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Abstract Reaction of Tl(OTf) with 2 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) in THF results in formation of [Tl(BAC)₂(OTf)] (1) in moderate yields. Subsequent reaction of1with [K][H₂‐9‐BBN] ([H₂‐9‐BBN]⁻ = dihydrido 9‐boratabicyclo[3.3.1]nonane) in THF results in formation of [Tl(BAC)(μ‐H₂‐9‐BBN)]₂(3), also in moderate yield. Complex3is the first reported thallium borohydride. We attribute its thermal stability to the strong donor ability of the BAC co‐ligand. Both1and3exhibit trigonal pyramidal geometries about Tl⁺in the solid‐state, indicative of the presence of stereochemically active lone pairs. The hydride environment in3is calculated to exhibit a 3.9 ppm downfield shift attributed to spin‐orbit effects from the adjacent Tl center. 

Reaction of [Ni(1,5-cod) 2 ] (30 equiv.) with PEt 3 (46 equiv.) and S 8 (1.9 equiv.) in toluene, followed by heating at 115 °C for 16 h, results in the formation of the atomically precise nanocluster (APNC), [Ni 30 S 16 (PEt 3 ) 11 ] (1), in 14% isolated yield. Complex 1 represents the largest open-shell Ni APNC yet isolated. In the solid state, 1 features a compact “metal-like” core indicative of a high degree of Ni–Ni bonding. Additionally, SQUID magnetometry suggests that 1 possesses a manifold of closely-spaced electronic states near the HOMO–LUMO gap. In situ monitoring by ESI-MS and 31 P{ 1 H} NMR spectroscopy reveal that 1 forms via the intermediacy of smaller APNCs, including [Ni 8 S 5 (PEt 3 ) 7 ] and [Ni 26 S 14 (PEt 3 ) 10 ] (2). The latter APNC was also characterized by X-ray crystallography and features a nearly identical core structure to that found in 1. This work demonstrates that large APNCs with a high degree of metal–metal bonding are isolable for nickel, and not just the noble metals.