Transition Metal-like Oxidative Addition of C–F and C–O Bonds to an Aluminum(I) Center

Abstract

Oxidative addition of very robust C−F and C− O bonds has been accomplished in reactions of the aluminum(I) compound NacNacAl (1, NacNac = [ArNC-(Me)CHC(Me)NAr] − and Ar = 2,6-Pr i2 C 6 H 3 ) with fluoroarenes, fluoroalkanes, and ethers. Similar to the transition metals, the ease of aryl C−F oxidative addition decreases as the degree of fluorination diminishes on the aromatic substrate. As well, kinetic studies on the addition of 1,2,3,4-tetrafluorobenzene to compound 1 revealed a second-order reaction characterized by a very negative entropy of activation (ΔS ⧧ = −113.6(3) J/K•mol), consistent with a transition metal-like oxidative addition process.

Understanding the Oxidative Addition of σ‐Bonds to Group 13 Compounds

“…These are associated with simultaneous H−X bond breaking and formation of Al−H and Al−X bonds, therefore leading to the Al I →Al III oxidation. This finding agrees nicely with the negative activation entropy measured experimentally by Nikonov and co‐workers for the strongly related C−F oxidation addition to compound 1 …”

Density Functional Theoretical Study on the CF and CO Oxidative Addition Reaction at an Al Center

“…Similar behavior was found in the present work involving the aluminum center. The calculated Gibbs energies of the activation of alkyl halides showed smaller values than fluorobenzene, which is in good agreement with the experiments …”

“…For alkyl halides, 1‐fluoropentane and fluorocyclohexane showed higher energy of activation due to both the electro‐donating nature and larger steric hindrance than fluoromethane. The Gibbs energy of activation depends on the number of F atoms on aryl fluorides, which is consistent with the experimental results . The oxidative addition of hexafluorobenzene to the complex 1 occurred at room temperature within 20 min; 1,2,4,5‐tetrafluorobenzene required 48 h at 70°C and no reaction for fluorobenzene at 100°C even after days of reaction time.…”

“…On the other hand, the counterpart studies involving main group elements have been reported in recent years. Two oxidative addition reaction studies at an Al center were reported . This paper reports the results of a computational study on the CF and CO oxidative addition reaction to the Al complex NacNacAl ( 1 , NacNac = [ArNC(Me)CHC(Me)Nar] − , where Ar = 2,6‐ i Pr 2 C 6 H 3 ) and its related complexes ( 2 and 3 shown in Scheme ).…”

Addition of Carbon–Fluorine Bonds to a Mg(I)–Mg(I) Bond: An Equivalent of Grignard Formation in Solution

“…Silylene, germylene, and related aluminum(I) reagents react with fluoroarenes by addition of the carbon–fluorine bond to the main group center (Figure 1, eqs 2–3). 9 …”