94250-10-9Relevant academic research and scientific papers
Ruthenium carbonyl 1,4-diaza-1,3-butadiene (R-DAB) reaction sequence. Reversible CO addition to a trinuclear species without rupture of a metal-metal bond. Molecular structure of [1,4-dicyclohexyl-1,4-diaza-1,3-butadiene]nonacarbonyltriruthenium, Ru3(CO)9(c-Hx-DAB): A unique 50e trinuclear compound with two elongated Ru-Ru bonds
Keijsper, Jan,Polm, Louis H.,Van Koten, Gerard,Vrieze, Kees,Seignette, Paul F. A. B.,Stam, Casper H.
, p. 518 - 525 (2008/10/08)
Ru3(CO)12 reacts with 1,4-disubstituted 1,4-diaza-1,3-butadienes, R-DAB = R-N=C(H)-C(H)=N-R (R = i-Pr, c-Hx, neo-Pent, i-Bu, p-Tol), to yield mononuclear Ru(CO)3(R-DAB) as a (c-Hx-DAB)) observable intermediate. This monomer reacts further with Ru3(CO)12 to give known dimeric Ru2(CO)n(R-DAB) (n = 5, 6) compounds. Dimeric Ru2(CO)6(c-Hx-DAB) reacts with Ru3(CO)12 to yield novel trinuclear Ru3(CO)9(c-Hx-DAB), which was characterized by an X-ray crystal structure determination. Crystals of Ru3(CO)9(c-Hx-DAB) are monoclinic, space group P21/n and cell constants a = 11.695 (2) ?, b = 10.306 (2) ?, c = 23.193 (3) ?, β = 102.73 (1)°, and Z = 4. A total of 2968 reflections have been used in the refinement, which results in a final R value of 0.034. In the triangular array of Ru atoms, there are two elongated Ru-Ru distances (Ru(1)-Ru(2) = 3.026 (1) ?, Ru(2)-Ru(3) = 2.956 (1) ?) while the third is normal (Ru(1)-Ru(3) = 2.793 (1) ?). All nine carbonyls are terminally bonded: four to Ru(3), three to Ru(2), and two to Ru(1). The c-Hx-DAB ligand is σ-N,σ-N′ coordinated to Ru(2) with equal, normal Ru-N distances of 2.13 (1) ? (mean). The four atoms of the N(1)=C(1)-C(2)=N(2) skeleton are located equal distances (2.22 (1) ?) (mean) from Ru(1), consistent with η2 coordination of both double bonds to Ru(1). Also, the bond lengths within this N(1)=C(1)-C(2)=N(2) part are equal (1.39 (1) ?) (mean), indicating that the diimine ligand is in a symmetrical 8e, σ-N,σ-N′,η2-C=N,η 2-C′=N′ coordination mode. As a consequence, Ru3(CO)9(c-Hx-DAB) is considered as a 50e - (3 × 8e (Ru) + 9 × 2e (CO) + 8e (c-Hx-DAB)) trinuclear species. Assuming 2e-2c Ru-Ru bonds, the structure does not obey the 18e rule, but it is shown that it can be interpreted on the basis of the polyhedral skeletal electron pair theory (PSEPT). Ru3-(CO)9(R-DAB) (R = neo-Pent, i-Bu), which have according to spectral data the same geometry as Ru3(CO)9(c-Hx-DAB), are instaneously formed in the reaction of Ru3(CO)8(R-DAB) with CO gas in toluene. This reaction can easily be reversed by heating Ru3(CO)9(R-DAB) in toluene or by treating it with Me3NO. The traffic light like color change during this reaction, which is reversible, is very remarkable: Ru3(CO)8(R-DAB) (bright green) + CO ? Ru3(CO)9(R-DAB) (bright red). Based on a structural comparison between Ru3(CO)8(R-DAB) and Ru3(CO)9(R-DAB), a rationale is given for the ease of CO addition, which does not lead to the complete rupture of bonds. Furthermore, the analogy between the reactions of Fe2(CO)9 and of Ru3(CO)12 with R-DAB is discussed. On the basis of PSEPT, the analogy between the reactions of Ru2(CO)5(R-DAB) and of isolobal Ru3-(CO)8(R-DAB) with CO is discussed.
