Hydroalkylation of Aryl Alkenes with Organohalides Catalyzed by Molybdenum Oxido Based Lewis Pairs

Abstract

Three molybdenum(VI) dioxido complexes [MoO 2 (L) 2 ] bearing Schiff base ligands were reacted with B(C 6 F 5 ) 3 to afford the corresponding adducts [MoO{OB(C 6 F 5 ) 3 }(L) 2 ], which were fully characterized. They exhibit Frustrated Lewis‐Pairs reactivity when reacting with silanes. Especially, the [MoO{OB(C 6 F 5 ) 3 }(L) 2 ] complex with L=2,4‐dimethyl‐6‐((phenylimino)methyl)phenol proved to be active as catalyst for the hydroalkylation of aryl alkenes with organohalides and for the Atom‐Transfer Radical Addition (ATRA) of organohalides to aliphatic alkenes. A series of gem ‐dichloride and gem ‐dibromide compounds with potential for further derivatization were synthesized from simple alkenes and organohalides, like chloroform or bromoform, using low catalyst loading.

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

“…These results are in contrast to our previously reported molybdenum dioxido and oxido imido complexes with B(C 6 F 5 ) 3 , where the Lewis acid is clearly coordinated to the oxido group as indicated by the splitting and/or shifting of the resonances in the NMR spectra as well as a by X‐ray diffraction analysis. Hence, the former combinations of Mo dioxido and oxido imido complexes with B(C 6 F 5 ) 3 are termed FLP‐adducts [23,29] …”

“…Hence, the former combinations of Mo dioxido and oxido imido complexes with B(C 6 F 5 ) 3 are termed FLP-adducts. [23,29] Frustrated Lewis pair reactivity of 1 a/B(C 6 F 5 ) 3 and 1 b/B(C 6 F 5 ) 3…”

“…[29] In presence of phenylsilane hydroalkylation and Atom-Transfer Radical Addition (ATRA) of organohalides to different alkenes was observed (Scheme 2, bottom). [29] In our mixed oxido imido complexes [MoO(NtBu)L 2 ] adduct formation is only observed with the oxido group while the imido base remained untouched due to the higher basicity of the former. [23] We therefore hypothesized that molybdenum(VI) bis(imido) complexes should lead to more frustrated Lewis pairs with boranes and thus to higher reactivity.…”

Visible‐Light‐Induced Photoredox 1,1‐Dichloromethylation of Alkenes with Chloroform

“…Various three‐component difunctionalization of olefins, that enables rapidly assembly of multi‐functionalized frameworks from readily available starting materials, have been developed (Scheme 2b) [13] . Recently, the hydroalkylation of styrene with chloroform (CHCl 3 ) was reported by Mösch‐Zanetti, in which a complex molybdenum‐oxido Frustrated Lewis Pair adduct [MoO{OB(C 6 F 5 ) 3 }(L) 2 ] (L=2,4‐dimethyl‐6‐((phenylimino)methyl)phenol) catalyst was used, and excess phenylsilane was employed to enable the halogen‐atom transfer of chloroform [14] …”

“…[13] Recently, the hydroalkylation of styrene with chloroform (CHCl 3 ) was reported by Mösch-Zanetti, in which a complex molybdenumoxido Frustrated Lewis Pair adduct [MoO{OB-(C 6 F 5 ) 3 }(L) 2 ] (L = 2,4-dimethyl-6-((phenylimino)methyl)phenol) catalyst was used, and excess phenylsilane was employed to enable the halogen-atom transfer of chloroform. [14] In recent years, visible-light catalyzed reactions have attracted considerable interest, which could generate polyhaloalkyl radical species via single electron transfer (SET) under mild reaction conditions, avoiding the use of unstable and toxic agents. [15] Reiser group reported an impressive example of bulk chemical iodoform for visible light mediated coppercatalyzed ATRA reactions to activated olefins.…”