Highly reactive transition metal powders. Oxidative insertion of nickel, palladium, and platinum metal powders into aryl-halide bonds

Abstract

Mass.Hydrogen removal has been shown to be at least partially rate determining in the reaction of MA0 with substrates: 8. Belleau and J. Moran, Ann. N. Y. Acad. Sci., 107, 822 (1963). The quaternary salts 10, 11, and 12 were prepared from the reaction of the corresponding unsaturated bromides or mesylate with trimethylamine. Solubilization of 10 in neutral deuterium oxide (25 'C) leads instantaneously (on the NMR time scale) to exchange of the terminal, acetylenic proton. The overwhelming preference for removal of propargyl vs. allylic protons is in accord with the much greater electron-withdrawing power of the ethynyl group than the vinyl g r~u p .~* -~' J. A. Landgrebe and R. H. Rynbrandt, J. Org. Chem., 31, 2585 (1966). T. L. Brown, Chem. Rev., 58, 595 (1958). R. W. Taft, Jr., in "Steric Effects in Organic Chemistry", M. S. Newman, Ed., Wiley, New York, N.Y., 1956, p 619. That negative charge is more rapidly generated at a site adjacent to a triple bond than at an allylic site is also known from studies of base-catalyzed isomerizations of allenes and acetylenes: R. J. Bushby, Quart. Rev.. 24, (1970).(a) The strong preference for removal of a propargyl proton compared to an allyl proton stands in contrast to the ease of removing the cwespondlng hydrogen atoms. The most recently determined value for propargyl stabilization is 4.8 kcal/mol (R. Walsh, Trans. Faraday Soc., 84, 2085 (1971)). which is considerably smaller than the commonly quoted value of 12 kcal/mol for allylic stabilization (P. Nangia and S. W. Benson, J. Am. Chem.

Copper Cyanide-Catalyzed Palladium Coupling of N-tert-Butoxycarbonyl-Protected α-Lithio Amines with Aryl Iodides or Vinyl Iodides

“…Utilization of [( p -MeOC 6 H 4 ) 3 P] 4 Pd absorbed on Celite gave a lower yield (Table , entry 6), while use of PdCl 2 (PPh 3 ) 2 (5 mol %)/CuCN (10 mol %) gave 57% yield (Table , entry 7; 20% yield with bromobenzene 15 ) of 5 . In an effort to produce a more reactive palladium catalyst, a PdCl 2 /CuCN/P, As, or Sb ligand mixture was reduced with K metal to afford activated Pd(0) . This active Pd(0) catalyst gave no coupled product in the absence of added phosphine ligands (Table , entry 8).…”

Nickel-Catalyzed Cross-Couplings Involving Carbon−Oxygen Bonds

“…Supplementary to Zn 0 - or hydride-mediated reduction of Ni II , Rieke and co-workers demonstrated that reduction of Ni II I 2 with potassium or lithium metal in the presence of PEt 3 produced a highly active fine metal powder, “Rieke nickel”. Treatment of this powder with bromopentafluorobenzene resulted in the formation of an isolable trans -haloaryl Ni II complex, BrNi II (PEt 3 ) 2 C 6 F 5 , in 60% yield .…”

Preparation of highly reactive metal powders and their use in organic and organometallic synthesis

“…This turned out to be particularly true in the case of the transition metals Pt, Ni, and Pd. 26 Initially we tried the standard approach of reduction of N1I2, NiBr2, or NiCl2 with potassium in refluxing THF. Finely divided black nickel powders were obtained; however, they showed rather limited reactivity toward oxidative addition to carbon-halogen bonds.…”