Synthesis of Molybdenum Imido Alkylidene Complexes That Contain Siloxides

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)(CHCMe 2 Ph)(Silox) 2 ( 1b ), Mo(NAd)(CHCMe 2 Ph)[OSi(SiMe 3 ) 3 ] 2 ( 4 ), Mo(NAd)(CHCMe 2 Ph)[OSi(O- t -Bu) 3 ] 2 ( 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 ═CHCMe 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 .