167032-92-0Relevant articles and documents
C2B3 and C2B4 carborane ligands as cyclopentadienyl analogues: Early transition metal complexes
Stockman, Kenneth E.,Houseknecht, Karl L.,Boring, Eric A.,Sabat, Michal,Finn,Grimes, Russell N.
, p. 3014 - 3029 (2008/10/09)
This paper reports the directed synthesis, characterization, and reactivity of a series of tantalum, niobium, and zirconium sandwich complexes incorporating small carborane or cobaltacarborane ligands, centered on the development of suitable families of reagents for eventual application to organic synthesis. Complexes of the types (R12C2B4H4)MCl 2Cp′ and (Et2C2B4H4)ZrCl·THFCp′ (R1 = Et, SiMe3, or Me; Cp′ = C5H5 or C5Me5; M = Ta, Nb) were prepared from Cp′MCln reagents (M = Ta, Nb, Zr) and the R12C2B4H5- monoanion in THF. Similar treatment of the Cp*Co(Et2C2B3H4)- cobaltacarborane anion (Cp* = C5Me5) afforded the bent triple-decker sandwich complexes [Cp*Co(Et2C2B3H3)]MCl 2Cp′ (M = Ta, Nb). Both families of compounds were obtained generally in high yield as air-stable crystalline solids that are readily soluble in organic solvents. In the Ta and Nb species, replacement of one or both chlorines with a variety of alkyl groups was effected via reactions with alkylating agents to generate (R12C2B4H 4)Ta(L)ClCp′ or (R12C2B4H4)ML 2Cp′ (M = Ta, Nb), and the corresponding alkylated triple-deckers [Cp*Co(Et2C2B3H 3)Ta(L)ClCp′ and [Cp*Co(Et2C2B3H3)]-TaL 2Cp′ (L = Me, Et, Ph, CH2Ph, CH2CMe3, or OPh). Yields of the mono- and dialkyl derivatives ranged from moderate to quantitative. The new complexes were characterized via 1H, 13C, and 11B NMR, mass spectrometry, and elemental analysis supplemented by FTIR and UV-visible spectroscopic data for many compounds, electrochemical studies on selected species, and crystal structure determinations on seven products. Exploratory studies of the reactivities of these complexes revealed significant differences from those of standard organometallic species such as Cp2TiCl2 or Cp2ZrR2. Thus, tantalum and niobium C2B4 dichloro complexes on treatment with Al2Me6 gave dimethyl derivatives rather than methylidene compounds. The reaction of (Et2C2B4H4)TaMe2Cp with excess HBF4 in acetonitrile formed a single isolable product identified as a difluoro derivative, (Et2C2B4H4)TaF2-Cp. X-ray crystal structures were obtained for [(Me3Si)2C2B4H4]TaCl 2Cp (1b), (Et2C2B4H4)TaCl 2-Cp* (1c), [Cp*Co(Et2C2B3H3)]TaCl 2Cp (4a), (Et2C2B4H4)TaPh2Cp (6d), Cp*Co(Et2C2B3H3)TaMe 2-Cp (Tb), Cp*Co(Et2C2B3H3)Ta(CH 2Ph)ClCp (7c), and (Et2C2B4H4)NbMe2Cp (8a). Crystal data for 1b: space group P21/a; Z = 4; a = 14.292(4) A?, b = 9.008(2) A?, c = 17.899(7) A?, β= 112.61(2)°; R = 0.043 for 2854 independent reflections. For 1c: space group P21/c; Z = 4; a = 8.650(2) A?, b = 12.362(5) A?, c = 18.601(7) A?, β= 90.10(3)°: R = 0.038 for 1831 independent reflections. For 4a: space group P21/n; Z = 4; a = 8.874(2) A?, b = 14.303(4) A?, c = 18.585(6) A?, β = 91.53(2)°; R = 0.036 for 3033 independent reflections. For 6d: space group P1; Z = 2; a = 8.943(1) A?, b = 15.726(2) A?, c = 7.843(2) A, α = 90.58(2)°; β= 102.78(2)°; γ= 103.53(1)°; R = 0.024 for 3376 independent reflections. For 7b: space group P21/n; Z = 4; a = 8.998(2) A?, b = 14.374(2) A?, c = 18.508(3) A?, β = 92.98(2)°; R = 0.027 for 3169 independent reflections. For 7c: space group P21/n; Z = 4; a = 12.780(2) A?, b = 16.084(2) A?, c = 13.442(2) A?, β= 104.16(1)°; R = 0.030 for 3684 independent reflections. For 8a: space group P21/c; Z = 4; a = 14.148(3) A?, b = 7.781(5) A?, c = 15.315(2) A?, β = 116.32(1)°; R = 0.031 for 2297 independent reflections.
