Carbon−Carbon Bond Formations Involving Organochromium(III) Reagents

Structural, mechanistic, and theoretical aspects of chelation-controlled carbonyl addition reactions

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

The structure and creativity spectrum of transition-metal carbene complexes has been widened significantly by the bent metallocenes of titanium, zirconium, and hafnium. Proceeding from metal carbonyls and reactive (butadiene)-, (aryne)-, or (olefin) MCp2 complexes, many new Fischer-type metaloxycarbene complexes of Zr, Hf, V, Nb, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Ni, and Rh have been synthesized. The incorporation of titanocene, zirconocene, or hafnocene fragments allows new types of carbene complexes to be prepared. For the (alkylidenamido)metallocene complexes 



, metallocene ylides 



, and binuclear (μ-alkynyl)metallocene compounds, some metalligand π bonding is indicated. Metallocene complexes with metallaoxirane units, 



, show similar chemical behavior to that of binuclear (μ-methylene)complexes 



. The methylene groups of zirconaoxirane complexes, which are derived from carbon monoxide, may be expelled as ethylene by thermally induced CC coupling. With metal hydrides, CH2 transfer with insertion into the metal–hydride bond occurs. In one case, methylene insertion into a metal–carbon bond can even be observed. These reactions of Ti-group metallaoxiranes could be models for postulated intermediates in the Fischer–Tropsch synthesis.

Metallocene Carbene Complexes and Related Compounds of Titanium, Zirconium, and Hafnium

Oxidative transformation of aryls using molybdenum pentachloride

Carbonyl Olefinating Carbene‐Tungsten Complexes and Their Suitability as Catalysts in Olefin‐Metathesis

Stark bevorzugte Alkylierung und Carbonylolefinierung von α- und β-Hydroxycarbonylverbindungen durch Organoübergangsmetallreagentien in Konkurrenzversuchen mit entsprechenden OH-freien Verbindungen

Strongly Preferential Alkylation and Carbonyl Olefination of α‐ and β‐Hydroxycarbonyl Compounds by Organo‐Transition Metal Reagents in Competition Experiments with the Corresponding Deoxy Compounds

Carbonylofefinierende Carbenwolframkomplexe und ihre Eignung als Olefinmetathese‐Katalysatoren

Organomolybdenum and Organotungsten Reagents, VI[1]. On the Carbonyl-Methylenating Molybdenum-Aluminium and Tungsten-Aluminium μ-Methylene Complexes



MoCl5, MoOCl3(THF)2, MoO2Cl2, (MeO)2MoCl3, (MeO)4MoCl, WOCl3(THF)2, and WOCl4 form carbonyl-methylenating complexes and 1–2 equiv. of CH4 by reacting with 2 equiv. of Me3Al. These thermolabile complexes are prepared in solution and differ in their properties (e.g. ability to transfer mostly more than 1 CH2 unit per Mo or W atom in carbonyl-olefinating processes; high sensitivity to water, no hydroxy ketone affinity) from the carbonyl-olefinating 1,3-dimetallacyclobutanes (M = Mo, W) and are believed to be mono- and bicyclic analogs (e.g. hypothic structures 3, 6–8) of the Tebbe reagent (1), containing Mo-μCH2 Al or W -μCH2 Al groups, respectively. Analogous complexes seem to be produced by treating MoOCl3(THF)2 with 2 Me2Zn or (MeO)2MoCl3 and (MeO)4MoCl with 2 MeMgBr in each case. Unlike the dimeric and, due to a MoMo bond, diamagnetic Mo derivatives (MeO)2MoCl3 and (MeO)4MoCl (according to 1HNMR structure 9 or 10 and 11 or 12, respectively) the complexes obtained by the reactions (MeO)2MoCl3 + 2 Me3Al and (MeO)4MoCl + 2 Me3Al are paramagnetic, indicating the expected absence of a MoMo bond. The 1HNMR spectrum of the reaction mixture obtained by treating the MoVI derivative MoO2Cl2 with 2 Me3Al in THF shows various signals for μCH2 groups, whereas signals of t-CH2 ligands are missing (t = terminal). In analogy to 1 the carbonyl-olefinating activity of the MoAl and WAl reagents is activated by the addition of 2 equiv. of HMPA. Treatment of PhCOCH2NEt2 (19) with {MoO2Cl2 + 2 Me3Al} leads to carbonyl olefination with formation of 20 and also to α-methylation with formation of PhCOCH(Me)-NEt2 (21), pointing to the intermediate formation of a t-CH2Mo ligand. {MoO2Cl2 + 2 Me3Al + 2 HMPA} has found to be the best reagent for the carbonyl olefination of aldehydes, whereas {WOCl3(THF)2 + 2 Me3Al + 2 HMPA} was optimal for ketones. In 1:1 reactions both reagents normally give better yields than the Tebbe reagent. By applying (WOCl3(THF)2 + 2 Me3Al} and {MoO2Cl2 + 2 Me3Al} on ketones 16–18 an interesting neighbour group effect of electron donor atoms in the δ position to the keto group was observed.

Siegfried Welke

Papers

Carbonyl Olefinating Carbene‐Tungsten Complexes and Their Suitability as Catalysts in Olefin‐Metathesis

Stark bevorzugte Alkylierung und Carbonylolefinierung von α- und β-Hydroxycarbonylverbindungen durch Organoübergangsmetallreagentien in Konkurrenzversuchen mit entsprechenden OH-freien Verbindungen

Strongly Preferential Alkylation and Carbonyl Olefination of α‐ and β‐Hydroxycarbonyl Compounds by Organo‐Transition Metal Reagents in Competition Experiments with the Corresponding Deoxy Compounds

Carbonylofefinierende Carbenwolframkomplexe und ihre Eignung als Olefinmetathese‐Katalysatoren

Zur Kenntnis der carbonylmethylenierenden Molybdän-Aluminium- und Wolfram-Aluminium-μ-methylen-Komplexe