The synthesis of reduced coordination (less than 6), unchelated manganese oxygen cluster systems is described. Addition of phenols to Mn(NR2)(2) (R = SiMe3) results in protolytic amide ligand replacement, and represents the primary entry into the described chemistry. Addition of PhOH to Mn(NR2)(2) results in the formation of the heteroleptic dimer Mn-2(mu-OPh)(2)(NR2)(2)(THF)(2) (1). Usage of the sterically larger 2,6-diphenylphenol (Ph2C6H3OH) as the ligand source results in the formation of a 3-coordinate heteroleptic dimer without THF coordination, Mn-2(mu-OC6H3Ph2)(2)(NR2)(2) (2). Attempts to generate 2 in the presence of THF or Et2O resulted in isolation of monomeric Mn(OC6H3Ph2)(2)L-2 (3, L = THF, Et2O). Use of the sterically intermediate 2,4,6-trimethylphenol (MesOH) resulted in formation of the linear trinuclear cluster Mn-3(mu-OMes)(4)(NR2)(2)(THF)(2) (4). Reaction of Mn(NR2)(2) with PhOH in the presence of water, or reaction of 1 with water, results in the formation of a 5-coordinate, unchelated Mn-O cluster, Mn-8(mu(5)-O)(2)(mu-OPh)(12)(THF)(6) (5). Preparation, structures, steric properties, and magnetic properties are presented. Notably, complex 5 exhibits a temperature-dependent phase transition between a 4-spin paramagnetic system at low temperature, and an 8-spin paramagnetic system at room temperature.