.sigma.-Alkyl and -aryl complexes of the group 4-7 transition metals

Schrock, R. R.; Parshall, G. W.

doi:10.1021/cr60300a004

Cited by 262 publications

(101 citation statements)

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“…The relative stabilities of high-oxidation-state "homoleptic" or "peralkyl" compounds such as [M{CH 2 Si-(CH 3 ) 3 } 4 ], [M(CH 2 C 6 H 5 ) 4 ], and [M{CH 2 C(CH 3 ) 3 } 4 ] (M = Ti, Zr, or Hf; Scheme 2), were rationalized on the basis of the fact that unlike a compound having an ethyl ligand, the alkyl ligands in these species lack b hydrogen atoms and so of course cannot undergo decomposition processes that involve b hydrogen atoms. [7] In 1973 Wilkinson published the synthesis of [W(CH 3 ) 6 ]. [8] Unlike [M(CH 3 ) 4 ] species (where M = Ti, Zr, or Hf) [W(CH 3 ) 6 ] is stable at 22 8C.…”

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confidence: 99%

Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture)

2006

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Its my great privilege to be here today, in a position I never thought possible. The story I will tell you I hope will give you some idea what I have contributed to the area for which the Nobel prize in chemistry was awarded this year.The story begins 32 years ago in 1973, the year the Nobel prize was shared by G. Wilkinson and E. O. Fischer. Wilkinsons Nobel lecture [1] concerned the nature of a single bond between a transition metal and a carbon atom in an alkyl group, and emphasized the fact that the metal-carbon bond is not inherently weak. E. O. Fischer in his Nobel Lecture [2] summarized the extensive chemistry of transitionmetal "carbene" complexes [3,4] that contain a metal-carbon double bond discovered by him and his group in 1964 (Scheme 1).[5] He also reported new "carbyne" complexes that contain a metal-carbon triple bond. [6] It was clear that metal-carbon single bonds were of great importance in the emerging area of homogeneous catalysis. However, no catalytic reactions involving species that contain metalcarbon double or triple bonds were known. When I went to the Central Research Department of E. I. DuPont de Nemours and Company in 1972, transition-metal organometallic chemistry and homogeneous catalysis were of great interest as a consequence of their huge potential in organic chemistry and therefore in industry.In the early 1970s inorganic chemists knew that many transition metal species containing a metal-carbon bond are subject to various modes of decomposition that are much more rapid than in a non-transition-metal species such as Zn(CH 2 CH 3 ) 2 or Al(CH 2 CH 3 ) 3 . The most common of these decomposition reactions involves transfer of a b hydrogen atom, from a metal-bound ethyl group (MÀCH 2 CH 3 ) for example, to the metal center (M) to yield a metal hydride and an alkene. The relative stabilities of high-oxidation-state "homoleptic" or "peralkyl" compounds such as [M{CH 2 Si-(CH 3 ) 3 } 4 ], [M(CH 2 C 6 H 5 ) 4 ], and [M{CH 2 C(CH 3 ) 3 } 4 ] (M = Ti, Zr, or Hf; Scheme 2), were rationalized on the basis of the fact that unlike a compound having an ethyl ligand, the alkyl ligands in these species lack b hydrogen atoms and so of course cannot undergo decomposition processes that involve b hydrogen atoms.[ 6 ] is stable at 22 8C. The methyl carbon is a with respect to the metal center; there is no b carbon atom and so no b hydrogens. However, methyl species are not

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confidence: 99%

Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture)

2006

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“…Similar metal hydride methylamine solution or in a vacuum (18). Although elimination reactions are known to occur in the this route does not appear to be an important one decomposition of transition metal alkyl complexes for the potassium case, there is evidence that the when a P-hydrogen is available (13,14). The formation of cyanide is the primary route in the stability of transition metal dialkylamides was lithium case (see below).…”

Section: Dmfa Therttral Stabilitymentioning

confidence: 99%

“…Aminals (gem-diamines) are also unstable (3), so that their salts, such as 4, 6 , and 8, should have short lifetimes in these solutions, decomposing to amines, imines, and the corresponding salts (3). Evidence for the involvement of the N-methylmethylenimine (5) comes from the observation that when the thermolysis run is carried out with high hydrogen overpressure (7-30 MPa), dimethylamine is formed as a minor product.4 This likely occurs through reaction of KH, produced to its solubility limit via equilibrium [13]: with 5 according to [14] and [15]. Methylenimine, Nmethylmethylenimine, and hydrogen cyanide have been, proposed as intermediates in the pyrolysis of methylamine (12).…”

Section: Dmfa Therttral Stabilitymentioning

confidence: 99%

“…Thus lithium methylamide (LMA). The rate of loss of the slow formation of KH probably occurs from the LMA, as measured by uv-visible spectrophotometry, PMA ion pair, [4], via intramolecular elimination was roughly a factor of 10 slower than for the (13) either in the a-mode (A) or, more likely, the potassium salt at the same temperature. Two other p-mode (B).…”

Section: Dmfa Therttral Stabilitymentioning

confidence: 99%

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The chemistry of N,N′-dimethylformamidine. I. Formation from potassium methylamide and its thermal stability

Halliday¹,

Symons²,

Bonnett³

1978

Can. J. Chem.

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Can. J. Chem. 56, 1455.The thernial decomposition of methylamine solutions of potassium methylaniide (PMA) t o form the potassium salt (PDMFA) of N,N'-dimethylformaniidine (DMFA) has been studied as a function of PMA concentration at 60°C. Although concentrated solutions yield normal pseudo-first-order plots (analysis by ultraviolet-visible spectrophotornetry), dilute solutions (<0.05 mol L-' PMA) show an increase to a new rate after about 20 h reaction.The mechanism for this novel amidine salt synthesis is discussed in terms of rate-limiting e-hydride elimination from the PMA ion pair. The relatively sharp rate increase with time for the low concentration runs may arise from a slow buildup of one or more intermediates. The resulting inverse dependence of k,,, on PMA concentration is probably related to ion pairdimer association phenomena.Pure DMFA has been produced by this reaction, and its thernial stability examined. DMFA decomposes above 100'C to form bis-N-(N'-methylmethylenin~ine)methylamine and niethylamine; the series of equilibria involved have been shown to be reversible.On a etudie, en fonction de la concentration de la MAP a GOT, la deconlposition thermique On a pu produire de la DMFA pure par cette rtaction et on a tvalue sa stabilitk thermique. La DMFA se decompose au-dessus de 100°C pour conduire a de la bis-N-(N'-methylmethylcnimine) methylamine et a de la methylamine; on a montre que la strie des iquilibres impliques est reversible.[Traduit par le journal]Although there are few references in the literThe potassium salt of DMFA had been identified2 ature to N,Nf-dimethylformamidine (DMFA) (I), as one of the major products formed when a solution ~ -the general chemistry of the amidine group,

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“…Metal-alkyl, [1] metal-alkylidene [2] and metal-alkylidyne [3] complexes are the core of modern fundamental organometallic chemistry and, with the catalytic metathesis reactions of single, [4] double [5] and triple bonds, [6] their applications have spread over organic synthesis [7] and materials science. [8] This area of chemistry is an outstanding example showing that homogeneous catalysis provides the best defined catalysts at the molecular level leading to excellent mechanistic information and, consequently, optimized selectivity.…”

Section: Introductionmentioning

confidence: 99%

Metallodendritic Catalysis for Redox and CarbonCarbon Bond Formation Reactions: A Step towards Green Chemistry.

et al. 2005

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Metallodendritic catalysts combine the advantages of homogeneous and heterogeneous catalysts: they are soluble and perfectly well defined on the molecular level, and yet they can be recovered by precipitation, ultra-filtration or ultra-centrifugation (as biomolecules) and recycled several times. In this article, we summarize our recent work in this field with examples operating under ambient conditions in metathesis, Pd-catalyzed Sonogashira coupling, redox catalysis of nitrate and nitrite cathodic reduction to ammonia and various oxidation reactions by H 2 O 2 catalyzed by polyoxometallates. The dendritic effects on the catalytic efficiencies are scrutinized, i.e., the comparison of the metallodentritic catalysts with their monomeric models and among the dendrimer generations. It is concluded that metallostars or low-generation metallodendrimers usually are optimized catalysts in terms of efficiency and recovery/re-use.

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.sigma.-Alkyl and -aryl complexes of the group 4-7 transition metals

Cited by 262 publications

References 57 publications

Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture)

Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture)

The chemistry of N,N′-dimethylformamidine. I. Formation from potassium methylamide and its thermal stability

Metallodendritic Catalysis for Redox and CarbonCarbon Bond Formation Reactions: A Step towards Green Chemistry.

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