N,N-DIALKYLCARBAMATES OF SILICON AND ALUMINUM

The N,N-dialkylcarbamates of silicon, [Si(O2CNR2)4, R=Me, Et, (i)Pr], and aluminium, [Al2(O2CNiPr2)6], have been prepared by the reaction of the metal halides with the appropriate secondary amine and carbon dioxide at room temperature or lower and at atmospheric pressure. The isopropyl silicon and aluminium derivatives have been studied by X-ray diffractometric method. Si(O2CNiPr2)4, Crystal data: MW 604.9; monoclinic, space group C2/c; a=25.152(8), b=10.787(4), c=14.396(5) angstrom; beta=111.45(2)-degrees; V=3635(2) angstrom3; Z=4; D(c)=1.105 g cm-3; Mo-K(alpha) radiation (lambda=0.71069 angstrom); mu(Mo-K(alpha))=1.05 cm-1; R=0.0532. The compound is monomeric with the slightly distorted tetrahedral silicon and monodentate terminal carbamato groups. Crystal symmetry (triclinic), space group (P1BAR) and a similar atom connectivity was established for the corresponding alkyl derivative Si(O2CNEt2)4. The three carbamato complexes of silicon have a strong IR absorption around 1710 cm-1 attributed to the C-O stretching vibration of the monodentate carbamato groups. Al2(O2CNiPr2)6, Crystal data, MW 919.1; orthorhombic, space group Pbca, a=22.650(15), b=11.211(7), c=21.556(11) angstrom; V=5474(5) angstrom3; Z=4; D(c)=1.115 g cm-3; Cu-K(alpha) radiation (lambda=1.54178 angstrom); mu(Cu-K(alpha)=9.21 cm-1; R=0.0444. The aluminium complex contains distorted hexacoordinate aluminium atoms surrounded by the four oxygen atoms of two terminal bidentate and two oxygen atoms of two bridging carbamato groups. The aluminium complex is fluxional at room temperature as shown by C-13- and H-1 NMR measurements.