Resource-problem-free catalyst: low-valent silicon(II) complexes – NOPROBLEM

We propose, in this project, the development of new stable low-valent silicon(II) complexes as “resource-problem-free catalysts” with a transition metal like behavior. The success of this project should open a new wide research domain in chemistry and could change the vision of catalysis.

The silicon congeners of well-known phosphonium ylides were considered only as short-lived reactive intermediates. In this project, we successfully synthesized a remarkably stable phosphonium sila-ylide which can also be considered as a Si (II)-complex stabilized by a phosphine ligand. An important result was the reactivity with ethylene. Indeed, under ethylene pressure, at RT, a [2 +1] cycloaddition led to the formation of the corresponding sila-cyclopropane, clearly demonstrating the behavior of phosphonium sila-ylides as nucleophilic silylenoids. In addition, we found that this reaction is in equilibrium in solution at RT.
This result is particularly interesting since the same type of phenomenon is frequently observed in the chemistry of transition metal complexes. Indeed, this type of association / dissociation of ethylene to the metal center, under mild conditions, is an important step in catalysis, particularly in the activation of olefins.

The first Si(II) complexes stabilized by a phosphine ligand were synthesized, and we have demonstrated that they behave as transition metal complexes with olefins.
In the next part of the project we will consider the activation of other chemical bonds, like sigma-bonds. In addition we will test the reactivity with inert molecules like CO2, in order to develop a catalytic systems.

1. R. Rodriguez, D. Gau, T. Kato, N. Saffon-Merceron, F. P. Cossio, A. Baceiredo, Angew. Chem. Int. Ed., 50, 10414 (2011)
2. R. Rodriguez, D. Gau, Y. Contie, T. Kato, N. Saffon-Merceron, A. Baceiredo, Angew. Chem. Int. Ed., 50, 11492 (2011)
3. J. Berthe, J. M. Garcia, E. Ocando, T. Kato, N. Saffon-Merceron, A. De Cózar, F. P. Cossío, A. Baceiredo, J. Am. Chem. Soc., 133, 15930 (2011).
4. R. Rodriguez, T. Troadec, T. Kato, J.-M. Sotiropoulos, N. Saffon-Merceron, A. Baceiredo, Angew. Chem. Int. Ed., 51, 7158 (2012).
5. R. Rodriguez, T. Troadec, D. Gau, J.-M. Sotiropoulos, N. Saffon-Merceron, A. Baceiredo, T. Kato, Angew. Chem. Int. Ed., 52, 4426-4430 (2013).
6. R. Rodriguez, Y. Contie, D. Gau, N. Saffon-Merceron, K. Miqueu, J.-M. Sotiropoulos, A. Baceiredo, T. Kato, Angew. Chem. Int. Ed., 52, 8437-3440 (2013).
7. R. Rodriguez, D. Gau, T. Troadec, N. Saffon-Merceron, V. Branchadell, A. Baceiredo, T. Kato, Angew. Chem. Int. Ed., 52, 8980-8983 (2013).
8. N. Nakata, R. Rodriguez, T. Troadec, N. Saffon-Merceron, J.-M. Sotiropoulos, A. Baceiredo, T. Kato, Angew. Chem. Int. Ed. in press (2013).

Transition-metal catalysts with a versatile coordination mode and reactivity, allowing highly efficient and selective reactions under mild conditions, are indispensable in actual organic synthesis. However, in spite of the significant importance of organometallic catalysts, the principal problem is the highly limited natural resource of precious transition metals.
This project principally concerns the use of silicon (the second most abundant element in the Earth’s crust) as catalyst instead of transition metals. Although the importance of its abundance is well recognized in material chemistry, as it can be seen by the vast world production of silicon based materials (polymers, rubber, semiconductors), real success in chemistry with such a vision has never been achieved. This is probably due to the lack of appropriate stable silicon species with particular and highly modulable electronic properties which can be applied for various catalytic systems.
For this purpose, low-valent silicon(II) complexes should be the most promising candidates, due to their particular coordination properties in contrast to other high valent silicon species with simple reactivity (classical Lewis acid). Another great advantage of these complexes is their structural flexibility, compared to the previously known extremely reactive low-valent species.
We propose, in this project, the development of new stable low-valent silicon(II) complexes as “resource-problem-free catalysts” with a transition metal like behavior. The success of this project should open a new wide research domain in chemistry and could change the vision of catalysis.