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
Haupt, HJ; Schwefer, M; Egold, H; Florke, U
In THF solution the dimanganese complex Mn2(μ-H)(μ-PCyH)(CO)8 (1) reacts with equimolar amounts of the non nucleophilic base DBU (1.8-diazabicyclo[5.4.0]undec-7-en) and ClAuPR3 (R = Cy, Ph, p-C6H4OMe, p-C6H4F) at 20°C within 1 h to afford the following mono- and diaurated pairs of isomers: Mn2(μ-AuPR3)(μ-PCyH)(CO)8 (A) and Mn2(μ-H)(μ3-PCy(AuPR3))(CO)8 (B); Mn2(μ-AuPR3)(μ-PCy(AuPR3))(CO)8 and Mn2(AuPR3)2(μ4-PCy)-(CO)8. Whereas we described the separated components of the last named pair in our previous publication, the monoaurated isomers are dicussed in this paper. These isomers have now been separated by a fractional crystallization procedure and identified by means of 1H NMR, 31P NMR, UV/vis, and v(CO) IR spectroscopic measurements. In the case of R = Ph, Mn2(μ-AuPPh3)(μ-PCyH)(CO)8 (2) and Mn2(μ-H)(μ3-PCy(AuPPh3))-(CO)8 (3) both crystallize triclinic, space group P1, Z = 2: 2, a= 10.687(2) Ã
, b = 11.605(2) Ã
, c = 14.369(2) Ã
, a = 103.91(1)°, β = 99.85(1)°, γ = 93.97(1)°; 3, a = 12.741(1) Ã
, b= 16.371(1)° Ã
, c = 9.068(2)° Ã
, a = 97.86(1)°, β = 110.73(1)°, γ = 74.99(1)°. Both molecular structures show a common edge-sharing coordination bioctahedron with an orthogonal Mn-Mn bond. Proceeding from 1, the μ-H atom is replaced by the isolobal group AuPPh3 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) Ã
in 2 and 2.927(1) Ã
in 3. In solution, A and B form a dynamic equilibrium whose displacement depends on the R groups and on the solvent used. A mechanistic pathway for the formation of 2 and 3 is proposed. In connection with this the anion [Mn2(μ-PCyH)-(CO)8]â la is described which was obtained as the salt Li[la] (yield 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 were obtained by UV/vis measurements in different solvents (n-hexane, CH2Cl2) at selected temperatures. The influence of solvent interactions and of electronic factors of the R groups (M, I effect) on the rate constants and the steady states, respectively, is discussed. © 1995, American Chemical Society. All rights reserved.