The reactivity of two Beta-dike-timinate coordinated magnesium(I) dimers, [LMgMgL], L=[(RNCMe)(2) CH](-) , R=C(6) H(3) iPr(2) -2,6 ((Dip) Nacnac(-) ) or mesityl ((Mes) Nacnac(-) ), towards a series of isonitriles and nitriles have been examined. Reactions with the isonitriles, RN equivalenceC: (R=tBu or C(6) H(3) Me(2) -2,6 (Xyl)), led to reductive C-C couplings and the formation of [ ((Dip) Nacnac)Mg (2) pi-(XylN=C-)(2) and [ ((Mes) Nacnac)Mg (2) pi-(tBuN=C-)(2) , or a reductive N-C cleavage and the generation of the magnesium cyanide complex, [ ((Dip) Nacnac)Mg(pi-CN) (3) ]. Reactions of the magnesium dimers with benzonitrile, PhCequivalenceN, afforded the C- C-coupled products, [((Dip) Nacnac)Mg[pi- N=C(Ph)- (2) ]Mg(NCPh)((Dip) Nacnac)], and [ ((Mes) Nacnac)Mg (2) [pi- N=C(Ph)- (2) ] (2) ], whereas the reductive C-C cleavage of tBuCequivalenceN gave rise to a mixture of [((Dip) Nacnac)Mg(tBu)(NCtBu)] and [ ((Dip) Nacnac)Mg(pi-CN) (3) ]. In contrast, a combination of net nitrile isomerization and C-C coupling processes was involved in the reduction of Me(3) SiCequivalenceN, which yielded [ ((Dip) Nacnac)Mg (2) pi-(Me(3) SiN=C-)(2) . All new compounds were crystallographically and spectroscopically characterized. The outcomes of the reported reactions were found to be dependent upon both the steric bulk of the magnesium(I) reagent, and the nature of the isonitrile/nitrile substituent. This combined with a high degree of selectivity for the reactions, indicates that magnesium(I) dimers may find use by organic and organometallic chemists as viable alternatives to currently available reducing agents that are utilized for the reduction of unsaturated organic substrates.