The donor strengths of the following triarylphosphine ligands P(Ar) 2(Ar′) (Ar = Ar′ = 4-Me 3SiC 6H 4, 1b; 4-Me 3CC 6H 4, 1d; 4-F 3CC 6H 4, 1e; Ar = C 6H 5, Ar′ = 4-Me 3SiC 6H 4, 1c) have been evaluated experimentally and theoretically. The measurements of the J(P-Se) coupling constants of the corresponding synthesised selenides Se=P(Ar) 2(Ar′), 2b,c and the DFT calculation of the energies of the phosphine lone-pair (HOMO) reveal insignificant influence on the electronic properties of the substituted phosphines when the trimethylsilyl group is attached to the aryl ring, in marked contrast to the strong electronic effect of the trifluoromethyl group. These triarylphosphine ligands P(Ar) 2(Ar′) reacted with (η 5-C 5H 5)Co(CO) 2, (η 5-C 5H 5)Co(CO)I 2 or PdCl 2 to yield the new compounds (η 5-C 5H 5)Co(CO)[P(Ar) 2(Ar′)], 3b,d; (η 5-C 5H 5)CoI 2[P(Ar) 2(Ar′)], 4b-e; and PdCl 2[P(Ar) 2(Ar′)] 2, 5b,c, respectively. These complexes have been characterized and their spectroscopic properties compared with those reported for the known triphenylphosphine complexes. Again, the contrast of the 31P NMR and 13C NMR chemical shifts or C-O or M-Cl stretching frequencies, when applied, does not show an important electronic effect on the metal complex of the trimethylsilyl substituted phosphines with respect to P(C 6H 5) 3 derivatives. Solubility measurements of complexes 3a and 3b in scCO 2 were performed. We conclude that Me 3Si groups on the triarylphosphine improve the solubility of the corresponding metal complex in scCO 2.