A Coordination Controlled Aryl–Halide Oxidative Addition to Platinum

Abstract

Aryl À halide bond activation and coordination of unsaturated substrates are key steps in many metal-mediated carbonÀcarbon bond-forming reactions. [1, 2] Numerous experimental and computational studies have been reported on these processes.[3] The electronic nature of the reactants is known to affect both steps. In particular, an electron withdrawing group (EWG: e.g., CF 3 , CN, NO 2 ) makes the C aryl À halogen bond more ionic, weakens this bond, and therefore increases the rate of the bond activation (Scheme 1, x = 0). [4] Such EWGs strengthen metalÀolefin bonds by increasing the p-backbonding between the metal center and the carbon À carbon double bond of the substrate.[5] How would the activation of aryl À halide bonds be affected if the same substrate also contains a carbon À carbon double bond capable of interacting with a metal center (Scheme 1, x = 1)? We have shown that halogenated arylarenes are versatile systems ideal for studying coordination chemistry coupled with aryl-bond activation. For instance, the reaction of MA C H T U N G T R E N N U N G (PEt 3 ) 4 (M = Ni, Pt) with a halogenated substrate results in h 2 -coordination to a -C=C-or -N=N-moiety, followed by "ringwalking" of the metal center, yielding the product of arylÀ halide oxidative addition. [6][7][8] However, partially fluorinated substrates kinetically prefer aryl À halide bond activation. [9] Thus, the metal center can be selectively directed to a specific site by varying the electronic properties of the reactants.We observe in the stilbene systems presented here that h 2 -coordination of the platinum center to a -C=C-unit is kinetically preferable over metal insertion into the carbonÀhalide bond regardless of the electronic properties of the substrate (Schemes 1 and 2). Nevertheless, the substituents of the stilbenes play a dominant role in the overall process. The reactivity trend is opposite from that of other aryl halides: The substrates with electron-deficient substituents are transformed much slower in the products of arylÀbromide activation than in those with electron-donation groups (EDGs). The overall reactivity is controlled by the coordination of the ligand to the metal center, whereas the activation of the aryl À Br bond is the rate-determining step. These findings are in good agreement with DFT calculations.A series of reactions with stilbenes 1-7 and PtA C H T U N G T R E N N U N G (PEt 3 ) 4 were used to explore the role of substrate coordination on arylÀhalide activation. Reaction of a stoichiometric amount of PtA C H T U N G T R E N N U N G (PEt 3 ) 4 with a stilbene (1-7) in THF results in the formation of complexes 8-14, respectively, by h 2 -coordination of the metal center to the central carbon À carbon double bond (see the Supporting Information for details). No products indicative of aryl À halide bond activation were observed by 1 H and 31 P{ 1 H} NMR spectroscopy prior to the formation of these complexes. The complexes 8-14 were characterized by NMR spectroscopy. In addition, complexes 9-12 and 14 were iso...

Substituent Effects on Stoichiometric and Catalytic Cleavage of Carbon–Nitrogen Bonds in Aniline Derivatives by Ruthenium–Phosphine Complexes

“…The substituent effect on the C–N bond cleavage was not cleanly correlated with the Hammett substituent constants, but the electron-donating substituent, such as OMe and Me groups, increased the reactivity of the C–N bonds. Therefore, the subsitutent effect observed here on the C–N bond cleavage is opposite to that of Wolczanski’s tantalum-mediated C–N bond cleavage and the general tendency of oxidative addition of polar aromatic C–X bonds. , …”

Structural Requirements for Palladium Catalyst Transfer on a Carbon–Carbon Double Bond

“…On the other hand, van der Boom and co-workers demonstrated that the reaction of Pt(0) or Ni(0) with a bromostilbene derivative resulted in selective η 2 -CC coordination, which was kinetically preferred at low temperature, followed by intramolecular “ring walking” of the metal center and intramolecular oxidative addition of the aryl-bromide bond, which was thermodynamically preferred when the temperature was raised . In accordance with this result, density functional theory calculation suggested that η 2 -CC coordination is more stable than the free state…”

Walking Metals in d8⋅⋅⋅d8 Hetero‐bimetallic Complexes: An Original Dynamic Phenomenon

“…Representative examples are the 1,3-metal-shift processes encountered by allyl, propargyl, and allenyl complexes [2] and, more generally, the shifts of metal centers over p-conjugated systems (including metal walking along rings and chains, haptotropic shifts, and so forth). [3][4][5] Strikingly, most studies have focused thus far on monometallic complexes, and, comparatively, metal-shift processes have only been rarely evidenced and studied in polymetallic complexes. [6] On the one hand, the unique properties associated with the presence of several metal centers make their dynamic behavior all the more interesting to be studied.…”