Two isomers of trichlorotris(dimethylphenylphosphine)tungsten and their potential for equilibration with W2Cl6(PMe2Ph)n

Rothfuss, Helmut; Barry, Jane T.; Huffman, John C.; Caulton, Kenneth G.; Chisholm, Malcolm H.

doi:10.1021/ic00073a018

Cited by 14 publications

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“…Although M−Cl distances are known to vary significantly with the oxidation state and coordination number of the metal, as well as the trans (and to a lesser extent, cis ) influence of the ligands trans (or cis ) to it, one can safely state that a typical terminal Mo−Cl or W−Cl distance is 2.4(1) Å for Mo or W in the +3 oxidation state. Such distances are seen in, for example, the mononuclear pseudo-octahedral complex fac -WCl 3 (PMePh 2 ) 3 and in the W−W triply bonded compound W 2 Cl 3 (NMe 2 ) 3 (PMe 2 Ph) 2 . Metal−metal multiple bonds are known to have a high trans -influence, and the most closely related compound, Re 2 (hpp) 4 Cl 2 , has a similar paddlewheel structure with axial chloride ligands, and a Re−Re quadruple bond (2.1913(2) Å), has Re−Cl = 2.749(5) Å .…”

Section: Resultsmentioning

confidence: 95%

M₂(hpp)₄Cl₂ and M₂(hpp)₄, Where M = Mo and W: Preparations, Structure and Bonding, and Comparisons with C₂, C₂H₂, and C₂Cl₂ and the Hypothetical Molecules M₂(hpp)₄(H)₂

et al. 2003

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The reaction between M(2)Cl(2)(NMe(2))(4), where M = Mo or W, and Hhpp (8 equiv) in a solid-state melt reaction at 150 degrees C yields the compounds M(2)(hpp)(4)Cl(2) 1a (M = Mo) and 1b (M = W), respectively, by the elimination of HNMe(2) [hpp is the anion derived from deprotonation of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, Hhpp]. Purification of 1a and 1b is achieved by sublimation of the excess Hhpp and subsequent recrystallization from either CH(2)Cl(2) or CHCl(3) (or CDCl(3)). By single-crystal X-ray crystallography, the structures of 1a and 1b are shown to contain a central paddlewheel-like M(2)(hpp)(4) core with Mo-Mo = 2.1708(8) A (from CH(2)Cl(2)), 2.1574(5) A (from CDCl(3)), W-W = 2.2328(2) A (from CDCl(3)), and M-N = 2.09(1) (av) A. The Cl ligands are axially ligated (linear Cl-M-M-Cl) with abnormally long M-Cl bond distances that, in turn, depend on the presence or absence of hydrogen bonding to chloroform. The quadruply bonded compounds M(2)(hpp)(4), 2a (M = Mo), and 2b (M = W), can be prepared from the reactions between 1,2-M(2)R(2)(NMe(2))(4) compounds, where R = (i)()Bu or p-tolyl, and Hhpp (4 equiv) in benzene by ligand replacement and reductive elimination. The compounds 2a and 2b are readily oxidized, and in chloroform they react to form 1a and 1b, respectively. The electronic structure and bonding in the compounds 1a, 1b, 2a, and 2b have been investigated using gradient corrected density functional theory employing Gaussian 98. The bonding in the M-M quadruply bonded compounds, 2a and 2b, reveals M-M delta(2) HOMOs and extensive mixing of M-M pi and nitrogen ligand lone-pair orbitals in a manner qualitatively similar to that of the M(2)(formamidinates)(4). The calculations indicate that in the chloride compounds, 1a and 1b, the HOMO is strongly M-Cl sigma antibonding and weakly M-M sigma bonding in character. Formally there is a M-M triple bond of configuration pi(4)sigma(2), and the LUMO is the M-M delta orbital. An interesting mixing of M-M and M-Cl pi interactions occurs, and an enlightening analogy emerges between these d(4)-d(4) and d(3)-d(3) dinuclear compounds and the bonding in C(2), C(2)H(2), and C(2)Cl(2), which is interrogated herein by simple theoretical calculations together with the potential bonding in axially ligated compounds where strongly covalent M-X bonds are present. The latter were represented by the model compounds M(2)(hpp)(4)(H)(2). On the basis of calculations, we estimate the reactions M(2)(hpp)(4) + X(2) to give M(2)(hpp)(4)X(2) to be enthalpically favorable for X = Cl but not for X = H. These results are discussed in terms of the recent work of Cotton and Murillo and our attempts to prepare parallel-linked oligomers of the type [[bridge]-[M(2)]-](n)().

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Section: Resultsmentioning

confidence: 95%

M₂(hpp)₄Cl₂ and M₂(hpp)₄, Where M = Mo and W: Preparations, Structure and Bonding, and Comparisons with C₂, C₂H₂, and C₂Cl₂ and the Hypothetical Molecules M₂(hpp)₄(H)₂

et al. 2003

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“…Similar to the reduction of Cp*TaCl 4 by 1 – 4 , the stronger reducing ability of the nitrogen-containing reductant 2b compared with that of 1a and 1b was clearly observed for the phosphine-coordinating tungsten complex, WCl 4 (PMe 2 Ph) 2 . The reaction of 2b with WCl 4 (PMe 2 Ph) 2 in the presence of PMe 2 Ph (3 equiv) provided mer -WCl 3 (PMe 2 Ph) 3 ( 16 ) in good yield (84% yield), in sharp contrast to the lack of reduction of WCl 4 (PMe 2 Ph) 2 by 1a and 1b due to their weaker reduction ability (eq ). Although compound 2c could reduce WCl 4 (PMe 2 Ph) 2 to give 16 , a long reaction time (7 days) was necessary to complete the reduction due to the weaker reducing ability of 2c .…”

Section: Resultsmentioning

confidence: 99%

“…1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2a ), 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2b ), 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2c ), 1,4-bis(trimethylsilyl)-1-aza-2,5-cyclohexadiene ( 3 ), and 1,1′-bis(trimethylsilyl)-1,1′-dihydro-4,4′-bipyridine ( 4 ) were prepared according to the modified procedure of the literature by replacing potassium metal by sodium metal except for the synthesis of 2c that needed the use of potassium . Cp*TiCl 3 , Cp*TaCl 4 , WCl 4 (PMe 2 Ph) 2 , and N , N ′-bis(4-methoxyphenyl)-1,4-diaza-1,3-butadiene were prepared according to the literature. Cp 2 TiCl 2 was purchased from TCI Co. Ltd. Cp* 2 TiCl 2 was obtained from Alfa Aesar and used as received.…”

Section: Methodsmentioning

confidence: 99%

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1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadienes as Strong Salt-Free Reductants for Generating Low-Valent Early Transition Metals with Electron-Donating Ligands

et al. 2014

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Electron-rich organosilicon compounds, such as 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2a), 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2b), 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2c), and 1,1'-bis(trimethylsilyl)-1,1'-dihydro-4,4'-bipyridine (4), served as versatile reducing reagents of group 4-6 metal chloride complexes, such as Cp2TiCl2, Cp*2TiCl2 (Cp* = η(5)-C5Me5), Cp*TiCl3, Cp*TaCl4, and WCl4(PMe2Ph)2, to generate the corresponding low-valent metal species in a salt-free manner. Nitrogen-containing reductants, such as 2a-c and 4, had stronger reducing ability than the parent organosilicon reductants, 3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (1a) and 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (1b), as well as a pyridine-derived reductant, 1,4-bis(trimethylsilyl)-1-aza-2,5-cyclohexadiene (3). These greater effects of 2a-c and 4 are likely due to their negative one-electron redox potentials, as typically demonstrated in the reduction of Cp2TiCl2, for which compounds 2a and 4 gave the corresponding one-electron reduced products, pyrazine-bridged and 4,4'-bipyridyl-bridged dimeric Ti(III) complexes 5 and 6, and compounds 2b and 2c afforded the same double chloride-bridged dimeric Ti(III) complex, [Cp2Ti]2(μ-Cl)2 (7), though 1a and 1b could not reduce Cp2TiCl2. Application of the organosilicon compounds as reducing agents for catalytic reactions revealed that the combination of 2c and a catalytic amount of Cp2TiCl2 assisted a Reformatsky reaction of nonanal and ethyl 2-bromoisobutyrate and its derivatives to give ethyl 3-hydroxy-2,2-dimethylundecanoate and its derivatives. In this coupling reaction, 2c served as the best reductant among 2a-c and 4 due to the suppression of an undesired reaction between 2c and ethyl 2-bromoalkanoates.

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“…The reactions we report here represent interesting main group versions of related chlorine atom transfer reactions between transition metal centers that have received some attention. In fact, some of these systems exchange phosphine ligands and chlorine atoms and thus suggest the potential catalytic role of phosphines in other chlorine atom transfer processes . Extensions of the method here to other sterically encumbered aryls and alkyls should allow a rapid means ( 31 P NMR spectroscopy) to determine the relative impact of bulky groups at main group centers and to begin the more challenging task of unraveling presumed electronic effects that may be overshadowed by dominating steric forces.…”

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An Unusual Equilibrium Chlorine Atom Transfer Process and Its Potential for Assessment of Steric Pressure by Bulky Aryls

et al. 2002

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An unusually facile intermolecular chlorine atom transfer process has been discovered between the phospha-Wittig reagents ArP=PMe3 and ArPCl2 (Ar is a sterically hindered aryl group). The atom transfer process is catalyzed by added PMe3. A mechanism is forwarded that is based upon a Me3P/Me3PCl2 couple that allows shuttling of chlorine atoms between ArP groups. This unique transfer process is exploited to evaluate the steric properties of aryl groups via an equilibrium process.

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Two isomers of trichlorotris(dimethylphenylphosphine)tungsten and their potential for equilibration with W2Cl6(PMe2Ph)n

Cited by 14 publications

References 0 publications

M₂(hpp)₄Cl₂ and M₂(hpp)₄, Where M = Mo and W: Preparations, Structure and Bonding, and Comparisons with C₂, C₂H₂, and C₂Cl₂ and the Hypothetical Molecules M₂(hpp)₄(H)₂

M₂(hpp)₄Cl₂ and M₂(hpp)₄, Where M = Mo and W: Preparations, Structure and Bonding, and Comparisons with C₂, C₂H₂, and C₂Cl₂ and the Hypothetical Molecules M₂(hpp)₄(H)₂

1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadienes as Strong Salt-Free Reductants for Generating Low-Valent Early Transition Metals with Electron-Donating Ligands

An Unusual Equilibrium Chlorine Atom Transfer Process and Its Potential for Assessment of Steric Pressure by Bulky Aryls

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Two isomers of trichlorotris(dimethylphenylphosphine)tungsten and their potential for equilibration with W2Cl6(PMe2Ph)n

Cited by 14 publications

References 0 publications

M2(hpp)4Cl2 and M2(hpp)4, Where M = Mo and W: Preparations, Structure and Bonding, and Comparisons with C2, C2H2, and C2Cl2 and the Hypothetical Molecules M2(hpp)4(H)2

M2(hpp)4Cl2 and M2(hpp)4, Where M = Mo and W: Preparations, Structure and Bonding, and Comparisons with C2, C2H2, and C2Cl2 and the Hypothetical Molecules M2(hpp)4(H)2

1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadienes as Strong Salt-Free Reductants for Generating Low-Valent Early Transition Metals with Electron-Donating Ligands

An Unusual Equilibrium Chlorine Atom Transfer Process and Its Potential for Assessment of Steric Pressure by Bulky Aryls

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M₂(hpp)₄Cl₂ and M₂(hpp)₄, Where M = Mo and W: Preparations, Structure and Bonding, and Comparisons with C₂, C₂H₂, and C₂Cl₂ and the Hypothetical Molecules M₂(hpp)₄(H)₂

M₂(hpp)₄Cl₂ and M₂(hpp)₄, Where M = Mo and W: Preparations, Structure and Bonding, and Comparisons with C₂, C₂H₂, and C₂Cl₂ and the Hypothetical Molecules M₂(hpp)₄(H)₂