Syntheses of rac/meso-{PhP(3-t-Bu-C5H3)2}-Zr{RN(CH2)3NR}, structural analyses of rac-{PhP(3-t-Bu-C5H3)2}Zr{RN(CH2)3NR} (where R is SiMe3 or Ph), and meso to rac isomerization

Syntheses of rac/meso-{PhP(3-t-Bu-C5H3)(2)} Zr{Me3SiN(CH2)(3)NSiMe3} (rac-3/meso-3) and rac/meso-{ PhP(3-t-Bu-C5H3)(2)}Zr{PhN(CH2)(3)NPh} (rac-4/meso-4) were achieved by metallation of K-2[PhP(3-t-Bu-C5H3)(2)]center dot 1.3 THF (2) with Zr{RN(CH2)(3)NR}Cl-2(THF)(2) (where R = SiMe3 or Ph, respectively) using ethereal solvent. These isomeric pairs were characterized by H-1, C-13{H-1}, and P-31{H-1} NMR spectroscopy; rac-3 and rac-4 were also examined via single crystal X-ray crystallography. The structures of rac-3 and rac-4 are notable in the tendency of the cyclopentadienyl rings towards eta(3) coordination. While isolated samples of rac-3/meso-3 and rac-4/meso-4 slowly isomerize in tetrahydrofuran-d(8) to equilibrium ratios, the isomerization rate for 3 is more than 15-fold greater than that for 4. In addition, equilibrium ratios are rapidly reached when isolated samples of rac-3/meso-3 and rac-4/meso-4 are exposed to tetrabutylammonium chloride in tetrahydrofuran-d8 solvent. We propose that a nucleophile (either chloride or the phosphine interannular linker) brings about dissociation of one cyclopentadienyl ring, thus promoting the rac/meso isomerization mechanism. (C) 2008 Elsevier B. V. All rights reserved.