Synthesis and reactivity of new silyl-substituted monocyclopentadienyl molybdenum and tungsten complexes

Abstract

The functionalized silylated cyclopentadienyl molybdenum and tungsten complexes [MCp Cl(CO) 3H] (M=Mo, W; Cp Cl= η 5-C 5H 4SiMe 2Cl) are prepared easily from the reaction of [M(CO) 3(NCMe) 3] with C 5H 5SiMe 2Cl in refluxing THF, via C–H activation and H transfer to the metal centre. Metathetical replacement of hydride by chloride is readily achieved when their methylene chloride solutions are treated with a few milliliters of CCl 4 to give the chloro complexes [MCp Cl(CO) 3Cl] (M=Mo, W). The chloro–molybdenum complexes react with 1/2 equivalent of deoxygenated water to give the corresponding dinuclear complexes [{Mo(CO) 3X} 2( μ-Cp OCp)], (X=H, Cl; Cp OCp= η 5-C 5H 4-SiMe 2-O-SiMe 2- η 5-C 5H 4), whereas their reaction with one equivalent of anhydrous LiOH in toluene leads to selective substitution of the silicon-bonded chlorine atom to give the hydroxo complexes [MoCp OH(CO) 3X] (X=H, Cl; Cp OH= η 5-C 5H 4SiMe 2OH). These hydroxosilyl complexes can be transformed into the dinuclear compounds [{Mo(CO) 3X} 2( μ-Cp OCp)] by heating (50°C, 2 h) or by their reaction with one equivalent of the respective hydrido and chloro derivatives [MoCp Cl(CO) 3X]. Total decarbonylation of the hydrido compounds results from oxidation with a stoichiometric amount of PCl 5 to give the paramagnetic molybdenum(V) and tungsten(V) complexes [MCp ClCl 4] (M=Mo, W). Reactions of these complexes with one equivalent of NH 2R in the presence of NEt 3 yield the imido derivatives [MCp Cl(NR)Cl 2] (M=Mo, R=2,6-Me 2-Ph; M=W, R= t Bu) and subsequent oxidation of the tungsten complex with 1/2 equivalent of PCl 5 gives [WCp Cl(N t Bu)Cl 3]. Reduction of [MoCp ClCl 4] with two equivalents of Na/Hg gives the dinuclear molybdenum(III) complex [MoCp Cl] 2( μ-Cl) 4. All of the reported compounds were characterized by elemental analysis and 1H- and 13C NMR-spectroscopy.