Possible planar hypercoordinate molecules with first row d-block metal atoms in the centers of boron rings are explored comprehensively by density-functional theory (DFT) computations. Many optimized MB, (n = 7, 8, 9, and 10) neutral and charged clusters have local D-nh minima, although these may not be the most stable isomers. The larger 69 and 610 rings are versatile in accommodating first row d-block metals, whereas the more compact 138 ring only can enclose smaller transition metals (such as Mn, Fe, and Co) effectively. Delocalized pi and radial molecular orbitals involving boron are crucial in stabilizing these highly symmetrical planar hypercoordinate molecules. Early and middle transition metal d-orbitals participate in metal-boron covalent bonding, whereas partial ionic bonding is more important for the late d-block elements. Potential energy surface scans established several of these species to have planar hypercoordinate global minima: D-8h FeB82-was identified here, and D-8h CoB8- and D-9h FeB9- were identified in an earlier complementary study.