The electroreduction of organo-substituted dichlorosilanes, Me2SiCl2, MeEtSiCl2, MePrSiCl2, MeHexSiCl(2), Me(c-Hex)SiCl2, MePhSiCl2, and Ph2SiCl2 in THF, is reported. A two-step reduction scheme (E-1: RR'SiCl2 reversible arrow [RR'SiCl2](-)(center dot) and E-2: [RR'SiCl2](-)(center dot) reversible arrow [RR'SiCl2](=)) is suggested in which the redox potentials E-1 and E-2 are separated by similar to 110 mV. A simulation of the irreversible voltammograms indicates multiple pathways in producing silyl anion, among them the decomposition of dianion and/or the disproportionation of silyl anion radicals, which is further corroborated by low-temperature cyclic voltammetric measurements. Subsequently, silyl anion undergoes S(N)2 nucleophilic attack on another chlorosilane molecule to form Si-Si bonds. Taft substituent constants have been applied and proved effective in correlating the substituent effect on the reduction of dichlorosilanes. For dialkyl-substituted chlorosilanes, the Taft analysis of the polar contribution of substituents to the cathodic peak shift gives a positive rho* similar to 2.4, which indicates an S(N)2 nucleophilic reaction in the formation of silyl dianion intermediate. The steric effect of substituents, however, is largely responsible for the stability of the SN2 transition state. (c) 2005 The Electrochemical Society. All rights reserved.