Recombination of an Fe-Si-P Linkage to an Fe-P-Si Linkage through an Isolable Intermediate Phosphasilaferracyclopropane

1. Recombination of an Fe-Si-P Linkage to an Fe-P-Si Linkage through an Isolable Intermediate Phosphasilaferracyclopropane Okazaki, M.; Yoshitomo, T.; Naito, J.; Sato, A.; Komuro, T.; Tobita, H.J. Am. Chem. Soc.2008, 130, 17674-17675 Peter H.M. Budzelaar

2. Recombination ... • What happens ? • synthesis, characterization • How does it happen ? • mechanism • Why is it important ? • according to the authors • Evaluation Fe-Si-P to Fe-P-Si

3. Synthesis and characterization • Complex 2 formed from 1 by irradiation in benzene • as reported previously • Now found not to be stable in the presence of CO • so if you do the synthesis, the CO released can react with 2 • Procedure for synthesis of 3: Irradiate sample of 1, then let it sit in the dark for a while with added CO • Characterization of 3: Xray, NMR • long Si-P bond, short (and strong) Fe-P bond Fe-Si-P to Fe-P-Si

4. Synthesis and characterization • In the absence of CO, 2 also rearranges, but now to 4 • characterized by NMR only • a possible alternative structure is also mentioned (4', note 7)but considered less probable • mixture of two isomers (1.7:1) Fe-Si-P to Fe-P-Si

5. Synthesis and characterization • Complex 5, the cyclohexyl analogue of 2, is stable in both absence and presence of CO • characterized by Xray, NMR Fe-Si-P to Fe-P-Si

6. Mechanisms of rearrangement • Formation of 2 is straightforward: • For its rearrangement, they draw parallels with silyl(silylene) chemistry: • the 1,3-migration is unusual, the 1,2-migration can be seenas 1,1-insertion or as reductive elimination Fe-Si-P to Fe-P-Si

7. Mechanisms of rearrangement • Proposed formation of 3: 1,3-shift 1,1-deins 1,1-ins Fe-Si-P to Fe-P-Si

8. Mechanisms of rearrangement • Proposed formation of 4: ox add red el Fe-Si-P to Fe-P-Si

9. Difference between Ph and Cy • Cy more bulky, opposes transfer to Si • Ph has "more nucleophilic p-electrons" (whatever that means), should make transfer easier • There is precedent for transfer of OR from phosphite to silylene, but this is the first example of transfer from phosphide Fe-Si-P to Fe-P-Si

10. Relevance • Silylenes exhibit relatively high tendencies to group migration • This extends such work to neighbour phosphorus • Migrations of organic groups between non-transition-metal elements are relatively rare. • Understanding them better can benefit organic synthesis and building of inorganic polymers Fe-Si-P to Fe-P-Si

11. Evaluation Correctness: • Looks OK, X-rays for most structures, in particular for Ph-migrated structure 3 • Where doubt remains (structure of 4), alternative structure mentioned • No outrageous general claims anywhere Significance: • Fairly limited, these are exotic combinations of ligand groups precisely because of their easy rearrangements • Apart from the P→Si Ph transfer, not much new chemistry • The idea of metallacyclopropanes reacting as (phosphide)(silylene) complexes is interesting and perhaps more general Fe-Si-P to Fe-P-Si

12. Evaluation Presentation • Very clear and to the point • Not speculative at all, maybe too limited • Terrible title! Is this a JACS paper ? • Not for its general relevance • Possibly for its nice science • I would have suggested Organometallics Fe-Si-P to Fe-P-Si