Synthesis of nickel-monocarbollide complexes by oxidative insertion

Treatment of the 11-vertex carborane anion [closo-2-CB(10)H(11)](-) with Ni(0) reagents in tetrahydrofuran (THF) affords-via oxidative insertion reactions-12-vertex Ni(II) complexes, isolated as the salts [N(PPh(3))(2)][2,2-L(2)-closo-2,1-NiCB(10)H(11)] (L = CO (1a), CNBu(t) (1b), and CNXyl (1c; Xyl = C(6)H(3)Me(2)-2,6); L(2) = cod (1d; cod = 1,2:5,6-eta-cyclo-octa-1,5-diene)). One CO ligand in 1a is readily replaced by donors L' in the presence of Me(3)NO to give the species [N(PPh(3))(2)][2-CO-2-L'-closo-2,1-NiCB(10)H(11)] (L' = PEt(3) (1e), PPh(3) (1f), CNBu(t) (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-NiCB(10)H(10)] (2b), while 1f with Me(+) in the presence of OEt(2) affords [2-CO-2,11-{mu-PPh(2)(C(6)H(4)-o)}-7-OEt(2)-closo-2,1-NiCB(10)H(9)] (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-PPh(3)-7-{(X)-N(Me)=C(H)Me}-closo-2,1-NiCB(10)H(10)] (X identical with E (5c) and Z (5d)). X-ray diffraction analyses of compounds 1a, 2b, 4, and 5c confirmed their important structural features.