Metal-Rich Metallaboranes: Synthesis, Structures and Bonding of Bi- and Trimetallic Open-Faced Cobaltaboranes

Abstract

Synthesis, isolation, and structural characterization of unique metal rich diamagnetic cobaltaborane clusters are reported. They were obtained from reactions of monoborane as well as modified borohydride reagents with cobalt sources. For example, the reaction of [Cp*CoCl]2 with [LiBH4·THF] and subsequent photolysis with excess [BH3·THF] (THF = tetrahydrofuran) at room temperature afforded the 11-vertex tricobaltaborane nido-[(Cp*Co)3B8H10] (1, Cp* = η5-C5Me5). The reaction of Li[BH2S3] with the dicobaltaoctaborane(12) [(Cp*Co)2B6H10] yielded the 10-vertex nido-2,4-[(Cp*Co)2B8H12] cluster (2), extending the library of dicobaltadecaborane(14) analogues. Although cluster 1 adopts a classical 11-vertex-nido-geometry with one cobalt center and four boron atoms forming the open pentagonal face, it disobeys the Polyhedral Skeletal Electron Pair Theory (PSEPT). Compound 2 adopts a perfectly symmetrical 10-vertex-nido framework with a plane of symmetry bisecting the basal boron plane resulting in two {CoB3} units bridged at the base by two boron atoms and possesses the expected electron count. Both compounds were characterized in solution by multinuclear NMR and IR spectroscopies and by mass spectrometry. Single-crystal X-ray diffraction analyses confirmed the structures of the compounds. Additionally, density functional theory (DFT) calculations were performed in order to study and interpret the nature of bonding and electronic structures of these complexes.

Polyhedral and Macropolyhedral Metal-Rich Cobaltaboranes: A 25-Vertex Hourglass-Shaped Cluster

“…Thus, we have used thin layer chromatography (TLC) that allowed us to perform the characterizations both spectroscopic and structural of the pure material of 2 . The reaction also yielded some low yielded cobaltaboranes, VI , VII , and VIII , reported earlier by Grimes and us …”

“…Having isolated several such cobaltaboranes by others and us, we aspired to parallelize their spectroscopic and structural data. Table listed such types of clusters that contrast the structural data and 11 B chemical shifts with formal electron counts of 12 SEPs …”

Thiolate-Bridged Heterodinuclear Manganese–Cobalt Complexes with Bridging Hydride Ligands

“…The reactions progressed with a change in color from red to brown leading to the formation of di- and trichalcogenate-bridged heterobimetallic MnCo complexes 1–6 , albeit in poor yields. Note that, in addition to 1–6 , the reactions also yielded known (hyper) nido -[(Cp*Co) 3 B 8 H 10 ] and few other species that could not be isolated due to lower yields. It should also be mentioned here that the reaction with Li­[BH 3 TePh] afforded compounds that were sensitive to air and moisture, in poor yields, and hence, we were unable to isolate them.…”

“…The solid residue underwent chromatographic workup on TLC plates {elution with n -hexane/CH 2 Cl 2 [60:40 (v/v)]} after the volatiles had been removed from the filtrate. This afforded violet 1 (0.056 g, 10%), green 2 (0.069 g, 11%), and orange 3 (0.012 g, 3%) along with (hyper) nido -[(Cp*Co) 3 B 8 H 10 ] and a few low-yield products that could not be isolated.…”

“…By following the same procedure that was used for compounds 1–3 , compounds 4–7 were synthesized by using a freshly prepared THF solution of Li­[BH 3 SePh] (1.04 mmol, in 10 mL). Elution with n -hexane/CH 2 Cl 2 [80:20 (v/v)] on TLC plates afforded brown 4 (0.049 g, 8%), brown 5 (0.080 g, 10%), and orange 6 + 7 (0.024 g, 6%) along with (hyper) nido -[(Cp*Co) 3 B 8 H 10 ] and a few low-yield products that could not be isolated.…”