New racemic planar-chiral metalloligands derived from donor-substituted indenes: A synthetic, structural, and catalytic investigation

Article abstract of DOI:10.1021/om700832f

The synthesis and characterization of a new family of (η⁵- indenyl)ML_n complexes (ML_n = Mn(CO)₃, Cp*Ru, or Cp*Fe; Cp* = η⁵-C₅Me ₅) derived from 3-PⁱPr₂-indene, 1-P ⁱPr₂-2-NMe₂-indene (1a[H]), or 1-P(S) ⁱPr₂-2-NMe₂-indene (1b[H]) are described. Lithiation of 1b[H] followed by treatment with BrMn-(CO)₅, 0.25 equiv of [Cp*RuCl]₄, or Cp*Li/FeCl₂ provided the corresponding (η⁵-1b)ML_n complexes (ML_n = Mn(CO)₃, 2a, 96%; Cp*Ru, 2b, 87%; or Cp*Fe, 2c, 55%). Similarly, treatment of 1a[Li] with 0.25 equiv of [Cp*RuCl]₄ or Cp*Li/FeCl₂ provided the corresponding (η⁵-1a) ML_n complexes (ML_n = Cp*Ru, 3b, 74%; or Cp*Fe, 3c, 62%). Whereas combination of 3b and 0.5 equiv of [(COD)RhCl]₂ afforded [(COD)Rh(κ²-P,N-3b)]⁺Cl^- ([4b]⁺Cl^-; 49% isolated yield), under similar conditions 3c was observed to undergo a decomposition reaction resulting in the formation of the zwitterionic complex (COD)Rh(κ²-P,N-1a) (5; COD = η⁴-1,5-cyclooctadiene). Each of 3a-c was observed to react cleanly with [(COD)Rh(THF)₂]⁺BF₄^- (prepared in situ) to give the corresponding [(COD)Rh(κ²-P,N- 3a-c)]⁺BF₄^- complex ([4a-C]⁺BF ^4-; 87%, 96%, and 89% isolated yield, respectively). Whereas lithiation of 3-Pⁱ-Pr₂-indene followed by the addition of BrMn(CO)₅ generated a complex mixture of products, similar reactions employing 0.25 equiv of [Cp*RuCl]₄ or Cp*Li/FeCl₂ afforded 6b or 6c in 98% and 43% yield, respectively. Treatment of 6b with 0.5 equiv of [(COD)RhCl]₂ allowed for the isolation of (COD)RhCl-(κ¹-P-6b) 7 in 96% isolated yield. Each of [4a-C]⁺BF₄^- proved to be an active catalyst for addition of pinacolborane to styrene, with the observed regioselectivity being dependent on the nature of the η⁵- coordinated metal fragment, as well as the solvent employed. Single-crystal X-ray diffraction data for 2a, 2b, 2c, 3b, [4c]⁺BF₄ ^-, and 7 are provided.