Organotransition-Metal Metallacarboranes. 43. Directed Synthesis of Carborane-Endcapped Multidecker Sandwiches^1,2

Triple-decker and tetradecker sandwich complexes having planar C2B3 or pyramidal C2B4 carborane ligands at one or both ends, the first examples of this genre, were prepared and characterized. A 3-way reaction of the Cp*Co(2,3-Et₂C₂B₃H₂-5-Me)^2–and 2,3-Et₂C₂B₄H₄ ^2–dianions with CoCl₂ gave the diamagnetic 30 ve (valence electron) triple-decker Cp*Co(Et2C2B3H2Me)CoH(Et2C₂B₄H4) (2) and the paramagnetic 29 ve triple-decker Cp*Co-(Et₂C₂B₃H₂Me)Co(Et₂C₂B₄H₄) (3). Decapitation of these species gave diamagnetic Cp*Co(Et₂C₂B₃H₂Me)CoH-(Et₂C₂B₃H₅) (4), whose triple-decker geometry was confirmed by an X-ray structure determination that established the location of the hydrogen atom capping a CoB₂ triangular face. Removal of the CoH proton in 4 followed by oxidation of the anion in air gave paramagnetic Cp*Co(Et₂B₃H₂Me)Co(Et₂C₂B₃H₅) (5). Treatment of neutral 4 and 5 with n-bromosuccinimide afforded the mono- and dibromo derivatives 6–8. The 30 ve triple-decker Cp*Co-(Et₂C₂B₃Me₃)Ni(Et₂C₂B₄H₄) (10) was prepared from the peralkylated synthon Cp*Co(2,3-Et₂C₂B₃Me₃)^2–, Et₂C₂B₄H₄ ^2–, and NiBr2. A similar approach employing the cymeneruthenacarborane dianion (CHMe₂C₆H₄Me)Ru(Et₂C₂B₃H₂Me)^2– gave the paramagnetic triple-decker (CHMe₂C₆H₄Me)Ru(Et₂C₂B3H₂Me)Co(Et₂C₂B₄H₄) (12), which was decapitated to yield diamagnetic (CHMe₂C₆H₄Me)Ru(Et₂C₂B₃H₂Me)CoH(Et₂C₂B₃H₅) (13); the latter species was air-oxidized to afford 29 ve (CHMe₂C₆H₄Me)Ru(Et₂C₂B₃H₂Me)Co(Et₂C₂B₃H₅) (14). Stacking reactions of the nido, closo dianion (Et₂C₂B₃H₄Me)Co(Et₂C₂B₄H₄)^2– (15^2–) with Co²⁺ or Ni²⁺ ions gave the paramagnetic carborane-bicapped tetradecker sandwiches M[(Et₂C₂B₃H₂Me)Co(Et₂C₂B₄H₄)]₂ (16, M = Co, 41 ve; 17, M = NiH, 43 ve). Reactions of the 15^3– trianion with Cp*Co(2,3-Et₂C₂B₃H₂Me)^2–ion and Co²⁺ or Ni²⁺ gave the carborane-monocapped tetradeckers Cp*Co-(Et₂C₂B₃H₂Me)M(Et₂C₂B₃H₂Me)CoH(Et₂C₂B₄H₄) (18, M = Co, 41 ve; 19, M = Ni, 42 ve, diamagnetic). Decapitation of 18 gave paramagnetic 41 ve Cp*Co(Et2C2B3H2Me)Co(Et2C2B3H2Me)CoH(Et2C2B3H5) (20), a 41 ve tetradecker sandwich having an open carborane end ligand. The new compounds were characterized via UV—visible and mass spectra, ¹H and ¹¹B NMR spectra (for diamagnetic species), and ESR spectra (for paramagnetic complexes). Features of the spectroscopic data are discussed and related to the electronic structures of these systems. Crystal data for 4: space group P2₁/a; a = 9.312(3) Å, b = 28.25(1) Å, c = 10.234(4) Å, β= 95.56(3)°; Z = 4; R = 0.048 for 3834 independent reflections having I > 3σ(I).