Refined general procedures for the preparation of arylcalcium halides were developed recently [1, 2] and a variety of monometalated and even dimetalated derivatives [3] were synthesized and isolated by reaction of the corresponding aryl iodides (or bromides) and activated calcium. However, the availability of derivatives containing coplanar extended p-systems seems to be limited. Although a few naphthylcalcium complexes have been reported, [2a, 4] it was noticed earlier that introduction of an additional phenyl group in the para-position of an aryl iodide prevented isolation of the corresponding 4-biphenylylcalcium iodide. [2b] In contrast, doubly reduced 1,3,5-triphenylbenzene radical dianions [5] were isolated from the reduction of 2,4,6-triphenylphenyl halides with activated calcium and subsequent ether degradation reactions. The formation of arene radical anions represents the basic reaction step in Birch [6] or Benkeser [7] reduction reactions. The observed (and rather unexpected) inaccessibility of simple and substituted 4-biphenylylcalcium derivatives of polycyclic aromatic hydrocarbons (PAH) clearly limits the synthetic value of organocalcium compounds, especially since the related lithium [8] and magnesium [9] derivatives can be prepared with good yields on a large scale. The unexpected behavior of the naphthyl derivatives seems to be related to the extremely negative second reduction potential of the parent naphthalene, [10] preventing it from being doubly reduced under the applied conditions.In general, bromo-and iodo-arenes with extended p-systems offer two reaction pathways with calcium, namely the electron transfer into the p*-system of the PAH and the formal insertion of this alkaline earth metal into the carbonÀhalogen bond yielding a Grignard-type reagent. This investigation was aimed at identifying reaction conditions to separate the two reactivities from each other and to evaluate conditions for an efficient synthesis of polycyclic arylcalcium halides.Generally, simple polycyclic aromatic hydrocarbons can be reduced to radical anions with biphenyl showing the highest first reduction potentials (E 1 = À2.68 V, E 2 = À3.18 V) except for benzene, lower reduction potentials were determined for instance for phenanthrene (E 1 = À2.49 V, E 2 = À3.13 V). [10] These radical anions and dianions [11] represent intermediates in Birch-type reduction reactions of arenes (Scheme 1). [12] In liquid ammonia also containing THF (to raise the solubility of biphenyl) approximately equimolar amounts of calcium and 4-bromobiphenyl gave a red suspension. After protolysis with methanol, a mixture of starting 4-bromobiphenyl and dihydrobiphenyl was observed with an approximate 3:1 ratio of 1,4-dihydrobiphenyl and 3,4-dihydrobiphenyl. [13] In order to gain more information on the red solid formed in this reaction, equimolar amounts of biphenyl and calcium were used in a second run, resulting again in the formation of a red precipitate, which was isolated and yielded 1,4-dihydrobiphenyl and 3,4-dihydrobiphenyl (ra...