Julian Brünig

The catalytic reduction of polar multiple bonds via molecular hydrogen is an important transformation in modern synthetic organic chemistry. Our group recently developed a highly efficient and selective [Fe(PNP^Me–iPr)(CO)(H)(Br)] catalyst for the homogeneous reduction of aldehydes.¹ In order to eliminate the major drawbacks of homogeneous catalysis, i.e., the need for separation and recovery of the catalysts at the end of the process, supported ionic-liquid-phase (SILP) catalysts can be applied. In a SILP system a homogeneous catalyst is dissolved in an ionic liquid and impregnated on a porous support material, thus the chemical nature of the homogeneous catalyst can be preserved.

Figure 1. Example of a scheme for the shape of a SILP catalyst

For that purpose three different base-tolerant SILP systems with mesoporous silica as support material containing the well-defined hydride Fe(II) PNP pincer complex have been prepared, structurally characterized and used as catalysts in the chemoselective hydrogenation of aldehydes to alcohols under mild conditions (25 °C, 10-50 bar H₂ pressure). The SILP systems showed high TONs and TOFs of up to 1000 and  4000 h^-1 at the optimum pore filling degree. They were successfully  used in recharge experiments to simulate a continuous flow system.²

Acknowledgements

The authors thank the Austrian Science Fund (FWF) for Financial support.

References

1. Gorgas, N.; Stöger, B.; Veiros, L. F.; Kirchner, K. ACS Catal., 2016, 6, 2664.
2. Brünig, J.; Csendes, Z.; Weber, S.; Gorgas, N.; Bittner, R. W.; Limbeck, A.; Bica, K.; Hoffmann, H; Kirchner, K. ACS Catal., 2018, 8, 1048.