New Racemic Planar-Chiral Metalloligands Derived from Donor-Substituted Indenes: A Synthetic, Structural, and Catalytic Investigation

The synthesis and characterization of a new family of (η5-indenyl)MLn complexes (MLn = Mn(CO)3, Cp*Ru, or Cp*Fe; Cp* = η5-C5Me5) derived from 3-PiPr2-indene, 1-PiPr2-2-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)MLn complexes (MLn = 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)MLn complexes (MLn = 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]+BF4-; 87%, 96%, and 89% isolated yield, respectively). Whereas lithiation of 3-PiPr2-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.