Abstract
The synthesis and characterization of a series of silyl hydrido iron complexes bearing a pincer-type [PSiP] ligand (2-R2PC6H4)2SiH2 (R = Ph (1) and iPr (5)) or (2-Ph2PC6H4)2SiMeH (2) were reported. Preligand 1 reacted with Fe(PMe3)4 to afford complex ((2-Ph2PC6H4)SiH)Fe(H)(PMe3)2 (3) in toluene, which was structurally characterized by X-ray diffraction. ((2-iPr2PC6H4)SiH)Fe(H)(PMe3) (6) could be obtained from the reaction of preligand 5 with Fe(PMe3)4 in toluene. Furthermore, complex ((2-iPr2PC6H4)Si(OMe))Fe(H)(PMe3) (7) was isolated by the reaction of complex 6 with 2 equiv. MeOH in THF. The molecular structure of complex 7 was also determined by single-crystal X-ray analysis. Complexes 3, 4, 6 and 7 showed good to excellent catalytic activity for transfer hydrogenation of aldehydes under mild conditions, using 2-propanol as both solvent and hydrogen donor. α,β-Unsaturated aldehydes could be selectively reduced to corresponding α,β-unsaturated alcohols. The catalytic activity of penta-coordinate complex 6 or 7 is stronger than that of hexa-coordinate complex 3 or 4.
Highlights
Phosphine-based [PSiP] pincer complexes of transition metals have been studied extensively in recent years.1–5 In particular, they are involved as key intermediates in a variety of catalytic reactions of silicon compounds such as hydrosilylation, hydrocarboxylation of allenes and transfer hydrogenation.6 Because silyl ligands have stronger s-donating characters and show a more potent trans-in uence than commonly-used ligands in transition metal chemistry,7 the introduction of strong electron-donating and trans-labilizing silyl groups into tridentate ligand architectures may promote the formation of electron-rich and coordinatively-unsaturated complexes that exhibit novel reactivity with s-bonds.8 it is considered that silyl coordination compounds have potential applications in catalytic organic synthesis
They are involved as key intermediates in a variety of catalytic reactions of silicon compounds such as hydrosilylation, hydrocarboxylation of allenes and transfer hydrogenation
In 2012 Colacino reported that four Ir(I) and Ir(III) N-heterocyclic carbene (NHC) based complexes were used as catalysts in the reduction of aldehydes and ketones with glycerol
Summary
Phosphine-based [PSiP] pincer complexes of transition metals have been studied extensively in recent years. In particular, they are involved as key intermediates in a variety of catalytic reactions of silicon compounds such as hydrosilylation, hydrocarboxylation of allenes and transfer hydrogenation. Because silyl ligands have stronger s-donating characters and show a more potent trans-in uence than commonly-used ligands in transition metal chemistry, the introduction of strong electron-donating and trans-labilizing silyl groups into tridentate ligand architectures may promote the formation of electron-rich and coordinatively-unsaturated complexes that exhibit novel reactivity with s-bonds. it is considered that silyl coordination compounds have potential applications in catalytic organic synthesis. Phosphine-based [PSiP] pincer complexes of transition metals have been studied extensively in recent years.1–5 They are involved as key intermediates in a variety of catalytic reactions of silicon compounds such as hydrosilylation, hydrocarboxylation of allenes and transfer hydrogenation.. In 2015, Hu described new iron pincer complexes These complexes could activate H2 and catalyze selective transfer hydrogenation of aldehydes at room temperature under a low pressure of H2 (4 bar).. In 2012 Colacino reported that four Ir(I) and Ir(III) N-heterocyclic carbene (NHC) based complexes were used as catalysts in the reduction of aldehydes and ketones with glycerol.20 In this contribution, we have developed novel silyl hydrido iron [PSiP] pincer complexes for catalytic transfer hydrogenation of aldehydes and a,b-unsaturated aldehydes under mild conditions, using 2-propanol as both solvent and hydrogen donor. We compared the catalytic effects of these complexes with different phosphorus groups on the results of catalytic reactions
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