The 31P NMR spectra of CpRu­(PR3)2Cl and Cp*Ru­(PR3)2Cl complexes with PR3 = PMe3, PPhMe2, PPh2Me, PPh3, PEt3, P n Bu3 have been measured; these data correlate with and can be used to predict Ru–P bond distances and enthalpies. Their 31P NMR coordination chemical shifts (Δ­(ppm) = δcomplex – δfree) show significant linear correlations with literature values of both the enthalpies of the ligand exchange reactions to form the Ru–P bonds and the average Ru–P bond distances from crystal structures. The strong correlation between Δ­(ppm) and Ru–P distance can be extended to include the first-generation Grubbs metathesis catalyst (PCy3)2Cl2RuC­(H)­Ph and four of its derivatives, (PCy3)2Cl2RuC­(H)­(p-C6H4X) (X = OCH3, CH3, Cl, Br), the four related Fischer carbenes (PCy3)2Cl2RuC­(H)­ER (ER = OEt, SPh, N­(carbazole), N­(pyrrolidinone)), the second-generation Grubbs catalyst (PCy3)­(IMes)­Cl2RuC­(H)­Ph, and its derivative (PCy3)­(IMes)­Cl2RuC­(H)­OEt. Other significant correlations in the Cp′Ru­(PR3)2Cl complexes are found between the enthalpies of reaction and Ru–P bond distances and between the cone angle and the Ru–P enthalpy, Ru–P bond distance, and Δ­(ppm) values. The 31P NMR shifts for six phosphines correlate nearly linearly with their crystallographic cone angles, allowing prediction of cone angles from 31P NMR data.