Reactions of M(N-2,6-i-Pr2C6H3)(CHR)(CH2R′)2 (M = Mo, W) complexes with alcohols to give olefin metathesis catalysts of the type M(N-2,6-i-Pr2C6H3)(CHR)(CH2R′)(OR")

The reaction between M(NAr)(CH-t-Bu)(CH2-t-Bu)(2) (M = Mo, W, Ar = 2,6-i-Pr2C6H3) and various alcohols (1-adamantyl-OH, t-BuOH, ArOH, (CF3)(2)CHOH, (CF3)(2)MeCOH, CF3Me2COH, (CF3)(3)COH, C6F5OH) in pentane or toluene yields either complexes of the type M(NAr)(CH-t-Bu)(CH2-t-Bu)(OR), through direct addition of ROH across a Mo-C bond, or complexes of the type M(NAr)(CH2-t-Bu)(3)(OR), through direct addition of ROH across a Mo=C bond. The trineopentyl species appear to be formed when the alcohol has a relatively low pK(a) value. The outcome also can depend on whether the alcohol is employed neat or in benzene, and mixtures are observed in some circumstances. The conversion of M(NAr)(CH2-t-Bu)(3)(OR) into M(NAr)(CH-t-Bu)(CH2-t-Bu)(OR) was shown to be unimolecular in several examples. Preliminary experiments have shown that M(NAr)(CH-t-Bu)(CH2-t-Bu)(OR) complexes are surprisingly active catalysts for various metathesis reactions, although conversion is sometimes limited by decomposition of intermediate alkylidenes to yield dimeric species that contain M=M bonds. In contrast, M(NAr)(CH-t-Bu)(CH2-t-Bu)(2) species are virtually inactive for metathesis. X-ray structures are reported for Mo(NAr)(CH2-t-Bu)(3)(OC6F5), Mo(NAr)(CH-t-Bu)(CH2-t-Bu)[OSi(O-t-Bu)(3)], [Mo(NAr)(CH-t-Bu)(CH2-t-Bu)(OC6F5)](2), and Mo(NAr)(CH-t-Bu)(CH2-t-Bu)(OC6F5)(PMe3).