108945-99-9Relevant academic research and scientific papers
Synthesis of molybdenum imido alkylidene complexes and some reactions involving acyclic olefins
Schrock, Richard R.,Murdzek, John S.,Bazan, Gui C.,Robbins, Jennifer,DiMare, Marcello,O'Regan, Marie
, p. 3875 - 3886 (2007/10/02)
The reaction between Mo(C-t-Bu)(dme)Cl3 (dme = 1,2-dimethoxyethane) and Me3SiNHAr (Ar = 2,6-diisopropylphenyl) yields Mo(C-t-Bu)(NHAr)Cl2(dme) (1), which upon treatment with a catalytic amount Of NEt3 is transformed into Mo(CH-t-Bu)(NAr)Cl2(dme) (2). Complexes of the type Mo(CH-t-Bu)(NAr)(OR)2 (OR = OCMe(CF3)2, OCMe2(CF3), O-t-Bu, or OAr) have been prepared from 2. Complexes of the type Mo(C-t-Bu)(NHAr)(OR)2 (OR = OCMe(CF3)2 or OAr) have been prepared from 1, but they cannot be transformed into Mo(CH-t-Bu)(NAr)(OR)2 complexes. A precursor to imido alkylidene complexes that is related to 2 has been prepared by the sequence MoO2 → MoO2Cl2 → Mo(NAr)2Cl2 → Mo-(NAr)2(CH2R′)2 → Mo(CHR′)(NAr)(OTf)2(dme) (R′ = t-Bu or CMe2Ph; OTf = OSO2CF3). Mo(CH-t-Bu)(NAr)(OTf)2(dme) crystallizes in the space group P1 with a = 17.543 ?, b = 19.008 ?, c = 9.711 ?, α = 91.91°, β = 99.30°, γ = 87.27°, Z = 4, Mr = 729.60, V = 3191.1 ?3, ρ(calcd) = 1.518 g cm-3. It is a pseudooctahedral species in which the imido and alkylidene ligands are cis to one another, the triflate ligands are mutually trans, and the tert-butyl group points toward the imido ligand (syn orientation). Neophylidene complexes, Mo(CHCMe2Ph)(NAr)(OR)2 (OR = O-t-Bu, OAr, or O-2-C6H4-t-Bu), have been prepared from Mo(CHCMe2Ph)(NAr)(triflate)2(dme). Activity for the metathesis of cis-2-pentene by Mo(CHR′)-(NAr)(OR)2 complexes roughly correlates with the electron-withdrawing ability of OR, being rapid when OR = OCMe(CF3)2 and slow to negligible when OR = O-t-Bu. In several cases it is clear from proton NMR studies that the alkylidene ligand can rotate on the NMR time scale; in Mo(CHSiMe3)(NAr)(OAr)2 it has been shown that ΔG?298 = 16.0 kcal mol-1 for this process. Mo[CH(SiMe3)CH(SiMe3)CH2](NAr)[OCMe 2(CF3)]2 has been observed and found to be ～3 orders of magnitude less stable than the analogous tungsten complex. Trigonal-bipyramidal Mo(CH2CH2CH2)(NAr)[OCMe(CF3) 2]2 can be prepared at 25 °C in high yield, but it decomposes over a period of 12 h. Instability of OCMe(CF3)2 metallacyclobutane complexes has been traced to reduction by β-hydride rearrangement to give an olefin. In one case a complex containing the olefin product, Mo(NAr)(Me3SiCH=CH2)[OCMe(CF3)2] 2, was isolated.
Well-characterized olefin metathesis catalysts that contain molybdenum
Murdzek, John S.,Schrock, Richard R.
, p. 1373 - 1374 (2008/10/08)
The reaction between Mo(C-t-Bu)(dme)Cl3 (dme = 1,2-dimethoxyethane) and Me3SiNHAr (Ar = 2,6-diisopropylphenyl) yields Mo(C-t-Bu)(NHAr)(dme)Cl2 (1), which upon treatment with a catalytic amount of NEt3 is transformed into Mo(CH-t-Bu)(NAr)(dme)Cl2 (2) virtually quantitatively. Complexes of the type Mo(CH-t-Bu)-(NAr)(OR)2 (OR = OCMe(CF3)2, OCMe2(CF3), or OCMe3) have been prepared. Mo(CH-t-Bu)(NAr)[OCMe(CF3)2]2 is an active metathesis catalyst (but less active than the tungsten analogue) while Mo(CH-t-Bu)(NAr)(OCMe3)2 does not react with ordinary olefins. Addition of Me3SiCH=CH2 to Mo(CH-t-Bu)(NAr)[OCMe(CF3)2]2 to yield Mo-(CHSiMe3)(NAr)[OCMe(CF3)2]2 is taken as evidence that molybdacyclobutane complexes lose an olefin more readily than analogous tungstacyclobutane complexes.
