Electronic interactions in 1-ethynyl-2-phenyltetramethyldisilanes HCtriple bond; length of mdashCSiMe2SiMe2C6H4X

1-Ethynyl-2-phenyltetramethyldisilanes HCtriple bond; length of mdashCSiMe2SiMe2C6H4X [X = NMe2 (1), H (2), CH3 (3), Br (4), CF3 (5)] are accessible from ClSiMe2SiMe2Cl, BrMgC6H4X and HCtriple bond; length of mdashCMgBr in a two step Grignard reaction. The crystal structure of 1 as determined by single crystal X-ray crystallography exhibits a nearly planar PhNMe2 moiety and an unusual gauche array of the phenyl and the acetylene group with respect to rotation around the Si–Si bond. Full geometry optimization (B3LYP/6-31+G∗∗) of the gas phase structures of 1–5 affords minima for the gauche and the anti rotational isomers, both being very close in energy with a rotational barrier of only 3–5 kJ/mol. Experimental and calculated (time-dependent DFT B3LYP/TZVP) UV absorption data of 1–5 show pronounced electronic interactions of the HCtriple bond; length of mdashC– and the C6H4X π-systems with the central Si–Si bond.