Neutral, trialkylruthenium complexes Ru(N)R3L (R = CH3, CH2SiMe3; L = pyridine, 2,6-lutidine, 4-picoline, PMe3, CNCMe3) were prepared by the reaction of [Ru(N)R4]- salts with HBF4 and the ligand, L. The molecular structure of Ru(N)(CH2SiMe33(py) was determined by X-ray diffraction. Crystals of Ru(N)(CH2SiMe3)3(py) are monoclinic in space group. P2(1)/n with a - 14.551(5) angstrom, b = 9.113(4) angstrom, c = 19.801(5) angstrom, alpha = gamma = 90-degrees, beta = 109.27(2), Z = 4, R = 0.032 and R(w) = 0.039. The neutral dialkyl complex, Ru(N)R2Cl, is in equilibrium with the dimer and adds a variety of neutral, two-electron ligands. Cationic complexes [Ru(N)R2L2][BF]4] (R=CH3, CH2SiMe3;L=NCCH3, pyridine) were prepared by the reactions of Ru(N)R3L with HBF4 and additional ligand. The addition of concentrated HNO3(aq) to [Ru(NO)R4]- gave the nitrato complexes [Ru(N)R2(ONO2)2]-. The complexes [Ru(N)R2L2][BF4] react with water to form the mu-hydroxo dimers, {Ru(N)R2(mu-OH)}2. The molecular structure of {Ru(N)(CH)2SiMe3)2(mu-OH)} was determined by X-ray diffraction. Crystals of {RU(N)(CH)]2SiMe3)2(mu-OH)} are monoclinic in space group P2(1)/a with a = 11.510(8) angstrom, b = 20.440(8) angstrom, c = 12.858(4) angstrom, alpha = gamma = 90-degrees, beta = 109.04, Z = 4, R = 0.027 and R(w) = 0.029. The acetonitrile complex, [Ru(N)(CH2SiMe3)2(NCMe)2][BF4], is a catalyst for the polymerization of ethylene.