FUNCTIONALIZED IRON KETENE COMPLEXES FROM CARBONYL COUPLING REACTIONS

The solution mixture of the dinitrogen complexes Fe(CO)(2)(PEt3)(2)(N- 2) (1a) and [Fe(CO)(2)(PEt3)(2)](2)(mu-N-2) (Ib) reacts with methyl or ethyl haloacetates to yield the oxidative addition products Fe(CO)(2) (PEt3)(2)(X)CH2COOR (X = Cl, R = Me, 2a; X = Br, R = Me, 2b; X = I, R = Et, 2e). These complexes can be transformed in ether to (trimethylsi ly)oxy)-2-(alkoxycarbonyl)ethenyl]iron compounds (X = Cl, R = Me, 7a; X = Br, R = Me, 7b; X = I, R = Et, 7c) in the presence of LDA and subs equent trapping of the formed anions with Me3SiCl. When DBU is used as a base and 1 bar CO is applied with otherwise similar reaction condit ions as before the transformations of 2a-c take the course of the form ation of ester-functionalized ketene compounds E,Z-Fe(CO)(2)(PEt3)(2){ eta(2)-(C,O)-[OCCH(COOR)]} (R = Me, 8a; R = Et, 8b) and of xy-1,3-diox opropen-3-yl)bis(triethylphosphane)iron derivatives (R = Me, 9a, R = E t, 9b). In the solid state only the Z form of complexes 8 is found. In a comparable manor as for the synthesis of compounds 2, it is possibl e to obtain Fe(CO)(2)(PEt3)(2)(X)(CH2R) (R = OMe, 10a; R = 1,3-dioxola n-2-yl, 10b; R = 2,4,10-trioxoadamantan-3-yl, 10c) species. While 10a does not react, the derivatives 10b,c are converted in the presence of DBU and CO to E,Z mixtures of ketene complexes Fe(CO)(2)(PEt3)(2) [et a(2)(C,O)-(COCHR)] (R = 1,3-dioxolan-2-yl, 13b(E,Z); R = 2,4,10-trioxo adamantan-3-yl, 13c(E,Z)). (13b,c)(Z) crystallize from solutions. In f urther attempts comparable to the reactions to 2 and 10, haloorganylir on complexes Fe(CO)(2)(PEt3)(2)(X)(CH2Y) (X = Y = Cl, 14a; X = Y = I, 14b; X = I, Y = CH2CN, 14c) could be obtained. All derivatives 14 cann ot be transformed to ketene complexes in the presence of DBU and CO. F inally the known complexes Fe(CO)(2)(I)(PEt3)(2)(Me, Et) (15a,b) and t he new species Fe(CO)(2)(I)(CH2SiMe3)(PEt3)2 (15c) were attempted to b e converted to ketene complexes. By IR spectroscopy it was possible to detect Fe(CO)(2)(I)(PEt3)(2)(OCCHR) compounds (R = H, 17a; R = Me, 17 b; R = SiMe3, 17c)-; however, these molecules could not be isolated fr om the reaction mixtures of the reaction of 15a-c with DBU and CO. 17c was then prepared by an independent route by reacting 1a,b with Me3Si CH=C=O. Under these conditions 17c was much more stable, In an exempla ry way it was shown that the ketene unit of 17c can be cleanly replace d by CO to afford Fe(CO)(3)(PEt3)(2) (18). The structures of 7a, 8a(Z) , 9b, and 14a have been determined by X-ray diffraction studies.