Cyclopentadienyl radical, molecular

N t/ l Five cyclopentadienyl molecular orbitals 4f Cyclopentadienyl cation (four 77 electrons) 4f Cyclopentadienyl radical (five 77 electrons) -H- Cyclopentadienyl anion (six 7r electrons)... 

The cyclopentadienyl radical is well established by ESR spectroscopy while the fate of the Sn(I) radical is uncertain183). It should nevertheless be noted that no Sn(III) radical is formed, proving again the difference between cyclopentadienylstannylenes and other molecular tin(II) compounds. 

Matsue et al. [43] attempted to study the molecular rocket reaction in a ruthenocene-/ -cyclodextrin inclusion compound using the I00Ru y, p) "raTc reaction. They noticed a parallel relationship between chemical processes and nuclear-recoil-induced processes in the non-included ruthenocene compound, as shown in Fig. 9. In the nuclear-recoil-induced processes no dimerization can be observed because of the extremely low concentration of the product, whereas in the chemical processes dimerization is possible, as demonstrated by Apostolidis et al. [48]. When ruthenocene included in /J-cyclodextrin is irradiated with y-rays, a part of the ruthenocene molecule is converted to [TcCp2-] which escapes from the jS-cyclodextrin cavity. The [TcCp2] rocket thus produced can attack neighboring inclusion compounds so as to extract the enclosed ruthenocene molecules and abstract H or Cp (Cp cyclopentadienyl radical). This process is shown schematically in Fig. 10. 

The degeneracy of the /a and is molecular orbitals in the cyclopentadienyl radical can be broken by the electronic effect of the substituent. The /A orbital has a node at Cl, and is unaffected, but the i /s orbital, with a high coefficient at Cl, has its energy raised by an electon-releasing substituent, and lowered by an electron-attracting substituent, placing the unpaired electron preferentially in the i /s or /a orbital, respectively, as shown in Figure 20-1. 

The state of the cyclopentadienyl radical may be described in terms of five molecular orbitals, which are formed from the jr-type orbitals of the five carbon atoms. These molecular orbitals, which are shown in Fig. 2, are one of iT-type (a), containing two electrons two of ZT-type c), containing one and two electrons,... 

Polymer-bound dinitrogen complexes containing Mn have been prepared [8] directly from the polymer bound (n5-vinylmethyl-cyclopentadienyl) tricar-bonylmanganese (VCM) and molecular nitrogen in THF/benzene. The metal-containing base polymer may be readily prepared by AIBN initiated radical polymerization of VCM with styrene or /V-vinylpyrrolidone (Fig. 4). 

Figure 4. Examples of low-temperature limit of rate constant of solid-state chamical reactions obtained in different laboratories of the USSR, United States, Canada, and Japan (1) formaldehyde polymerization chain growth (USSR, 1973 [56]) (2) reduction of coordination Fe-CO bond in heme group of mioglobin broken by laser pulse (United States, 1975 [65]) (3) H-atom transfer between neighboring radical pairs in y-irradiated dimethylglyoxime crystal (Japan, 1977, [72], (4, 5) H-atom abstraction by methyl radicals from neighboring molecules of glassy methanol matrix (4) and ethanol matrix (5) (Canada, United States, 1977 [11, 78]) (6) H-atom transfer under sterically hampered isomerization of aryl radicals (United States, 1978 [73]) (7) C-C bond formation in cyclopentadienyl biradicals (United States, 1979 [111]) (8) chain hydrobromination of ethylene (USSR, 1978 [119]) (9) chain chlorination of ethylene (USSR, 1986 [122]) (10) organic radical chlorination by molecular chlorine (USSR, 1980 [124,125]) (11) photochemical transfer of H atoms in doped monocrystals of fluorene (B. Prass, Y. P. Colpa, and D. Stehlik, J. Chem. Phys., in press.).

Five (yclopcntadienyl molecular orbitals Cyciopentadienyi cation (four 7T electrons) Cydopeufadienyi radical (five electrons) Cyclopentadienyl anion (six 71 electrons)... 

Five Q clopcDtadienyl molecular orbitals (tyi opentadienyi cation (four fT electrons) CVcIopenfadionyl radical five fx electrons) Cyclopentadienyl anion (.[Pg.596]

For the lanthanide metals, Sm, Eu, and Yb, which have a readily accessible ( + 2) oxidation state, oxidative addition reactions of M(1I) complexes with halogens and organic halides are dominated by the atom transfer or free radical mechanism (cf. 5.S.2.9.1.) in which two metal ions are each oxidized to the -I- 3 state. Numerous examples illustrate the ability of cyclopentadienyl or indenyl Ln(II) complexes (Ln = Sm, Eu, Yb) to abstract halogen atoms from molecular halogens ", halogenated solvents sueh as CH2CI2 and and alkyl halides . An archetypieal example is ... 

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