Active catalysts for stereoselective ring-opening reactions

A method of making chiral catalyst complex, comprising:

• contacting an asymmetric tetradentate ligand according to the structural formula (2) or a salt thereof:
• 19
• wherein:
• R40, R41, R42, R43 R44, X1, X2, X3, X4, X5, X6, X7 and X8 are each independently H, hydroxyl, halo, alkyl, alkynyl, amino, nitro, thio, imino, amido, phosphoryl, phosphonato, carbonyl, carboxyl, silyl, or an ether, thioether, sulfonyl, selenoether, ketone, aldehyde, ester or —(CH2)n—R23, or, alternatively, may be fused with another one of the R40, R41, R42, R43 R44, X1, X2, X3, X4, X5, X6, X7 and X8 substituents to form a carbocyclic or heterocyclic ring structure having from 4 to 8 atoms in its ring structure, provided that R44 may be absent, in which case, the carbon atom bearing the R40 and R41 substituents is covalently bonded to the carbon atom bearing the R42 and R43 substituents and R40 and R41 may each independently be fused with one of R42 or R43 to form a ring structure that includes the carbon atoms to which they are bound,
• Y1 and Y2 are each independently H, hydroxyl, halo, alkyl, alkynyl, amino, nitro, thio, imino, amido, phosphoryl, phosphonato, carbonyl, carboxyl, silyl, or an ether, thioether, sulfonyl, selenoether, ketone, aldehyde, ester or —(CH2)n—R23,
• R23 is aryl, cycloalkyl, cycloalkenyl or heterocyclyl or polycyclyl, and
• n is zero or an integer of from 1 to 8,
• further provided that the substituents of the ligand of formula (2) are selected such that the ligand is asymmetric,
• with a Brønsted acid selected from acetic acid, propionic acid, isobutyric acid, trifluoroacetic acid, and methane sulfonic acid, a Co(II) or Cr(II) salt selected from cobalt acetate, cobalt propionate, cobalt isobutyrate, cobalt trifluoroacetate, chromium acetate, chromium propionate, chromium isobutyrate and chromium trifluoroacetate, and air under conditions effective to allow formation of a chiral catalyst complex of Co(III) or Cr(III) and the ligand
• forming a solution of the complex in a water-miscible, protic solvent comprising a compound selected from methanol, ethanol and n-propanol, and
• adding water to the solution to precipitate at least a portion of the complex.

A method for providing a chiral catalyst complex having known activity in catalyzing a stereoselective ring opening reaction, comprising:

• isolating a chiral catalyst complex of Co(III) or Cr(III) with an asymmetric tetradentate ligand,
• using a portion of the isolated complex to catalyze a first stereoselective ring opening reaction, and
• characterizing the reaction rate of the first reaction, and
• providing the remaining isolated complex for use in catalyzing stereoselective ring opening reactions analogous to the first stereoselective ring opening reaction.