Synthesis of Molybdenum Imido Alkylidene Complexes That Contain Siloxides

Monosiloxide and disiloxide complexes have been prepared through the addition of silanols to Mo(NR)(CHCMe2Ph)(pyrrolyl)2 species [R = 1-adamantyl (Ad) or 2,6-i-Pr2C6H3 (Ar)]. The silanols employed include (t-Bu)3SiOH (HSilox), (i-Pr)3SiOH, (Me3Si)3SiOH, (t-Bu-O)3SiOH, Me2(t-Bu)SiOH, and Ph3SiOH. The monoSilox complex, Mo(NAr)(CHCMe2Ph)(Silox)(pyrrolyl) (2a), could be isolated, while Mo(NAd)(CHCMe2Ph)(Silox)(pyrrolyl) was observed in situ but could not be crystallized. Disiloxides that could be crystallized include Mo(NAd)(CHCMe2Ph)(Silox)2 (1b), Mo(NAd)(CHCMe2Ph)[OSi(SiMe3)3]2 (4), Mo(NAd)(CHCMe2Ph)[OSi(O-t-Bu)3]2 (5), and Mo(NAr)(CHCMe2Ph)[OSiMe2(t-Bu)]2 (6); other disiloxide examples could be observed in situ but could not be crystallized. Compound 2a reacts readily with (CF3)Me2COH, (CF3)2MeCOH, (CF3)2CHOH, ArOH, C6F5OH, (−)-menthol, and (−)-borneol to give compounds of the type Mo(NAr)(CHCMe2Ph)(Silox)(OR) (3a−g) in situ. No reaction was observed upon heating of 1b under 5 atm of ethylene at 120 °C in toluene-d8; only at 240 °C in o-dichlorobenzene-d4 did 1b react with ethylene to yield CH2CHCMe2Ph, but the Mo-containing product could not be identified. Compound 2a reacts with ethylene at 120 °C to give Mo(NAr)(CH2)(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.