C–H activation of a MeN grouping in one of the CH 2NMe 2ortho substituents of a NCN ‘pincer’ ligand in tungsten chemistry: X-ray structure of [WCl 2(NPh)(C 6H 3{CH 2NMeCH 2}-2-{CH 2NMe 2}-6)

Abstract

Reaction of the aryl and alkyl metal derivatives, [Li(C 6H 3(CH 2NMe 2) 2-2,6)] 2 ( 1), in situ prepared ‘Zn(C 6H 3(CH 2NMe 2) 2-2,6) 2’ ( 2), [Li(CH 2{C 6H(CH 2NMe 2) 2-2,6-Me 2-3,5})] ( 3) and [Zn(CH 2{C 6H(CH 2NMe 2) 2-2,6-Me 2-3,5}) 2] ( 4), respectively, with either WOCl 4 or [W(NPh)Cl 4(Et 2O)] in Et 2O yielded insoluble products. According to elemental analysis and mass balance the adducts that were formed contained all of the starting compounds, including the respective Li and Zn salts eventually formed. However, when the arylzinc reagent 2 was reacted with [W(NPh)Cl 4(Et 2O)] in CH 2Cl 2, [WCl 2(NPh)(C 6H 3{CH 2N(Me)CH 2}-2-{CH 2NMe 2}-6)] ( 6) was formed, which was isolated in high yield. The single-crystal X-ray determination of 6 showed a NCN ligand that is η 3- mer- N,C,N-bonded to the tungsten(VI) center via the (aryl)C ipso carbon and the two ortho- N-donor atoms. As one of the NCH 3 groups has undergone C–H activation, thus forming an azatungstacyclopropane ring, the NCN-pincer ligand is overall bonded to the tungsten centre as a tetradentate, η 4- N,C,N,C coordinating dianionic ligand. The corresponding tungsten(VI) alkylidene complex [W(CH 2SiMe 3)(NPh)(C 6H 3{CHN(Me)CH 2}-2-(CH 2NMe 2)-6)] ( 7) was generated by reaction of 6 with two equivalents of LiCH 2SiMe 3.