Mixed Ruthenium-Rhodium Carbonyl Clusters

The anion [Ru2Rh2(CO)12]2- (1) has been obtained by reaction of Ru3(CO)12 with [Rh(CO)4]- as [N(PPh3)2]+ or (PPh4)+ salts; this species reacts with acids or AuPPh3Cl to give respectively [Ru2Rh2(CO)12H]- (2) and [Ru2Rh2(CO)12(AuPPh3)]- (3). The phosphonium salts (PPh4)2[Ru2Rh2(CO) 12]·THF (I), (PPh4)[Ru2Rh2(CO)12H] (II), and (PPh4)[Ru2Rh2(CO)12(AuPPh 3)] (III) were characterized by single-crystal X-ray diffraction: I, space group P21/n, Z = 4, a = 11.256(2) Å, b = 26.712(2) Å, c = 20.048(5) Å, β= 90.45(2)°, R1 = 0.048 for 4049 independent reflections with I > 3σ(I); II space group P21/a, Z = 4, a = 12.453(2) Å, b = 24.074(3) Å, c = 13.174(2) Å, β= 90.67(1)°, R1 = 0.039 for 4034 independent reflections with I > 3σ(I); III, space group P21/n, Z = 4, a = 11.720(2) Å, b = 13.133(3) Å, c = 35.614(2) Å, β= 95.70(1)°, R1 = 0.054 for 4231 independent reflections with I > 3σ(I). Anions 1 and 2 have a tetrahedral Ru2Rh2 metal frame, while in 3 there is a trigonalbipyramidal frame with one ruthenium atom and the gold atom in apical positions; in 2 the H atom bridges the Ru-Ru edge. 1H and 31P NMR spectra of, respectively, 2 and 3 are consistent with the crystal structures. 13C NMR spectra of both 1 and 2 show evidence of fluxional behavior at 295 K which cannot be frozen at 178 K, where the signals collapse; compound 3 at room temperature shows a partially fluxional solution structure which becomes static at ca. 250 K. 1 [PPh4]2[Ru2Rh2(CO)12]: bis(tetraphenylphosphomum) 1,3;1,4;2,3;2,4;3,4-pentakis(μ-carbonyl)-1,1.2,2,2,3,4-heptacarbonyl- tetrahedro-1,2-diruthenium-3,4-dirhodiate. [PPh4][Ru2Rh2(CO)12H]: tetraphenylphosphonium 1,2-(μhydrido)-1,3;1,4;3,4-tris(μ-carbonyl)-1,1,2,2,2,3,3,4,4- nonacarbonyl-tetrohedro-1,2-diruthenium-3,4-dirhodiate. [PPh4][Ru2Rh2(CO)12(AuPPh 3)]: tetraphenylphosphonium 1,3,4-(μ3-triphenylphosphine)aurio)-1,3; 1,4;2,3;2,4;3,4-pentakis(μ-carbonyl)-1,1,2,2,2,3,4-heptacarbonyl-/tetrahedro- 1,2-dinithenium-3,4-dirhodiate.