Organic reactions catalyzed by metal complexes are an effective way to improve atom economy and environmental friendliness for many synthetic transformations. Among the various synthetic transformations, hydrosilylation reaction has huge industrial applications for manufacturing consumer goods. The alkylsilanes from alkene hydrosilylation are widely used as raw materials in manufacturing silicon rubbers, molding implants and adhesive. The hydrosilylation reactions can also produce various organosilicon reagents, which are used in fine chemical synthesis for stereospecific oxidation and cross coupling reaction. Over the long decades, numerous reports on metal-catalyzed hydrosilylations include the use of platinum, palladium, rhodium, ruthenium, iridium, lanthanides and actinides, early transition metals, iron, cobalt to a limited extent nickel. This work has shown that readily accessible (iPrPDI)CoCl2 reacts with 2 equivalents NaEt3BH at -78 oC in toluene to generate a catalyst that effects highlyselective anti-Markovnikov hydrosilylation of the terminal double bond in alkene, 1,3- and 1,4-dienes. Primary and secondary silanes such as PhSiH3, Ph2SiH2 and PhSi(Me)H2 react with a broad spectrum of dienes without affecting the configuration of the other double bond. A slight modification of the reaction conditions using a less reactive silane (OEt)2Si(Me)H leads to unprecedented and highly selective reduction of the terminal double bond with no contamination from the silane or reduction products of the more substituted double bond. The major limitation for cobalt catalyzed hydrosilylation reaction using redox active PDI ligand is its terminal selectivity. However, this active catalyst did not work for 1,1-disubstituted alkenes. In this connection, we also observed efficient cobalt catalyst system for hydrosilylation of 1,1-disubstituted alkenes using chelating phosphine ligand at room temperature, which is able to do hydrosilylation for numerous substrates such as alkene, vinyl arene, conjugated diene, 1,4-skipped diene and 1,1-disubstituted alkenes. Carbocyclizations of a,¿-p-systems are extremely important and useful reactions for the synthesis of a variety of carbocyclic and heterocyclic compounds. Although metal catalyzed cyclization has been long known, controlling the selectivity (chemo- and regio-) remains an important challenge in this field. Nickel complexes have been known to be specifically effective for cyclic homo-and co-oligomerization of alkenes, alkynes and dienes. During the past few years, through an approach that relied mostly on mechanistic insights and systematic examination of ligand effects, RajanBabu group has discovered a number of protocols for Ni(II)-catalyzed heterodimerization reactions of vinylarenes, selected 1,3-dienes and strained olefins. Substitution of one of the phenyl groups of triphenylphosphine with a 2-benzyloxy-(e.g., L18), 2-benzyloxy-methyl-(L19) or 2-benzyloxyethyl-(L20) phenyl moiety results in a set of simple ligands, which exhibit strikingly different behavior in various nickel (II)-catalyzed olefin dimerization reactions including related cycloisomerization of 1,6-dienes. Nickel(II)-catalyzed cycloisomerization of 1,6-dienes into methylenecyclopentanes, a reaction mechanistically related to the other heterodimerization reactions, is also uniquely affected by nickel(II) complexes of L18, but not of L19 or L20. In an attempt to prepare authentic samples of the methylenecyclohexane products, nickel(II) complexes of N-heterocyclic carbene ligands were examined. In contrast to the phosphine, which gives the methylenecyclopentanes, methylenecyclohexanes are the major products in the N-heterocyclic carbine ligated nickel (II)-mediated reaction. This dissertation discusses the ligand effect on hydrofuctionalization of alkenes using nickel or cobalt metal complexes.