiMe3)2}2(thf)], respectively. Surprisingly, the reaction of CrCl3(thf)3 with only two equivalents of KOSi(OtBu)3 yielded the homoleptic ate complex K[Cr{OSi(OtBu)3}4]. The compounds were characterized by elemental analysis and DRIFT spectroscopy as well as X-ray crystallography.

Ionothermal syntheses and optical property of chromium selenidostannates containing linear polyamine ligand

Ternary chromium selenidostannates [Cr(tepa)(OH)]2Sn2Se6·H2O (tepa=tetraethylenepentamine) (1) and [Cr(peha)]2(Sn2Se6)Cl2 (peha=pentaethylenehexamide) (2) were successfully synthesized by the reaction of CrCl3·6H2O, Sn, Se and tepa or peha in ionic liquid 1-ethyl-3-methylimidazolium chloride at 160°C. In the ionic liquid, the Cr3+ ion forms [Cr(tepa)(OH)]2+ or [Cr(peha)]3+ chelating complex cations, which lead to the formation of chromium selenidostannates 1 and 2. But the reactions in pure tepa or peha under solvothermal conditions produced amorphous powders. 1 and 2 are the first examples of TM-complex contained chalcogenidostannates synthesized by ionothermal technique. Both 1 and 2 form three-dimensional networks via intermolecular NH⋯Se, OH⋯Se and NH⋯O or NH⋯Cl interactions, respectively. 1 and 2 exhibit possible semiconducting properties with the band gaps at 2.08 and 2.19eV, respectively.

Ethylene polymerization by new chromium catalysts based on carborane [SSO] ligands

Tridentate carborane [S, S, O] ligands 2a-2b [(HOC6H2R2-4,6)(CH2)SC(B10H10)C(Ph)2P=S, R = (t)Bu (2a), R = Me (2b)] were synthesized and characterized. Reaction of CrCl3(THF)3 with the sodium salts of ligands 2a and 2b afford six-coordinated chromium complexes 3a and 3b. EXAFS spectroscopy performed on complex 3a to describe the coordination chemistry of ligand 2a around chromium center. DFT calculations were also performed on complex 3a to analyze the structure. The preliminary screening results revealed that six-coordinated chromium complexes 3a-3b displayed good catalytic activities towards ethylene polymerization in the presence of modified methylaluminoxane. The effect of polymerization parameters such as cocatalyst, reaction temperature, ethylene pressure, and reaction time on polymerization behavior were investigated in detail. The polymer obtained from this homogeneous catalytic reaction has a fibroid morphology.

New Self-Activating Organochromium Catalyst Precursor for Selective Ethylene Trimerization.

Two catalytic systems based on anionic ligands with the NPN structural motif, bearing tri- and pentavalent phosphorus, respectively, have been compared vis-a-vis their ability to selectively trimerize ethylene. In the case of the trivalent phosphorus ligands, reaction of the Cr(II) catalyst precursor [(t-Bu)NPN(t-Bu)]2Cr (1) with 2 equiv of MeLi afforded the Cr(III) species [(t-Bu)NP(Me)N(t-Bu)]2CrLi(OEt2) (2). The same reaction with 3 equiv of MeLi yielded instead the Cr(II) species {[(t-Bu)NP(Me)N(t-Bu)]Cr(μ-Me)}2{Li(THF)}2 (3). The P atoms of both 2 and 3 have been methylated. Activation of 2 and 3 with MAO produced an S-F distribution of oligomers. Conversely, activation of 3 with EtAlCl2 exclusively afforded 1-hexene together with a small amount of polymer as a byproduct. Treatment of 2 with EtAlCl2 did not yield an active catalyst. The reaction of CrCl2(THF)2 with [(t-Bu)NP(Ph)2N(t-Bu)]−Li+, containing pentavalent phosphorus, afforded the Cr(II) derivative [(t-Bu)NP(Ph)2N(t-Bu)]Cr(μ-Cl)2Li(THF)2 (4)...

New Chromium(III) Complexes with Imine−Cyclopentadienyl Ligands: Synthesis, Characterization, and Catalytic Properties for Ethylene Polymerization

A series of new half-sandwich chromium(III) complexes chelated with (2-((arylimino)methyl)phenyl)tetramethylcyclopentadienyl ligands, 2-(ArN═CH)C6H4Me4CpCrCl2 (Ar = 2,6-Me2C6H3 (1), 2,6-Et2C6H3 (2), 2,6-iPr2C6H3 (3), 4-MeC6H4 (4)), have been synthesized from the reaction of CrCl3 with the lithium salt of the corresponding ligand 2-(ArN═CH)C6H4Me4CpLi (Ar = 2,6-Me2C6H3 (LiL1), 2,6-Et2C6H3 (LiL2), 2,6-iPr2C6H3 (LiL3), 4-MeC6H4 (LiL4)). Free ligands HL1−HL4 were prepared by the condensation reaction of 2-(tetramethylcyclopentadienyl)benzaldehyde with 2,6-dialkylaniline. The free ligands were characterized by 1H NMR spectroscopy, while the chromium(III) complexes were characterized by elemental analyses and single-crystal X-ray crystallography. The X-ray crystallographic analysis indicates that the imine N atom in these complexes coordinates to the central chromium atom. Upon activation with AlR3 and Ph3CB(C6F5)4, these complexes exhibit high catalytic activity for ethylene polymerization and produce polyethylene with moderate to high molecular weights. These chromium(III) complexes can also be activated with AlR3 alone. In the latter case, they show slightly lower catalytic activity for ethylene polymerization in comparison to the AlR3/Ph3CB(C6F5)4 activated catalyst systems. The effects of ligand structure, polymerization temperature, AlR3, and Al/Cr molar ratio on the catalytic behavior of these complexes were examined.

Bimetallic Ethylene Tetramerization Catalysts Derived from Chiral DPPDME Ligands: Syntheses, Structural Characterizations, and Catalytic Performance of [(DPPDME)CrCl3]2 (DPPDME = S,S- and R,R-chiraphos and meso-achiraphos)

Chromium-based ethylene tetramerization catalyst precursors of the type {(DPPME)CrCl2(μ-Cl)}2 with a chiraphos ligand backbone [DPPME = {Ar(R1R2)}2PCH(CH3)CH(CH3)P{Ar(R1R2)}2] were prepared and characterized, in which substituents on the aryl phosphine varied with electron-donating and -withdrawing groups (S,S-ArR1 = H, R2 = H 1; R,R-ArR1 = H, R2 = H 2; meso-ArR1 = H, R2 = H 3; S,S-ArR1 = Me, R2 = H 4; S,S-ArR1 = OMe, R2 = H 5; S,S-ArR1 = H, R2 = Me 6; S,S-ArR1 = H, R2 = OMe 7; S,S-ArR1 = H, R2 = F 8). Depending on the coordination of chiraphos or achiraphos ligands, the corresponding bimetallic chromium complexes were prepared from the reaction of CrCl3(THF)3. S,S- and R,R-Chiraphos-based chromium metal complexes, 9 and 10, were crystallographically characterized to be dimeric, bridged by two chlorine ligands, whereas a meso achiraphos ligand resulted in a monomeric chromium complex, 17, when crystallized in acetonitrile. The observed average Cr−P bond distances of 9 [2.491(1) A] and 10 [2.489(2) A] were...

ChemInform Abstract: Preparation and Reactions of Chromium(III) Alkoxides.

Abstract Reactions of CrCl3.3THF with lithium alkoxides in 1:3 molar ratio in the respective primary alcohols yield insoluble trialkoxides, Cr(OR)3 (where R = Me, Et, Bu-n). The corresponding reactions with isopropyl and tertiary butyl alcohols, however, yield hydrolysed products only. We have been able to synthesize the isopropoxide and t. butoxide also by alternative routes. All the alkoxides have been characterized by physico-chemical methods and attempts have been made to study their alcoholysis reactions.

Metalation and Transmetalation Studies on Ph2PN(iPr)P(Ph)N(iPr)H for Selective Ethene Trimerization to 1-Hexene

Different organometallic compounds of the new aminodiphosphinoamine ligand Ph2PN(iPr)P(Ph)N(iPr)-H (1) are reported that are relevant model complexes for the selective ethene trimerization system consisting of ligand 1, CrCl3(THF)3, and Et3Al that produces 1-hexene in more than 90% yield and high purity. The lithiation of 1 by n-BuLi in the presence of tetramethylethylenediamine (tmeda) yields the mononuclear compound Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2). Without using tmeda the dinuclear species [Ph2N(iPr)P(Ph)N(iPr)-Li]2 (3) was obtained. By addition of a Grignard reagent to the ligand solution the bis(aminodiphosphinoamide)magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4) could be isolated. Reaction of Li[CpCrCl3] with 3 leads to the formation of the model compound CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5), which can be alkylated with Na[Et4Al] to form the corresponding ethyl compound CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7). In THF the formation of EtCrCl2(THF)3 (8) directly from the reaction of CrCl3[Ph2PN(iPr)...

Chromium(III) Bis(diketiminate) Complexes

Reaction of two equivalents of the lithium salt of N,N′-dibenzyl-2-amino-4-iminopent-2-ene, nacnacBnLi(THF), 1, with CrCl3(THF)3 or CrCl3 yielded nacnacBn2CrCl as a putative intermediate, which could be trapped by addition of 2,6-xylyl isocyanide to give the isocyanide-coordinated, octahedral complex nacnacBn2CrCl(CNC6Me2H3), 5. In the absence of isocyanide, ligand redistribution to the homoleptic tris(diketiminate) complex nacnacBn3Cr, 3, occurred upon concentration, standing, or workup with apolar solvents. Workup with diethyl ether afforded the bimetallic-bridged complex nacnacBn2Cr(μ-Cl)2Li(THF)2, 6. Reaction of CrCl3(THF)3 with one equivalent of 1 afforded the monodiketiminate complexes {nacnacBnCrCl(THF)(μ-Cl)}2 or {nacnacBnCrCl(μ-Cl)}2, depending on reaction conditions. Reaction of CrCl2(THF)x with two equivalents of 1 gave rise to nacnacBn2Cr, 4. Complexes 3−6 were characterized by X-ray diffraction studies. All octahedral complexes display a cis geometry with two nacnac ligands in a distorted, boat-like conformation.

Synthesis and ethylene trimerisation capability of new chromium(ii) and chromium(iii) heteroscorpionate complexes

Reaction of (Me(2)pz)(2)CHSiMe(2)N(H)R (R = (i)Pr or Ph) or (Me(2)pz)(2)CHSiMe(2)NMe(2) with CrCl(3)(THF)(3) or CrCl(2)(THF)(2) gave Cr{(Me(2)pz)(2)CHSiMe(2)NR(1)R(2)}Cl(3) (R(1) = H, R(2) = (i)Pr (10) or Ph (11); R(1) = R(2) = Me (15)) or Cr{(Me(2)pz)(2)CHSiMe(2)NR(1)R(2)}Cl(2)(THF) (R(1) = H, R(2) = (i)Pr (12) or Ph (13); R(1) = R(2) = Me (16)), respectively. Compounds 10 and 11 were crystallographically characterized and the magnetic behaviour of all the new compounds was evaluated using SQUID magnetometry. Reaction of CrCl(3)(THF)(3) with Li{C(Me(2)pz)(3)}(THF) gave the zwitterionic complex Cr{C(Me(2)pz)(3)}Cl(2)(THF) (17) containing an apical carbanion. Reaction of the analogous phenol-based ligand (Me(2)pz)(2)CHArOH (ArO = 2-O-3,5-C(6)H(2)(t)Bu(2)) with CrCl(3)(THF)(3) gave Cr{(Me(2)pz)(2)CHArOH}Cl(3) (19) whereas the corresponding reaction with CrCl(2)(THF)(2) unexpectedly gave the Cr(III) phenolate derivative Cr{(Me(2)pz)(2)CHArO}Cl(2)(THF) (20) which could also be prepared from CrCl(3)(THF)(3) and the sodiated ligand [Na{(Me(2)pz)(2)CHArO}(THF)](2). Reaction of the corresponding ether (Me(2)pz)(2)CHArOMe with CrCl(3)(THF)(3) or CrCl(2)(THF)(2) gave Cr{(Me(2)pz)(2)CHArOMe}Cl(3) (23) and Cr{(Me(2)pz)(2)CHArOMe}Cl(2)(THF) (24), respectively. The catalytic performance in ethylene oligomerisation/polymerisation of all of the new Cr(II) and Cr(III) complexes was evaluated. Most of the complexes showed high activity, but produced a Schultz-Flory distribution of alpha-olefins. Compound 23 had an exceptionally low alpha-value of 0.37 and showed a preference for 1-hexene and 1-octene formation. While replacing a secondary amine (10-13) for a tertiary amine (15-16) resulted in loss of catalytic activity, replacing a phenol (19) for an anisole (23) group afforded a more selective and more active catalyst. Changing from MAO to DIBAL-O as cocatalyst induced a switch in selectivity to ethylene polymerisation.