Reaction of Fe(bda)(CO) 3 (bda = benzylideneacetone) and Ph 2P-2-C 6H 4CHO (PCHO) affords the bisphosphine bisalkoxide complex Fe[(Ph 2PC 6H 4) 2C 2H 2O 2](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 Fe 2(CO) 9. Compound 2 decarbonylates to give tricarbonyl Fe(κ 1,η 2-PCHO)(CO) 3 (3), which features a π-bonded aldehyde. Photolysis of 2 gives a mixture of 3 and isomeric hydride HFe(κ 2-PCO)(CO) 3. Complex 3 reacts with an additional equivalent of PCHO to afford 1, whereas treatment with PPh 3 afforded the substituted product Fe(κ 1, η 2-PCHO)(PPh 3)(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 Ph 2PC 6H 4CH=NC 6H 4Cl (abbreviated as PCHNAr), derived by condensation of 4-chloroaniline and PCHO. PCHNAr reacts with Fe 2(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 2PC 6H 4) 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 Ph 2PC 6H 4-2-Li with DMF-d 7. Reaction of 6 with PCDO gave 7-d 1 with no scrambling of the deuterium label. Attempted oxidation of 1 with FcBF 4 (Fc + = ferrocenium) gave the adduct Fe[(Ph 2PC 6H 4) 2C 2H 2O 2(BF 3) 2](CO) 2 (8). The structures of 1 and 8 are almost identical. Compound 8 was independently synthesized by treating 1 with BF 3OEt 2 via the intermediacy of the 1:1 adduct, which was detected spectroscopically. Qualitative tests showed that 1 also reversibly protonates with HOSO 2CF 3 and binds TiCl 4.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry