Unexpected carbon-carbon bond clevage in the reactions of the pentagonal bupyramidal cluster Fe3(CO)8[>RCC(Et)C(Et)CR] with styrene. Synthesis and X-ray structure of Fe3CO)6[(EtC2CR]2 (R= CH3(CH)2)

The thermal reactions of 2-methyl-1-hexen-3-yne [CH 3 CH 2 C : CC (=CH 2 )CH 3 , metey ] with Fe 3 (CO) 12 have been studied: cluster opening or frag- mentation and alkyne dimerization occur. Main products are the open triangular isomers [Fe 3 (CO) 6 ( l -CO) 2 {CH 3 (=CH 2 )CC(Et)C(Et)C(=CH 2 )CH 3 }] (complex 3a ) and [Fe 3 (CO) 6 ( l -CO) 2 {C(Et)CCH 3 (=CH 2 )C(Et)CCH 3 (=CH 2 )}] (complex 3b ). The structure and isomerism of the complexes has been confirmed by X-ray studies. The minor products of the reaction have been characterized by spectroscopic techniques. An attempt at exploiting the reactivity of the ‘‘free’’ C=C bonds of the coordinated ene-yne was made: complex 3a was reacted with styrene under thermal conditions. Unexpectedly considerable yields of the closed triangular cluster [Fe 3 (CO) 6 {EtC 2 C(=CH 2 )CH 3 } 2 ] (complex 5 ) have been obtained. This behaviour had not been previously observed. The unprecedented structure of complex 5 has been confirmed with an X-ray study