Synthesis, structure, and dynamics of nickelacarboranes incorporating the [nido-7,9-C(2)B(9)H(11)](2)(-) ligand.

The nickelacarboranes [NEt 4 ][2-(η 3 -C 3 H 4 R)-closo-2,1,7-NiC 2 B 9 H 1 1 ] (R = H (1a), Ph (1b)) have been synthesized via reaction between [Na] 2 [nido-7,9-C 2 B 9 H 1 1 ] and [Ni 2 (μ-Br) 2 (η 3 -C 3 H 4 R) 2 ] in THF (THF = tetrahydrofuran), followed by addition of [NEt 4 ]Cl. Protonation of 1a in the presence of a donor ligand L affords the complexes [2,2-L 2 -closo-2,1,7-NiC 2 B 9 H 1 1 ] (L = CO (2), CNBu t (3)). Addition of PEt 3 (1 equiv) to 2 produces quantitative conversion to [2-CO-2-PEt3-closo-2,1,7-NiC 2 B 9 H 1 1 ], 4. Species 2-4 exhibit in solution hindered rotation of the NiL 2 fragment with respect to the η 5 -C 2 B 9 cage unit. Protonation of 1a in the presence of a diene affords the neutral complexes [2-(η 2 :η 2 -diene)-closo-2,1,7-NiC 2 B 9 H 1 1 ] (diene = C 5 Me 5 H (5), dcp (6), cod (7), nbd (8), chd (9), and cot (10a); dcp = dicyclopentadiene, cod = 1,5-cyclooctadiene, nbd = norbornadiene, chd = 1,3-cyclohexadiene, and cot = cyclooctatetraene). Variable temperature 1 H NMR experiments show that the {Ni(diene)} fragments are freely rotating even at 193 K. A small quantity of the di-cage species [2,2'-μ-(1,2:5,6-η-3,4:7,8-η-cot)-(closo-2,1,7-NiC 2 B 9 H 1 1 ) 2 ] (10b) is formed as a coproduct in the synthesis of 10a. This species can be rationally synthesized by protonation of 1a and subsequent addition of 10a.