Synthesis of heterodinuclear FeRu(CO) 6(R-DAB(6e))(R-DABRNC(H)C(H)NR) Part XV. Comparison of the reactivities of heterodinuclear FeRu(CO) 6(R-DAB(6e)) and homodinuclear analogues M 2(CO) 6(R-DAB(6e)) (M = Fe, Ru). Single-crystal x-ray structures of FeRu(CO) 6(i-Pr-DAB(6e)) and FeRu(CO) 5(i-Pr-DAB(4e))(C 3H 4)

Abstract

The reactions of Fe(CO) 3(R-DAB; R 1, H(4e)) ( 1a: R = i-Pr, R 1 = H; 1b: R = t-Bu, R 1 = H; 1c: R = c-Hex, R 1 = H; 1e: R = p-Tol, R 1 = H; 1f: R = i-Pr, R 1 = Me) with Ru 3(CO) 12 and of Ru(CO) 3(R-DAB; R 1, H(4e)) ( 2a: R = i-Pr, R 1 = H; 2d: R = CH(i-Pr) 2, R 1 = H) with Fe 2(CO) 9 in refluxing heptane both afforded FeRu(CO) 6(R-DAB; R 1, H(6e)) (3) in yields between 50 and 65%. The coordination mode of the ligand has been studied by a single crystal X-ray structure determination of FeRu(CO) 6(i-Pr-DAB(6e)) ( 3a). Crystals of 3a are monoclinic, space group P2 1/ a, with four molecules in a unit cell of dimensions: a = 22.436(3), b = 8.136(3), c = 10.266(1) Å and β = 99.57(1)°. The structure was refined to R = 0.049 and R w = 0.052 using 3045 reflections above the 2.5σ( I) level. The molecule contains an FeRu bond of 2.6602(9) Å, three terminally bonded carbonyls to Fe, three terminally bonded carbonyls to Ru and bridging 6e donating i-Pr-DAB ligand. The i-Pr-DAB ligand is coordinated to Ru via N(1) and N(2) occupying an apical and equatorial site respectively (RuN(1) = 2.138(4) RuN(2) = 2.102(3) Å). The C(2)N(2) moiety of the ligand is η 2-coordinated to Fe with C(2) in an apical and N(2) in an equatorial site (FeC(2) = 2.070(5) and FeN(2) = 1.942(3) Å). The 1H and 13C NMR data indicate that in all FeRu(CO) 6(R-DAB(6e)) complexes ( 3a to 3f) exclusively η 2-CN coordination to the Fe atom and not to the Ru atom is present irrespective of whether 3 was prepared by reaction of Fe(CO) 3(R-DAB(4e)) ( 1) with Ru 3(CO) 12 or by reaction of Ru(CO) 3(R-DAB(4e)) ( 2) with Fe 2(CO) 9. In the case of FeRu(CO) 6(i-Pr-DAB; Me, H(6e)) ( 3f) the NMR data show that only the complex with the C(Me)N moiety of the ligand σ-N coordinated to the Ru atom and the C(H)N moiety η 2-coordinated to the Fe atom was formed. Variable temperature NMR experiments up to 140 °C showed that the α-diimine ligand in 3a is stereochemically rigid bonded. FeRu(CO) 6(R-DAB(6e)) ( 3a and 3e) reacted with allene to give FeRu(CO) 5(R-DAB(4e))(C 3H 4) ( 4a and 4e). A single crystal X-ray structure determination of FeRu(CO) 5(i-Pr-DAB(4e))(C 3H 4) ( 4a) was performed. Crystals of 4a are triclinic, space group P1, with two molecules in a unit cell of dimensions: a = 9.7882(7), b = 12.2609(9), c = 8.3343(7) Å, α = 99.77(1)°, β = 91.47(1)° and γ = 86.00(1)°. The structure was refined to R = 0.028 and R w = 0.043 using 4598 reflections above the 2σ( I) level. The molecule contains an FeRu bond of 2.7405(7) Å and three terminally bonded carbonyls to iron. Two carbonyls are terminally bonded to the Ru atom together with a chelating 4e donating i-Pr-DAB ligand [RuN = 2.110(1) (mean)]. The allene ligand is coordinated in an η 3-allylic fashion to the Fe atom while the central carbon of the allene moiety is σ-bonded to the Ru atom (FeC(14) = 2.166(3), FeC(15) = 1.970(2), FeC(16) = 2.127(3) and RuC(15) = 2.075(2) Å). The 1H and 13C NMR data show that in solution the coordination modes of the R-DAB and the allene ligands are the same as in the solid state. Thermolysis reactions of 3a with R-DAB or carbodiimides gave decomposition and did not afford C(imine)C(reactant) coupling products. Thermolysis reactions of 3a with M 3(CO) 12 (M = Ru, Os) and Me 3NO gave decomposition. When the reaction of 3a with Me 3NO was performed in the presence of dimethylacetylenedicarboxylate (DMADC) the known complex FeRu(CO) 4(i-Pr-DAB(8e))(DMADC) ( 5a) was formed in low yield. In 5a the R-DAB ligand is in the 8e coordination mode with both the imine bonds η 2-coordinated to iron. The acetylene ligand is coordinated in a bridging fashion, parallel with the FeRu bond.