A series of cis and trans Fe(II) complexes containing the diphosphine ligand PNP (where PNP is bis((diethylphosphino)methyl)methylamine) have been prepared and isolated. These include cis-[Fe(PNP) 2(CH 3CN) 2](BF 4) 2 (3), cis-[Fe(PNP) 2(CH 3CN)(CO)](BF 4) 2 (4), trans-[Fe-(PNP)(dmpm)(CH 3CN) 2](BF 4) 2 (5), trans-Fe(PNP)(dmpm)Cl 2 (6), trans-[Fe(PNP)(dmpm) (CO)-Cl] 2[FeCl 4] (7), trans-HFe(PNP)(dmpm)Cl (8), and trans-[HFe(PNP)(dmpm)(CH 3CN)]BPh 4 (9) (where dmpm is bis(dimethylphosphino)methane). In addition, the cations trans-[HFe-(PNP)(dmpm) (CO)] + (10) and trans-[(H 2)Fe(PNP)(dmpm)(H)] + (11) have been observed in solution. These complexes all possess a pendant base that bridges the two phosphorus atoms of the PNP ligand. A cis geometry is observed for those complexes containing two PNP ligands, whereas a trans geometry is observed for the complexes containing one PNP ligand and one dmpm ligand. The molecular structures of cis-[Fe(PNP) 2(CH 3CN)(CO)](BPh 4) 2 and trans-[HFe(PNP)(dmpm) (CH 3CN)]BPh 4 have been confirmed by X-ray diffraction studies. Protonation of 5, 7, and 10 occurs at the nitrogen atom of the PNP ligand, and pK a values are reported for the corresponding protonated complexes. The formation of the dihydrogen complex [trans-[(H 2)Fe(PNP)(dmpm)(H)] + and the protonated PNHP complex trans-[HFe-(PNHP)(dmpm)(CO)] 2+ demonstrate that intramolecular heterolytic cleavage of the dihydrogen ligand can be controlled by varying the nature of the ligand trans to the incipient dihydrogen ligand.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry