An Exploration of the Acid-Catalyzed Interconversion of Mo(NAr)(CR1R2)(OR)<sub>2</sub> Complexes and Their Mo(NAr)(Olefin)(OR)<sub>2</sub> Isomers (Ar = 2,6-<i>i</i>-Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>, OR = OSiPh<sub>3</sub> or OAr)
Sumeng Liu, Richard R. Schrock, Matthew P. Conley, Charlene Tsay, Veronica Carta
Abstract
Four new Mo(NAr)(CR1R2)(OSiPh 3 ) 2 complexes (Ar = 2,6- i -Pr 2 C 6 H 3; CR1R2 = CMe 2, CMeCH 2 Ph, CEtPh, or CHCH 2 Ph) were prepared through addition of CH 2 ═CR1R2 to a neopentylidene or a neophylidene complex. Three new olefin complexes with the formula Mo(NAr)(olefin)(OSiPh 3 ) 2 were prepared from Mo(NAr)(CH 2 ═CH 2 )(OSiPh 3 ) 2, namely, Mo(NAr)( trans -CH 3 CH═CHPh)(OSiPh 3 ) 2, Mo(NAr)(CH 2 ═CMePh)(OSiPh 3 ) 2, and Mo(NAr)(CH 2 ═CHCMe 3 )(OSiPh 3 ) 2 . Syntheses of other olefin complexes were complicated by relatively facile cis/trans isomerization of the olefin and isomerization of the C═C bond within the olefin carbon chain. Addition of [(Et 2 O) 2 H][B(C 6 F 5 ) 4 ] to the alkylidene complexes generates cationic 12e alkyl complexes [Mo(NAr)(CHMe 2 )(OSiPh 3 ) 2 ] +, [Mo(NAr)(CHMeCH 2 Ph)(OSiPh 3 ) 2 ] +, [Mo(NAr)(CHEtPh)(OSiPh 3 ) 2 ] +, and [Mo(NAr)(CH 2 CH 2 Ph)(OSiPh 3 ) 2 ] + . Deprotonation of the cationic alkyl complexes by NEt 3 generates the disubstituted alkylidene complexes as the major product. In the case of [Mo(NAr)(CHMeCH 2 Ph)(OSiPh 3 ) 2 ] +, both Mo(NAr)(CMeCH 2 Ph)(OSiPh 3 ) 2 and Mo(NAr)(CH 2 ═CHCH 2 Ph)(OSiPh 3 ) 2 are formed initially ([alkylidene]/[olefin] = 1.5:1), but the latter then isomerizes to Mo(NAr)(CH 3 CH═CHPh)(OSiPh 3 ) 2 . [Mo(NAr)(CHMePh)(OAr) 2 ][B(C 6 F 5 ) 4 ] was prepared through the protonation of Mo(NAr)(CMePh)(OAr) 2 with [(Et 2 O) 2 H][B(C 6 F 5 ) 4 ]. Mo(NAr)(CMePh)(OAr) 2 does not react with [PhNMe 2 H][B(C 6 F 5 ) 4 ] at room temperature. Mo(NAr)(CH 2 ═CH 2 )(OAr) 2 decomposes in solution at room temperature to yield Mo(NAr)(OAr)(η 1,η 2 -2-isopropyl-6-(prop-1-en-2-yl)phenolate)(Et 2 O) through CH activation in the isopropyl group of the OAr ligand followed by loss of ethane; Mo(NAr)(CH 2 ═CHPh)(OAr) 2 decomposes similarly. Eight single-crystal X-ray diffraction studies are reported.