Reversible syntheses of mono-(cyclopentadienyl)rhodium-tri-ruthenium cluster complexes and (η-C 5Me 5) 2Rh 2Ru 2(CO) 7; crystal and molecular structures of CpRhRu 3{μ-H} 2{μ-CO}(CO) 9, Cp = η-C 5H 5 or η-C 5Me 5 and (η-C 5Me 5)Rh{μ-H} 2Ru 3{μ-H} 2(CO) 9

Abstract

The mixed metal complexes CpRhRu 3{μ-H} 2{μ-CO}(CO) 9, ( 3a: Cp = η-C 5H 5; 3b: Cp = η-C 5Me 5) 4b: (η-C 5Me 5)RhRu 3{μ-H} 4(CO) 9, 5: (η-C 5Me 5) 2Rh 2Ru 2(CO) 7) are formed when H 2 is bubbled through solutions of Ru 3(CO) 12 and the respective CpRh(CO) 2 at 70–90°C. These are easily disrupted at 25°C back into the starting materials under an atmosphere of CO. Using 13CO, the starting materials are obtained with complete 13CO exchange. While CpRh(CO) 2 undergoes exchange at 25°C with 13CO at atmospheric pressure, Ru 3(CO) 12 does not, nor does it exchange in the presence of simply an added amount of CpRh(CO) 2. Attachment of the CpRh moiety to the Ru 3 skeleton as in the products obtained in this work thus leads, under 13CO, to the completely enriched starting materials Ru 3( 13CO) 12 and CpRh( 13CO) 2. Structures of three new products have been determined using a Picker (FACS-1) four circle automated diffractometer and graphite-monochromatized Mo- K α radiation. For 3a, 3831 unique reflections with I > 3σ( I) were used in the refinement; final discrepancy indices, R = 0.030 and R w = 0.050. Complex 3a crystallizes in the monoclinic space group P2 1/ n; cell dimensions a 8.1856(5), b 15.0706(10), c 16.3013(12) Å, and β 91.033(1)°; calculated density 2.49 g cm −3. For 3b, 4801 unique reflections with I > 3σ( I) were used in the refinement; final discrepancy indices, R = 0.026 and R w = 0.042. Complex 3b crystallizes in the monoclinic space group P2 1/ n in a cell having the dimensions of a 8.7580(5), b 14.5578(8), c 19.829(1) Å, and β 97.591(2)°; calculated density 2.18 g cm −3. For 4b, 6756 unique reflections with I > 3σ( I) were used in the refinement; final discrepancy indices, R = 0.030 and R w = 0.040. Complex 4b crystallizes in the monoclinic space group P2 1/ a; cell dimensions a 17.470(1), b 18.451(1), c 17.200(1) Å, and β 114.684(1)°; calculated density 2.10 g cm −3. Metal atoms in all three structures were located by direct methods (MULTAN80). All other nonhydrogen atoms were then located by difference maps. Hydrogen atoms bridging various edges of the clusters were located after all hydrogen atoms in the η-C 5H 5 (= Cp) or η-C 5(CH 3) 5 (= Cp★) groups were refined isotropically in calculated positions. Each of the crystals studied consists of discrete molecules of the complexes, each with a triangle of ruthenium atoms capped by a CpRh or Cp★Rh group. Isomeric structures are observed for 3a and 3b. In the former, a CO group is found bridging between one Ru atom and the Rh atom while one each of two cluster-bound hydrogen atoms bridge two separate edges of the Ru 3 triangle. In 3b, both a CO group and one of the cluster-bound hydrogen atoms are found bridging between Rh and two separate Ru atoms of the Ru 3 triangle. The remaining cluster-bonded hydrogen atom is found bridging one edge of the Ru 3 triangle. In 4b, two of the cluster-bound hydrogen atoms are found (one each) on two edges of the Ru 3 triangle. The other two are found bridging each of two of the RuRh bonds. The metal—metal separations in the three structures are summarized as follows. Unbridged RuRu and RhRu fall in the ranges 2.765(1) to 2.813(1) Å and 2.707(1) to 2.752(1) Å, respectively; the Rh-μ-(CO)-Ru separations are 2.727(1) (in 3a) and 2.7515(1) (in 3b). Ru-μ-(H)-Ru separations fall in the range 2.870(1) to 2.938(1) Å while Rh-μ-(H)-Ru fall in the range 2.871(1) to 2.9169(1) Å.