MÖSSBAUER STUDIES ON SOME π-CYCLOPENTADIENYLIRON CARBONYL COMPLEXES

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Abstract
The Mössbauer spectra of a number of π-cyclopentadienyliron carbonyl complexes were measured at 96 K. The general formula of the complexes studied is CpFe(CO)2L where L = SMe2, SEt2, SPrn2, SBun2, PP43, etc., and SiCl2Me. An extremely broad line was observed at 96 K for CpFe(CO)2SiCl2Me. This complex (and most of the others included in this work) has a structure which permits rotational isomers about the Fe-Si bond. The line broadening is interpreted in terms of hindered rotation about the Fe-Si bond giving rise to a range of slightly different field gradients or isomer shifts due to the random orientation of the groups on the Si (or S) with respect to the groups on the Fe atom. To check this idea, spectra were measured to 5 K on both the CpFe(CO)2SiCl2Me and CpFe(CO)2THT samples. From the temperature dependence of the line width of the CpFe(CO)2THT complex, a maximum rotation frequency of about 15 MHz and a barrier to rotation of about 30 calories were estimated. A somewhat larger barrier to rotation is expected for the CpFe(CO)2SiCl2Me complex (about 800 cal) which accounts for the broadening which was observed in this complex even at 96 K

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