Mono-and dibenzoannelated [2.2]paracyclophanes 12 and 1 were synthesized by palladium-catalyzed twoand four-fold alkenylation of vicinal di-and tetrabromides 5 and 6, respectively, and subsequent electrocyclization/ dehydrogenation of the resulting (E,Z,E)-trienes. Further extensions of the annelated ring systems, leading to the tetrahydronaphthalene derivative 15, the bis-terphenylene derivative 16, and the benzobis[2.2]paracyclophane 18, were achieved through derivatization of suitable substituents introduced with the alkene coupling component. Mono-and polyanions of some derivatives were generated and studied by ESR, E N D O R , and N M R spectroscopy, as well as by cyclic voltammetry. The assembly of mutually orthogonal r-systems in arene annelated [2.2]paracyclophanes allows the reversible incorporation of up to six additional electrons per molecule, which is the upper limit for hydrocarbons reported to date. Recently, we developed a general method for annelating sixmembered carbocycles onto 1 ,2-dibromocycloalkenes1 ' by Heck-type12 alkenylation and subsequent cyclization/dehydrogenation of the resulting (E,Z,E)-1,3,5-trienes. Preliminary studied3 had previously established that this protocol is applicable to vicinal dibromoalkenes derived from (3) Jacobson, N.; Boekelheide, V.

ESR, ENDOR, and TRIPLE-resonance studies are reported on the radical anions of 7(1,0), 7(2,0), and 7(1,1) in which a completely rigid spacer separates two naphthalene n-moieties by 2, 4, and 6 C-C single bonds, respectively. Whereas 7(1,0)' has to be considered as a 'truly' charge-and spin-delocalized radical anion of a homobinaphthylene-like system, the frequency of intramolecular electron transfer in 7(2,0): and 7(1,1)7 is governed by the migration rate of the counterion (K+) between two equivalent sites at the n-moieties. Under conditions of tight ion pairing (solvent 2-methyltetrahydrofuran), the unpaired electron in 7(2,0)' and 7(1,1)7 is localized on one n-moiety and the pertinent spectra resemble that of the radical anion produced from an analogous mononaphthalene derivative 8. On the other hand, with solvents of higher cation-solvating power (1,2-dimethoxyethane or its mixtures with N, N, N,":N:'N"-hexamethylphosphoric triamide), delocalization of the electron spin over both n-moieties becomes evident, thus indicating that the electron-transfer rate exceeds the hypefie time-scale (cu. lo7 s-I). Simultaneous occurrence of 'localized' and 'delocalized' radical anions is also observed, in particular for 7(1,1)7. Previous findings for the radical anion of 6(1) which, l i e 7(1,1)7, contains two naphthalene n-moieties separated by 6 C-C single bonds are reinterpreted in the light of the results obtained in the present work. Exhaustive reduction of 7(2,0) and 7(1,1) leads to the formation of triplet dianions in which each of the two n-moieties houses one unpaired electron.Introduction. -Recently, much experimental evidence has been gathered, demonstrating that both thermal and photoinduced electron transfer between a donor and an acceptor can occur over distances that are considerably greater than the sum of the donor and acceptor van der Waals radii. From the studies of this long-range electron transfer, a picture is emerging of how the transfer rate depends on such factors as the driving force, the solvent and vibrational reorganization energies, and, in particular, the distance and orientation of the donor and the acceptor [ 11. The dependence of the transfer dynamics on the donor-acceptor distance and orientation can unambiguously be delineated when the donor and the acceptor are attached to a rigid spacer. Thus, in this respect, intramolecular electron transfer plays a pivotal role [2].High rates (> 109s-') of intramolecular thermal electron transfer in donor-spaceracceptor systems were determined from pulse radiolysis studies for the radical anions of 1 (donor = biphenyl radical anion, acceptor = cinnamoyl, spacer = steroid nucleus) and

arm protonated. The relatively long time scale for the onset of dissociation of one arm of the tpen ligand in acidic media as compared to the NMR experiment rules out the possibility of a dissociative enantiomerization process.Conclusions. [ Fe(tpen)] (C104)2-2/3H20 undergoes a spincrossover transformation with T, = 365 K in the solid state and T, = 363 K in a DMF solution. This is the first Fe" spin-crossover complex to have a spin-state interconversion rate in the solid state which is faster than can be sensed by 57Fe Mossbauer spectroscopy.The absence of intermolecular interactions, Le., a simple spinequilibrium for each [ Fe(tpen)12' complex, has been demonstrated by, inter alia, dilution studies with the isostructural Zn2+ complex. The results of X-ray structure determinations at 298 and 358 K show that the [Fe(tpen)12' complex has an appreciable trigonal twist up and beyond what is expected for an octahedral complex. Furthermore, this trigonal twist increases as the amount of high-spin content increases. It is suggested that the trigonal twist in [Fe(tpen)12+ leads to an increased spin-orbit interaction between 'Al and 5T2 states as a result of decreasing the energy of intermediate triplet states. This then results in an increased rate of spin-state interconversion. In solution [Fe(tpen)12' exhibits a relatively fast rate of enantiomerization which supports the idea that a trigonal twisting motion is coupled to the spin-state interconversion process.Acknowledgment. We are grateful for funding from National Institutes of Health Grant HLI 3652 (D.N.H.).Supplementary Material Available: Tables of anisotropic thermal parameters for [Fe(tpen)](C104)2 at 298 K and [Fe-(tpen)](C104)2.2/3H20 at 298 and 358 K, as well as chemical analysis, S7Fe Mossbauer, and magnetic susceptibility data and figures showing Mossbauer spectra, magnetic moment vs temperature plots, and temperature dependence of the 60-MHz 'H NMR spectrum of [Fe(tpen)]12 in 1:l MeOH/H,O (31 pages); listing of observed and calculated structure factors (36 pages).Ordering information is given on any current masthead page.

To find out whether the 1,4‐addition to 1,2:3,4‐diepoxides, which so far has been observed only once, is of a more general character, we investigated the reaction of a variety of O‐, C‐, N‐, and S‐nucleophiles with the model compound 1,2:3,4‐diepoxy‐2,3‐dimethylbutane (Scheme 4). In several cases, 1,4‐addition products could, indeed, be observed besides the expected 1,2‐adducts (Table).

ESR and ENDOR studies have been carried out on the radical cations obtained consecutively by reaction of rrans-lob, 10c-dimethyl-lob, 10c-dihydropyrene (4) with AICI, in CH,CI,. The primarily formed 4' rearranges at 253 K to the radical cation(s) of 1.6-(5a) and/or 1,8-dimethylpyrene (5b). At 323 K, the spectra of 5a'/5b' are replaced by that of the highly persistent radical cation of 1,3,6&tetramethylpyrene (6). Surprisingly, 6' is also the only observable paramagnetic product resulting from a treatment of 4,5,7,8-(l), 4,7,13,16-