TY - JOUR
T1 - Biomimics of [FeFe]-hydrogenases with a pendant amine
T2 - Diphosphine complexes [Fe2(CO)4{µ-S(CH2)nS}{κ2-(Ph2PCH2)2NR}] (n = 2, 3; R = Me, Bn) towards H2 oxidation catalysts
AU - Orton, Georgia R.F.
AU - Belazregue, Sara
AU - Cockcroft, Jeremy K.
AU - Hartl, František
AU - Hogarth, Graeme
N1 - Funding Information:
We thank King's College London for PhD funding (GRFO), the Royal Society of Chemistry for an Undergraduate Bursary (SB) and Rosie Nash for re-recording IR and NMR data for 5.
Publisher Copyright:
© 2023 The Authors
PY - 2023/6/1
Y1 - 2023/6/1
N2 - We report the synthesis and molecular structures of [FeFe]-ase biomimics [Fe2(CO)4{µ-S(CH2)nS}{κ2-(Ph2PCH2)2NR}] (1–4) (n = 2, 3; R = Me, Bn) and a comparative study of their protonation and redox chemistry, with the aim of assessing their activity as catalysts for H2 oxidation. They are prepared in good yields upon heating the hexacarbonyls and PCNCP ligands in toluene, a minor product of one reaction (n = 3, R = Bn) being pentacarbonyl [Fe2(CO)5(µ-pdt){Ph2PCH2N(H)Bn}] (5). Crystal structures show short Fe-Fe bonds (ca. 2.54 Å) with the diphosphine occupying basal-apical sites. Each undergoes a quasi-reversible one-electron oxidation and IR-SEC shows that this results in formation of a semi-bridging carbonyl. As has previously been observed, protonation products are solvent dependent, nitrogen being the favoured site of protonation site upon addition of one equivalent of HBF4.Et2O in d6-acetone, while hydride formation is favoured in CD2Cl2. However, the rate of N to Fe2 proton-transfer varies greatly with the nature of both the dithiolate-bridge and amine-substituent. Thus with NMe complexes (1–2) N-protonation is favoured in acetone affording a mixture of endo and exo isomers, while for NBn complexes (3–4) proton-transfer to afford the corresponding μ-hydride occurs in part (for 3 edt) or exclusively (for 4 pdt). In acetone, addition of a further equivalent of HBF4.Et2O generally does not lead to hydride formation, but in CD2Cl2 dications [Fe2(CO)4{µ-S(CH2)nS}(μ-H){κ2-(Ph2PCH2)2NHR}]2+ result, in which the diphosphine can adopt either dibasal or basal-apical positions. Proton-transfer from Fe2 to N has been previously identified as a required transformation for H2 oxidation, as has the accessibility of the all-terminal carbonyl isomer of cations [Fe2(CO)4{µ-S(CH2)nS}{κ2-(Ph2PCH2)2NR}]+. We have carried out a preliminary H2 oxidation study of 3, oxidation by Fc[BF4] in the presence of excess P(o-tolyl)3 affording [HP(o-tol)3][BF4], with a turnover of ca. 2.3 ± 0.1
AB - We report the synthesis and molecular structures of [FeFe]-ase biomimics [Fe2(CO)4{µ-S(CH2)nS}{κ2-(Ph2PCH2)2NR}] (1–4) (n = 2, 3; R = Me, Bn) and a comparative study of their protonation and redox chemistry, with the aim of assessing their activity as catalysts for H2 oxidation. They are prepared in good yields upon heating the hexacarbonyls and PCNCP ligands in toluene, a minor product of one reaction (n = 3, R = Bn) being pentacarbonyl [Fe2(CO)5(µ-pdt){Ph2PCH2N(H)Bn}] (5). Crystal structures show short Fe-Fe bonds (ca. 2.54 Å) with the diphosphine occupying basal-apical sites. Each undergoes a quasi-reversible one-electron oxidation and IR-SEC shows that this results in formation of a semi-bridging carbonyl. As has previously been observed, protonation products are solvent dependent, nitrogen being the favoured site of protonation site upon addition of one equivalent of HBF4.Et2O in d6-acetone, while hydride formation is favoured in CD2Cl2. However, the rate of N to Fe2 proton-transfer varies greatly with the nature of both the dithiolate-bridge and amine-substituent. Thus with NMe complexes (1–2) N-protonation is favoured in acetone affording a mixture of endo and exo isomers, while for NBn complexes (3–4) proton-transfer to afford the corresponding μ-hydride occurs in part (for 3 edt) or exclusively (for 4 pdt). In acetone, addition of a further equivalent of HBF4.Et2O generally does not lead to hydride formation, but in CD2Cl2 dications [Fe2(CO)4{µ-S(CH2)nS}(μ-H){κ2-(Ph2PCH2)2NHR}]2+ result, in which the diphosphine can adopt either dibasal or basal-apical positions. Proton-transfer from Fe2 to N has been previously identified as a required transformation for H2 oxidation, as has the accessibility of the all-terminal carbonyl isomer of cations [Fe2(CO)4{µ-S(CH2)nS}{κ2-(Ph2PCH2)2NR}]+. We have carried out a preliminary H2 oxidation study of 3, oxidation by Fc[BF4] in the presence of excess P(o-tolyl)3 affording [HP(o-tol)3][BF4], with a turnover of ca. 2.3 ± 0.1
KW - Amino-diphosphine
KW - H oxidation
KW - Hydrogenase-biomimic
KW - IR-SEC
KW - Proton-transfer
UR - http://www.scopus.com/inward/record.url?scp=85150054714&partnerID=8YFLogxK
U2 - 10.1016/j.jorganchem.2023.122673
DO - 10.1016/j.jorganchem.2023.122673
M3 - Article
AN - SCOPUS:85150054714
SN - 0022-328X
VL - 991
JO - JOURNAL OF ORGANOMETALLIC CHEMISTRY
JF - JOURNAL OF ORGANOMETALLIC CHEMISTRY
M1 - 122673
ER -