RESUMO
Olefin metathesis catalyzed by iron complexes has garnered substantial interest due to iron's abundance and nontoxicity relative to ruthenium, yet its full potential remains untapped, largely because of the propensity of iron carbenes to undergo cyclopropanation instead of cycloreversion from a metallacycle intermediate. In this report, we elucidate the reactions of [{PC(sp2)P}Fe(L)(N2)], ([PC(sp2)P] = bis[2-(diisopropylphosphino)phenyl]methylene) with strained olefins, unveiling their capability to yield metathesis-related products. Our investigations led to the isolation of a structurally characterized metallacyclobutane during the reaction with norbornadiene derivatives, ultimately leading to a ring-opened iron alkylidene. These findings provide compelling evidence that iron complexes adhere to the Chauvin olefin metathesis mechanism.
RESUMO
Ruthenium carbenes, famously used in olefin metathesis, have impacted numerous research areas, ranging from synthesis to materials and biology. Although in the same group as ruthenium, iron carbenes showing similar reaction patterns have not been reported. Such targets are of high interest because the use of a sustainable metal would lead to a decreased cost, toxicity, and environmental impact of the corresponding compounds. Herein, we report the synthesis of an iron carbene complex, [{PC(sp2)P}Fe(N2)(PMe3)] ([PC(sp2)P] = (bis[2-(di-isopropylphosphino)phenyl]methylene), which is capable of performing [2+2] cycloaddition reactions in the presence of alkynes. Specifically, η3-vinyl carbenes are formed stoichiometrically through a [2+2] cycloaddition between the alkyne and the metal carbene. Additional reactivity of the η3-vinyl carbenes with alkynes yields a second insertion product containing a new iron carbene moiety.
Assuntos
Alcinos/química , Ferro/química , Metano/análogos & derivados , Catálise , Complexos de Coordenação/química , Cristalografia por Raios X , Reação de Cicloadição , Metano/química , Conformação Molecular , Teoria QuânticaRESUMO
A series of chalcogen analogues encompassing a ketone and chalcogenoketones [{PC(=E)P}Pd(PMe3 )] (E=O, S, Se, Te) was generated from a nucleophilic palladium carbene compound, [{PC(sp2 )P}Pd(PMe3 )] ([PC(sp3 )HP]=bis[2-(diisopropylphosphino)-phenyl]methyl, iPr2 P-C6 H4 -CH-C6 H4 -PiPr2 ). The thio-, seleno-, and telluroketone were all synthesized by means of an atom transfer from the respective chalcogens. The ketone analogue, however, required the use of nitrobenzene or nitrosobenzene as the oxygen-atom transfer agent.
RESUMO
The synthesis and characterization of two new carbene complexes, (dtbpe)NiâCH(dmp) (1; dtbpe = 1,2-bis(di-tert-butylphosphino)ethane; dmp = 2,6-dimesitylphenyl) and (dippn)NiâCH(dmp) (2; dippn = 1,8-bis(di-iso-propylphosphino)naphthalene), are described. Complexes 1 and 2 were isolated by photolysis of the corresponding side-bound diazoalkane complexes, exemplified by (dtbpe)Ni{η(2)-N2CH(dmp)} (3). The carbene complexes feature Ni-C distances that are short and Ni-C-C angles at the carbene carbon that are intermediate between 120° and 180° (155.7(3)° and 152.3(3)°, respectively). The difference between the two carbenes became obvious when their reactivity toward 1-electron oxidizing agents was studied: the oxidation of 1 led to an internal rearrangement and the formation of a nickel(I) alkyl [{κ(2)-P,C-di-tert-butylphosphino-di-tert-butyl-PCH(dmp)ethane}Ni][BAr(F)4] (4), while the oxidation of 2 allowed the isolation of an unrearranged product, formulated as the cationic nickel(III) carbene complex[(dippn)NiâCH(dmp)][BAr(F)4] (6). Both oxidations are chemically reversible and the respective reductions lead to the neutral carbene complexes, 1 and 2.
RESUMO
A PNP ligand, PN(pyr)P ((PN(pyr)P)H = 2,5-bis((di-iso-propylphosphino)methyl)pyrrole), which employs a pyrrole unit as a central anionic nitrogen donor, was designed. The corresponding group 10 metal chlorides as well as iridium and ruthenium compounds were isolated. In order to conduct this work, [(PN(pyr)P)Tl] and [(PN(pyr)P)Ag]2 were synthesized and characterized. The thallium and silver species were paramount in the formation of the iridium and ruthenium complexes, which could not be isolated using (PN(pyr)P)H or the corresponding lithium pyrrolide salt. Interestingly, the solid state molecular structure of [(PN(pyr)P)Tl] indicates that the metal center engages in an η(2) intermolecular interaction with the backbone of a neighboring pyrrole molecule instead of the expected bonding to the phosphine arms.
RESUMO
A series of diphosphine ligands (i)Pr2P-C6H4-X-C6H4-P(i)Pr2 (for ligand L(1), X = CH2; for ligand L(2), X = CH2CH2) was investigated to determine the preference for cis/trans coordination to palladium(0), palladium(II), and rhodium(I). Increasing the length of the bridging alkyl backbone from one to two carbons changes the geometry of the resulting palladium(II) complexes, with L(1) coordinating preferentially cis, while L(2) coordinates in a trans fashion. Coordination to Pd(0) leads to L(1)Pd(dba) and L(2)Pd(dba), in which both ligands accommodate a P-M-P angle close to 120°. L(2) was found to coordinate cis in a rhodium(I) complex ([L(2)Rh(nbd)][BF4], where nbd = norbornadiene).
RESUMO
The coordination chemistry of a neutral tPCHâCHP pincer (tPCHâCHP = 2,2'-bis(di-iso-propylphosphino)-trans-stilbene) with metals that form stable complexes in the +1 oxidation state was studied and (tPCHâCHP)CoCl, (tPCHâCHP)CoCl(CO), (tPCHâCHP)RhCl, (tPCHâCHP)Cu(OTf), [(tPCHâCHP)Cu][PF6], and [(tPCHâCHP)Ag][PF6] were synthesized and characterized. In order to determine whether the coordination mode is dependent on the oxidation state of the metal, some +2 metal complexes, (tPCHâCHP)CoCl2 and (tPCHâCHP)FeBr2, were also investigated. The coordination of the olefinic backbone is not observed in (tPCHâCHP)FeBr2, (tPCHâCHP)CoCl2, (tPCHâCHP)Cu(OTf), or [(tPCHâCHP)Ag][PF6], but η(2)-coordination is present in [(tPCHâCHP)CoCl][BAr(F)4], [(tPCHâCHP)FeBr][BAr(F)4], (tPCHâCHP)CoCl, (tPCHâCHP)CoCl(CO), (tPCHâCHP)RhCl, and [(tPCHâCHP)Cu][PF6]. Cobalt(II), iron(II), and copper(I) formed complexes with the ligand in both coordination modes. All metal complexes were characterized by multinuclei NMR spectroscopy, X-ray crystallography, and elemental analysis.
RESUMO
The three-coordinate imidos (dtbpe)NiâNR (dtbpe = (t)Bu2PCH2CH2P(t)Bu2, R = 2,6-(i)Pr2C6H3, 2,4,6-Me3C6H2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni-N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6-(i)Pr2C6H3, reductive carbonylation results in formation of the (dtbpe)Ni(CO)2 along with the N-C coupled product keteneimine PhCHâCâN(2,6- (i)Pr2C6H3). Given the ability of the NiâN bond to have biradical character as suggested by theoretical analysis, H atom abstraction can also occur in (dtbpe)NiâN{2,6-(i)Pr2C6H3} when this species is treated with HSn((n)Bu)3. Likewise, the microscopic reverse reaction--conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6-(i)Pr2C6H3)} to the imido (dtbpe)NiâN{2,6-(i)Pr2C6H3}--is promoted when using the radical Mes*O(â¢) (Mes* = 2,4,6-(t)Bu3C6H2). Reactivity studies involving the imido complexes, in particular (dtbpe)NiâN{2,6-(i)Pr2C6H3}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C-N and N-N bonds by coupling reactions. In addition to NMR spectroscopic data and combustion analysis, we also report structural studies for all the cycloaddition reactions involving the imido (dtbpe)NiâN{2,6-(i)Pr2C6H3}.
Assuntos
Complexos de Coordenação/química , Imidas/química , Níquel/química , Carbono/química , Complexos de Coordenação/síntese química , Reação de Cicloadição , Hidrogênio/química , Imidas/síntese química , Ligantes , Modelos MolecularesRESUMO
Reaction of [(IPr)Ni(µ-Cl)]2 (1-Cl; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with ClMg{CH(SiMe3)2}·Et2O affords (IPr)Ni{CH(SiMe3)2} (2), a two-coordinate Ni(I) alkyl complex. An analogous two-coordinate aryl derivative, (IPr)Ni(dmp) (dmp = 2,6-dimesitylphenyl), can be similarly prepared from Li(dmp) and 1-Cl. Reaction of 2 with alkyl bromides gives the three-coordinate Ni(II) alkyl halide complex (IPr)Ni{CH(SiMe3)2}Br. Evidence for a radical mechanism is presented to explain the reaction of 2 with alkyl halides.
RESUMO
A new family of low-coordinate nickel imides supported by 1,2-bis(di-tert-butylphosphino)ethane was synthesized. Oxidation of nickel(II) complexes led to the formation of both aryl- and alkyl-substituted nickel(III)-imides, and examples of both types have been isolated and fully characterized. The aryl substituent that proved most useful in stabilizing the Ni(III)-imide moiety was the bulky 2,6-dimesitylphenyl. The two Ni(III)-imide compounds showed different variable-temperature magnetic properties but analogous EPR spectra at low temperatures. To account for this discrepancy, a low-spin/high-spin equilibrium was proposed to take place for the alkyl-substituted Ni(III)-imide complex. This proposal was supported by DFT calculations. DFT calculations also indicated that the unpaired electron is mostly localized on the imide nitrogen for the Ni(III) complexes. The results of reactions carried out in the presence of hydrogen donors supported the findings from DFT calculations that the adamantyl substituent was a significantly more reactive hydrogen-atom abstractor. Interestingly, the steric properties of the 2,6-dimesitylphenyl substituent are important not only in protecting the NiâN core but also in favoring one rotamer of the resulting Ni(III)-imide, by locking the phenyl ring in a perpendicular orientation with respect to the NiPP plane.
Assuntos
Imidas/síntese química , Níquel/química , Compostos Organometálicos/síntese química , Espectroscopia de Ressonância de Spin Eletrônica , Imidas/química , Ligantes , Modelos Teóricos , Estrutura Molecular , Compostos Organometálicos/química , TemperaturaRESUMO
Hydrogen-atom abstraction from M-E(H) to generate MâE-containing complexes (E = PR, NR) is not well studied because only a few complexes are known to undergo such reactions. Hydrogen-atom abstraction from nickel(I) phosphide and amide complexes led to the corresponding phosphinidene and imide compounds. These reactions are unparalleled in the organometallic chemistry of nickel and feature an unusual example of a transition-metal phosphinidene synthesized by hydrogen-atom abstraction.
Assuntos
Amidas/química , Hidrogênio/química , Imidas/química , Níquel/química , Fosfinas/química , Eletroquímica , Ligantes , Modelos Moleculares , Conformação MolecularRESUMO
Reaction of the dimeric Ni(I) chloride complex [(dtbpe)NiCl](2) (1) with dimesitylsilyl potassium affords the three-coordinate Ni(I) silyl complex (dtbpe)Ni(SiHMes(2)) (2). Alternatively, 2 can be prepared by an oxidative-addition reaction of Mes(2)Si(H)OTf (Tf = CF(3)SO(3)) with the nickel(0) complex [(dtbpe)Ni](2)(mu-C(6)H(6)) (3), with (dtbpe)Ni(OTf) (4) formed as an easily separable byproduct. The one-electron oxidation of 2 by ferrocenium affords diamagnetic [(dtbpe)Ni(mu-H)SiMes(2)][BAr(F)(4)] (5), a Ni(II) complex formed by partial 1,2-H migration from silicon to nickel and featuring an unusual 3-center, 2-electron bonding motif between Ni, Si, and the bridging H. Complex 5 was also obtained from Mes(2)SiH(2) activation by the neopentyl complex salt [(dtbpe)Ni(CH(2)CMe(3))][BAr(F)(4)] (6) with elimination of neopentane.
Assuntos
Hidrogênio/química , Níquel/química , Compostos Organometálicos/química , Silício/química , Simulação por Computador , Cristalografia por Raios X , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Compostos Organometálicos/síntese química , OxirreduçãoRESUMO
Reaction of CS(2) with [(dtbpe)Ni](2)(η(2),µ-C(6)H(6)) (1; dtbpe =1,2-bis(di-tert-butylphosphino)ethane) in toluene gives the carbon disulfide complex (dtbpe)Ni(η(2)-CS(2)) (2), characterized by standard spectroscopic methods and X-ray crystallography. Reaction of CS(2) with the Ni(I) complex (dtbpe)Ni(OSO(2)CF(3)) gives the diamagnetic, trimetallic cluster [{(dtbpe)Ni(κ(1),η(2)-CS(2))}(2)(dtbpe)Ni][SO(3)CF(3)](2) (3-OTf). The solid-state structure of 3-OTf reveals that the two CS(2) ligands bind η(2) to two (dtbpe)Ni centers and κ(1) to the third, unique (dtbpe)Ni in the complex dication, and NMR spectroscopic data indicate that this structure is maintained in solution. Oxidation of 2 by ferrocenium hexafluorophosphate affords the identical trimetallic complex dication as the PF(6)(-) salt, [{(dtbpe)Ni(κ(1),η(2)-CS(2))}(2)(dtbpe)Ni][PF(6)](2) (3-PF(6)). These results are consistent with the intermediacy of a Ni(I)-CS(2) complex, [(dtbpe)Ni(CS(2))(+)], that is unstable with respect to disproportionation. Reaction of 1 with one equivalent of CO(2) provides the carbon dioxide adduct (dtbpe)Ni(η(2)-CO(2)) (4), that was also crystallographically characterized. Thermolysis of 4 in benzene solution at 80 °C results in reduction of the CO(2) ligand to CO, trapped as (dtbpe)Ni(CO)(2), and partial oxidation of a dtbpe ligand to give OâP(tert-Bu)(2)CH(2)CH(2)P(tert-Bu)(2).
Assuntos
Dióxido de Carbono/química , Dissulfeto de Carbono/química , Níquel/química , Compostos Organometálicos/síntese química , Cristalografia por Raios X , Ligantes , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/químicaRESUMO
Elemental sulfur reacts with a bulky bis(phosphine)nickel(0) complex to give a monomeric nickel(II) eta(2)-disulfido complex, oxidation of which results in the elimination of sulfur with dimerization to give an eta(2),eta(2)-disulfidodinickel(II) derivative in which the S-S bond can be reductively cleaved in a redox-reversible fashion.
Assuntos
Dimerização , Dissulfetos/química , Níquel/química , Compostos Organometálicos/química , Modelos Moleculares , Conformação Molecular , Compostos Organometálicos/síntese química , Oxirredução , Enxofre/químicaRESUMO
Palladium(ii) cationic carbene radical and neutral bi-radical complexes were synthesized from a previously reported Pd(ii) carbene in the presence of one and two electron oxidants. When [{PC(sp2)P}tBuPd(PMe3)] (1, [PC(sp2)P]tBu = (bis[2-(di-iso-propylphosphino)-4-tertbutylphenyl]methylene)) was treated with [Cp2Fe][X] (X = BArF4, ArF = 3,5-(CF3)2C6H3, or PF6), the corresponding radical cationic complexes [{PCË(sp2)P}tBuPd(PMe3)][X] (2: X = BArF4, 3: PF6) were isolated and characterized. Magnetic moment measurements and EPR spectroscopy indicated the presence of a ligand centered unpaired electron. In the presence of two electron oxidants such as 1,8-naphthylene disulfide or 9,10-anthracenedione, 1 converts to [{PCË(sp2)P}tBuPdS(C10H6)SPd{PCË(sp2)P}tBu] (4) or [{PCË(sp2)P}tBuPdO(C14H10)OPd{PCË(sp2)P}tBu] (5), respectively. Single crystal X-ray diffraction and EPR spectroscopy confirmed the bi-radical nature of 4 and 5.
RESUMO
The reaction between [(PNpyrP)NiCl] (1, PNpyrP = 2,5-bis((di-iso-propylphosphino)-methyl)-1H-pyrrolide) and TlPF6 in the presence of a monodentate phosphine ligand led to cationic nickel phosphine and phosphite complexes, [(PNpyrP)Ni(PHPh2)][PF6] (2), [(PNpyrP)Ni(PMe3)][PF6] (3), and [(PNpyrP)Ni{P(OMe)3}][PF6] (4). Compound 2 can be deprotonated resulting in the generation of a terminal phosphido complex, [(PNpyrP)Ni(PPh2)] (5). When 3 is subjected to a base, a methyl proton of PMe3 is abstracted to afford [(PNpyrP)Ni(CH2PMe2)] (6), containing a methylene bridge between Ni and the external phosphine. Compounds 2-6 were characterized by single crystal X-ray diffraction in addition to multi-nuclear NMR spectroscopy and elemental analysis.
RESUMO
The structure of a pincer ligand consists of a backbone and two `arms' which typically contain a P or N atom. They are tridentate ligands that coordinate to a metal center in a meridional configuration. A series of three iron complexes containing the pyrrole-based PNP pincer ligand 2,5-bis[(diisopropylphosphanyl)methyl]pyrrolide (PNpyrP) has been synthesized. These complexes are possible precursors to new iron catalysts. {2,5-Bis[(diisopropylphosphanyl)methyl]pyrrolido-κ3P,N,P'}carbonylchlorido(trimethylphosphane-κP)iron(II), [Fe(C18H34NP2)Cl(C3H9P)(CO)] or [Fe(PNpyrP)Cl(PMe3)(CO)], (I), has a slightly distorted octahedral geometry, with the Cl and CO ligands occupying the apical positions. {2,5-Bis[(diisopropylphosphanyl)methyl]pyrrolido-κ3P,N,P'}chlorido(pyridine-κN)iron(II), [Fe(C18H34NP2)Cl(C5H5N)] or [Fe(PNpyrP)Cl(py)] (py is pyridine), (II), is a five-coordinate square-pyramidal complex, with the pyridine ligand in the apical position. {2,5-Bis[(diisopropylphosphanyl)methyl]pyrrolido-κ3P,N,P'}dicarbonylchloridoiron(II), [Fe(C18H34NP2)Cl(CO)2] or [Fe(PNpyrP)Cl(CO)2], (III), is structurally similar to (I), but with the PMe3 ligand replaced by a second carbonyl ligand from the reaction of (II) with CO. The two carbonyl ligands are in a cis configuration, and there is positional disorder of the chloride and trans carbonyl ligands.
RESUMO
The reactivity of two nucleophilic palladium carbenes, [PC(sp(2))P]Pd(PMe3) and [PC(sp(2))P]Pd(PPh3), where [PC(sp(2))P] = bis[2-(di-iso-propylphosphino)phenyl]methylene, toward the E-H bond activation of Ph4-nEHn (E = Si, Ge; n = 1-3) and pinacolborane (HBpin) is discussed. Unlike previous reports, both types of isomer species, hydride [PC(EHn-1Ph4-n)P]PdH or [PC(Bpin)P]PdH and silyl/germyl [PC(H)P]Pd(EHn-1Ph4-n), were observed depending on the substrate and the phosphine ligand, showing that the polarity of the Pd-C bond can be tuned by the phosphine substituents.
RESUMO
Iridium PCsp3P complexes featuring a novel bis(2-diphenylphosphinophenyl)-2-pyridylmethane ligand (PC(Py)HP) are reported. C-H activation reactions between the dihydride complex [(PC(Py)P)Ir(H)2] and tetrahydrofuran or methyl tert-butyl ether in the presence of a hydrogen acceptor, norbornene (NBE), at ambient temperature led exclusively to the hydrido oxyalkyl complexes, [(PC(Py)P)IrH(C4H7O)] and [(PC(Py)P)IrH(CH2O(t)Bu)], respectively. The internal pyridine donor is important and stabilizes these species by coordination to the iridium center. The coordination of pyridine to the iridium center is labile, however, and its dissociation occurs in the presence of a suitable substrate, as demonstrated by the intramolecular nucleophilic attack of pyridine on a vinylidene intermediate generated from PhC[triple bond, length as m-dash]CH.
RESUMO
Heterobimetallic Pd-K carbenes featuring Pd-Ccarbene-K moieties were synthesized via an unprecedented sequential substitution/reduction reaction from a radical precursor, [{PCË(sp2)P} tBuPdI] ([PC(sp2)P] tBu = bis[2-(di-iso-propylphosphino)-4-tert-butylphenyl]methylene). Polymeric structures were observed in the solid state for the heterobimetallic compounds that can be interrupted in the presence of a donor solvent.