A transition‐metal‐free visible‐light‐promoted radical phosphorylation/cyclization of N‐allylbenzamides with phosphine oxides for the synthesis of phosphoryl‐substituted dihydroisoquinolones was developed under room temperature. This protocol features mild reaction conditions, simple operation, broad substrate scope as well as scale‐up ability.magnified image

Investigating the synthesis and properties of diiron azadithiolate complexes is one of the key topics for mimicking the active site of [FeFe]‐hydrogenases, which might be very useful for the design of new efficient catalysts for hydrogen production and the development of a future hydrogen economy. A series of new phosphine‐substituted diiron azadithiolate complexes as models for the active site of [FeFe]‐hydrogenases are described. A novel and efficient way was firstly established for the preparation of phosphine‐substituted diiron azadithiolate complexes. The reaction of Fe2(μ‐SH)2(CO)6 and phosphine ligands L affords the intermediate Fe2(μ‐SH)2(CO)5L (A). The intermediate reacts in situ with a premixed solution of paraformaldehyde and ammonium carbonate to produce the target phosphine‐substituted diiron azadithiolate complexes Fe2[(μ‐SCH2)2NH](CO)5L (1a–1f) (L = P(C6H4–4‐CH3)3, P(C6H4–3‐CH3)3, P(C6H4–4‐F)3, P(C6H4–3‐F)3, P(2‐C4H3O)3, PPh2(OCH2CH3)). Furthermore, reactions of the intermediate A with I‐4‐C6H4N(CH2Cl)2 in the presence of Et3N give the phosphine‐substituted diiron azadithiolate complexes Fe2[(μ‐SCH2)2NC6H4–4‐I](CO)5L (2a–2e) (L = P(C6H4–4‐CH3)3, P(C6H4–3‐CH3)3, P(C6H4–4‐F)3, P(C6H4–3‐F)3, P(2‐C4H3O)3). All the complexes were fully characterized using elemental analysis, IR and NMR spectroscopies and, particularly for 1a, 1c–1e, 2a and 2c, single‐crystal X‐ray diffraction analysis. In addition, complexes 1a–1f and 2a–2e were found to be catalysts for H2 production under electrochemical conditions. Density functional theory calculations were performed for the reactions of Fe2(μ‐SH)2(CO)6 + P(C6H4–4‐CH3)3.

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Density functional the ory ( DFT) calculations on Fe 2 S 2 (CO) 6−2n (PMe 3 ) 2n for n = 0, 1, and 2 reveal that the most electron-rich derivatives (n = 2) exist as diferrous disulfides lacking an S−S bond. The thermal interconversion of the Fe II 2 (S) 2 and Fe I 2 (S 2 ) valence isomers is symmetry-forbidden. Related electron-rich diiron complexes [Fe 2 S 2 (CN) 2 (CO) 4 ] 2− of an uncertain structure are implicated in the biosynthesis of [FeFe]-hydrogenases. Several efforts to synthesize electron-rich derivatives of Fe 2 (μ-S 2 )(CO) 6 (1) are described. First, salts of iron persulfido cyanides [Fe 2 (μ-S 2 )(CO) 5 (CN)] − and [Fe 2 (μ-S 2 )(CN)-(CO) 4 (PPh 3 )] − were prepared by the reactions of NaN(tms) 2 with 1 and Fe 2 (μ-S 2 )(CO) 5 (PPh 3 ), respectively. Alternative approaches to electron-rich diiron disulfides targeted Fe 2 (μ-S 2 )(CO) 4 (diphosphine). Whereas the preparation of Fe 2 (μ-S 2 )(CO) 4 (dppbz) was straightforward, that of Fe 2 (μ-S 2 )(CO) 4 (dppv) required an indirect route involving the oxidation of Fe 2 (μ-SH) 2 (CO) 4 (dppv) (dppbz = C 6 H 4 -1,2-(PPh 2 ) 2 , dppv = cis-C 2 H 2 (PPh 2 ) 2 ). DFT calculations indicate that the oxidation of Fe 2 (μ-SH) 2 (CO) 4 (dppv) produces singlet diferrous disulfide Fe 2 (μ-S) 2 (CO) 4 (dppv), which is sufficiently longlived as to be trapped by ethylene. The reaction of 1 and dppv mainly afforded Fe 2 (μ-SCH=CHPPh 2 )(μ-SPPh 2 )(CO) 5 , implicating a S-centered reaction.