Publisher Summary This chapter discusses the organometallic compounds containing oxygen atoms. At present, the range of organic ligands found in organometallic oxo compounds is quite restricted, the majority being either η-C 5 R 5 or alkyls or aryls having no β-hydrogen atom. Two basic routes to organometallic oxo compounds may be envisaged addition of an organic ligand to an inorganic oxo complex or addition of oxygen to an organometallic compound. Exhaustive decarbonylation with concomitant oxidation of a cyclopentadienyl metal carbonyl has proved to be a useful preparative route to cyclopentadienyl metal oxo compounds having no other ligands. In the ethylene complex, the oxo and ethylene ligands are cis to one another and the C–C axis of the ethylene is perpendicular to the M–O bond, a configuration that maximizes π bonding between the W(IV) (d 2 ) and the ethylene. Complexes containing cyclopentadienyl and oxygen as coligands are of two basic types: those containing a terminal double bond between a metal and oxygen, [M=O], and those containing one or more doubly bridging oxygen atoms, [M(μ 2 -O) n M]. The clusters are held together by M–O bonds and the M–( η 5 -C 5 H 5 ) bonding is of the usual type. Parallel to the development of organometallic clusters containing oxygen atoms has been the preparation of organometallic polyoxometallates. Although the organometallic groups are on the surface of the polyoxometallate, they are strongly and covalently bonded to the peripheral oxygen atoms.

Organometallic Compounds Containing Oxygen Atoms

This review article is largely concerned with the efforts to gather structural information on hydrogen bridge bonds with neutron diffraction data. 11 figures, 1 table.

Structures of transition-metal hydride complexes

Addition of LiOHMT (OHMT = O-2,6-dimesitylphenoxide) to W(O)(CH-t-Bu)(PMe2Ph)2Cl2 led to WO(CH-t-Bu)Cl(OHMT)(PMe2Ph) (4). Subsequent addition of Li(2,5-Me2C4H2N) to 4 yielded yellow W(O)(CH-t-Bu)(OHMT)(Me2Pyr)(PMe2Ph) (5). Compound 5 is a highly effective catalyst for the Z-selective coupling of selected terminal olefins (at 0.2% loading) to give product in >75% yield with >99% Z configuration. Addition of 2 equiv of B(C6F5)3 to 5 afforded a catalyst activated at the oxo ligand by B(C6F5)3. 5·B(C6F5)3 is a highly active catalyst that produces thermodynamic products (∼20% Z).

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Z-Selective olefin metathesis reactions promoted by tungsten oxo alkylidene complexes.

During the last decade, advances in computational techniques and in the extraction of chemically useful concepts from electronic wave functions have put theorists into the mainstream of chemistry. Some recent examples of the prediction of spectroscopic quantities and the elucidation of catalytic processes for homogeneous and heterogeneous reactions from theoretical calculations are used to illustrate how theory and experiment are now full partners in chemical research. It is expected that during the next decade the thrust of theoretical chemistry will be to combine the knowledge of fundamental chemical steps and fundamental interactions with advances in chemical dynamics and irreversible statistical mechanics and in computer technology to produce simulations of chemical systems with competing reactions taking place simultaneously at various reaction sites. The promise of such simulation is illustrated by a study of the enzyme thermolysin.

https://science.sciencemag.org/content/sci/227/4689/917.full.pdf

Theoretical Chemistry Comes Alive: Full Partner with Experiment.

Several studies suggest the importance of oxygen in the reactive intermediates for alkene metathesis, M=CH2 + H2C=C*H2 ⇌ M=C*H2 + H2C=CH2 (1) and of additional metal=oxo bonds in epoxidations, For example: (1) catalytic amounts of oxygen were found to be essential for the formation of a stable metathesis catalyst in the WCl6/C2H5AlCl2 system1; (2) alkene epoxidation (and general oxidation) reactants such as CrCl2O2, OsO4, and SeO2 all have at least two oxygen ligands2; and (3) recently Osborn (personal communication) has described an Mo=oxo carbene as an effective metathesis catalyst. From extensive ab initio theoretical studies of Cr and Mo complexes, we show here that the presence of spectator metal–oxo bonds drives the formation of metallocycles, thereby playing a crucial role in the chemistry.

M. T. Mocella

Papers

Mechanism of the olefin metathesis reaction. 4. Catalyst precursors in tungsten(VI) based systems