Reactivity of Deprotonated Mn2(μ-H)(μ-PCyH)(CO)8: Selective Monoauration to Mn2(μ-AuPR3)(μ-PCyH)(CO)8 and Mn2(μ-H)(μ3-PCy(AuPR3))(CO)8 (R = Cy, Ph, p-C6H4F, p-C6H4OMe) and Kinetic Studies of Their Conversion

Article abstract of DOI:10.1021/ic00126a015

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 isomersare dicussed in this paper. These isomers have now been separated by a fractional crystallization procedure and identified by means of (1)H NMR, (31)P NMR, UV/vis, and ν(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) ?, b = 11.605(2) ?, c = 14.369(2) ?, α = 103.91(1)°, β = 99.85(1)°, γ = 93.97(1)°; 3, a = 12.741(1) ?, b = 16.371(1) ?, c = 9.068(2) ?, α = 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 onthe 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) ? in 2 and 2.927(1) ? 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](1-) 1a is describedwhich was obtained as the salt Li[1a] (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.