A COMPARATIVE-STUDY OF THE USE OF TRIETHYLAMMONIUM SALTS OF THE [FE2(CO)6(MU-CO)(MU-SR)]- ANION IN THE SYNTHESIS OF IRON-GOLD CLUSTERS - CRYSTAL-STRUCTURES OF [FE2(CO)6(MU-CO)(MU-SIPR)(MU-AUPPH3)] AND [FE2(CO)5(PPH3)(MU-SET)2]

Salts of the type (NEt3H)[Fe2(CO)6(mu-CO)(mu-SR)] (R = (i)Pr, (t)Bu, Ph) react with [ClAuPPh3] in the presence of TlBF4 to produce the neutral iron-gold clusters [Fe2(CO)6(mu-CO)(mu-SR)(mu-AuPPh3)] (R = (i)Pr, 1; R = (t)Bu, 2; R = Ph, 3) in high yields. The structure of 1 has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P2(1)/c, with a = 11.373(1), b = 14.899(3), c = 17.997(8) angstrom, beta = 95.12(2)-degrees and Z = 4, R = 0.030 and R'= 0.035 for 3579 unique reflections with I greater-than-or-equal-to 2sigma(I). The basic skeleton consists of an Fe2Au triangle where the Fe-Fe bond is bridged by a carbonyl and a thiolate group. In contrast, the reaction of the salts (NEt3H)[Fe2(CO)6(mu-CO)(mu-SR)] (R = Et or C6F5) with [ClAuPPh3] does not afford the corresponding mixed iron-gold clusters, and the diiron mono- or di-substituted complexes [Fe2(CO)5(PPh3)(mu-SR)2] (R = Et, 4; R = C6F5, 5) and [Fe2(CO)4(PPh3)2(mu-SEt)2] (6) are obtained instead. The structure of 4 has been established by single-crystal X-ray diffraction studies. Crystals are triclinic, space group, P1BAR, with a = 10.472(4), b = 11.329(2), c = 13.437(2) angstrom, alpha = 80.34(2), beta = 92.62(3), gamma = 114.46(2), and Z = 2, R = 0.027 and R' = 0.030 for 3732 unique reflections with I greater-than-or-equal-to 2sigma-(I). The Fe-Fe bond in 4 is almost symmetrically double-bridged by two thiolate ligands and the phosphine group attached to the Fe(l) is trans to the iron-iron bond.