Magnesium dihalide complexes

The second route (Scheme 1) is a redistribution reaction, in fact the Schlenk equilibrium. This route may be used in the reverse direction for the preparation of pure diorganomagnesium compounds from organomagnesium halides. Addition of a ligand, usually dioxane, that forms an insoluble complex with magnesium dihalide, shifts the Schlenk equilibrium completely to the left side and allows isolation of pure diorganomagnesium compounds from the remaining solution. ... 

Magnesium dihalides form complexes with certain donors [e.g., dioxane, (CH3)2NCH2CH2N(CH3)2TMEDA], which may precipitate from solution and shift the equilibrium to the right, yielding the diorganyls ... 

Synthesis. These macrocycles are prepared from seven-membered ring dinitrile complexes, 84a-84c (Scheme 17), which contain either methylene, sulfur or oxygen in the five position (129). These cyclic dinitriles are synthesized by alkylating maleonitrile dithiolate or derivatives thereof with the corresponding dihalide. The dinitriles 84a-84c can be cyclized in magnesium propoxide to form porphyrazines 85a (33%), 85b (19%), and 85c (27%) (Scheme 17), which can be demetalated with trifluoroacetic to form 86a-86c. Additionally, 86a has been remetalated with nickel (87a, 92%), copper (88a, 95%), and zinc (89a, 94%). The sulfur and oxygen derivatives 85b, 85c, 86b, and 86c are of low solubility and are not suitable for further manipulation. 

For the magnesium reagents, the influence of 1,4 dioxane or other complexing agents typically results in the formation of the diorganomagnesium species, owing to the precipitation of the dihalide dioxane adduct, which can be removed by filtration (equation 15). 

In contrast with the general 1,2-cyclizations of symmetric (2-butene-l,4-diyl)magnesium complexes with a,a>-alkylene dihalides, reactions of both symmetric and asymmetric (2-butene-l,4-diyl)magnesium complexes with diorganosilyl dichlorides yield exclusively overall 1,4-additions, generating silicon-containing five-membered rings. Some of these results are summarized in Table 5. 

The synthesis and spectroscopic features of a number of titanocene dicarbonyl derivatives have been reviewed previously.41 Typically, these complexes are prepared via magnesium reduction of the corresponding dihalide derivative under 1 atm of carbon monoxide. New compounds prepared since COMC(1995) are presented in Scheme 10. Mixed cyclopentadienyl phosphinimide dicarbonyl compounds such as (if-CsMcs)-(Buc3PN)Ti(CO)2 61 have also been isolated.46... 

Complexes related to 57 described above were prepared with the diimino pyridine ligands with the benefit that a larger set of R groups could be linked to Co. The compounds 58 were made by reaction between the dihalide or monohalide cobalt complexes with magnesium or lithium reagents (Figure... 

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