Nucleophilicity common reagents, Table

Typical protic nucleophiles, like water or alcohols (R OH), readily add to nitrile ligands (Table 2), which can also be activated by coordination toward other, less common nucleophilic OH reagents, such as oximes or hydroxylamine, producing imine-type species (Scheme 2 (2)) or, in the case of water, an amidate or derivative. 

Apart from the common heteroatom-derived nucleophiles described, cleavage with other nucleophiles is also possible. For example, reductive cleavage with hydride sources is possible. For ester-linked substrates, Kurth et al. reported an example in which substituted propane-1,3-diols were prepared (Table 1.2, Entry 11). In related work, Chandrasekhar et al. prepared tertiary alcohols by treating an ester-linked substrate with excess Grignard reagent (Table 1.2, Entry 12). If, however, it is desirable to prepare the carbonyl derivative (and not reduce all the way to the corresponding alcohol), then Weinreb-type linker units can be used (Table 1.2, Entries 13 and 14). Treatment of substrates attached via such linkers... 

Table 15.1 Features of common nucleophilic fluorination reagents.

The stereoselectivities in nucleophilic additions to various hexopyran-osid-2-163, -3-164, and -4-ulosesI6S 167 were extensively examined (see Tables II and III). The results in the Grignard reactions in Table III were commonly explained by the approach of the reagent from the sterically favored direction to the magnesium-coordinated conformations (left-hand side in the equilibration formulas), but the concept for the methyl-... 

Carbonyl metallates find their widest application as reagents for introducing electrophilic functionality to the metal centre, which is highly nucleophilic. Table 3.3 indicates nucleophilicities for a range of common carbonyl metallates estimated from conventional SN2 reaction rates with iodomethane. This illustrates their versatility in metal-carbon bond forming reactions however, as shown in Figure 3.6, this reactivity is not limited to carbon electrophiles but allows a wide range of metal-element bonds to be easily formed (see also reactions of metal carbonyls below). 

Metal carbonyls are reduced by a variety of reagents, of which sodium amalgam is the most common, to produce air-sensitive low-valent anionic complexes. These anions vary widely in nucleophilicity and by far the greatest use has been made of the most nucleophilic, [Fe(CO)2(t/ -CjH5)]". However, [M(CO),] (M = Mn, Re), [M(CO)J- (M = Co, Ir), [M(CO)3( -C5Hj)]- (M = Cr, Mo, W), [V(CO)J- and [Fe(CO)4] have all found limited application. Examples are collected in Table 1. In general, fast, ionic reactions ... 

Tetraalkylborates are mild and selective alkylation reagents [186, 187], and they are commonly considered as sources of nucleophilic alkyl groups (R ) just as borohy-drides are depicted as hydride (H ) sources. However, since organoborates represent excellent electron donors (see Table 5, Section 2.2.1), the question arises as to what role electron donor-acceptor interactions play in the nucleophilic alkyl transfer. Phenyl- and alkyl-substituted borate ions form highly colored charge-transfer salts with a variety of cationic pyridinium acceptors [65], which represent ideal substrates to probe the methyl-transfer mechanisms. Most pyridinium borate salts are quite stable in crystalline form (see for example Figure 5C), but decompose rapidly when dissolved in tetrahydrofuran to yield methylated hydropyridines (Eq. 65). 

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