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

Abstract

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

Metathesis Polymerization Reactions Induced by the Bimetallic Complex (Ph4P)2[W2(μ-Br)3Br6]

“…NMR spectra were recorded on a Varian Unity Plus 300 A wide range of catalytic systems have been explored, including uni-, bi-, and multicomponent ones, based mainly on mononuclear transition metal complexes along the periodic table (Ti, Nb, Ta, Cr, Mo, W, Re, Co, Ru, Os) [9,10]. In any case, the active catalytic species for metathesis polymerization reactions is a metallocarbene, which is either generated in situ, or has been previously synthesized and isolated, such as the well-defined Katz ([(OC) 5 W = C(Ph)R]; R = OMe, Ph) [11,12], Schrock (Mo-and W-based) [13], and Grubbs (Ru-based) [14] alkylidenes and their numerous variations. Many of the catalytic systems in which metallocarbenes are formed in situ are ill-defined, because the exact nature of the active species remains unknown.…”

“…All possible products are shown in Scheme 3. Soluble polymers were characterized using 1 H NMR spectroscopy ( Figures S7-S9) and insoluble polymers using 13 C Cross Polarization Magic Angle Spinning (CPMAS) spectroscopy. Addition of AgBF4 was required, otherwise 1 was inactive towards polymerization reactions.…”

“…Polymer characterization for insoluble polymers PNBD and PDCPD was done using 13 C CPMAS spectroscopy (Figures 2 and 3). Peaks at 133 (PNBD) and 129 (PDCPD) ppm are due to olefinic carbons, and peaks in the regions 30-53 (PNBD) and 26-60 ppm (PDCPD) are due to aliphatic carbons.…”

Interests and challenges of organic solvent nanofiltration for sustainable chemistry: the case of homogeneous catalysis of metathesis

“…The three major contributors to olefin metathesis development and achievements shared the Nobel Prize in Chemistry in 2005 [6][7][8]. These reactions, usually conducted in toluene, can be catalyzed by homogeneous catalysts (soluble) containing ruthenium, as Grubbs or Hoveyda-type (figure 1) whose molecular weights are around 600 g mol -1 [9].…”

Síntese de monômeros luminescentes com norborneno e suas polimerizações via metátese

“…Os compostos ácido-2-carboxílico-5-norborneno; cloreto de oxalila (COCl) 2 NEt 3 foi destilada na presença de CaH 2 em atmosphera de N 2 .…”