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Bimetallic Hydroformylation Catalysis: The Uses of Homobimetallic Cooperativity in Organic Synthesis
Published in Mike G. Scaros, Michael L. Prunier, Catalysis of Organic Reactions, 2017
We believe that the high linear aldehyde regioselectivity arises from the shape of the bimetallic catalyst. When an alkene coordinates to the catalyst (Fig. 1) it will likely add to the exo coordination site of either rhodium center. As it coordinates to the rhodium, the other ligands will bend away to form a trigonal bipyramid (or square pyramid), which is the least congested coordination geometry. Our bimetallic catalyst, however, cannot attain this ideal geometry because the other half of the face-to-face bimetallic complex limits the motion of the ligand environment away from the coordinating alkene towards trigonal bipyramidal (or square pyramidal). Minimizing the geometric reorganization about the rhodium maximizes the et,ph- P4 ligand’s steric effect, directing the alkene insertion into the M-H bond to form a linear alkyl group, which goes on to form the linear aldehyde.
Selected Topics
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
By comparison, phosphorus has five valence electrons plus available vacant d orbitals. These five valence electrons typically form three (molecular geometry of trigonal pyramid; sp3) and five (sp3 with one pi-bond such as occurring in nucleic acids and polyphosphate and phosphonate esters and sp3d trigonal bipyramid) bonds. The focus, with respect to electrical conductivity, is on the three-bonded phosphorus polymers because they contain an unbonded electron pair. The unbonded electron pair is capable of bridging the electron gap between conjugated units automatically creating increased electrons that can promote conductivity. The structures of some of these central units are shown below.
Fluorescent silicon clusters and nanoparticles
Published in Klaus D. Sattler, Silicon Nanomaterials Sourcebook, 2017
The FELIX free electron laser source provides intense and tunable infrared radiation including in the spectral range from 166 to 600 cm−1 where silicon clusters absorb. Vibrational spectroscopy of small silicon cluster cations was performed using multiple photon dissociation spectroscopy. The ions were analyzed in a time-of-flight mass spectrometer. Also, isotopically selected 129Xe atoms were attached to the clusters. Absorption of multiple IR photons would lead to a depletion of the ion signal, allowing the requisition of spectra of size-selected clusters. Comparison of the spectra with calculations using density functional theory (DFT) revealed novel structures and a growth motif that started with a pentagonal bipyramid building block and changed to a trigonal prism for larger clusters (Lyon et al. 2009).
Shapes of undecanuclear clusters and undecacoordinated metal complexes§
Published in Journal of Coordination Chemistry, 2018
Two structures found for a family of Cu11 and Ag11 clusters can be described as the composition of one polyhedron and its dual. A trigonal bipyramid capped by six atoms that form a trigonal prism can be called a hexacapped trigonal bipyramid (hcTBP-11), while the opposite composition gives a pentacapped trigonal prism (pcTPR-11), both shown in Figure 4. Although those structures are similar to “stellated” polyhedra, they do not fit into the geometric definition of stellated polyhedral [13] and for that reason they will be referred to here as “capped” polyhedra.