Cyclopentadienyl Grignard Reagents

Another convenient method of preparing this Jt-complex of iron is a two-step process in which the first step involves preparation of cyclopentadienyl Grignard reagent, such as 2,4-cyclopentadienylmagnesium bromide CsHsMgBr which may then be combined with ferric chloride to yield dicyclopen tadienyl iron ... 

In like manner, the addition product (110) of cyclopropanone and cyclopentadienyl Grignard reagent readily rearranges to the spiro ketone... 

Scheme 5.1 The proposed course of the reaction of the cyclopentadienyl Grignard reagent with FeCl3...

The first metallocene was discovered by accident independently by two groups. In one group, an attempt was made to synthesize fiilvalene by oxidation of the cyclopentadienyl Grignard reagent 112... 

Reaction of Cyclopentadienyl Grignard Reagent with Metal Salts Method 5)... 

Allyl Complexes. Allyl complexes of uranium are known and are usually stabilized by cyclopentadienyl ligands. AEyl complexes can be accessed via the interaction of a uranium halide and an allyl grignard reagent. This synthetic method was utilized to obtain a rare example of a "naked" homoleptic allyl complex, U(T -C2H )4 [12701 -96-17, which decomposes at 0°C. Other examples, which are more stable than the homoleptic allyl complex have been synthesized, ie, U(allyl)2(OR)2 (R = alkyl), U(allyl)2X (X = halide), and U(allyl)(bipy)2. 

Catenated Organic Compounds of the Group IV Elements, 4,1 Conjugate Addition of Grignard Reagents to Aromatic Systems, 1, 221 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365 Diene-Iron Carbonyl Complexes, 1, 1... 

On August 7, 1951, Kealy and Pauson reported the formation of Cp2pe starting from CpMgBr and FeCls (3.5 g from 9.05 g FeCls, Fig. 2) [2]. Initially, it was planned to form fulvalene via generation of a cyclopentadienyl radical by SET from Cp to Fe(lll), radical combination and subsequent oxidation of Cp2 by Fe(lll). Instead, Fe(ll) formed by reduction with the Grignard reagent reacted further by transmetallation. 

Complexes of (7)-C5H5)2Ti(III)R, where R may be an aryl, i)3-aUyl, or T 2-cyclopentadienyl group, are known. The aryl (40) and 7j3-allyl (41) complexes are prepared by reaction of bis(i)-cyclopentadienyl)titanium monochloride, or dichloride, with the appropriate Grignard reagent. 

A second group of complexes that have received detailed attention are the (i73-allyl)nickel(i75-cyclopentadienyl) complexes, which may be prepared by reacting nickelocene with an allyl-Grignard reagent (69). Data for typical examples are shown in Table IX. In this particular case, a sufficiently large number of complexes have been studied that a series of chemical shift increments can be extracted from the data (shown in Table X) and have been used with considerable success in assigning structures to ij3-allyl nickel complexes of unknown structure. 

As noted earlier, the chloride ligand in Cp3 And (An = Th, U, Np) is labile and this feature has facilitated the synthesis of a great many tris(cyclopentadienyl)actinide(IV) alkyl derivatives by metathesis with alkyllithium or Grignard reagents. The properties and reactivity of these complexes have been extensively studied and reviewed. They exhibit remarkable thermal stability. As members of the general class of CpsAnX complexes, they adopt the ubiquitous pseudotetrahedral coordination geometry that was illustrated earlier in (2). 

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