Metalation formamidines

Formamidine, N,N -di-2-anthraquinonyI-metal complexes, 2,275 Formamidine, IV.AT-diaryl-metal complexes, 2, 275 Formamidine, N, N -dibenzyl-metal complexes, 2,276 Formamidine, IV.N -diisopropyl-metal complexes, 2, 276 Formamidinesulfinic acid technetium complexes, 6, 974 Formate dehydrogenases bacteria... 

In the presence of N,N,N, N",N"-pentamethyldiethylenetriamine ( = PMDETA), monomeric lithium complexes of bulky formamidinate ligands can be isolated. The compounds (Scheme 12) comprise a Li(PMDETA) center coordinated by a bulky formamidinate in either the E-syn- or E-anti-isomeric form. Two of the structures display coordination of the pendant amidinate imine, and can therefore be considered the first examples of if. r -C = N,N metal amidinate coordination. ... 

Structural studies have also been carried out on related alkali metal complexes of N,N -di(o-fluorophenyl)formamidine (= HFPhF). Preparations... 

In closely related studies, the molecular and crystal structures of lithium, sodium and potassium N,N -di(p-tolyl)formamidinate and N,N -di(2,6-dialkyl-phenyl)formamidinate complexes have been elucidated. These showed the anions to be versatile ligands for alkali metals, exhibiting a wide variety of binding modes. ... 

The heavy alkaline earth metals Ca, Sr, and Ba react with 2 equivalents of NJ -bis(2,6-diisopropylphenyl)formamidine in the presence of bis(pentafluorophenyl)-mercury to afford the bis(formamidinato) species as THF adducts in good to moderate yield (Scheme 23). When the same reactions are carried out in a 1 1 molar ratio, N-p-tetrafluorophenyl-N,N -bis(2,6-diisopropylphenyl)formamidine is isolated as the sole product in all cases (Scheme 23). Other substituted N -bis(aryl)formamidinate complexes of the heavy alkaline earth metals were synthesized accordingly. ... 

Continuing his studies on the metallation of tetrahydro-2-benzazepine formamidines, Meyers has now shown that the previously unsuccessful deprotonation of 1-alkyl derivatives can be achieved with sec-butyllithium at -40 °C <96H(42)475>. In this way 1,1-dialkylated derivatives are now accessible. The preparation of 3//-benzazepines by chemical oxidation of 2,5- and 2,3-dihydro-l/f-l-benzazepines has been reported <96T4423>. 3Af-Diazepines are also formed by rearrangement of the 5//-tautomers which had been previously reported to be the products of electrochemical oxidation of 2,5-dihydro-lAf-l-benzazepine <95T9611>. The synthesis and radical trapping activities of a number of benzazepine derived nitrones have been reported <96T6519, 96JBC3097>. 

To conclude the section, we recall that ligands somewhat related to dpa also give rise to linear trinuclear complexes. This is the case of 2,6-bis(phenylamino)pyridine,36 2,6-bis(phenylamino)piperidine,37 and bis (2-pyridyl)formamidine.38 At the moment, however, no (significant) electrochemical investigation has been carried out on their metal complexes. 

The lithiation of 2,3-pyrrolines has received only moderate attention, but two different nitrogen protection systems have been found acceptable. Thus the terf-butylformamidine derivative metalates readily with either n-or t-butyllithium, and after reaction with a variety of electrophiles the formamidine group can be removed with hydrazine to give 2-substituted... 

More reactive carbon nucleophiles than enolates can also be prepared on insoluble supports (see Chapter 4) and are used to convert aldehydes or ketones into alcohols. Organolithium compounds have been generated on cross-linked polystyrene by deprotonation of formamidines and by metallation of aryl iodides (Table 7.5). Similarly, support-bound organomagnesium compounds can be prepared by metallation of aryl and vinyl iodides with Grignard reagents. The resulting organometallic compounds react with aldehydes or ketones to yield the expected alcohols (Table 7.5). 

N,N -Dibenzyl- or -diisopropyl-formamidines react84 with Os3(CO)l2 or Os3(CO)i0(cyclooctene)2 to give different types of nonacarbonyl, HOs3(CO)9(PriNCHNPr1) and HjOs CO),-(PhCH2NCHNCH2C6H4), the difference being in the ability of the benzyl group to be ortho-metal-... 

Metallation-alkylation of chiral formamidine derivatives of 1,2,3,4-tetrahydroisoquin-oline provides optically active 1-alkyl-1.2,3,4-tetrahydroisoquinolines. The formam-idines of 10 optically active amino alcohols have been examined as the chiral auxiliaries and of these, the bistrimethylsilyl ether 2 (S.S-BISPAD) of 1 proved to be the mc>st efficient as well as consistent (equation II). The configuration (S) was established by synthesis of the benzoquinolizine (S)-5, a degradation product of an alkaloid. 

A most interesting class of oxygen functionalised NHC ligands was presented by Cesar et al. [227] when they reacted a 1,3-aminoimine (formamidine) with a monosub-stituted malonic acid [228,229]. The result is a zwitterionic six-membered betaine that can be deprotonated to an anionic NHC ligand and coordinated to transition metals (see Figure 3.77)... 

Potentially bidentate ligands, such as the formamidinates [RNCR NR], the monoanion derived from 2,6-bis(phenylamino)pyridine and 7-methyl-l,8-naphthyridin-2-one, and others, formed complexes with a paddle wheel structural motif. Figure 5(d), and some of these complexes could be oxidized by ferrocenium cations to give mixed-valent species. Generally, such oxidation led to a slight lengthening of the metal-metal bond. 

Seebach also compared the same pivaloylisoquinoline to a tetrahydroisoquinoline formamidine to evaluate die face-selectivity in the addition of die metalated derivatives to aldehydes. 2,i63 cases, the organolithium showed significantly lower diastereoselectivity than the Grignard obtained by transmetalation with MgBr2-Et20, as shown by the examples in Scheme 47. The transmetalation protocol was used to prepare a number of racemic isoquinoline alkaloids. 

Formamidines whose a-protons are allylic are easily metalated, but the predominant site of electrophilic attack is the y-position, as shown by the example in Scheme 49. ... 

Amidinium salts (obtainable by various methods, compare Section 2.1.2.5) which are not peralkylated at nitrogen are converted to amidines by treatment with strong bases, e.g. aqueous alkali metal hydroxides, alcoholic alkoxides, tertiary amines etc. As already mentioned it is not difficult to alkylate amidines (see Section 2.7.2.5.4), thus by subsequent alkylation and deprotonation reactions amidines can be synthesized carrying the desired substituents at nitrogen, e.g. (308 Scheme 47). A series of trisubstituted formamidines have been prepared by reaction of anilines with the azavinylogous form-amidinium salt (309). ... 

Metalated piperidine amides and formamidines may be converted to a-alkylated piperidines, as illustrated in Scheme 9. Again, the two examples illustrate the superiority of the formamidine moiety in both yield and ease of removal. 

An a-substituted piperidine formamidine may be metalated at the a -position selectively, but the alkylation is not stereoselective, providing a 1 1 mixture of cis and trans stereoisomers, as illustrated in Scheme 10. ... 

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