The reaction of (N∧N)PdMe 2 (N∧N is Ar−NCMe-MeCN−Ar; Ar = 2,6-bis(diphenylmethyl)-4-methylbenzene) and sulfated zirconia (SZO) in diethyl ether forms organometallic Pd-sites that polymerize ethylene and copolymerize ethylene and methyl acrylate. The Pd-sites bind CO and were studied by infrared and solid-state NMR spectroscopies. Analysis of the reaction mixture shows that more methane than expected evolves during the grafting reaction, suggesting that some Pdsites do not contain a Pd-Me group. Consistent with this observation, deuterium labeling experiments show that ∼9% of palladium sites are active in polymerization reactions. (N∧N)PdMe 2 /SZO polymerizes ethylene with activity as high as 1342 kg PE /(mol active Pd *h) and incorporated up to 0.46% methyl acrylate in copolymerization reactions.
The reaction of (α-diimine)NiMe 2 (α-diimine = (2,6-i Pr 2 -C 6 H 3 )NCMeMeCN(2,6-i Pr 2 -C 6 H 3 )) with partially dehydroxylated sulfated zirconia (SZO 300 ) in MeCN results in the formation of [(αdiimine)NiMe(NCMe)][SZO 300 ] ([1][SZO 300 ]) and methane. Reactions in Et 2 O resulted in mixtures of [(α-diimine)NiMe(OEt 2 )][SZO 300 ] ([2][SZO 300 ]) and [(α-diimine)NiMe(OEt 2 )][MeSZO 300 ] ([2]-[MeSZO 300 ]), which were characterized by solid-state NMR spectroscopy. Contacting these solids with ethylene and monitoring the reaction by solid-state NMR showed that Ni−Me sites insert ethylene. [1][SZO 300 ] and [2][SZO 300 ]/[2][MeSZO 300 ] are active ethylene polymerization catalysts and show properties similar to those of closely related homogeneous catalysts. [2][SZO 300 ]/[2][MeSZO 300 ] copolymerizes ethylene and methyl 10-undecenoate to form copolymers with up to 0.4% incorporation of the polar monomer.
C–H bond activation via σ-bond
metathesis is typically
observed with transition-metal alkyl compounds in d0 or
d0fn electron configurations, e.g., biscyclopentadienyl
metal alkyls. Related C–H activation processes are also observed
for transition-metal alkyls with higher d-electron counts, such as
W(II), Fe(II), or Ir(III). A σ-bond metathesis mechanism has
been proposed in all cases with a preference for an oxidative addition–reductive
elimination pathway for Ir(III). Herein we show that, regardless of
the exact mechanism, C–H activation with all of these compounds
is associated with π-character of the M–C bond, according
to a detailed analysis of the 13C NMR chemical shift tensor
of the α-carbon. π-Character is also a requirement for
olefin insertion, indicating its similarity to σ-bond metathesis.
This observation explains the H2 response observed in d0 olefin polymerization catalysts and underlines that σ-bond
metathesis, olefin insertion, and olefin metathesis are in fact isolobal
reactions.
We report on the design of abundant and highly active VB 2 for hydrogen production. Density functional theory (DFT) calculations have predicted very high HER activity of the graphene-like B-layer, the V-terminated {100} layer, and the mixed V/B-terminated {101} layer of VB 2 . Bulk samples and nanoparticles of VB 2 were synthesized and tested for their HER performance. The results indicate that both bulk and nano-VB 2 are active for HER, consistent with theoretical predictions. In addition, the HER activity of VB 2 is significantly increased at the nanoscale if compared to the bulk, reaching an overpotential of 192 mV at 10 mA/cm 2 current density. Increased surface area and higher density of active sites are responsible for the higher nanoscale activity, making nano-VB 2 the best HER boride to date in terms of abundance, stability, and activity in acidic solution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.