Synthesis of Nickel−Monocarbollide Complexes by Oxidative Insertion

Treatment of the 11-vertex carborane anion [closo-2-CB10H11]- with Ni(0) reagents in tetrahydrofuran (THF) affordsvia oxidative insertion reactions12-vertex Ni(II) complexes, isolated as the salts [N(PPh3)2][2,2-L2-closo-2,1-NiCB10H11]
(L = CO (1a), CNBut (1b), and CNXyl (1c; Xyl = C6H3Me2-2,6); L2 = cod (1d; cod = 1,2:5,6-η-cyclo-octa-1,5-diene)). One CO ligand in 1a is readily replaced by donors L‘ in the presence of Me3NO to give the species
[N(PPh3)2][2-CO-2-L‘-closo-2,1-NiCB10H11] (L‘ = PEt3 (1e), PPh3 (1f), CNBut (1g), and CNXyl (1h)). The anionic
complexes themselves readily react with hydride abstracting reagents in the presence of donor ligands to yield
zwitterionic complexes in which boron vertexes bear substituents that are bound through C, N, or O atoms. Thus,
for example, 1c with H+ and CNXyl gives [2,2,7-(CNXyl)3-closo-2,1-NiCB10H10] (2b), while 1f with Me+ in the presence
of OEt2 affords [2-CO-2,11-{μ-PPh2(C6H4-o)}-7-OEt2-closo-2,1-NiCB10H9] (4), in which an additional cycloboronation
of one phosphine phenyl ring has occurred. In contrast, 1f with Me+ in the presence of NCMe gives a mixture of
the isomers [2-CO-2-PPh3-7-{(X)-N(Me)C(H)Me}-closo-2,1-NiCB10H10] (X ≡ E (5c) and Z (5d)). X-ray diffraction
analyses of compounds 1a, 2b, 4, and 5c confirmed their important structural features.