Hydrocarbyl derivatives of dppm- or dppa-bridged alkoxysilyl heterobimetallic Fe–Pd complexes and CO insertion reactions. Crystal structures of [(OC)3{(MeO)3Si}Fe(μ-dppm)Pd(8-mq)] (dppm = Ph2PCH2PPh2), [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-dppa)PdCl] and [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-dppa)PdPh] (dppa = Ph2PNHPPh2) †

Abstract

The complexes [(OC)3Fe{µ-Si(OMe)2(OMe)}(µ-dppm)PdR] (R = alkyl, aryl) have been obtained either by treatment of [(OC)3Fe{µ-Si(OMe)2(OMe)}(µ-dppm)PdCl] 1a with organolithium or Grignard reagents or, in the case where R = Me, by reaction of [PdCl(Me)(COD)] (COD = 1,5-cyclooctadiene) with the metallate K[Fe{Si(OMe)3}(CO)3(dppm-P)] 2a. When dppa was used as an assembling ligand, reaction of the hydrido complex mer-[HFe- {Si(OMe)3}(CO)3(dppa-P)] 7b with [PdCl(Me)(COD)] or [Pd(η3-allyl)(µ-Cl)]2 proceeded via elimination of methane or propene, respectively, to afford [(OC)3Fe{µ-Si(OMe)2(OMe)}(µ-dppa)PdCl] 1b and not via HCl elimination which would have resulted in hydrocarbyl complexes. However, reaction of 7b with [PdX(R)(TMEDA)] (X = Cl, R = Me; X = I, R = Ph; TMEDA = Me2NCH2CH2NMe2) afforded the hydrocarbyl complexes [(OC)3Fe{µ-Si(OMe)2(OMe)}(µ-dppa)PdMe] 3b or [(OC)3Fe{µ-Si(OMe)2(OMe)}(µ-dppa)PdPh] 5b. The latter and [(OC)3{(MeO)3Si}Fe(µ-dppa)Pd(η3-allyl)] 8b were obtained by reaction of the carbonylmetallate 2b with [PdCl(Me)(COD)], [PdI(Ph)(TMEDA)] or [Pd(η3-allyl)(µ-Cl)]2, respectively. The stabilizing but labile four-membered µ-η2-SiO→Pd bridging interaction facilitates CO insertion into the Pd–Me bond of 3a or 3b to afford the corresponding acetyl complexes. For comparison, [(OC)3{(MeO)3Si}Fe(µ-dppm)Pd(8-mq)] 6a which contains a stable five-membered (C,N) chelate at Pd did not insert CO under similar conditions. The reaction of CO with the benzyl derivative [(OC)3Fe{µ-Si(OMe)2(OMe)}(µ-dppm)Pd(CH2Ph)] 4a was more complex since the resulting acyl [(OC)3Fe{µ-Si(OMe)2(OMe)}(µ-dppm)Pd{C(O)CH2Ph}] 11a rearranged into the µ-siloxycarbene complex [(OC)3Fe{µ-C(CH2Ph)OSi(OMe)3}(µ-dppm)Pd(CO)] 12a. Comparisons are made between complexes containing dppm or dppa and different R groups. The structures of complexes 1b, 5b·THF and 6a·hexane have been determined by X-ray diffraction.