Synthetic pathways to hydrogen-rich polysilylated arenes from trialkoxysilanes and other precursors

The use of tri(alkoxy)silanes (RO)₃SiH, which have recently become commercially available in greater than research scale quantities (R = Me, Et), has been probed for the preparation of hydrogen-rich arylsilanes ArSiH₃. It was found that the silylation of aryl-lithium or (in situ) aryl-Grignard reagents is followed by RO/H ligand redistribution and can lead to fully hydrogenated products in a one-pot reaction without employment of any additional metal hydride. After hydrolytic workup, the overall yields are between 20 and 30%. Silane gas and tetra(alkoxy)silanes are the main byproducts. At an early stage of the reactions, the whole set of mixed-ligand silanes (RO)_3-nH_nSiAr can be detected by GLC/MS techniques. Induced by the organometallic base, the reaction also includes aryl scrambling to give silanes Ar_nSiH_4-n, Ar_nSi(OR)_4-n, and Ar_nSi(H/OR)_4-n. A reaction scheme is proposed that accounts for the product distribution. Examples are given for Ar = phenyl, 4-biphenylyl, 4,4′-biphenyldiyl, 1-naphthyl, and 2-anisyl. The reaction gives only very poor yields of di(silyl)arenes. Silanes of this type were therefore prepared from (RO)₃SiH compounds and the corresponding di(halo)arenes by the in situ Grignard procedure followed by LiAlH₄ reduction. Representative cases are 1,2- and 1,4-di(silyl)benzene and 1,4-di(silyl)-2,5-dimethylbenzene. The primary reaction products 1,4-(EtO)₃SiC₆H₄Si(OEt)₃ and 1,4-[(EtO)₃Si]₂-2,5-(CH₃)₂C₆ H₂ have been isolated, and the crystal structure of the latter was determined.