The reaction of trimethylsilyldiazomethane with complexes of the type [PtX(CH₃)(diphosphine)] (X = Cl, Br, I). Some observations on β-hydrogen migrations in PtCHRCH₃ species and organoplatinum(II)-catalysts for alkene formation from trimethylsilyldiazomethane

Abstract

Treatment of [PtX(CH₃)(diphos)] 1 {X = Cl, Br, I; diphos = (4R,5R)-4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane (diop), (2S,4S )-2,4-bis(diphenylphosphino)pentane (skewphos), (2S,3S )-2,3-bis(diphenylphosphino)butane (chiraphos)} with N₂CHSiMe₃ gives two series of products: “α-products“, [PtX(CH₂SiMe₃)(diphos)] 2 and “β-products“ [PtX(CH₂CH₂SiMe₃)(diphos)] 3. Which product is formed and their stability depends on the ancillary ligands X and diphos. Treatment of [PtCl(CH₃)(diop)] 1a with an excess of N₂CHSiMe₃ gives the α-product [PtCl(CH₂SiMe₃)(diop)] 2a in high yield. The structure of 2a was confirmed by X-ray crystallography. Under similar conditions [PtCl(CH₃)(skewphos)] 1d reacts with an excess of N₂CHSiMe₃ to give the β-product [PtCl(CH₂CH₂SiMe₃)(skewphos)] 3d as shown unambiguously by a combination of ¹H-COSY and ³¹P NMR spectroscopy. It is established that the reaction sequence is 1 → 3 → 2 and the conversion of 3 → 2 is via a β-hydrogen migration and elimination of CH₂[double bond, length half m-dash]CHSiMe₃. The stability of 3 with respect to β-hydrogen elimination is in the order Cl > Br > I and chiraphos > skewphos > diop; a mechanism is proposed based on five-coordinate platinum(II) intermediates to rationalize these trends. The reactions of [PtX(CH₃)(diphos)] with N₂CHSiMe₃ and N₂CHCOOEt are contrasted and it is concluded that in PtCHRMe species, a SiMe₃ group facilitates β-hydrogen migration while a CO₂Et group retards β-hydrogen migration. The complexes 2 are catalysts for the conversion of N₂CHSiMe₃ to Me₃SiCH=CHSiMe₃.

References

1. J. P. Collman, L. S. Hegedus, J. R. Norton and R. G. Finke, Principles of Organotransition Metal Chemistry, University Science Books, Mill Valley, CA 1987.
2. P. Bergamini, E. Costa, A. G. Orpen, P. G. Pringle and M. B. Smith, Organometallics, 1995, 14, 3178.
3. T. Kégl, L. Kollár and L. Radics, Inorg. Chim. Acta, 1997, 267, 249.
4. B. Wozniak, J. D. Ruddick and G. Wilkinson, J. Chem. Soc. A, 1971, 3116.
5. G. Alibrandi, L. M. Scolaro, D. Minniti and R. Romeo, Inorg. Chem., 1990, 29, 3467 and refs. therein.
6. R. Kapadia, J. B. Pedley and G. B. Young, Inorg. Chim. Acta, 1997, 265, 235.
7. H. E. Bryndza, L. K. Fong, R. A. Paciello, W. Tam and J. E. Bercaw, J. Am. Chem. Soc., 1987, 109, 1444 and refs. therein.
8. (a) G. M. Whitesides, J. F. Gaash and E. R. Stedronsky, J. Am. Chem. Soc., 1972, 94, 5258; (b) P. J. Davidson, M. F. Lappert and R. Pearce, Chem. Rev., 1996, 219; (c) H. E. Bryndza, J. C. Calabrese, M. Marsi, D. C. Roe, W. Tam and J. E. Bercaw, J. Am. Chem. Soc., 1986, 108, 4805; (d) G. Alibrandi, D. Minniti, R. Romeo and P. Vitarelli, Inorg. Chim. Acta, 1984, 81, L23; (e) G. Alibrandi, D. Minniti, R. Romeo, G. Cum and R. Gallo, J. Organomet. Chem., 1985, 291, 133.
9. (a) T. J. McCarthy, R. G. Nuzzo and G. M. Whitesides, J. Am. Chem. Soc., 1981, 103, 1676; (b) G. Alibrandi, M. Cusumano, D. Minniti, L. M. Scolaro and R. Romeo, Inorg. Chem., 1989, 28, 342; (c) R. Romeo, G. Alibrandi and L. M. Scolaro, Inorg. Chem., 1993, 32, 4688.
10. W. Colvin, Chem. Soc. Rev., 1978, 7, 15.
11. (a) R. Favez, R. Roulet, A. A. Pinkerton and D. Schwarzenbach, Inorg. Chem., 1980, 19, 1356; (b) F. P. Fanizzi, F. P. Intini, L. Maresca, G. Natile, M. Lanfranchi and A. Tiripicchio, J. Chem. Soc., Dalton Trans., 1991, 1007 and refs. therein.
12. G. Bernardinelli and H. D. Flack, Acta Crystallogr., Sect. A, 1985, 41, 500.