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The reaction ofY(DAC)(CH2SiMe3) (1) with phenylacetylene produces an equilibrium mixture of the alkynide-coupled butatrienediyl complex [ (µ-µ• (Z)-PhC=C-C=CPh) (2) and the uncoupled bridging alkynide dimer [(DAC)Y(p-C=CPh)]2 (3). Unlike other butatrienediyl complexes of yttrium or the lanthanides, this unit adopts a Z conformation in complex 2.Recently, we reported the synthesis and thermal stability of a monomeric yttrium alkyl complex, (DAC)Y-(CILSiMes) (1), containing the deprotonated macrocycle 4,13-diaza-18-crown-6 (DAC)* 1 as the only ancillary ligand.2 In our earlier studies, it became apparent that the DAC ligand is the approximate steric equivalent of two Cp* units.34 4However, in terms of electronic properties, DAC differs substantially from two Cp* ligands, since it can donate a variable number of electrons to the metal center. In addition, the coordination geometry provided by DAC is more flexible than that of the bis-Cp* system. Currently, we are exploring the reactivity of 1 with small molecules in order to develop a better understanding of ancillary ligand effects in group 3 and f-element chemistry.5Earlier work by Evans,6 Teuben,7 and Marks8 revealed a fascinating reaction in which two bridging alkynide units couple to form a butatrienediyl complex, several examples of which have been characterized by X-ray crystallography (eq 1). Interestingly, this reaction [Cp*2Ln(/f-C=CR)]2 -[Cp*2Ln]2^-(E)-RC=C=C=CR] (1)

The preparation of hydroxy bridged complexes, [M,(OH) ,

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. Can. J. Chem. 57, 3080 (1979).The crystal structure of syn-2,l I-dithia[3,3]metacyclophane, C16H16S2, has been determined by single crystal X-ray diffraction and refined to an R-value of 0.049. The crystal is monoclinic with cell dimensions a = 1898.2(5), b = 795.7(3), c = 924.1(4) pm, p = 100.03"(4). The 'Hmr data have been re-examined and compared with those obtained for other cyclophanes, together with 13Cmr data and are consistent with the fact that in solution 2,ll-dithia[3,3]metacyclophane, 1, exists as the syn-conformer with no appreciable participation of the anriconformer. All related dithia[3,3]metacyciophanes which have internal aryl hydrogens (i.e., no internal substituents) likewise appear to be syn from 'Wmr data.