1,4-Bis(triisopropylsilyl)buta-1,3-diyne and 1,4-bis(biphenyl-4-yl)buta-1,3-diyne.

We have been interested in the development of polyalkynebased stars and dendrimers and their reactions with Co2(CO)8 to produce organometallic cluster-decorated architectures (Constable et al., 2006). We have used Sonogashira palladiumcatalysed cross-coupling reactions (Sonogashira et al., 1975; Sonogashira, 2002) for the divergent assembly of polyalkynes containing rigid frameworks with well-de®ned structures. Under Sonogashira conditions, reactions between terminal alkynes (RC CH) and aryl halides can give rise to diynes (RC CÐC CR) as side-products (these most often arise from bromo precursors) (Sonogashira et al. 1975; Sonogashira 2002). Related reactions (Liu & Burton, 1997) or modi®ed Sonogashira conditions (Rossi et al., 1985) have been used for the speci®c formation of diynes. Two molecular cores that we have investigated are hexakis[(triisopropylsilyl)ethynyl]benzene and 4,40-bis(biphenyl-4-ylethynyl)biphenyl. During attempts to synthesize these compounds, we found that 1,4bis(triisopropylsilyl)buta-1,3-diyne, (I), and 1,4-bis(biphenyl4-yl)buta-1,3-diyne, (II), could be produced quantitatively. With the aim of preparing C6(C CSi Pr3)6, we treated C6I6 with six equivalents of Pr3SiC CH under Sonogashira crosscoupling conditions. Instead of the desired product, compound (I) was formed quantitatively under the conditions shown in the scheme. This was also the case when C6Br6 was used as the precursor. Similarly (see scheme), the palladium-catalysed cross-coupling reaction between 4-ethynylbiphenyl and 4,40dibromobiphenyl led to the quantitative formation of (II). Compounds (I) and (II) have been reported previously (Eisler et al., 2005; Hlavaty et al., 2002; Ried & Saxena, 1970; Toda & Tokumaru, 1990), but have not, to our knowledge, been structurally characterized. We report here their single-crystal structures, which illustrate a number of facets of weak CÐ H interactions in dictating solid-state structures. Such hydrogen bonds are now well established as important components in solid-state supramolecular assemblies (Desiraju, 2002, 2005; Desiraju & Steiner, 1999; Nishio, 2004; Nishio et al., 1998; Steiner, 2002), and their role in organic reactions has recently been assessed (Nishio, 2005).