1394246-07-1Relevant articles and documents
C 2-symmetric iron(II) diphosphine-dialkoxide dicarbonyl and related complexes
Lei, Hao,Royer, Aaron M.,Rauchfuss, Thomas B.,Gray, Danielle
, p. 6408 - 6414 (2012)
Reaction of Fe(bda)(CO)3 (bda = benzylideneacetone) and Ph 2P-2-C6H4CHO (PCHO) affords the bisphosphine bisalkoxide complex Fe[(Ph2PC6H4) 2C2H2O2](CO)2 (1) arising from the head-to-head coupling of two formyl groups concomitant with oxidation of Fe(0) to Fe(II). Crystallographic studies show that 1 features cis alkoxide ligands that are trans to CO; the two phosphine groups are mutually trans with a P-Fe-P angle of 167.44(4)°. The pathway leading to 1 was examined, starting with the adduct Fe(PCHO)(CO)4 (2), which was obtained by addition of PCHO to Fe2(CO)9. Compound 2 decarbonylates to give tricarbonyl Fe(κ1,η2-PCHO)(CO)3 (3), which features a π-bonded aldehyde. Photolysis of 2 gives a mixture of 3 and isomeric hydride HFe(κ2-PCO)(CO)3. Complex 3 reacts with an additional equivalent of PCHO to afford 1, whereas treatment with PPh3 afforded the substituted product Fe(κ1, η2-PCHO)(PPh3)(CO)2 (4). In 4, the phosphine ligands are trans and the aldehyde is π-bonded. The geometry around Fe is pseudo trigonal bipyramidal. To gain insights into the mechanism and scope of the C-C coupling reaction, complexes were prepared with the imine Ph2PC6H4CH=NC6H4Cl (abbreviated as PCHNAr), derived by condensation of 4-chloroaniline and PCHO. PCHNAr reacts with Fe2(CO)9 and with Fe(bda)(CO) 3 to afford the tetra- and tricarbonyl compounds Fe(PCHNAr)(CO) 4 (5) and Fe(PCHNAr)(CO)3 (6), respectively. Treatment of 6 with PCHO gave the unsymmetrical C-C coupling complex Fe[(Ph 2PC6H4)2CH(O)CH(NAr)](CO) 2 (7). Compound 7 was also prepared by the reaction of 3 and PCHNAr. The solid-state structure of 7, as established by X-ray crystallography, is similar to that of 1 but with an amido group in place of one alkoxide. The deuterium-labeled phosphine aldehyde PCDO was prepared by the reaction of ortho-lithiated phosphine Ph2PC6H4-2-Li with DMF-d7. Reaction of 6 with PCDO gave 7-d1 with no scrambling of the deuterium label. Attempted oxidation of 1 with FcBF 4 (Fc+ = ferrocenium) gave the adduct Fe[(Ph 2PC6H4)2C2H 2O2(BF3)2](CO)2 (8). The structures of 1 and 8 are almost identical. Compound 8 was independently synthesized by treating 1 with BF3OEt2 via the intermediacy of the 1:1 adduct, which was detected spectroscopically. Qualitative tests showed that 1 also reversibly protonates with HOSO 2CF3 and binds TiCl4.
