Syntheses and reactions of ansa-[2,2-bis(η-cyclopentadienyl)propane]-tungsten and -molybdenum compounds

Abstract

Reaction between [MCl,(dme)] ( M = W or Mo; dme = 1.2-dimethoxyethane) with Li, [C,H,CMe,C,H,] gave the ansa-bridged metallocene dichlorides [M{(q-C,H,)CMe,(q-C,H,)}CI,]( M = W or Mo). Treatment of these with LiAIH, or ZnMe, gave respectively the dihydrides [M{(q-C,H,)CMe,(q-C,H,)}H,] (M = W or Mo) and the dimethyl derivatives [M{(q-C,H,)CMe,(q-C,H,)}Me,](M = W or Mo).Treatment of [W{(q-C,H,)CMe,(q-C,H,))Me,] with HX (X = PhCO, or NHJ) gave [W{(q-C,H,)CMe,-(q-C5H4)}Me(Y)] with Y = PhCO, or I, respectively. Both of these react with Na[AIH,(OCH,CH,OMe),] giving the methylhydride [W{(q-C,H,)CMe,(q-C,H,)}Me(H)].The latter is thermally stable in refluxing benzene. Ultraviolet photolysis of [Mo{(q-C,H,)CMe,(q-C,H,))H,] in benzene gave the phenylhydride derivative [ Mo{ (q-CsH4) CMe,(q -C,H,)}Ph( H )I ; the corresponding tungsten derivative [W{ (q -C,H,) -CMe,(q-C,H,)}H,] is not photosensitive. The crystal structures of [W{(q-C,H,)CMe,(q-C5H4)}Cf2],[W{(q-C,H,)CMe,(q-CsH4)}H2], (two modifications) and [Mo{(q-C,H,)CMe,(q-C,H,)}H,] have been determined by X-ray diffraction. The ansa-bridged bis(q-cyclopentadienyl) compounds show marked differences in reactivity compared to non-ansa analogues and this is discussed in terms of the modifications of the electronic structure as a consequence of the ansa bridge.

New ansa-2,2-bis(η-cyclopentadienyl)propane molybdenum and tungsten compounds and intramolecular hydrogen–deuterium exchange in methyl-hydride and ethyl-hydride derivatives

“…The synthons for the chemistry described below are the previously described compounds [M{(η-C 5 H 4 )CMe 2 (η-C 5 H 4 )}Cl 2 ] (M = Mo 1 or W 2) which were prepared from the reaction between [MCl 4 (dme)] (dme = 1,2-dimethoxyethane) and Li 2 -[(C 5 H 4 )CMe 2 (C 5 H 4 )]. 6 Owing to the especially low yields for 1, most of the reactions described below were undertaken purely for 2. During the work-up of the reaction mixtures the first formed solids of the reaction mixture were washed with ethanol.…”

“…Recently we described the synthesis and reactions of ansa-metallocenes of molybdenum and tungsten and found unexpected and interesting observations such as a substantially increased stability of the methylhydride [W{(η-C 5 H 4 )CMe 2 (η-C 5 H 4 )}Me(H)] towards reductive elimination of methane compared to the non-ansa analogue [W(η-C 5 H 5 ) 2 -Me(H)]. 5, 6 Here we describe further studies on the synthesis and reactions of ansa-metallocene derivatives of molybdenum and tungsten.…”

Understanding the reactivity of transition metal complexes involving multiple spin states

“…This phenomenon has been termed the "ansa effect". [39,40] Computations by Jennifer Green by the partial optimization method, restricted to the two tungsten systems, have provided a first rationalization of this behavior (see Figure 6). [41] The internal coordinate chosen for this particular study was the W-C bond length.…”

Theoretical investigation of the spin crossover transition states of the addition of methane to a series of Group 6 metallocenes using minimum energy crossing points

“…Experimental studies of thermal stability of alkyl hydrides give information on the pathways for alkane activation, which is the reverse of reductive elimination of alkanes. The three metallocene systems which have been most thoroughly studied, (C5H5)2W(H)(CH3), [5][6][7] (C5Me5)2W(H)(CH3) 8 and CMe2(C5H4)2W(H)(CH3) 9,10 show significant differences in their thermal stability. The unbridged methyl hydrides decompose over the range 40 -100° C eliminating methane, whereas the ansa-bridged compound is thermally stable up to 120° C. Thus there is a strong indication that the reactivity of the bare metallocenes are also likely to differ and that the ansa-bridged metallocene is likely to activate C-H bonds more readily than the others.…”