7r-cyclopentadienyl

Harrison, W. Trotter, J. (1972) Crystal and molecular structure of tricarbony [(trimethylsilyl)-7r-cyclopentadienyl]rhenium, J. Chem. Soc. Dalton Trans., 678-681. 

Modification of the acceptor properties of the metal atom may be achieved by using complexes containing 7r-cyclopentadienyl ligands. 

An approach other than steric hindrance has been used to overcome the previously mentioned instability of the actinide homoalkyls. It was found that the inclusion of jT-bonding ligands in the coordination sphere considerably enhanced the stability of the alkyl complex. Recently, the same line of reasoning has also yielded a new series of 7r-cyclopentadienyl lanthanide alkyls (C5H5)2LnR where Ln =Gd, Er, Yb and R = C=C, and CH3 120,121). The infrared data for these complexes are consistent with u-bonded structures and the room temperature magnetic susceptibilities are very close to the free ion values. The actinide complexes (75,... 

The ESR spectra of a series of triarylboron anion radicals have been determined and show selective line-broadening effects (95). The radical anions of diborane, generated in an argon matrix at 77 K by irradiation with a-rays have been studied by ESR (121). The vanadium-aluminum complex obtained on mixing dichlorobis(7r-cyclopentadienyl)vanadium with ethylaluminum dichloride, a system that catalyzes the polymerization of ethylene to give a polymer with good characteristics, has been characterized by ESR and ultraviolet studies (44). 

However, its isoelectronic unsymmetrical counterpart, 7r-cyclopen-tadienyl-7r-cycloheptatrienylchromium(0) can be reduced to a stable anion radical (41). The orbital occupied by the unpaired electron has dominant ligand tt character. It appears to consist of a combination of the antibonding e2 MO s of the cyclopentadienyl (Cp) and cyclohepta-trienyl (Tr) 7r-systems with about one-third Cp and two-thirds Tr, respectively (41). Reduction of 7r-cyclopentadienyl-7r-methylcyclohepta-trienylchromium leads to an unstable radical anion that decomposes by loss of the seven-membered ligand (41). 

Still other 7r-cyclopentadienyl-metal compounds have been shown to undergo acylation. The successful acylation of cyclopentadienylmanganese tricarbonyl has opened up yet another interesting aromatic-type system for exploration (9, 10, 11, 13, 20, 45, 99). An example of this type concerns the benzoylation of methyl-cyclopen tadienylmanganese tricarbonyl (XII) (10, 45). Both l-methyl-2-ben-zoylcyclopentadienylmanganese tricarbonyl (XIII) and the corresponding 1,3-isomer (XIV) are readily obtained. 

The failure of various 7r-cyclopentadienyl-metal and 7r-arene-metal complexes to undergo aromatic-type substitution reactions does not necessarily mean... 

Recently, in a study of a large number of organo-iron compounds 120), it has been found possible to treat the isomer shift as being due to a sum of partial isomer shifts 8,. from individual ligands which for 7r-cyclopentadienyl derivatives could be correlated with proton NMR chemical shifts in the same compounds. The Mossbauer spectra of two cases of theoretical interest are worthy of mention. First, the spectra of both the mono- and binuclear iron tricarbonyl derivatives of cyclooctatetraene 115) show similar 8 and A values. The small 8 values are consistent with zero oxidation state for the iron atom and essentially complete covalent bonding between the iron and the tt electrons of the ring, so that, at least for the mononuclear... 

D. E. Bublitz and K. L. Rinehart, Jr., The Synthesis of Substituted Ferrocenes and Other 7r-Cyclopentadienyl-Transition Metal Compounds, Organic Reactions 17, 1 (1969). 

A number of readily reversible cr-7r rearrangements have been observed wherein a labile ligand such as carbon monoxide is lost by pyrolysis or photolysis, producing a coordinatively unsaturated metal center, which then regains coordinative saturation by means of a tr-n rearrangement. For example, irradiation of o--alkyl-7r-cyclopentadienyl-molybdenum tricarbonyl (15) produces the rr-allene complex (16) (25). These... 

The compounds CsHsM(CO)3X (M =Mo, W X = alkyl, Hal and so on) have square pyramidal structures with the 7r-cyclopentadienyl ring on top of the pyramid44-46. ... 

In one of the earliest detailed mass spectroscopic studies with transition metal organometallic compounds, Friedman, Irsa, and Wilkinson 3> showed that in the mass spectra of (C5H5) 2M derivatives the molecular ion was more stable in the covalent 7r-cyclopentadienyls than in the ionic cyclopentadienides. 

Several monosubstituted derivatives have been made in a similar manner, except that a unidentate ligand is used in place of the carbon monoxide, namely NH3, N2H4 (88) C2H4 (75) PPh3, AsPh3, CH3CN (231). Alternatively, substituted monooleiin derivatives have been synthesized by protonation of the metal a-allyl 7r-cyclopentadienyl tricarbonyl (55, 112). 

Similarly protonation of diphenylfulveneiron tricarbonyl generates a substituted 7r-cyclopentadienyl cation (241, 242). Hydride abstraction from cyclopentadieneiron tricarbonyl releases the 77-cyclopentadienyl cation complex (172). The Mossbauer spectra of the [CpFe(CO)3]1 cation and related iron carbonyl cations have been determined (121). 

Bisiir-cyclopentadienyllbislbenzenetellurolatolzircoiiiuinflV)1 A solution of phenyl lithium is prepared from 1.88 g (12 mmol) of bromobenzene and 0.20 g (29 mmol) of lithium in 40 ml of anhydrous diethyl ether. Under nitrogen, 1.53 g (12 mmol) of tellurium powder are added, and the mixture is stirred for 6h. Then, a suspension of 1.46 g (5.0 mmol) of bis[7r-cyclopentadienyl]dichlorozirconium in 30 ml of benzene is added and the mixture is stirred for 2 h. The solvent is removed under reduced pressure and the residue is recrystallized from benzene/hexane yield 2.4 g (77%). 

Hart-Davis AJ, Graham WAG. Silicon-transition metal chemistry. VI. Kinetics and mechanism of the replacement of triphenylsilane by triph-enylphosphine in hydridolriphenylsilyl(7r-cyclopentadienyl)dicarbonyhnanga-nese. J Am Chem Soc 1971 94(18) 4388-4393. 

C. Giannotti, andM. L. H. Green, Photo-induced Insertion of Bis-7r-cyclopentadienyl-tungsten into Aromatic Carbon-Hydrogen Bonds, J. Chem. Soc., Chem. Comm. 1972, 1114-1115. 

A98. N. N. Greenwood and T. C. Gibb, Mossbauer Spectroscopy. Chapman Hall, London, 1971. Chapter 9, pp. 221-238 Covalent iron compounds (41), treats binary carbonyls, carbonyl anions, hydride anions, substituted iron carbonyls, ferrocene and other 7r-cyclopentadienyl iron derivatives. 

Similarly, with spiro[4.4]nona-1,3-diene and spiro[2.4]hepta-4,6-diene, Fe(CO)5 produces the 7r-cyclopentadienyl-type binuclear complexes (248, reference 3), while Fe2(CO)fl affords the tt complexes (90) and (91), respectively. With the latter olefin, the complex of structure... 

Wilkinson had observed an associative exchange of CjH, rings analogous to that of (77-allyl)(7r-cyclopentadienyl)palladium and other related complexes discussed below. 

The reactivity of such compounds has been studied in detail 201-212). Substitution of the 7r-cyclopentadienyl group has been investigated for monocyclopentadienyl halogen and alkoxytitanium derivatives, dicyclo-pentadienyltitanium halides and alkoxides 201-211), and for (77-a llyl) (77-cyclopentadienyl)palladium 212a). The stereochemistry of these complexes has been confirmed unequivocally by physical methods including X-ray studies. The structures of (77-allyl)(7T-cyclopentadienyl)palladium 213) and of (77-cyclopentadienyl)titanium trichloride 214) are shown. 

Compounds of a specified type such as mono-7r-cyclopentadienyl derivatives (Table VIII) may be listed in such an ACQ matrix. For the sake of convenience the following two special features are present in the ACQ matrix of Table VIII. 

Since these important findings near the end of the last century, metal carbonyls of a majority of the transition metals have been isolated and characterized. Many of these compounds are pure metal carbonyls, containing only the metal and CO. Many other types are also known, including metal carbonyl-halides, -hydrides, -anions, -7r-cyclopentadienyls, etc. A number of earlier reviews dealing primarily with metal carbonyls has been published 169, 197). Fortunately, there are also two recent reviews on the subject by Abel ) and Hileman ISO). A useful, recent... 

By 1957, a variety of both 7r-cyclopentadienyl and arene-metal complexes was known, and it was interesting to determine whether mixed-sandwich complexes containing both of these ligands around the same could be produced. Two early examples of such complexes are given below ... 

Lithium benzenetellurolate and bis[7r-cyclopentadienyl]dichloroniobium(IV) in diethyl ether/benzene at 0° produced the very unstable bis[n-cyclopentadieny1 bis benzenetelluro-lato]niobium(IV) L... 

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