Cockcroft. Z. Anorg. A/lg. Chem. 1991, 59x1599. 25. The sample was hydrolyzed, and the ammonia formed was precipitated with Hg,(NO,), as [HgNH,]NO, . a ) RbTh,,N,C12,: space group P i (no. 2). Z=1; P2, diffractometer, Mo,, radiation. 1. =71.073 pm; u =1071.95(10), b =1198.44 (11), c = 1210.12(11) pm, a =112.676(7). /r =102.443 (7), y =104.952 (7)"; 4597 reflections. 4595 unique. 3899 with Fo t 3u(F0); R = 0.0416, R, = 0.0420, pE.l,id = 5.1 g~m -~: b) KTh,,N,Br,,: space group Pnnm (no. 58). 2 = 2: P2, diffractometer. Mo,, radiation, E. =71.073 pm; u =1752.4(4). b =1194.3(2), c = 1403.1(3) pni; 9720 reflections. 2418 unique, 2172 with Fo t 3u(F0); R = 0.0589. R, = 0.0445, [ i r r l L d = 5.909 gcm-3. Further details of the crystal structure investigation may he obtained from the Fachinformationszentrum Karlsruhe. D-76344 Eggenstein-Leopoldshafen (FRG), on quoting the depository number CSD-58681.

The synthesis of fused organometallic dehydroannulenes containing cyclobutadiene(cyclopentadienyl)cobalt or ferrocene units separated by butadiyne linkers is presented. Starting from the corresponding 1,2-diethynylated sandwich complexes, either Eglinton, Hay, or Vögtle-type coupling furnishes the desired dehydroannulenes. The choice of the coupling variant is critical for the success of this reaction. It was found that for diethynylferrocene a variant of the classic Eglinton system utilizing a Cu2Cl2/CuCl2 mixture in pyridine works successfully, while for the case of the cyclobutadiene(cyclopentadienyl)cobalt complexes the Vögtle coupling utilizing Cu(OAc)2 in acetonitrile gave the most impressive results, leading to a 87% yield of cyclized material. To obtain perethynylated organometallic dehydroannulenes, a novel synthesis of tetraethynylated cyclobutadiene complexes was developed. Flash vacuum pyrolysis of a bisbutadiynylated CpCo-ligated cyclobutadiene furnishes the desired tetraethynylated cyclobutadiene complex via a Bergman-type rearrangement. The two TMS and two TIPS substituents of the cyclobutadiene complex are oriented pairwise ortho with respect to each other. Removal of the TMS groups accesses a monomer, which under the conditions of the Vögtle coupling cyclizes to novel trimeric and tetrameric, perethynylated, cyclobutadieno fused, organometallic dehydroannulenes.

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