Olefin carbonyl complexes, structures

Wender and Sternberg (37) have suggested that the structure of the olefin-carbonyl complex (I) is... 

These facts may be explained in the following manner, using 1-pentene and 2-pentene as examples. Because of steric hindrance, 2-pentene reacts with dicobalt octacarbonyl to form a complex more slowly than 1-pentene, and this accounts for the differences in rates observed with these olefins. It appears that the energy required for the rearrangement of the complex subsequent to its initial formation is small we may therefore conclude that essentially the same complex is obtained from both terminal and internal olefiins. The structure given for the olefin-carbonyl complex I probably represents the complex as it initially forms from either a terminal or internal olefin. It is not possible at present to write an adequate structure... 

Isonitrile complexes, having a similar electronic structure to carbonyl complexes, can also react with nucleophiles. Amino-substituted carbene complexes can be prepared in this way (Figure 2.6) [109-112]. Complexes of acceptor-substituted isonitriles can undergo 1,3-dipolar cycloaddition reactions with aldehydes, electron-poor olefins [113], isocyanates [114,115], carbon disulfide [115], etc., to yield heterocycloalkylidene complexes (Figure 2.6). 

Isomeric (s-cis- and (i-fra/w-V-conjugated diene)zirconocene and -haf-nocene complexes exhibit pronounced differences in their characteristic structural data as well as their spectroscopic features. These differences exceed by far the consequences expected to arise simply from the presence of conformational isomers of the 1,3-diene unit. While (f-rra/u-butadiene)-zirconocene (3a) shows a behavior similar to a transition metal olefin TT-complex, the (.r-cu-diene)ZrCp2 isomer 5a exhibits a pronounced alkylmetal character (23, 45). Typical features are best represented by a tr, 7T-type structure for 5 (55). However, the distinctly different bonding situation of the butadiene Tr-system/bent-metallocene linkage is not only reflected in differences in physical data between the dienemetallocene isomers 3 and 5, but also gives rise to markedly different chemical behavior. Three examples of this are discussed in this section the reactions of the 3/5 isomeric mbcture with carbon monoxide, ethylene, and organic carbonyl compounds. 

The nature of ligand substituent on effectiveness and diastereoselectivity of this reaction was also explored [70]. A number of catalysts of type [Ru2(CO)4(BL)2], where BL are bridging 2-pyridonate ligands (Scheme 35) were s3mthesized (53-61). The 6-halop3Tidin-2-olato complexes exist in head-to-head (HH) as weU as head-to-taU (HT) arrangement. These were employed for the cyclopropanation reaction of MDA with a variety of olefins (Scheme 36) [70]. It was found that 6-bromopyridonate complexes are better than their chloro counterpart, and in some cases, even superior to acetate/carbonyl complexes [200]. X-ray crystal structures... 

The B-allyl-9-BBN derivatives formed by hydroboration of allenes are utilized for addition of the allyl group to the carbonyl moiety of aldehydes, ketones, and other carbonyl derivatives (allylboration). Since allenes are easily prepared from corresponding olefins [12, 13], the route the olefin-allene-allylborane-carbonyl addition adduct is a general allylation procedure, which provides an attractive alternative to Grignard-based sequences for the syntheses of complex structures. 

Since allenes are easily obtained from the corresponding olefins [6, 7], the route olefin-allene-allylborane-carbonyl addition is general sequence and is a viable alternative to Grignard-based process for the synthesis of complex structures. 

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