Metalloboranes and metal–boron bonding

Metallaboranes of the Early Transition Metals: Direct Synthesis and Characterization of [{(η5‐C5Me5)Ta}2BnHm] (n=4, m=10; n=5, m=11), [{(η5‐C5Me5)Ta}2B5H10(C6H4CH3)], and [{(η5‐C5Me5)TaCl}2B5H11]

“…Their structures are predicted by the electron-counting rules to be a bicapped tetrahedron (1), bicapped trigonal bipyramids (2, 3), and a nido structure based on a closo dodecahedron (4). Yellow tantalaborane 1 has a nido geometry with C 2v symmetry and is isostructural with [(Cp*M) 2 The spectroscopic data are consistent with the solid-state structure (Figure 1). Compound 1 is a dimetallatetrahedron capped on each Ta 2 B face by a BH 3 group such that extra four hydrogen atoms reside on the butterfly-shaped face generated by the Ta 2 B 2 tetrahedron.…”

“…The NMR spectra imply a diamagnetic compound. The mass spectrum of 2 is consistent with a formula containing two Ta and five B atoms, and the parent-ion mass corresponds to addition of a BH unit to [(Cp*Ta) 2 H and 13 C NMR spectra imply two equivalent Cp* ligands. Consistent with empirical observations, [26] the signal of one pair (B2 and B4 in Figure 3) is found at low field, whereas those of the other (B1 and B5) lie within the range typical of boranes.…”

“…Despite the availability of well-developed routes to metallaboranes of Group 6-9 metals, to our knowledge examples of characterized Group 5 metallaboranes are very rare. [21] Tantalaboranes [(Cp*Ta) 2 A C H T U N G T R E N N U N G (B 2 H 6 ) 2 ] [22] and [(Cp*Ta)Cl 2 B 4 H 8 ] [23] were synthe- (4) in modest yield. Compounds 1-3 are air-and moisture-sensitive but 4 is reasonably stable in air.…”

“…[1][2][3][4][5][6][7][8] Although it continues to be a topic of intense research, development in this area has been slow, [1,3,5,9,10] partly due to the lack of convenient high-yield synthetic methods. Synthetic methods for the generation of transition-metal cluster compounds have historically been based around conditions that favor more stable products.…”

“…The important geometrical differences among the bicapped tetrahedral cores of [(Cp*M) 2 [13a] On the other hand, the increased average Ta À B distance (2.38 ) and dihedral angle (1678) of the hydrogen-bridged butterfly may reflect the larger metal radius of Ta. Although the average BÀB distance in 1 is similar, that between the two capping boron atoms of 3.68 is much wider than those of its Cr and Re analogues.…”