Conversion of 48e Os3(CO)10(R-DAB(4e)) via 50e Os3(CO)10(R-DAB(6e)) to 50e Os3(CO)9(R-DAB(8e)) (R-DAB = RN=C(H)C(H)=NR). X-ray structure of Os3(CO)9(i-Pr-DAB(8e)), with two elongated Os-Os bonds

Article abstract of DOI:10.1021/om00100a006

The 48e cluster Os₃(CO)₁₀(i-Pr-DAB(4e)) (1b)^1b with a chelating 4e-donating i-Pr-DAB ligand (abbreviated as i-Pr-DAB(4e)) is converted in refluxing n-hexane into the 50e cluster Os₃(CO)₁₀(i-Pr-DAB(6e)) (2b) with a bridging 6e-donating i-Pr-DAB ligand (abbreviated as i-Pr-DAB(6e)). By further heating 2b is decarbonylated to give Os₃(CO)₉(i-Pr-DAB(8e)) (3b) with an 8e-donating i-Pr-DAB ligand (abbreviated as i-Pr-DAB(8e)). Under similar reaction conditions Os₃(CO)₁₀(C-Pr-DAB(6e)) (2a) reacted to give Os₃(CO)₉(C-Pr-DAB(8e)) (3a). Thermolysis of Os₃(CO)₁₀(neo-Pent-DAB(4e)) (1c) in refluxing n-hexane gave a complicated mixture of products from which no pure compound could be isolated. The complexes have been characterized by NMR, IR, and FD-mass spectroscopy while a single-crystal X-ray structure determination has been carried out for 3b. Crystals of Os₃(CO)₉(i-Pr-DAB(8e)) (3b) are monoclinic, space group C2/c, with a = 31.145 (2) ?, b = 10.228 (1) ?, c = 15.429 (1) ?, β = 110.13 (1)°, and Z = 8. The structure has been solved via the heavy-atom method and refined to R = 0.041 and R_w = 0.045 using 3150 independent reflections above the 2.5σ(I) level. The compound contains a triangular array of Os atoms with two elongated Os-Os distances [Os(1)-Os(2) = 3.0839 (7) ? and Os(2)-Os(3) = 2.9513 (7) ?] while the third Os-Os distance is shortened [Os(I)-Os(3) = 2.7969 (7) ?] when compared to the Os-Os distances in Os₃(CO)_12- The i-Pr-DAB ligand is σ,σ-N,N′-coordinated to Os(2) while both imine bonds are η²-coordinated to Os(1). The latter is indicated by the equal distances between Os(1) and the C and N atoms of the flat N(1)=C(10)-C(11)=N(2) skeleton as well as the lengthened C=N and shortened C(10)-C(11) bond distances [1.390 (8) ? (mean)]. Accordingly the diimine ligand is in a symmetrical 8e-coordination mode. Electron counting shows that 3b sould be considered as a 50e trinuclear species in which no Os-Os bond seems realy to be broken. It is shown that this structure may be interpreted by the polyhedral skeletal electron pair theory (PSEP). FTIR kinetic measurements show that, with approximately first-order kinetics, Os₃(CO)₁₀(i-Pr-DAB(4e)) (1b) converts to Os₃(CO)₁₀(i-Pr-DAB(6e)) (2b) and subsequently to Os₃(CO)_10-(i-Pr-DAB(8e)) (3b).