Oxidative addition reaction of allyl or propargyl bromide with a diarylplatinum(II) complex

Isolation of Cationic η3-Allenylnickel(II) Key Intermediate Complexes: Origins of Enantioselectivity and Regioselectivity in Nickel(0)-Catalyzed Asymmetric Propargylic Substitutions

Herein, we report the synthesis and isolation of cationic η3-allenylnickel(II) complexes that bear rac-BINAP as a bidentate ligand for the first time via Me3SiOTf-promoted C-O bond cleavage of propargylic tert-butyl carbonate. In contrast, in the presence of the monodentate phosphine ligand PEt3, treatment of propargylic tert-butyl carbonate with Ni(cod)2 resulted in a gradual C-O bond cleavage leading to η1-allenylnickel(II) complexes, i.e., trans-(PEt3)2Ni(η1-CPh═C═CHR)(OBoc). X-ray diffraction and NMR spectroscopy studies of [(η3-RCH-CCPh)Ni(rac-BINAP)](OTf) revealed that the complex adopts an η3-allenyl coordination mode both in the crystal lattice and in solution. A thorough structural comparison between [(η3-RCH-CCPh)Ni(rac-BINAP)](OTf) and palladium and platinum analogues revealed that the η3-allenyl moiety in the nickel complex is similar to that observed in palladium and platinum complexes, albeit that each Ni-C bond is shorter than the corresponding Pd-C and Pt-C bonds due to the smaller ionic radius of nickel to that of Pd or Pt. The reactions of either N-methylaniline or sodium N-methylanilide with [(η3-RCH-CCPh)Ni((R)-BINAP)](OTf) furnished (R)-PhC≡CCH(NMePh)Me as an asymmetric propargylic substitution (APS) product with excellent enantioselectivity. Furthermore, when the nickel-catalyzed APS reaction of propargylic tert-butyl carbonate with N-methylaniline was conducted in DMSO at 60 °C in the presence of 5 mol % of [(η3-RCH-CCPh)Ni((R)-BINAP)](OTf) and 7.5 mol % of sodium N-methylanilide as a catalytic precursor and an additive, respectively, (R)-PhC≡CCH(NMePh)Me was obtained in 79% yield with 90% ee. The experimental results and computational calculations strongly suggest that the nickel-catalyzed APS reaction might proceed via a cationic η3-allenylnickel(II) species as the key reaction intermediate.

Ene Reactivity of an Fe═NR Bond Enables the Catalytic α-Deuteration of Nitriles and Alkynes

Herein, we report the reactions of an Fe(II) imido complex [Ph₂B(^tBuIm)₂Fe═NDipp]^- (1) with internal alkynes and isobutyronitrile, affording the Fe amido allenyl complexes [Ph₂B(^tBuIm)₂Fe(NHDipp)((R₁)C═C═C(R₂)(H))]^- (R₁ = Et or ⁿPr; R₂ = Me or Et, 2-5) and the Fe amido keteniminate complex [Ph₂B(^tBuIm)₂Fe(NHDipp)(N═C═CMe₂)K(THF)]_n (8-K), respectively. These transformations represent the previously unknown ene-like reactivity of a metal-ligand multiple bond. Stoichiometric reactions of 2 and 8-K with DippNH₂ lead to the regeneration of 3-hexyne and isobutyronitrile, respectively, with concomitant formation of the bis(anilido) complex [Ph₂B(^tBuIm)₂Fe(NHDipp)₂]^- (9). These results provide the platform for 1 as an efficient catalyst for the selective α-deuteration of nitriles and alkynes by RND₂. These results demonstrate a new reaction mode for metal imido complexes and suggest new avenues for using the imido ligand in catalysis.

A Bridging Peroxide Complex of Platinum(IV)

The photolysis of the allylplatinum(IV) complex [PtBr(C₃H₅)(4-MeC₆H₄)₂(bipy)], 1, bipy = 2,2'-bipyridine, in air yielded [{PtBr(4-MeC₆H₄)₂(bipy)}₂(μ-O₂)], 2, the first diplatinum(IV) complex containing a single bridging peroxide ligand. The PtO-OPt bond distance in 2 is 1.481(3) Å. Complex 2 is thought to be formed by homolysis of the allyl-platinum bond of 1, followed by reaction of the platinum(III) intermediate [PtBr(4-MeC₆H₄)₂(bipy)] with oxygen.