Synthesis and reactivity of bimetallic iron-rhenium silyl complexes: Crystal structures of [(OC)3{(MeO)3Si}Fe(μ-dppm) Re(CO)4] and [(OC)3Fe(μ-Br)(μ-dppm)Re(CO)3]

Article abstract of DOI:10.1016/S0022-328X(96)06524-2

The dppm-bridged heterobimetallic alkoxysilyl complex [(OC)₃{(MeO)₃Si}Fe(μ-dppm)Re(CO)₄] (2a) has been prepared by the reaction of K[Fe{Si(OMe)₃}(CO)₃(η¹-dppm)] (K · 1) with fac-[Re(μ-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 · xEt₂O resulted in replacement of one methoxy group of the Si(OMe)₃ ligand by fluorine to afford [(OC)₃{(MeO)₂FSi}Fe(μ-dppm)Re(CO)₄] (3). Upon treatment of [HFe{Si(OMe)₃}(CO)₃(η¹-dppm)] (H · 1) with fac-[Re(μ-Br)(CO)₃(THF)]₂ elimination of HSi(OMe)₃ occurred, yielding the bromide-bridged complex [(OC)₃Fe(μ-Br)(μ-dppm)Re(CO)₃] (4). The reactivity of 4 towards phosphines, phosphites, isonitriles and CO has been investigated. Addition of two equivalents of PR₃ to 4 opens the metal-metal bond, yielding [(OC)₃(R₃P)Fe(μ-dppm)ReBr(CO)₃(PR₃)] (5) (PR₃ = P(OPh)₃, PMePh₂, PMe₂Ph). The complexes [(OC)₃(RN≡C)Fe(μ-dppm)ReBr(CO)₃] (8) (R = 2,6-xylyl, ^tBu) containing a dative metal-metal bond 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 equivalent of isonitrile to afford [(OC)₃(RN≡C)Fe(μ-dppm)ReBr(C≡NR)(CO)₃] (9). The related complex [(OC)₄Fe(μ-dppm)ReBr(CO)₄] (11) was obtained by carbonylation of 4 in an autoclave. The corresponding bis(diphenylphosphino)amine-bridged derivative [(OC)₄Fe(μ-dppa)ReBr(CO)₄] (13) was isolated after refluxing a mixture of [Fe(CO)₄(dppa-P)] (12) and [ReBr(CO)₅] in toluene. The molecular structures of 2a and 4 · 0.5CH₂Cl₂ have been determined by X-ray diffraction methods. 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) A] and by a bridging dppm ligand, whereas in 4 the metal-metal bond linking the Re(CO)₃ and Fe(CO)₃ moieties is much shorter [Fe-Re 2.866(4) A], being supported by a double bridge: a dppm and a bromine ligand.