Metalation zincate preparation

Led by the efforts of Westerhausen and coworkers, a variety of heavy alkaline earth metal zincates or aluminates under formation of alkaline earth metal-carbon contacts have been prepared. Examples include the reaction of trialkylalanes with donor-free calcium i)fr-amides to afford dimeric aluminates, shown in Figure 30. Noteworthy is the planar Ca2N2 center of this complex, in addition to close calcium-aluminum contacts, which may indicate the presence of three-center, two-electron bonding. 

Even though zincation of secondary amines was already studied by Frankland in 1856 and 1867, it is only in the past few decades that some efforts were made to isolate and characterize the products. Numerous compounds of the type RZnNR2 or Zn(NR2)2 can now be prepared nsing two principal procedures, namely the zincation of amines with simple dialkylzinc compounds " (equation 26) and the metathesis reaction of alkali metal amides with anhydrons zinc dihalide (equation 27). 

Other examples of this series include a selection of ate complexes prepared by the treatment of alkylzinc reagents with freshly distilled alkaline earth metals under extrusion of elemental zinc. This route was employed to prepare a strontium zincate in which the alkaline earth metal center adopts a distorted octahedral geometry completed by two THF solvent donors. Similar reactions with barium metal lead to structurally closely related compounds. Flexibility in solvent choice is noted by the preparation of related complexes in toluene, displaying metal-toluene itt-interactions. 

The tetraphenyl arsonium or phosphonium salts of DSIT-zincate (PPh4)2(ZnC3Ses)2 can be prepared in 13% overall yield by sodium metal reduction of carbondiselenide in organic solvents <90JCS(D)115>. This method is similar to the procedure used for the sulfur analogue. 

The alkylzinc anions, defined as ate complexes see Ate Complexes), are heterodimetallic systems which can be divided in two different classes, namely, the trialkylzincates of general formula M+RsZn and the tetraalkylzincates of general formula M +R4Zn. The first zincate derivatives, that is, NaZnEts and KZnEts, were prepared by Wanklyn in 1858 from the reaction of metallic sodium or potassium with diethylzinc (equation 38). In spite of this early discovery, many of the efforts to study this class of compounds are... 

In a comparative study (Scheme 4) of different methods for the preparation of 2-arylthieno[3,2-fc]thiophenes 7, the lithiated species 6 was treated with zinc chloride to effect zincation, tributyl borate to effect boronation, and tri(n-bntyl)stannyl chloride to effect stannylation. Aryl bromides or iodides were nsed. The yields of the 2-aryl prodnct 7 depend on the substituents in the benzene ring, the metallated species, and the palladium catalyst,... 

---