Tetranuclear cluster complexes of the type [MM '(AuR3)(2)(mu-H)(mu-PCy2)(mu(4)-PCy)(CO)(6)] (M,M ' = Mn, Re; R = Ph, Cy, Et): Synthesis, structure, and topomerisation

The dirhenium complex [Re-2(mu -H)(mu -PCy2)-(CO)(7)(ax-H2PCy)] (1) reacts at room temperature in thf solution with each two equivalents of the base D BU and of ClAuPR3 (R = Ph, Cy, Et) in a photochemical reaction process to a fford the tetranuclear clusters [Re-2(AuPR3)(2)(mu -H)(mu -PCy2)(mu (4)-PCy )(CO)(6)] (R = Ph (2), Cy (3), Et (4)) in yields of 35-48%. The homologue [ Mn-2(mu -H)(mu -PCy2)(CO)(7)(ax-H2PCy)] (5) leads under the same reaction c onditions to the corresponding products [Mn-2(AuPR3)(2)(mu -H)(mu -PCy2)(mu (4)-PCy)(CO)(6)] (R = Ph (6), Et (8)). Also [MnRe(mu -H)(mu -PCy2)(CO)(7)( ax/eq-H2PCy)] (9) reacts under formation of [MnRe(AuPR3)(2)(mu -H)(mu -PCy2 )(mu (4)-PCy)(CO)(6)](R = Ph (10), Et (11)). All new cluster complexes were identified by means of H-1-NMR, P-31-NMR and nu (CO)-IR spectroscopic meas urements. 2, 4 and 10 have also been characterized by single crystal X-ray structure analyses with crystal parameters: 2 triclinic, space group P (1) over bar, a = 12.256(4) Angstrom, b = 12.326(4) Angstrom, c = 24.200(6) Ang strom, alpha = 83.77(2)degrees, beta = 78.43(2)degrees, gamma = 68.76(2)deg rees, Z = 2; 4 monoclinic, space group C2/c, a = 12.851(3) Angstrom, b = 18 .369(3) Angstrom, c = 40.966(8) Angstrom, beta = 94.22(1)degrees, Z = 8; 10 triclinic, space group P (1) over bar, a = 12.083(i) Angstrom, b = 12.185( 2) Angstrom, c = 24.017(6) Angstrom, alpha = 83.49(29)degrees, beta = 78.54 (2)degrees, gamma = 69.15(2)degrees, Z = 2. The trapezoid arrangement of th e metal atoms in 2 and 4 show in the solid structure trans-positioned an op en and a closed Re . . . Au edge. In solution these edges are equivalent an d, on the P-31 NMR time scale, represent two fluxional Re-Au bonds in the c ourse of a topomerization process. Corresponding dynamic properties were ob served for the dimanganese compounds 6 and 8 but not for the related MnRe c lusters 10 and 11. 2 and 4 are the first examples of cluster compounds with a permanent Re-Au bond valence isomerization.