Novel anionic metallacycles (6: [(1) W(CO)₄]; 7: ([(2) W(CO)₄])₂; 8: [(3) W(CO)₄]; 9: [(4) W(CO)₄]; and 10: [(5) W(CO)₄]) were selectively synthesized from the reaction of the flexible anionic pnictogenylborane derivatives [M(C₁₂H₂₄O₆)][H₂E-BH₂-EH₂] [E = P, M = Na (1); E = As, M = K (2)], [Na(C₁₂H₂₄O₆)][H₂As-BH₂-PH₂-BH₂-AsH₂] (3), and [Na(C₁₂H₂₄O₆)(thf)₂][^tBuHE-BH₂-EH^tBu] [E = P (4); E = As (5)], with [W(CO)₄(nbd)] (nbd = bicyclo[2.2.1]hepta-2,5-diene). In addition, the reaction of 1, 4, and 5 with [Cu(MeCN)₄][BF₄] leads to unique coordination assemblies of the general formula [Cu₂Na₂(RHE-BH₂-EHR)₄]_n[E = P, R = H (11); E = P, R = ^tBu (12); E = As, R = ^tBu (13)]. The solid-state structure of compound 11 possesses an inorganic 3D scaffold with an adamantane-like repeating unit of Cu(I) ions.