This paper presents aspects of the coordination chemistry of mono- and divalent manganese complexes supported by the anionic tris(phosphino)borate ligand, [PhBP^(iPr)_3] (where [PhBP^(iPr)_3] = [PhB(CH_2P^(iPr)_2)_3]-). The Mn(II) halide complexes, [PhBP^(iPr)_3]MnCl (1) and [PhBP^(iPr)_3]MnI (2), have been characterized by X-ray diffraction, SQUID magnetometry, and EPR spectroscopy. Compound 2 serves as a precursor to a series of Mn azide, alkyl, and amide species: [PhBP^(iPr)_3]Mn(N_3) (3), [PhBP^(iPr)_3]Mn(CH_2Ph) (4), [PhBP^(iPr)_3]Mn(Me) (5), [PhBP^(iPr)_3]Mn(NH(2,6-iPr_2-C_6H_3)) (6), [PhBP^(iPr)_3]Mn(dbabh) (7), and [PhBP^(iPr)_3]Mn(1-Ph(isoindolate)) (8). The complexes 2−8 feature a divalent-metal center and are pseudotetrahedral. They collectively represent an uncommon structural motif for low-coordinate, polyphosphine-supported Mn complexes. Two Mn(I) species have also been prepared. These include the Tl−Mn adduct [PhBP^(iPr)_3]Tl−MnBr(CO)_4 (9) and the octahedral complex [PhBP^(iPr)_3]Mn(CN^tBu)_3 (10). Some of our initial synthetic efforts to generate [PhBP^(iPr)_3]Mn_≡Nx species are briefly described, as are DFT studies that probe the electronic viability of these types of multiply bonded target structures.