PHOTOCHEMICAL-SYNTHESIS AND STEREODYNAMIC BEHAVIOR OF ALKOXY-BRIDGED (SILYLENE)(GERMYLENE)IRON COMPLEXES

Mixed (silylene)(germylene)iron complexes have been synthesized for the first time and are internally stabilized by a donor bridging alkoxy group: [Cp'(CO)Fe{GeMe2--O(R)--SiMe2}] (CP'= C5Me5; R = Me, Bu(t)). Two-dimensional and variable-temperature H-1 NMR spectroscopies establish germylene-methyl group exchange. Computer simulation of the spectra and calculation using the Eyring equation yield values for DELTA-G(double dagger)298 for the process of 62 kJ mol-1 (R = Me) and 61 kJ mol-1 (R = Bu(t)). A mechanism involving cleavage of the Ge--O partial bond, followed by rotation of the resulting coordinated germylene moiety about the Fe=Ge double bond, is proposed for this exchange. The (silylene)(germylene)iron complexes are weighted toward the (methoxysilyl) (germylene) form, indicating that germylene ligands are more stable than their silicon analogues.