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

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Abstract
31P spin‐lattice relaxation times, T1, and 31P‐1H NOE values, η, for CDCl3, solutions of the compounds P(C6H4‐p‐X)3, [IrCl(CO){P(C6H4‐p‐X)3}2] (X = H, CH3, F, Cl, OCH3) and [AuCl{P(C6H4‐p‐X)3}] (X = H, OCH3) are reported. For the uncoordinated tertiary phosphines T1 = 26–28 s, except for X = OCH3 for which T1 = 14 s. For the iridium(I) complexes T1 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 OCH3, respectively. The data are discussed in terms of the differing relaxation mechanisms within each class of compound. The unusually low T1 values observed when X = OCH3 is attributed to a relatively large change in the dipole‐dipole contribution to T1, such that T1 (dipole‐dipole) decreases.