Bis[μ-N,N′-bis(2,6-diisopropylphenyl)ethene-1,2-diamido]-1,4(η2);1:2κ4 N:N;3:4κ4 N:N-bis(diethyl ether)-1κO,4κO-di-μ-hydrido-2:3κ4 H:H-2,3-dichromium(II)-1,4-dilithium(I) pentane hemisolvate

The title compound, [Cr2Li2(C26H36N2)2(μ-H)2(C4H10O)2]·0.5C5H12, is a binuclear chromium complex bridged by two hydrogen atoms. Each chromium atom is coordinated in a distorted square-planar geometry by one chelating bis­(2,6-diisopropyl­phen­yl)ethene-1,2-diamido ligand via its two N atoms. Additionally, two diametrically opposed lithium ether adducts coordinate in an η4 mode on the backbone of the ligands. There is a crystallographic inversion center in the middle of the Cr2H2 ring. One of the isopropyl groups is disordered over two positions in a 0.567 (7):0.433 (7) ratio. Disorder is also observed in the pentane hemisolvate molecule

Methyl Complexes of the Transition Metals

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M-CH compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.Ministerio de Ciencia e Innovación Projects CTQ2010–15833, CTQ2013-45011 - P and Consolider - Ingenio 2010 CSD2007 - 00006Junta de Andalucía FQM - 119, Projects P09 - FQM - 5117 and FQM - 2126EU 7th Framework Program, Marie Skłodowska - Curie actions C OFUND – Agreement nº 26722

Study of the Factors Affecting the Selectivity of Catalytic Ethylene Oligomerization

Over the past decade, advances in ethylene oligomerization have witnessed explosive growth of interest from both commercial and academic standpoint, with chromium metal invariably being the metal of preference. A common feature in this literature was the extended long debate regarding the mechanism, metal oxidation states responsible for selectivity and the role of the ligand. This thesis work embarked on the isolation and characterization of new active intermediates called “single component catalysts” (or self activating) to address two important questions: (1) how the catalyst precursors re-arrange upon activation and (2) the real oxidation state of the activated species. Four different ligands systems have been examined for this purpose. The first part is a study on the NPIIIN ligand which can be described as a dynamic and non-spectator ligand. Upon aluminum alkyl activation, a series of single component chromium catalysts for selective ethylene oligomerization and polymerization have been isolated, fully characterized and tested. New selective single component chromium(I) catalysts have also been isolated and tested positively for ethylene trimerization. The second part includes a new series of chromium complexes based on the NPVN ligand. This ligands enabled to obtain the first polymer-free extremely active catalytic system. In both NPN ligand systems, a new activation pathway was discovered by using vinyl Grignard reagent [(CH2=CH)MgCl] as activator and/or reducing agent. The third part explores new modified pyrrole-chromium complexes which were found to be highly active and selective ethylene trimerization catalysts. This part was a continuation of previous work from our lab to complete the mechanistic picture of this highly successful pyrrole-chromium catalyst independently commercialized by Phillips-Chevron and Mitsubishi. Interestingly upon aluminum alkyl treatment, the first example of a Schrock-type chromium ethylidene complex has been isolated and characterized and found to be a potent catalyst for selective ethylene trimerization. Finally, the other ligands introduced in this thesis are new systems called pyridine-SNS and Si-SNS that introduce some modification to the known commercial SNS catalyst (Sasol technology). The introduction of a pyridine ring or a silyl unit in the ligand scaffold has allowed to understand the mechanism of action of this remarkable system

Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System

The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy (a), (t-Bu)SCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2S(t-Bu) (b), and PhSCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl3(THF)(3) to afford the corresponding monomeric [CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]CrCl3 (1a) or dimeric {[CySCH2Si(CH3)(2)NSi(CH3)(2)CH2SCy] CrCl(mu-Cl)}(2) (2a). One-pot reaction of a in the presence of Et2AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]Cr{(mu-Cl)Al(CH2CH3)(2)Cl)(2) (3a). To deprotonate the N-H function of the Si-SNS ligand, n-BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH2Si(CH3)(2)NSi(CH3)(2)CH2SCy]Cr(mu-Cl)}(2) (4a) and {[(t-Bu)SCH2Si(CH3)(2)NSi(CH3)(2)CH2S(t-Bu)]Cr(mu-Cl)}(2) (4b) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl3 or AlMe3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl3, two isostructural complexes, {[CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]Cr{(mu-Cl)AlCl3}(2) (5a) and {[PhSCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SPh]C{(mu-Cl)AlCl3}(2) (5c), have been obtained. The reaction with AlMe3 afforded {[CySCH2Si(CH3)(2)N(Al(CH3)(2)(mu-Cl)Si(CH3)(2)CH2SCy] Cr{(mu-Cl)Al(CH3)(3)} (6a). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N-H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me2AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH2Si(CH3)(2)N(CH3)Si(CH3)(2)CH2SCy]Cr(mu-Cl)}(2){(Al(CH3)(2)Cl)(2))(mu-Cl)}(2) (7d). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers

Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System

The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy (a), (t-Bu)SCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2S(t-Bu) (b), and PhSCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl3(THF)(3) to afford the corresponding monomeric [CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]CrCl3 (1a) or dimeric {[CySCH2Si(CH3)(2)NSi(CH3)(2)CH2SCy] CrCl(mu-Cl)}(2) (2a). One-pot reaction of a in the presence of Et2AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]Cr{(mu-Cl)Al(CH2CH3)(2)Cl)(2) (3a). To deprotonate the N-H function of the Si-SNS ligand, n-BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH2Si(CH3)(2)NSi(CH3)(2)CH2SCy]Cr(mu-Cl)}(2) (4a) and {[(t-Bu)SCH2Si(CH3)(2)NSi(CH3)(2)CH2S(t-Bu)]Cr(mu-Cl)}(2) (4b) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl3 or AlMe3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl3, two isostructural complexes, {[CySCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SCy]Cr{(mu-Cl)AlCl3}(2) (5a) and {[PhSCH2Si(CH3)(2)N(H)Si(CH3)(2)CH2SPh]C{(mu-Cl)AlCl3}(2) (5c), have been obtained. The reaction with AlMe3 afforded {[CySCH2Si(CH3)(2)N(Al(CH3)(2)(mu-Cl)Si(CH3)(2)CH2SCy] Cr{(mu-Cl)Al(CH3)(3)} (6a). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N-H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me2AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH2Si(CH3)(2)N(CH3)Si(CH3)(2)CH2SCy]Cr(mu-Cl)}(2){(Al(CH3)(2)Cl)(2))(mu-Cl)}(2) (7d). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers

Chromium catalysts that switch the selectivity

Abstract only

Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System

The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy (a), (t-Bu)SCH2Si(CH3)2N(H)Si(CH3)2CH2S(t-Bu) (b), and PhSCH2Si(CH3)2N(H)Si(CH3)2CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl3(THF)3 to afford the corresponding monomeric [CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy]CrCl3 (1a) or dimeric {[CySCH2Si(CH3)2NSi(CH3)2CH2SCy]CrCl(μ-Cl)}2 (2a). One-pot reaction of a in the presence of Et2AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy]Cr{(μ-Cl)Al(CH2CH3)2Cl}2 (3a). To deprotonate the N–H function of the Si-SNS ligand, n-BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH2Si(CH3)2NSi(CH3)2CH2SCy]Cr(μ-Cl)}2 (4a) and {[(t-Bu)SCH2Si(CH3)2NSi(CH3)2CH2S(t-Bu)]Cr(μ-Cl)}2 (4b) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl3 or AlMe3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl3, two isostructural complexes, {[CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy]Cr{(μ-Cl)AlCl3}2 (5a) and {[PhSCH2Si(CH3)2N(H)Si(CH3)2CH2SPh]C{(μ-Cl)AlCl3}2 (5c), have been obtained. The reaction with AlMe3 afforded {[CySCH2Si(CH3)2N(Al(CH3)2-μ-Cl)Si(CH3)2CH2SCy]Cr{(μ-Cl)Al(CH3)3} (6a). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N–H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me2AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH2Si(CH3)2N(CH3)Si(CH3)2CH2SCy]Cr(μ-Cl)}2{(Al(CH3)2Cl)2)(μ-Cl)}2 (7d). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers

Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System

The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy (a), (t-Bu)SCH2Si(CH3)2N(H)Si(CH3)2CH2S(t-Bu) (b), and PhSCH2Si(CH3)2N(H)Si(CH3)2CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl3(THF)3 to afford the corresponding monomeric [CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy]CrCl3 (1a) or dimeric {[CySCH2Si(CH3)2NSi(CH3)2CH2SCy]CrCl(μ-Cl)}2 (2a). One-pot reaction of a in the presence of Et2AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy]Cr{(μ-Cl)Al(CH2CH3)2Cl}2 (3a). To deprotonate the N–H function of the Si-SNS ligand, n-BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH2Si(CH3)2NSi(CH3)2CH2SCy]Cr(μ-Cl)}2 (4a) and {[(t-Bu)SCH2Si(CH3)2NSi(CH3)2CH2S(t-Bu)]Cr(μ-Cl)}2 (4b) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl3 or AlMe3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl3, two isostructural complexes, {[CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy]Cr{(μ-Cl)AlCl3}2 (5a) and {[PhSCH2Si(CH3)2N(H)Si(CH3)2CH2SPh]C{(μ-Cl)AlCl3}2 (5c), have been obtained. The reaction with AlMe3 afforded {[CySCH2Si(CH3)2N(Al(CH3)2-μ-Cl)Si(CH3)2CH2SCy]Cr{(μ-Cl)Al(CH3)3} (6a). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N–H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me2AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH2Si(CH3)2N(CH3)Si(CH3)2CH2SCy]Cr(μ-Cl)}2{(Al(CH3)2Cl)2)(μ-Cl)}2 (7d). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers