Synthesis and characterization of two isomers of decacarbonyl(1,4-dialkyl-1,4-diaza-1,3-butadiene)triosmium: Os3(CO)10(R-DAB). Fluxional behavior of Os3(CO)10(i-Pr-DAB(4e)). Molecular structures of the 48e cluster Os3(CO)10(i-Pr-DAB(4e)) and of the 50e cluster Os3(CO)10 ...

Robert Zoet, Johann T B H Jastrzebski, Gerard Van Koten, Taasje Mahabiersing, Kees Vrieze*, Dick Heijdenrijk, Casper H. Stam

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Full title: Synthesis and characterization of two isomers of decacarbonyl(1,4-dialkyl-1,4-diaza-1,3-butadiene)triosmium: Os3(CO)10(R-DAB). Fluxional behavior of Os3(CO)10(i-Pr-DAB(4e)). Molecular structures of the 48e cluster Os3(CO)10(i-Pr-DAB(4e)) and of the 50e cluster Os3(CO)10(C-Pr-DAB(6e)) containing a 4e donor σ,σ-N,N′ and a 6e donor σ-N, μ2-N′, η2-C=N′ bonded R-DAB ligand, respectively. Os3(CO)10(MeCN)2 reacts at room temperature with 1,4-disubstituted-1,4-diaza-1,3-butadiene (R-DAB)1b to yield two isomers (1 and 2) of Os3(CO)10(R-DAB). The product ratio depended on the R group and in one case on the polarity of the solvent. When R = neo-Pent, Os3(CO)10(neo-Pent-DAB(4e)) (1c) was isolated, whereas with R = c-Pr, Os3(CO)10(c-Pr-DAB(6e)) (2a) was the only product. In the case of R = i-Pr reactions in MeCN and THF gave Os3(CO)10(i-Pr-DAB(4e)) (1b), whereas the reaction in toluene afforded Os3(CO)10(z-Pr-DAB(6e)) (2b). The structure in the solid state of both isomers (1b and 2a) has been determined. Crystals of Os3(CO)10(i-Pr-DAB(4e)) (isomer 1) are triclinic, space group P1, with a = 10.777 (2) Å, b = 13.562 (2) Å, c = 8.426 (2) Å, α = 98.92 (2)°, β = 96.45 (2)°, γ = 90.00 (2)°, and Z = 2. The structure was solved via the heavy-atom method and refined to R = 0.047 and Rw = 0.097 by using 3949 independent reflections above the 3σ(I) level. The structure consists of a Os3(CO)10 unit to which a R-DAB ligand is chelate (4e) bonded. One N atom occupies an axial site and the other an equatorial site [Os(1)-N(1) = 2.07 (1) Å and Os(1)-N(2) = 2.11 (1) Å]. The C=N bonds are slightly lengthened compared to the free ligand [C=N = 1.30 (3) Å (mean)] while the central C-C′ bond is slightly shortened [C(11)-C(12) = 1.41 (2) Å]. Variable-temperature 13C (125 MHz) and 1H NMR (500 MHz) experiments for 1b and 1c demonstrated that there are at least three fiuxional processes for 1b depending on the temperature range. From 193 K a rocking motion of the R-DAB ligand is observed above the osmium triangle about one axial and two equatorial sites on one osmium atom. Above 203 K a second process is observed involving pairwise bridge-terminal carbonyl interchanges perpendicular to the plane of the osmium triangle, while above 293 K various processes occur whereby all carbonyls are scrambled. Crystals of Os3(CO)10(c-Pr-DAB(6e)) (isomer 2) are triclinic, space group P1, with a = 9.775 (3) Å, b = 13.730 (4) Å, c = 9.222 (5) Å, α = 107.39 (3)°, β = 101.04 (5)°, γ = 87.84 (3)°, and Z = 2. The structure was solved via the heavy-atom method and refined to R = 0.052 and Rw = 0.059 by using 4243 independent reflections above the 2.5σ(I) level. The molecule contains a bridging 6e donating R-DAB ligand, bonded in the σ-N, μ2-N′, η2-C=N′ coordination mode: σ-N to Os(1) [Os(1)-N(1) = 2.12 (1) Å], symmetrically μ2-N′ bridging Os(1) and Os(2) [Os(1)-N(2) = 2.12 (1) Å and Os(2)-N(2) = 2.12 (1) Å], and η2-C=N′ bonded to Os(2) by means of the C(2)-N(2) π-bond of the imine system [Os(2)-C(2) = 2.14 (2) Å]. This 50e cluster comprises an opened metal polyhedron with two normal Os-Os bonds [Os(1)-Os(3) = 2.931 (3) Å and Os(2)-Os(3) = 2.928 (5) Å] and a nonbonding Os(1)⋯Os(2) distance of 3.591 (3) Å. Os(1) and Os(2) are held together by the bridging ligand. The Os(1)-Os(3)-Os(2) angle is 75.6 (1)°.

Original languageEnglish
Pages (from-to)2108-2117
Number of pages10
JournalOrganometallics
Volume7
Issue number10
Publication statusPublished - 1988
Externally publishedYes

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