SYNTHESIS AND REACTIVITY OF BIMETALLIC IRON-RHENIUM SILYL COMPLEXES -CRYSTAL-STRUCTURES OF [(OC)(3)((MEO)(3)SI)FE(MU-DPPM)RE(CO)(4)] AND [(OC)(3)FE(MU-BR)(MU-DPPM)RE(CO)(3)]

The dppm-bridged heterobimetallic alkoxysilyl complex [(OC)(3){(MeO)(3 )Si}Fe(mu-dppm)Re(CO)(4)] (2a) has been prepared by the reaction of K[ Fe{Si(OMe)(3)}(CO)(3)(eta(1)-dppm)] (K . 1) with fac-[Re(mu-Br)(CO)(3) (THF)](2) in THF. The Re centre prefers to coordinate an additional CO molecule rather than a lone pair from the potentially bridging Si(OMe )(3) ligand. Addition of BF3 . xEt(2)O resulted in replacement of one methoxy group of the Si(OMe)(3) ligand by fluorine to afford [(OC)(3){ (MeO)(2)FSi}Fe(mu-dppm)Re(CO)(4)] (3). Upon treatment of [HFe(Si(OMe)( 3)](CO)(3)(eta(1)-dppm)] (H . 1) with fac-[Re(mu-Br)(CO)(3)(THF)](2) e limination of HSi(OMe)(3) occurred, yielding the bromide-bridged compl ex [(OC)(3)Fe(mu-Br)(mu-dppm)Re(CO)(3)] (4). The reactivity of 4 towar ds phosphines, phosphites, isonitriles and CO has been investigated. A ddition of two equivalents of PR(3) to 4 opens the metal-metal bond, y ielding [(OC)(3)(R(3)P)Fe(mu-dppm)ReBr(CO)(3)(PR(3))] (5) (PR(3)=P(OPh )(3), PMePh(2), PMe(2)Ph). The complexes [(OC)(3)(RN=C)Fe(mu-dppm)ReBr (CO)(3)] (8) (R = 2,6-xylyl, (t)Bu) containing a dative metal-metal bo nd were formed by addition of one equivalent of RNC to a solution of 4 . This dative metal-metal bond is cleaved after addition of a second e quivalent of isonitrile to afford [(OC)(3)(RN=C)Fe(mu-dppm)ReBr(C=NR)( CO)(3)] (9). The related complex [(OC)(4)Fe(mu-dppm)ReBr(CO)(4)] (11) was obtained by carbonylation of 4 in an autoclave. The corresponding bis(diphenylphosphino)amine-bridged derivative [(OC)(4)Fe(mu-dppa)ReBr (CO)(4)] (13) was isolated after refluxing a mixture of [Fe(CO)(4)(dpp a-P)] (12) and [ReBr(CO)(5)] in toluene. The molecular structures of 2 a and 4 . 0.5CH(2)Cl(2) have been determined by X-ray diffraction meth ods. In the former, the Re(CO)(4) and Fe(CO)(3){Si(OMe)(3)} fragments are linked by a rather long metal-metal bond [Fe-Re 3.013(2) Angstrom] and by a bridging dppm ligand, whereas in 4 the metal-metal bond link ing the Re(CO)(3) and Fe(CO)(3) moieties is much shorter [Fe-Re 2.866( 4) Angstrom], being supported by a double bridge: a dppm and a bromine ligand.