31 P spin‐sattice relaxation times of tertiary aryl phosphines and their iridium(I) and gold(I) complexes

31 P spin‐lattice relaxation times, T 1 , and 31 P‐ 1 H NOE values, η, for CDCl 3 , solutions of the compounds P(C 6 H 4 ‐p‐X) 3 , [IrCl(CO){P(C 6 H 4 ‐p‐X) 3 } 2 ] (X = H, CH 3 , F, Cl, OCH 3 ) and [AuCl{P(C 6 H 4 ‐p‐X) 3 }] (X = H, OCH 3 ) are reported. For the uncoordinated tertiary phosphines T 1 = 26–28 s, except for X = OCH 3 for which T 1 = 14 s. For the iridium(I) complexes T 1 falls in the range 4.4–8.7 s, whereas for the gold(I) compounds the values are 15.7 and 11.3 s for X = H and OCH 3 , respectively. The data are discussed in terms of the differing relaxation mechanisms within each class of compound. The unusually low T 1 values observed when X = OCH 3 is attributed to a relatively large change in the dipole‐dipole contribution to T 1 , such that T 1 (dipole‐dipole) decreases.