Inclusion properties of 1,4-(triorganostannyl and -silyl)buta-1,3-diynes:: Thermal, structural, and NMR spectroscopic aspects

The tin-containing diyne Ph3SnC equivalent to CC equivalent to CSnPh3 (4) forms 1:1 host-guest complexes with a large variety of organic molecules. These complexes have been characterized by H-1 NMR spectroscopy, thermogravimetry (TGA), and differential scanning calorimetry (DSC). Weak interactions between the host and guest molecules are observed with toluene, tetrachloroethane, and p-xylene (the latter gives a 2:1 complex). Strong interactions are found with dichloromethane, chloroform, tetrahydrofuran, and dioxane. An intermediate behavior is observed with acetone, benzene, and pyridine. Guest-selectivity studies have been carried out on some of these complexes that confirm the results obtained from the TGA measurements. A single-crystal X-ray diffraction analysis of 4:dioxane shows that it has a true clathrate (cage) structure with the guest molecule being surrounded by 12 phenyl groups from 6 Ph3Sn moieties. Inclusion compounds do not form when the length of the spacer is shortened, i.e. with Ph3SnC equivalent to CSnPh3, or when the SnPh3 groups of 4 are replaced by SnMe3 moieties. On going from Ph3SnC equivalent to CC equivalent to CSnPh3 to Ph3Sn(CH2)(4)SnPh3, i.e. when the rigid diacetylene fragment is replaced by the flexible butanediyl group, formation of a clathrate is observed only in the case of dioxane. When Ph2PC equivalent to CC equivalent to CPPh2 or Ph3SiC equivalent to CC equivalent to CSiPh3 is used as host instead of Ph3SnC equivalent to CC equivalent to CSnPh3, there is no evidence for clathrate formation. However, in the case of Ph3SiC equivalent to CC equivalent to CSi*MePhNp (5: Np = 1-naphthyl), a 1:1 clathrate is obtained with dioxane. A single-crystal X-ray diffraction analysis of the 5:dioxane inclusion compound shows that the guest molecule lies exclusively in channels formed by phenyl substituents from the Ph3Si groups. Solid-state C-13, Sn-119, and Si-29 NMR and X-ray powder diffraction analyses have been carried out on 4:CHCl3, 4:dioxane and 5:dioxane prior to and after removal of the guest molecules, and the results demonstrate the structure-stabilizing ability of these molecules. It has been possible to obtain single crystals of 4 with no included solvent, and the X-ray crystal structure of this material shows that the organization of the diacetylenic compound is such that it leads to a more compact packing as compared to that found in 4:dioxane.