Alkali-metal cyclopentadienides complexes

Alkali metal boratabenzenes have a wide synthetic applicability just like alkali metal cyclopentadienides. Two syntheses have been developed Ashe s synthesis via organotin intermediates (23) and our cyanide degradation of bis (boratabenzene) cobalt complexes (61). 

Reactions of the (Tj5-C5Hs)cobaIt-olefin complexes (26) prepared according to Eqs. (25) and (26) with alkali metals (Li, Na, K) in the presence of olefins lead to the elimination of the second C5H5 ligand from the cobalt (Scheme 5). Complexes 27a and 27b, or the mixed complex 27c are obtained in high yields [Eq. (28)]. The syntheses of the pure complexes 27a and 27b do not, of course, require the isolation of intermediates 26a and 26b. As mentioned previously, synthesis is readily achieved from cobaltocene (24) by reaction with either stoichiometric amounts or excess alkali metal in the presence of COD or ethylene [Eq. (24)]. The alkali metal cyclopentadienides which are formed are easily separated from the cobalt complexes and can be used for the synthesis of cobaltocene (51) [Scheme 5 Eq. (29)]. 

Alkali metal cyclopentadienide salts are important reagents in organometallic chemistry, having been used to prepare innumerable cyclopentadienyl complexes. Potassium cyclopentadienide, KCp, is usually made by deprotonation of cyclo-pentadiene with potassium metal either in organic solvents such as THF and benzene or in liquid ammonia, or by deprotonation with KH" or KOH. The analogous sodium compound, NaCp, was reported by the groups of Fischer and... 

For the synthesis of these derivatives, just as other Cp-complexes of REM, the reaction of anhydrous halides LnX3 with alkali metal cyclopentadienide at the ratio 1 2 is utilized [269-271, 275] ... 

The ionic heterobimetallic compounds of the general formula [(RxC5H5.x)2LnCl2]M(B) (M - Li, Na, K) are formed as a major product in the synthesis of REM cyclopenta-dienyl complexes via the metathesis reaction of LnClj with alkali metals cyclopentadienides at the ratio 1 2 [215, 221, 234, 269, 276, 277, 278, 279]. 

Many 7i-cyclopentadienyl complexes may be prepared from the reaction of alkali metal cyclopentadienides with ammonia-soluble transition metal salts such as nitrates and thiocyanates in liquid ammonia (2-30). The amine complexes, [M(NH3) ] (C5H5)2, lose ammonia when heated in vacuo, and the uncharged dicyclopentadienyl complexes of iron, cobalt, nickel, chromium, and manganese are obtained. 

Treatment of metal carbonyls with alkali metal cyclopentadienides in tetrahydrofuran can give u cyclopentadienyl metal complexes, e.g. 

The third class consists of the cyclopentadienides which behave chemically like the essentially ionic, alkali metal cyclopentadienides (see Vol. I). There is no abrupt transition between the ionic and covalent C5H5-metal bond. Indeed there is considerable ionic character in a number of complexes which are considered under the formal heading yr-cyclopenta-dienyl complexes . Even ferrocene, which is considerably covalent, has a charge separation between the metal atom and the tt-CsHs rings (see p. 102). Broadly speaking, the covalent character of the CsHs-metal bond increases steadily across the J-block transition series, i.e. with increasing atomic number, except in the case of manganocene which shows a sudden reversion to ionic character. This anomaly is discussed later. Transition metal cyclopentadienides are discussed on p. 110. 

Reaction of alkali metal cyclopentadienides with metal complexes. The most generally applicable and convenient method of preparation of jt-... 

The interaction of [MN(SiMe3)2] (M = Li, Na, K) and LiTMP with carbenes (1) (R = i-Pr, R = Me), (3) (R = i-Pr) and (4) (R = Me) in solution was also reported. Evidence of complexation of these carbenes with the Li, Na, and K species in solution was given by the NMR shifts for the relevant carbene center. Recently, the reaction of carbene (1) with lithium l,2,4-tris(trimethylsilyl)cyclopentadienide was reported to result in monomeric carbene complexes with 1 1 stoichiometry (R = H R = f-Bu (6), adamantyl (7), or 2,4,6-trimethylphenyl(8)). The crystal structure of (6) showed that the cyclopentadienyl ring is coordinated in an -fashion to the lithium center (see Alkali Metals Organometallic Chemistry) and there is a single a-interaction present between the lithium and the carbene center (Li-C(carbene)... 

Several types of supramolecular self-assembly are found in indenyl and fluorenyl complexes of the alkali metals. It has recently become possible for the first time to elucidate the crystal structures of unsolvated lithium indenide, [LiC9H7] , 26, and sodium fluorenide, [NaCoHgjn, 27 [24]. The crystal structure of 26 closely resembles that of unsolvated lithium cyclopentadienide because it also consists of a polymeric multidecker array in which the Li atoms are symmetrically coordinated by two rj -cyclopentadienyl rings of the indenyl ligands. In contrast, unsolvated sodium fluorenide, 27, forms a two-dimensional supramolecular structure in the solid state (Figure 7.3). In this unusual coordination polymer both the five- and six-membered rings of the fluorene system participate in coordination to sodium via and rj -interactions, respectively. 

Other naked phosphorns nnits inclnde the aromatic species P/ , P and P/ that are not stable as free ligands H P, HP and H Pg. Alkali salts of P/ and Pg can be isolated, whereas MP (M=Na, K) is only stable in dilnte solntions or in form of transition metal complexes where the Pj ring takes the place of a cyclopentadienide moiety. The closely related species P/ and Pjj " will not be discussed here, as they exhibit a complicated coupling pattern that cannot be discussed from a first-order point of view. 

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