Synthesis of Molybdenum Olefin Metathesis Catalysts through Protonation Reactions

Chapter 1 The attempted syntheses of molybdenum imido alkylidene complexes of the type Mo(NArc,)(CH-t-Bu)[Biphen] and Mo(N-2-CF 3C6H4)(CHCMe 2Ph)[Biphen] (Biphen2 = 3,3'-di-t-butyl-5,5',6,6'-tetramethyl1,1'-biphenyl-2,2'-diolate) from Mo(NArcl)(CH-tBu)(OTf)2(dme) and [Biphen]K2 have sporadically afforded mixtures containing the desired products along with the corresponding amido alkylidyne complexes, Mo(NHArcl)(C-t-Bu)[Biphen] and Mo(NH-2-CF 3C6H4)(CCMe 2Ph)[Biphen], respectively. The reaction of [Biphen]K 2 with Mo(NArc,)(CH-t-Bu)(OTf) 2(dme) and 10 equivalents of triethylamine reproducibly gave Mo(NHArc,)(C-t-Bu)[Biphen] in 40% yield. An X-ray crystal structure of a related complex, Mo(NHArc,)(CCMe 2Ph)[SBiphen] confirmed the proposed structure and also revealed that one ortho chloride approaches within 2.93 A of the metal approximately trans to the alkylidyne ligand. Attempts to prepare three other amido alkylidyne complexes in an analogous manner from Mo(NR")(CH-t-Bu)(OTf)2(dme) (NR" = N-2-CF3C6H4, N-2,6-i-Pr2C6H 5, N-2,6Me2C6H5) with [Biphen]K2 in the presence of 10-20 equivalents of triethylamine failed. Chapter 2 The reaction between Mo(NAr)(CH-t-Bu)(CH2 -t-Bu)2 (Ar = 2,6-i-Pr2 C6 H3) and various alcohols (1-AdamantylOH, t-BuOH, ArOH, (CF3)2CHOH, (CF3)2MeCOH, (CF3)3COH, C6F5OH) in pentane or toluene yielded either complexes of the type Mo(NAr)(CH-tBu)(CH2-t-Bu)(OR) through direct addition of ROH across a Mo-C bond, or complexes of the type Mo(NAr)(CH 2-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 pKa. The outcome also can depend upon whether the alcohol is employed neat, or in benzene, and mixtures are observed in some circumstances. The conversion of Mo(NAr)(CH 2-t-Bu)3(OR) into Mo(NAr)(CH-t-Bu)(CH 2-t-Bu)(OR) was shown to be unimolecular in several examples. Mo(NAr)(CH-t-Bu)(CH2-t-Bu)(OR) complexes have been found to be surprisingly active catalysts for various metathesis reactions. In contrast, M(NAr)(CH-t-Bu)(CH2-t-Bu)2 species are virtually inactive for metathesis. Xray structures are reported for Mo(NAr)(CH2-t-Bu)3(OC6F5), Mo(NAr)(CH-t-Bu)(CH2-tBu)IOSi(O-t-Bu)3], [Mo(NAr)(CH-t-Bu)(CH 2-t-Bu)(OC6 F)1 2, and Mo(NAr)(CH-tBu)(CH 2-t-Bu)(OC 6F5)(PMe3).