Anionic nitrogen

Thorium compounds of anionic nitrogen-donating species such as [Th(NR2)4], where R = alkyl or sdyl, are weU-known. The nuclearity is highly dependent on the steric requirements of R. Amides are extremely reactive, readily undergoing protonation to form amines or insertion reactions with CO2, COS, CS2, and CSe2 to form carbamates. Tetravalent thorium thiocyanates have been isolated as hydrated species, eg, Th(NCS)4(H20)4 [17837-16-0] or as complex salts, eg, M4 Th(NCS)g] vvH20, where M = NH, Rb, or Cs. 

Addition of phosphinomethyl spirophosphorane 260 to isocyanates and azides presumaby generates anionic nitrogen intermediates that cyclize with the phosphorane to give spirophosphoranides 96, 97, and 261 (Scheme 35) <1996PS493>. 

Other anionic nitrogen-containing ligands which have been examined in the search for new non-metallocene catalysts include macrocyclic porphyrins and tetraazaannulenes. However, activities with these catalysts are low. 

Isocyanides are converted, on addition of f-BuLi at the electrophilic carbon atom, to lithioimines—another class of anionic, nitrogen-containing functions which turn out to have good orf/zo-directing ability. The electrophile reacts at both lithium-bearing centres of 129 (Scheme 56). 

Electrophiles that have been used for the second alkylation of this tandem Michael addition -alkylation sequence are limited to primary iodoalkanes, (bromomethyl)benzenes and 3-bromo-propenes. Tables 9 and 10 provide details of the alkylations of enolate species prepared by 1,4-additions of -a,/j-unsaturated iron-acyl complexes by anionic carbon nucleophiles and anionic nitrogen nucleophiles, respectively. 

Complexes with Anionic Nitrogen Donor Ligands 879... 

For zirconia with hydroxyl group of bridge type and anion nitrogen, orbital connected with nitrogen appear in the forbidden gap. Thus, zirconia with anion nitrogen and hydrogen on surface must be deep donor. 

A considerable number of nucleophiles have been shown to react through this mechanism stabilized carbanions, anions derived from elements of the VIA group (S, Se, Te) and anions from elements of the V A group (P, As, Sb). More recently cyanide anion, nitrogen and oxygen (e.g. aromatic alkoxides) nucleophiles have been added to the list. These nucleophiles behave as C— rather than as N— or O— nucleophiles. 

The corresponding Tc-N-C bond angles of 128.3(4)°, 126.6(4)°, and 129.1(4)°, however, seem to offer little distinction between neutral and anionic nitrogen. Cationic complexes of the type [TcC12L]+ have been prepared by the reaction of [TcCl4(PPh3)2] with the tetradentate ligands (27) (310). 

In the reaction of 3,5-dimethyl-2,6-diphenylpiperid-4-one oxime (10) with acetylene and RbOH-DMSO, migration of the 3a-Me group to the anionic nitrogen atom occurred, leading to 5,7-dimethyl-4,6-diphenyl-4,5,6,7-tetrahydropyrrolo[3,2-c]pyridine (11) (04CHE326). The formation of the N-anion caused aromatization of the tetrahydropyridine ring. Tetrahydropyrrolo[l,2-c]pyrimidine 12 resulted from the decomposition of the intermediate 3H-pyrrole in a retro-Mannich reaction (Scheme 3). 

In addition to attack by a basic nitrogen, there exists also the possibility of an intramolecular attack by an anionic nitrogen, i.e., a deprotonated amido nitrogen. This is exemplified by A-(2-carbamoylphenyl)carba-mates of model phenols (Fig. 5 X = H, Cl,... 

Like sulfur mustard, the nitrogen mustards combine predominantly with the thiol group of molecules and are excreted as conjugated cysteinyl derivatives. Both nitrogen and sulfur mustards have structural similarities and have common chemical reactions. A key reaction is the intramolecular cyclization in a polar solvent such as water to form a cyclic onium cation and a free anion. Nitrogen mustards form the immonium cation, while the sulfur mustard forms the sulfonium cation. The cyclized form is responsible for the varied effects of mustards, which are similar. In nitrogen mustard the sulfur is replaced by nitrogen. 

Second, the tin could act as a Lewis acid in stabilizing the Wheland intenuediate by coordination to an anionic nitrogen, as shown in Scheme 6.3.13. 

More recently, Enders group has described the X-ray crystal structure of the chiral hydrazone anion (19). This internally chelated chiral hydrazone crystallizes as the bis(tetrahydrofuran) monomeric adduct. The lithium in this structure is 17° out of the C—C— N plane and is predominantly associated with the anionic nitrogen (and the chelating methoxy group). Interactions with the =CH2 carbon are minimal. Earlier studies by Bauer and Seebach had examined the association behavior of (19). They found that in THF this azaallyllithium reagent was monomeric. While there is no or ri -interaction with the azaallyl anion, the lithium in this structure is tetracoordinate and prochiral. Preferential coordination of lithium to an electrophile such as a carbonyl oxygen with selective replacement of one THF moiety could be involved in some of the asymmetric aldol reactions discussed below. 

---