Transition metals Lewis base-carbonyl complexes

Sulphur- and phosphorus-bridged complexes of transition metals Lewis-base-metal carbonyl complexes... 

Extensive studies on the Lewis acid [( 7 " -C5H5)Re(NO)(PPh3)] have yielded detailed insight into transition metal Lewis acid-Lewis base interactions and the question of a or coordination of carbonyl groups [100]. The Re Lewis acid binds aldehydes via the TT-system whereas ketones coordinate to form M-O cr-complexes. Both react with Et4N CN to give Re-bound cyanohydrins. Diastereoselectivity ranges from 53 to 89 % de for additions to aldehydes and 71 to 99 % de for additions to ketones (Sch. 19) [101]. Diastereoselective reductions to primary and secondary alcohols have also been reported [102]. 

Keto Derivatives of Group IV Organometalloids, 7, 95 Lewis Base-Metal Carbonyl Complexes, 3, 181 Ligand Substitution in Transition Metal ir-Complexes, 10, 347 Literature of Organo-Transition Metal Chemistry 1950-1970, 10, 273 Literature of Organo-Transition Metal Chemistry 1971,11, 447 Literature of Organo-Transition Metal Chemistry 1972, 12, 379 Mass Spectra of Metallocenes and Related Compounds, 8, 211 Mass Spectra of Organometallic Compounds, 6, 273... 

Ethers, sulfides, amines, carbonyl compounds, and imines are among the frequently encountered Lewis bases in the ylide formation from such metal carbene complex. The metal carbene in the ylide formation can be divided into stable Fisher carbene complex and unstable reactive metal carbene intermediates. The reaction of the former is thus stoichiometric and the latter is usually a transition metal complex-catalyzed reaction of a-diazocarbonyl compounds. The decomposition of a-diazocarbonyl compounds with catalytic transition metal complex has been the most widely used approach to generate reactive metal carbenes. For compressive reviews, see Refs 1,1a. 

Addition of a persistent silylene (see Section V.III.C) to nickel carbonyl resulted in the first bis-silylene transition metal complex without Lewis base stabilization... 

Catalytic asymmetric allylation of aldehydes and ketones with allylsilanes can be achieved by using chiral Lewis acids, transition metal complexes, and Lewis bases. In recent years, much attention has been paid for the chiral Lewis base-catalyzed system using allyltrichlorosilanes. Advances in catalytic asymmetric carbonyl allylation have been described in detail in recent reviews.116,117,117a... 

Transition metal carbonyl derivatives of magnesium can be prepared readily by the reductive cleavage of the metal-metal bond in numerous dimeric transition metal carbonyl complexes or by the removal of halogen from transition metal carbonyl halide complexes with an excess of 1 % magnesium amalgam in the presence of a Lewis base. These preparations may be represented by the general equations... 

Silanes are widely recognized as efficient reagents for reduction of carbonyl and heterocarbonyl functionality. In the case of alkyl and arylsilanes, the reaction requires catalysis by Lewis acids or transition metal complexes 1, 3] however, with more Lewis acidic trichloro or trialkoxysilanes, an altemative metal free activation can be accomplished. Thus, it has been demonstrated that extracoordinate silicon hydrides, formed by the coordination of silanes to Lewis bases, such as tertiary amines 7a], DMF [7b] or MeCN, and so on [7], can serve as mild reagents for the reduction of imines to amines [8]. In the case of trichlorosilane, an inexpensive and relatively easy to handle reducing reagent, and DMF as a Lewis basic promoter, the intermediacy of hexacoordinate species has been confirmed by Si NMR spectro scopy [7b]. 

Although CO is an exceedingly weak Lewis base, one of its most important properties is the ability to act as a donor ligand toward transition metals, giving metal carbonyls. For example, nickel metal reacts with CO to form Ni(CO)4, and iron reacts under more forcing conditions to give Fe(CO)5 many other carbonyl complexes are also known. The ability of CO to form bonds to transition-metal atoms is discussed in detail in Chapter 22, and catalytic reactions whereby CO is incorporated into organic compounds are discussed in Chapters 23 and 24. 

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