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The location of the positions of terminal hydride ligands in transition metal complexes using x-ray diffraction techniques is examined by reference to some recent structure determinations. Both complexes have approximate C3vsymmetry. In H3Ni4 Cp 4, the three hydride ligands are face bridging, and their mean displacement from the faces of the cluster is 0.
The H3Ni4 core may be envisaged as a distorted cube with one vertex unoccupied.
Although the hydride ligands were not located in H3Ir PMe2Ph 3, the arrangement of phosphorus atoms about the iridium atom suggests a distorted octahedral geometry for this molecule. X-ray analysis of H7Re PMe2Ph 2 reveals a bent phosphorus-rhenium-phosphorus backbone for the molecule, that is consistent with a tricapped trigonal prism with phosphorus atoms in equatorial positions.
Neutron diffraction analysis of H4Os PMe2Ph 3 shows that the molecule is a distorted pentagonal bipyramid, with one equatorial and two axial phosphine ligands. The neutron diffraction analysis of the H8Re2 PEt2Ph 4 dimer reveals a molecule with four terminal and four bridging hydride ligands. This molecule provides the first example of a metal-metal bond bridged by four hydrogen atoms. X-ray diffraction results revealed the common geometry of the anions as a atom nickel fragment of a hcp metal lattice containing two octahedral and six tetrahedral holes surrounded by nine terminal and 12 doubly bridging carbonyl ligands.
Neutron diffraction results showed hydrogen occupation of one octahedral hole in the trianion and both octahedral holes in each dianion. Stereochemical implications are discussed with respect to possible proton migration within these nickel clusters and to their observed reversible protonation-deprotonation reactions.
The complexes are efficient hydrosilylation catalysts. The Ru II complexes Ru2Cl4 diop 3, HRuCl diop 2, and Ru-Cl2 diop 2, were synthesized and found to be effective in solution for catalytic asymmetric hydrogenation of some prochiral olefinic substrates. There is evidence for hydride intermediates. Structure 7 promotes the reduction of CO and olefins. Several intermediates in these reactions have been identified, and possible mechanisms for these transformations are discussed.
Based on the chemistry of transition metal hydride and carbonyl complexes, a mechanism for the homogeneously catalyzed reduction of CO by H2 that involves inserting CO into a metal-hydrogen bond might not be feasible. An alternate route for formation of the first C-H bond, nucleophilic attack by a hydridic metal hydride on CO, suggests several criteria for the type of complex that might be a successful catalyst. In the latter compounds, the terminal thioether is uncoordinated. A hydride on one metal is necessary to interact with a vacant coordination site on the other in the dinuclear transition state.
With Os CO 4- H CH3, the vacant site is created by a facile rate-determining isomerization which we suggest is to an acetyl hydride. The unique instability of hydridoalkyl carbonyls thus is explained. Dinuclear hydridoalkyls are excellent starting points for the synthesis of more complex polynuclear alkyls.
The photochemical studies of transition metal hydride complexes that have appeared in the chemical literature are reviewed, with primary emphasis on studies of iridium and ruthenium that were conducted by our research group. The photoinduced elimination of molecular hydrogen from di- and polyhydride complexes of the transition elements is proposed to be a general reaction pathway.
The results lead to the following significant conclusions. The PH3 group takes on a net negative change Recommend Documents. Recent advances in analytical chemistry. Recent advances in oxidation chemistry. Recent advances in electro-chemistry. Recent advances in receptor chemistry.
Recent advances in medicinal chemistry. Recent advances in thiasteroids chemistry.
Recent advances in azasteroids chemistry. Recent Advances in Organotin Chemistry. Peruzzini, R.
Poli, Elsevier, Amsterdam, It was intended that he should have been a contributor, both to the conference from which this volume grew and to the book itself. Unfortunately, Luigi died before he could do these things. The book turns out to be a fitting memorial of a talented scientist.