1553932-15-2Relevant academic research and scientific papers
Synthesis and structure of six-coordinate iron borohydride complexes supported by PNP ligands
Koehne, Ingo,Schmeier, Timothy J.,Bielinski, Elizabeth A.,Pan, Cassie J.,Lagaditis, Paraskevi O.,Bernskoetter, Wesley H.,Takase, Michael K.,Wuertele, Christian,Hazari, Nilay,Schneider, Sven
, p. 2133 - 2143 (2014/03/21)
The preparation of a number of iron complexes supported by ligands of the type HN{CH2CH2(PR2)}2 [R = isopropyl (iPrPNP) or cyclohexyl (CyPNP)] is reported. This is the first time this important bifunctional ligand has been coordinated to iron. The iron(II) complexes (iPrPNP)FeCl2(CO) (1a) and ( CyPNP)FeCl2(CO) (1b) were synthesized through the reaction of the appropriate free ligand and FeCl2 in the presence of CO. The iron(0) complex (iPrPNP)Fe(CO)2 (2a) was prepared through the reaction of Fe(CO)5 with iPrPNP, while irradiating with UV light. Compound 2a is unstable in CH2Cl2 and is oxidized to 1a via the intermediate iron(II) complex [(iPrPNP) FeCl(CO)2]Cl (3a). The reaction of 2a with HCl generated the related complex [(iPrPNP)FeH(CO)2]Cl (4a), while the neutral iron hydrides (iPrPNP)FeHCl(CO) (5a) and (CyPNP)FeHCl(CO) (5b) were synthesized through the reaction of 1a or 1b with 1 equiv of nBu4NBH4. The related reaction between 1a and excess NaBH4 generated the unusual η1-HBH3 complex (iPrPNP)FeH(η1-HBH3)(CO) (6a). This complex features a bifurcated intramolecular dihydrogen bond between two of the hydrogen atoms associated with the η1-HBH3 ligand and the N-H proton of the pincer ligand, as well as intermolecular dihydrogen bonding. The protonation of 6a with 2,6-lutidinium tetraphenylborate resulted in the formation of the dimeric complex [{(iPrPNP)FeH(CO)} 2(μ2,η1:η1-H 2BH2)][BPh4] (7a), which features a rare example of a μ2,η1:η1-H 2BH2 ligand. Unlike all previous examples of complexes with a μ2,η1:η1-H2BH 2 ligand, there is no metal-metal bond and additional bridging ligand supporting the borohydride ligand in 7a; however, it is proposed that two dihydrogen-bonding interactions stabilize the complex. Complexes 1a, 2a, 3a, 4a, 5a, 6a, and 7a were characterized by X-ray crystallography.
