Synthesis of Molybdenum Imido Alkylidene Complexes That Contain Siloxides

Abstract

Monosiloxide and disiloxide complexes have been prepared through the addition of silanols to Mo(NR)(CHCMe 2 Ph)(pyrrolyl) 2 species [R ) 1-adamantyl (Ad) or 2,6-i-Pr 2 C 6 H 3 (Ar)]. The silanols employed include (t-Bu) 3 SiOH (HSilox), (i-Pr) 3 SiOH, (Me 3 Si) 3 SiOH, (t-Bu-O) 3 SiOH, Me 2 (t-Bu)SiOH, and Ph 3 SiOH. The monoSilox complex, Mo(NAr)(CHCMe 2 Ph)(Silox)(pyrrolyl) (2a), could be isolated, while Mo(NAd)(CHCMe 2 Ph)(Silox)(pyrrolyl) was observed in situ but could not be crystallized. Disiloxides that could be crystallized include Mo(NAd 5), and Mo(NAr)(CHCMe 2 Ph)[OSiMe 2 (t-Bu)] 2 (6); other disiloxide examples could be observed in situ but could not be crystallized. Compound 2a reacts readily with (CF 3 )Me 2 COH, (CF 3 ) 2 MeCOH, (CF 3 ) 2 CHOH, ArOH, C 6 F 5 OH, (-)-menthol, and (-)borneol to give compounds of the type Mo(NAr)(CHCMe 2 Ph)(Silox)(OR) (3a-g) in situ. No reaction was observed upon heating of 1b under 5 atm of ethylene at 120 °C in toluene-d 8 ; only at 240 °C in o-dichlorobenzene-d 4 did 1b react with ethylene to yield CH 2 dCHCMe 2 Ph, but the Mo-containing product could not be identified. Compound 2a reacts with ethylene at 120 °C to give Mo(NAr)(CH 2 )(Silox)(pyr), while 3a-e react with ethylene at ∼60 °C; methylene species could be observed in several cases but could not be isolated. X-ray studies were carried out for 1b and 2a.

Isostructural Molecular and Surface Mimics of the Active Sites of the Industrial WO3/SiO2 Metathesis Catalysts

“…In contrast, using Surface Organometallic Chemistry, [3][4][5][6] a large family of highly active supported alkene metathesis catalysts has been reported based on welldefined metal alkylidenes in the past 15 years. [7][8][9][10][11][12][13][14][15] These numerous complexes have given access to a large number of spectroscopic and catalytic data set that have contributed to a better understanding of the mechanism and reaction intermediates involved in alkene metathesis. 10,12,14 In an attempt to bridge the gap between these and classical illdefined WO 3 /SiO 2 catalysts, 1,2,16 we have recently investigated the synthesis of silica supported oxo alkylidene complexes, which present very high activity ( Figure 1b).…”

Recent Advances in High Oxidation State Mo and W Imido Alkylidene Chemistry

“…For example, it has been shown that ligands can be so sterically demanding that a 14e species simply does not react readily even with ethylene. A rare example of this type is Mo(NAdamantyl)(CHCMe 2 Ph)(Silox) 2 (Silox = OSi(t-Bu) 3 ), which is unchanged after being heated in toluene-d 8 under five atm of ethylene at 120 °C for several hours, in contrast to facile reactions of many other siloxide, aryloxide, or alkoxide derivatives xix. However, Mo(NAd)(CHCMe 2 Ph)(pyrrolide)(Silox) ( vide infra ) does react with ethylene and terminal olefins.…”

Rendering Schrock‐type Molybdenum Alkylidene Complexes Air Stable: User‐Friendly Precatalysts for Alkene Metathesis

“…50 % intact after four weeks). Other prototype molybdenum alkylidenes such as the triphenylsilanolate complex 4 [11] and the chiral variant 6 [12] also form adducts that remain intact when stored without any precautions for extended periods (Scheme 1).The structure of the particularly robust complex 3 in the solid state is depicted in Figure 1. The coordination geometry about the Mo VI center can be described as distorted octahedral, with the imido ligand and one of the two inequivalent hexafluoro-tert-butanolates residing trans to each other, even though the corresponding N3-Mo1-O2 angle (167.04(4)8) strongly deviates from linearity.…”