Speaker:
Mitch Rivers
I. Kinetic Analysis of Benzylidene Transfer from Gold(I) Carbenoids
II. Kinetic Analysis of Protodeauration of β-Styrenyl Gold Complexes
III. Palladium (II) Catalyzed Homobenzylic Diazirine Activation
I. Aliphatic and aromatic alkenes react rapidly and efficiently with the gold sulfonium benzylide complex [(P)AuCHPh(SPh2)]+{B [3,5-CF3C6H3]4− [P= P (t-Bu)2o-biphenyl;1] at room temperature via the cationic two-coordinate gold benzylidene complex [(P)AuCHPh]+(1.I) to form phenyclyclopropanes. The reactivity of p-substituted vinyl arenes toward 1.I decreased with the decreasing electron donor ability of the vinyl arene and the reactivity of aliphatic alkenes toward 1.I depended strongly on the number of alkyl groups attached to the more substituted alkene terminus.. Benzylidene transfer to vinyl arenes led to predominant formation of cis-cyclopropanes. All our experimental observations were consistent with a concerted, asynchronous, electrophilic benzylidene transfer mechanism.
II. Treatment of gold β-styrenyl complexes (E)-(PPh3)AuC(H)═C(H)(4-C6H4X) with excess acetic acid in CD2Cl2 containing PPh3 at 4 °C led to quantitative protodeauration to form the corresponding vinyl arene as the exclusive organic product. Kinetic analysis of the protodeauration under these conditions established the rate law for the protodeauration of : rate =k[β-styrenyl complex][AcOH]mon,, and established the superior correlation of log(kobs) with the Hammett σ parameter (ρ = −1.26;R2> 0.99) These and additional observations are consistent with a mechanism for the preponderation of complexes involving transfer of proton from monomeric acetic acid to the Au-C bond with concerted C-H bond formation/Au-C(σ) bond cleavage.
III. Treatment of homobenzylic diazirines 3-(4-chlorobenzyly)-3H-diazirine and 3-benzyl-3H diazirine with a catalytic amount of PdCl2(PhCN)2 (15 mM Pd) at 25 °C led to consumption of the diazirine and yielding corresponding vinyl arenes as the exclusive organic product. Kinetic analysis of this palladium catalyzed diazirine activation under these conditions established the rate law rate = k[diazirine][Pd]. The elimination also proceeded using {PdCl2[π(p-chlorostyrene)}2 as a catalyst in the same conditions. The mechanism is proposed to proceed through an oxidative addition, followed by diazometallacyclobutane formation, then expulsion of nitrogen produces the palladium carbene, which then proceeds through a facile 1,2-elimination.