Camphopyrazole-based N,N- and N,P-ligands and chiral complexes of Ni, Pd, and Rh: P–N bond activation upon Rh(I) complexation

Enantiomerically pure C1 and C2-symmetric bidentate N,N- and N,P-ligands are accessible from (+)-camphor in good yields (60–90%). Modified syntheses of precursors 1 and 2 are disclosed as well as the crystal structures of three hydroxy-pyrazoline intermediates. Ligands 3, 4, 6, and 11 were fully characterized including an X-ray crystal structure of C2-symmetric 6, which showed an E-configuration in the solid state. These ligands form complexes with Ni(II), Pd(II), and Rh(I) in good yields (84–96%); the X-ray crystal structures of complexes 12, 14, and 16 confirmed the bidentate coordination modes of ligands 4, 6, and 11 and distorted tetrahedral [for Ni(II)] and square planar [for Rh(I)] coordination geometries. Furthermore, the structure of the Rh(I) complex 16 revealed the presence of a Ph2PCl ligand, which, along with spectroscopic data, is proof of an almost quantitative P–N bond cleavage upon coordination of ligand 11 to [RhCl(COD)]2.

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(4S,7R)-7,8,8-Trimethyl-4,5,6,7-tetrahydro-4,7-methano-1-phenylindazol-3-carboxylic acidC18H20N2O2[α]D20 = +72.4 (c 1.021, CHCl3)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (4S,7R)

(4S,7R)-7,8,8-Trimethyl-4,5,6,7-tetrahydro-4,7-methano-1-phenyl-indazol-3-carbonyl chlorideC18H19ClN2O[α]D20 = +59.1 (c 0.305, CHCl3)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (4S,7R)

((4S,7R)-7,8,8-Trimethyl-4,5,6,7-tetrahydro-4,7-methano-1-phenyl-indazol-3-yl)(3,4,5-trimethyl-pyrazol-1yl)methanoneC24H28N4O[α]D20 = +46 (c 0.21, THF)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (4S,7R)

((4S,7R)-7,8,8-Trimethyl-4,5,6,7-tetrahydro-4,7-methano-1-phenyl-indazol-3-yl)(3,5-di-tert-butyl-pyrazol-1yl)methanoneC29H38N4O[α]D20 = +47 (c 0.06, THF)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: 4S,7R

(+)-(1R,1′R)-3,3′-(1,2-Dihydroxyethane-1,2-diylidene)bis[(1,7,7-trimethyl-bicyclo[2,2,1]-heptan-2-one]C22H30O4[α]D20 = +520.8 (c 1.02, CHCl3)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (1R,1′R)

(+)-(1R,1′R)-3,3′-Bi(1,1′-diphenyl-pyrazole-camphor)C34H38N4[α]D20 = +105.7 (c 1.01, CHCl3)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (1R,1′R)

(+)-3,3′-[(4S,7R)-(1,2-Dihydroxyethane-1,2-diylidene)(1,7,7-trimethyl-bicyclo[2,2,1]-heptan-2-one)]-((4′S,7′R)-7′,8′,8′-trimethyl-4′,6′,7′-trihydro-5′-ol-4′,7′-methano-1′-phenyl-indazol)C28H36N2O3[α]D20 = +228.6 (c 1.01, CHCl3)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (4S,7R,4′S,7′R)

(E)-3,3′-((4S,7R)-7,8,8-Trimethyl-4,6,7-trihydro-5-ol-4,7-methano-1-phenyl-indazol-hydroxymethylene)-((4′S,7′R)-1′,7′,7′-trimethylbicyclo[2′.2′.1′]-heptan-2′-one)C28H34N2O2[α]D20 = +252 (c 1.00, CHCl3)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (4S,7R,4′S,7′R)

3,3′-((4S,7R)-7,8,8-Trimethyl-4,6,7-trihydro-5-ol-4,7-methano-1-phenyl-indazol)-((4′S,7′R)-7′,8′,8′-trimethyl-4′,5′,6′,7′-tetrahydro-4′,7′-methano-2′H-indazol)C28H36N4O[α]D20 = +215.3 (c 0.538, CHCl3)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (4S,7R,4′S,7′R)

3,3′-((4S,7R)-7,8,8-Trimethyl-4,5,6,7-tetrahydro-4,7-methano-1-phenyl-indazol)-((4′S,7′R)-7′,8′,8′-trimethyl-4′,5′,6′,7′-tetrahydro-4′,7′-methano-2′H-indazol)C28H34N4[α]D25 = +170 (c 0.160, CHCl3)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (4S,7R,4′S,7′R)

3,3′-((4S,7R)-7,8,8-Trimethyl-4,5,6,7-tetrahydro-4,7-methano-1-phenyl-indazol)-((4′S,7′R)-7′,8′,8′-trimethyl-4′,5′,6′,7′-tetrahydro-4′,7′-methano-2′-diphenylphosphine-indazol)C40H43N4P[α]D20 = +1.4 (c 0.512, THF)Source of chirality: (1R)-(+)-CamphorAbsolute configuration: (4S,7R,4′S,7′R)