Reaction of HgCl2 with two equivalents of MCl3 in an aromatic solvent yields Hg(arene)2(MCl4) 2 where arene = C6H5Me, C6H5Et, o-C6H4Me2, C6H3 -1,2,3-Me3, M = Al, Ga. Reaction of HgCl2 with MCl3 in benzene, m-xylene, and p-xylene results in the formation of liquid clathrates whose spectroscopic characterization is reported. In the solid state, all compounds, with the exception of o-xylene complexes, exist as neutral complexes in which two arenes are bound to the mercury and the MCl3 groups are bound through bridging chlorides to the mercury. o-xylene complex exists as a cation anion pair [Hg(o-C6H4Me 2)2(AlCl4)][AlCl4]. However, in solution all mercury-arene compounds exist as neutral complexes. The structures of Hg(arene)2(AlCl4)2 and [Hg(arene)2(AlCl 4)]+ have been optimized by DFT calculations to facilitate the assignment of the 13C CPMAS NMR spectra, and are in good agreement with the X-ray diffraction structures. Dissolution of Hg(arene)2(MCl4)2 in C6D6 results in a rapid H/D exchange and the formation of the appropriate dn-arene and C6D5H. H/D exchange between excess arene and C6D6 is also found to be catalyzed by Hg(arene)2(MCl4)2 including those with a different arene ligand. Based on DTF calculations the inter- and intra-molecular mechanism of the exchange is proposed. Mercury-arene complexes are found to be very active catalysts for the alkylation of arenes by olefins. Ethylene, propylene, and cyclohexene reacts with benzene or toluene to form mono- and polyalkylated products, the distribution being dependent on the nature of olefin. Based on the deuterium labeling experiments two different mechanisms of arene alkylation are discussed. Reaction of K[CpFe(CO)2] with a large excess of GaCl 3 yields [{CpFe(CO)2}Ga(Cl·GaCl3)(mu-Cl)] 2, while reactions with 1 and 0.5 equivalents yields [{CpFe(CO) 2}GaCl2]n, and [{CpFe(CO)2}2Ga(mu-Cl)] infinity, respectively. [{CpFe(CO)2}GaCl2] n reacts with MeCN to yield [CpFe(CO)2]GaCl2(MeCN). Reduction of [{CpFe(CO)2}2Ga(mu-Cl)]infinity with potassium in Et2O yields the previously reported [CpFe(CO) 2]3Ga and gallium metal. Reaction of K[CpFe(CO)2] with GaI3 yields [CpFe(CO)2]GaI2, which upon hydrolysis gives the unusual galloxane, [CpFe(CO)2]6Ga 6(mu3-O)4(mu-OH)2I2. Reaction of K[CpFe(CO)2] with InCl in toluene results in the formation of previously reported [CpFe(CO)2]3In and indium metal. Reaction of CpMo(CO)3H with Ga(tBu)3 yields [CpMo(CO)3]Ga(tBu)2 which forms a Lewis acid-base complex with MeCN: [CpMo(CO)3]Ga(tBu) 2(MeCN). The structure of [CpMo(CO)3]Ga(tBu) 2 shows evidence of unusual intra- and inter-molecular carbonyl &cdots; gallium interactions.