(2-(Dimethylammonium)ethyl)cyclopentadienyltricarbonylmetalates:  Group VI Metal Zwitterions. Attenuation of the Brønsted Basicity and Nucleophilicity of Formally Anionic Metal Centers

Fischer, Paul J.; Krohn, K.; Mwenda, Edward T.

doi:10.1021/om050484d

Cited by 11 publications

(12 citation statements)

References 48 publications

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“…The coordination geometry around the tungsten atom is that of a three-legged piano stool, with C–W–C and C–W–P angles between 86.5 and 90.5° (see Figure ). The 1,3-dimethylimidazolium proton that is nearest to tungsten is H11; the H···W separation is 3.10 Å, too long for a covalent interaction, but the occurrence of a weak C–H···M hydrogen-bonding interaction cannot be excluded . In comparison to the structure of the precursor cis -CpW(CO) 2 (PMe 3 )H, reported by Norton and co-workers, the metrical parameters reflect the increased amount of metal-to-ligand back-bonding in the anion.…”

Section: Resultsmentioning

confidence: 80%

“…The 1,3-dimethylimidazolium proton that is nearest to tungsten is H11; the H•••W separation is 3.10 Å, too long for a covalent interaction, but the occurrence of a weak C−H•••M hydrogen-bonding interaction cannot be excluded. 37 In comparison to the structure of the precursor cis-CpW(CO) 2 (PMe 3 )H, reported by Norton and co-workers, 38 the metrical parameters reflect the increased amount of metal-to-ligand back-bonding in the anion. For example, the )] − in toluene at 100 °C (Scheme 2) and was recrystallized from toluene/hexane to afford the hydride in 69% isolated yield as orange crystals.…”

Section: Pk Amentioning

confidence: 95%

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Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO)₂(IMe)]₂

et al. 2012

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The thermal W–W bond homolysis in [CpW(CO)2(IMe)]2 (IMe = 1,3-dimethylimidazol-2-ylidene) was investigated and was found to occur to a large extent in comparison to other tungsten dimers such as [CpW(CO)3]2. CpW(CO)2(IMe)H was prepared by heating a solution of [IMeH]+[CpW(CO)2(PMe3)]−, and it exists in solution as a mixture of interconverting cis and trans isomers. The carbene rotation in CpW(CO)2(IMe)H was explored by DFT calculations, and low enthalpic barriers (<3.5 kcal mol–1) are predicted. CpW(CO)2(IMe)H has pK a MeCN = 31.5(3), and deprotonation with KH gives K+[CpW(CO)2(IMe)]− (·MeCN). Hydride abstraction from CpW(CO)2(IMe)H with Ph3C+PF6 – in the presence of a coordinating ligand L (MeCN or THF) gives [CpW(CO)2(IMe)(L)]+PF6 –. Electrochemical measurements on the anion [CpW(CO)2(IMe)]− in MeCN, together with digital simulations, give an E 1/2 value of −1.54(2) V vs Cp2Fe+/0 for the [CpW(CO)2(IMe)]•/– couple. A thermochemical cycle provides the solution bond dissociation free energy of the W–H bond of CpW(CO)2(IMe)H as 61.3(6) kcal mol–1. In the electrochemical oxidation of [CpW(CO)2(IMe)]−, reversible dimerization of the electrogenerated radical CpW(CO)2(IMe)• occurs, and digital simulation provides kinetic and thermodynamic parameters for the monomer–dimer equilibrium: k dimerization ≈ 2.5 × 104 M–1 s–1, k homolysis ≈ 0.5 s–1 (i.e., K dim ≈ 5 × 104 M–1). Reduction of [CpW(CO)2(IMe)(MeCN)]+PF6 – with cobaltocene gives the dimer [CpW(CO)2(IMe)]2, which in solution exists as a mixture of anti and gauche rotamers. As expected from the electrochemical experiments, the dimer is in equilibrium with detectable amounts of CpW(CO)2(IMe)•. This species was observed by IR spectroscopy, and its presence in solution is also in accordance with the observed reactivity toward 2,6-di-tert-butyl-1,4-benzoquinone, chloroform, and dihydrogen.

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Section: Resultsmentioning

confidence: 80%

Section: Pk Amentioning

confidence: 95%

Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO)₂(IMe)]₂

et al. 2012

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“…Isolable [M‘ ‘CH 3 (CO) 3 (η 5 -Cp NMe )]I (M‘ ‘ = Mo ( 17) , W ( 18 )), spectroscopically identical in the IR ν(CO) region with those obtained more conveniently via Na[M(CO) 3 (η 5 -Cp N )], were obtained from reactions of CH 3 I with 8 and 9 , respectively. Although aqueous HCl stoichiometrically reacts with 6 to provide [WH(CO) 3 (η 5 -Cp NH )]Cl, attempts to isolate [MH(CO) 3 (η 5 -Cp NMe )]Cl were uniformly unsuccessful. Aqueous HCl (1 equiv) reacted with 7 and 9 in CH 3 CN to afford metal hydride 8 and starting zwitterion in solution.…”

Section: Resultsmentioning

confidence: 99%

“…The (2-(dimethylamino)ethyl)cyclopentadienyl (Cp N ) group VI metal carbonyl anions seemed excellent precursors to such complexes. Protonation of these anions proceeds at the amine to afford zwitterionic [(2-(dimethylammonium)ethyl)cyclopentadienyl]tricarbonylmetalates, M(CO) 3 (η 5 -Cp NH ) (M = Cr ( 4 ), Mo ( 5 ), W ( 6 )), which engage in N−H···M hydrogen bonding . The interaction between the separated charges distorts the M(CO) 3 fragments and renders the formally negatively charged metal centers less reactive than those in [M(CO) 3 (η 5 -Cp)] - .…”

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confidence: 99%

[(2-(Trimethylammonium)ethyl)cyclopentadienyl]tricarbonylmetalates: Group VI Metal Zwitterions

2007

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Zwitterionic [(2-(trimethylammonium)ethyl)cyclopentadienyl]tricarbonylmetalates, M(CO) 3 (η 5 -Cp NMe ) (M ) Cr (7), Mo (8), W (9)), proVide useful models to assess intramolecular through-space electrostatic interactions on the reactiVity of formally negatiVely charged metals. The C 3V M(CO) 3 units in these zwitterions appear largely unperturbed by the tethered 2-(trimethylammonium)ethyl group; neither significant intra-nor intermolecular ion pairing occurs either in solution or in the solid state. Although the donor ability of the Cp group in these zwitterions is essentially identical with that in [M(CO) 3 (η 5 -Cp)] -on the basis of spectroscopic and crystallographic data, the metal-based reactiVity of 7-9 appears to be decreased relatiVe to that of [M(CO) 3 (η 5 -Cp)] -. While the latter reacts with HCl, AuPPh 3 Cl, CH 3 I, and I 2 to proVide robust M(II) complexes, isolable products could only be obtained from reactions of 7-9 with I 2 and CH 3 I. One important strategy in the design of zwitterionic organometalates is that metal-based reactiVity is enhanced as the tethered counterion steric bulk increases to decrease significant ion-pairing interactions. The relatiVe inertness of 7-9 compared to their protonated analogues M(CO) 3 (η 5 -Cp NH ), despite the absence of structural perturbations in 7-9 due to ion pairing, indicates that ion-pairing interactions are not the only important factors that determine metal-based reactiVity in organometallic zwitterions.The design of organometallic zwitterions for catalytic applications 1 and as building blocks for metallodendritic assemblies 2 is an active research area. The potential of tuning the reactivity of metal centers by incorporating an intramolecular charge separation motivates these studies. Two strategies have emerged to rationally modulate the steric and electronic metal environment in organometallic zwitterions with covalently interconnected cationic and anionic sites. Either the tether length or substituents at the charged sites can be varied. One strategy that informs the design of zwitterionic organometalates is that metal-based reactivity is enhanced as tethered counterion steric bulk increases to decrease significant ion-pairing interactions. Few organometallic zwitterions with formally anionic metal centers have been reported, despite speculation that intramolecular through-space electrostatic interactions in the coordination sphere of reduced metal centers could modulate catalyst activity and selectivity. 3 Baird recently reported group VI metal carbonyls of methyldiphenylphosphonium cyclopentadienylide, M(CO) 3 (η 5 -C 5 H 4 -PMePh 2 ) (M ) Cr (1), Mo (2), W (3)). 4 This ligand exhibits considerable zwitterionic character in its electronic ground state, and its donor ability toward M(CO) 3 fragments was classified as less than that of cyclopentadienyl anion but much greater than that of benzene. Spectroscopic and reactivity comparisons to [M(CO) 3 (η 5 -Cp)] -were instrumental for this determination. While the zwitterionic resonance forms of 1-3...

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“…However, such systems are present in some clusters containing m-p-tolylmethylidyne or carbonyl groups[126,127] or m 3 -hydride bridging the AuMo 2 core in (Ph 3 P)Au(m 3 -H)[Mo(CO) 4 ] 2 (m-dppm) 138 [Au-Mo 2.900(3)/2.914 (2) Å][128]. In contrast, dinuclear complexes with an unsupported Au-W bond are much rarer[113,129], a recent example being the tungsten analog 139 of compound 136 [Au-W 2.7121(5)/2.7060(5) Å][113]. Much more common are dinuclear and polynuclear compounds in which the metal centers of an Au-W bond are bridged by m-arylmethylidene[130,131], m-arylmethylidyne[132][133][134][135][136][137][138][139][140], m-C:C t Bu[141], m-CN (Et)Me[142], m-CO or m-CS ligands[127,[143][144][145].A recent example, (Ph 3 P)AuW(m-CO)(m-C:C t Bu)(h 5 -Cp)(NO) 140, features both alkynyl and carbonyl groups supporting the Au-W bond [2.803(3) Å] (Figure 4.36a)…”

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confidence: 99%

Gold–Heterometal Interactions and Bonds

Silvestru

2008

Modern Supramolecular Gold Chemistry

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(2-(Dimethylammonium)ethyl)cyclopentadienyltricarbonylmetalates: Group VI Metal Zwitterions. Attenuation of the Brønsted Basicity and Nucleophilicity of Formally Anionic Metal Centers

Cited by 11 publications

References 48 publications

Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO)₂(IMe)]₂

Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO)₂(IMe)]₂

[(2-(Trimethylammonium)ethyl)cyclopentadienyl]tricarbonylmetalates: Group VI Metal Zwitterions

Gold–Heterometal Interactions and Bonds

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(2-(Dimethylammonium)ethyl)cyclopentadienyltricarbonylmetalates: Group VI Metal Zwitterions. Attenuation of the Brønsted Basicity and Nucleophilicity of Formally Anionic Metal Centers

Cited by 11 publications

References 48 publications

Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO)2(IMe)]2

Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO)2(IMe)]2

[(2-(Trimethylammonium)ethyl)cyclopentadienyl]tricarbonylmetalates: Group VI Metal Zwitterions

Gold–Heterometal Interactions and Bonds

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Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO)₂(IMe)]₂

Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO)₂(IMe)]₂