Three coordinate phosphorus and boron as π-donor and π-acceptor moieties respectively, in conjugated organic molecules for nonlinear optics: crystal and molecular structures of E-Ph–CHCH–B(mes)2, E-4-MeO–C6H4–CHCH-B(mes)2, and E-Ph2P–CHCH–B(mes)2[mes = 2,4,6-Me3C6H2]

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Abstract
Hydroboration of π-donor substituted alkynes D–CC–H [D = Ph2P, 4-X–C6H4-(X = H, MeS, MeO, H2N), and (η5-C5H5)Fe(η5-C5H4-)] with dimesitylborane {[(mes)2BH]2, mes = 2,4,6-Me3C6H2} yields air-stable ‘push–pull’E-alkenes of the form E-D–CHCH–B(mes)2, which possess large molecular hyperpolarizabilities, β, as shown by electric-field induced second-harmonic generation (EFISH) experiments at 1.91 µm; single crystal X-ray diffraction studies indicate that E-Ph–CHCH–B(mes)2 and E-4-MeO–C6H4–CHCH–B(mes)2 crystallise in centrosymmetric space groups, whereas E-Ph2P–CHCH–B(mes)2 crystallises in the acentric space group P212121 and exhibits powder SHG of 1.064 µm laser light.