REACTIVITY OF DEPROTONATED MN-2(MU-H)(MU-PCYH)(CO)(8) - SELECTIVE MONOAURATION TO MN-2(MU-AUPR(3))(MU-PCYH)(CO)(8) AND MN-2(MU-H)(MU(3)-PCY(AUPR(3)))(CO)(8) (R=CY, PH, P-C6H4F, P-C(6)H(4)OME) AND KINETIC-STUDIES OF THEIR CONVERSION

In THF solution the dimanganese complex Mn-2(mu-H)(mu-PCyH)(CO)(8) (1) reacts with equimolar amounts of the non nucleophilic base DBU (1.8-d iazabicyclo[5.4.0]undec-7-en) and ClAuPR(3) (R = Cy, Ph, p-C(6)H(4)OMe , p-C6H4F) at 20 degrees C within 1 h to afford the following mono- an d diaurated pairs of isomers: Mn-2 mu-AuPR(3)(mu-PCyH)(CO)(8) (A) and Mn-2(mu-H)(mu(3)-PCy(AuPR(3)))(CO)(8) (B); Mn-2(mu-AuPR(3))(mu-PCy(AuP R(3)))(CO)(8) and Mn-2(AuPR(3))(2)(mu(4)-PCy)(CO)(8). Whereas we descr ibed the separated components of the last named pair in our previous p ublication, the monoaurated isomers are dicussed in this paper. These isomers have now been separated by a fractional crystallization proced ure and identified by means of H-1 NMR, P-31 NMR, UV/vis, and v(CO) IR spectroscopic measurements. In the case of R = Ph, Mn-2(mu-AuPPh(3))( mu-PCyH)(CO)(8) (2) and Mn-2(mu-H)(mu(3)-PCY(AuPPh(3)))(CO)(8) (3) bot h crystallize triclinic, space group P ($) over bar 1, Z = 2: 2, a = 1 0.687(2) Angstrom, b = 11.605(2) Angstrom, c = 14.369(2) Angstrom, alp ha = 103.91(1)degrees, beta = 99.85(1)Angstrom, gamma = 93.97(1)degree s; 3, a = 12.741(1) A, b = 16.371(1)degrees Angstrom, c = = 9.068(2)de grees Angstrom, alpha = 97.85(1)degrees, beta = 110.73(1)degrees; gamm a = 74.99(1)degrees. Both molecular structures show a common edge-shar ing coordination bioctahedron with an orthogonal Mn-Mn bond. Proceedin g from 1, the mu-H atom is replaced by the isolobal group AuPPh(3) to obtain 2 on the one hand, and on the other hand, the phosphorus bound H atom is exchanged by the same group to get 3. The Mn-Mn bond length is 3.136(2) Angstrom in 2 and 2.927(1) Angstrom in 3. In solution, A a nd B form a dynamic equilibrium whose displacement depends on the R gr oups and on the solvent used. A mechanistic pathway for the formation of 2 and 3 is proposed. In connection with this the anion [Mn-2(mu-PCy H)(CO)(8)](-) 1a is described which was obtained as the salt Li[1a] (y ield 81%) by the reaction of PhLi and 1 in THF solution. Finally, the kinetic data for the mutual conversion of the isomer pairs A and B wer e obtained by UV/vis measurements in different solvents (n-hexane, CH2 Cl2) at selected temperatures. The influence of solvent interactions a nd of electronic factors of the R groups (M, I effect) on the rate con stants and the steady states, respectively, is discussed.