Syntheses of rac/meso-{PhP(3-t-Bu-C 5 H 3 ) 2 }Zr{Me 3 SiN(CH 2 ) 3 NSiMe 3 } (rac-3/meso-3) and rac/meso-{PhP(3-t-Bu-C 5 H 3 ) 2 }Zr{PhN(CH 2 ) 3 NPh} (rac-4/meso-4) were achieved by metallation of K 2 [PhP(3-t-Bu-C 5 H 3 ) 2 ]·1.3 THF (2) with Zr{RN(CH 2 ) 3 NR}Cl 2 (THF) 2 (where R=SiMe 3 or Ph, respectively) using ethereal solvent. These isomeric pairs were characterized by 1 H, 13 C{ 1 H}, and 31 P{ 1 H} 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 η 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-d 8 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.