Rational Synthesis of Tetranuclear Ruthenium Polyhydride Clusters and Their Mixed-Ligand Analogues

Abstract

The reactivity of transition-metal cluster complexes has recently been attracted considerable attention because of their potential applicability to organic synthesis. [1] There have been a number of examples of unique reaction modes, such as successive cleavage of the carbon±hydrogen bond of alkanes, [2] the cleavage of the carbon±carbon double bond of 1,1'-disubstituted alkenes, [3] and the catalytic hydrogenation of aromatic compounds in aqueous media, [4] originating from the cooperative action of the metal centers. The advantageous properties of a multimetallic system over a monometallic one in the substrate activation step are its ability to multiply coordinate the substrate and the multielectron transfer between the substrate and the cluster. Such unique reactivity of the cluster likely comes from these two remarkable properties. The reactivity is most probably affected by the nuclearity of the cluster because the reactivity strongly depends on the number of transferable electrons: the more nuclei in the cluster, the more effectively electrons are transferred. [5] It is well established for mononuclear transition-metal complexes that the auxiliary ligand allows control over the reactivity of the complex through electronic and steric perturbation of the reaction site. Thus, the development of a rational method for the synthesis of clusters with higher nuclearity and a variety of auxiliary ligands seems to be essential for the application of such clusters to organic synthesis.Recently, we have established the high and unique reactivity of the di-and trinuclear ruthenium polyhydride com- plexes [{(h 5 -C 5 Me 5 )Ru} 2 (m-H) 4 ] (1) and [{(h 5 -C 5 Me 5 )Ru} 3 -(m-H) 3 (m 3 -H) 2 ](2). [6] As an extension of the chemistry of ™trimetallic activation∫, we tackled the development of a rational method for the synthesis of a tetranuclear ruthenium polyhydride cluster. We report herein, to the best of our knowledge, the first example of a rational synthesis of a series of tetranuclear polyhydride complexes having several combinations of the auxiliary cyclopentadienyl ligands.Treatment of [CpRuCl 2 (h 3 -C 3 H 5 )] (3 a) [7] (Cp ¼ h 5 -C 5 H 5 ) with LiAlH 4 in tetrahydrofuran followed by workup with ethanol [Eq. (1)] gave a new complex which was identified as the tetranuclear ruthenium hexahydride [(CpRu) 4 H 6 ] (4 a) by 1 H and 13 C NMR spectroscopy and an X-ray diffraction study. In a similar manner, tetranuclear clusters [{(h 5 -C 5 H 4 Me)Ru} 4 H 6 ] (4 b) and [{(h 5 -1,3-Me 2 C 5 H 3 )Ru} 4 H 6 ] (4 c) were derived from the corresponding Ru IV precursors, [(h 5 -C 5 H 4 Me)RuCl 2 (h 3 -C 3 H 5 )] (3 b) and [(h 5 -1,3-Me 2 -C 5 H 3 )RuCl 2 (h 3 -C 3 H 5 )] (3 c), [8] respectively. Although the yields of 4 a and 4 c were not high (ca. 40 %), the 1 H NMR spectra of the crude products obtained after removal of the aluminum salt showed that the tetranuclear hydride complexes 4 a and 4 c were formed exclusively. In the reaction of 3 b with LiAlH 4 , however, the formation of 4 b was accompanied by a significant ...

Mechanisms of Reduction of M(H2O)kn+ To Form M°-Nano-Particles in Aqueous Solutions Differs from That Commonly Assumed: The Reduction of Ag(H2O)2+ by H2

“…Analogous structures were reported for other silver compounds. 28,31 Even a tridentate hydrogen is obtained in Ag 6 (H 2 O) 3 H 6 , analogous μ3-H were observed previously. 32 In all the clusters discussed above Ag−Ag bonds are formed.…”

“…The results are in good agreement with other Ag–Ag bond lengths. − In the cyclic structures there are bidentate hydrogens. Analogous structures were reported for other silver compounds. , Even a tridentate hydrogen is obtained in Ag 6 (H 2 O) 3 H 6 , analogous μ3-H were observed previously . In all the clusters discussed above Ag–Ag bonds are formed.…”

16 The noble metals

“…52 The neo-menthyl cyclopentadienyl (L) complex [RuL(Me)(CO)PPh 3 ] undergoes Ru-Me bond cleavage with retention of configuration using hydrogen halides, but the slower reaction with halogens allowed an intermediate to isomerise. 53 Studies of complexes derived from the 16-electron cation [Ru(Cp)ClL 2 ] (L = phosphine) resulted in the isolation and structural characterization of 55 An unusual stable Ru(0) aqua complex has been isolated using dimethylfumarate (MeO 2 CCH᎐ ᎐ CHCO 2 Me, L) as alkene ligand. [Ru(η 6 -cot)L] reacts with dppe in C 2 H 4 Cl 2 to give the known complexes [Ru(dppe) 2 L] and [Ru(dppe)L 2 ], but also as major product [Ru(dppe)L 2 (H 2 O)], in which the coordinated water is stabilised by hydrogen bonding with the ester carbonyl groups.…”

Group 15 ligand migration in the heteronuclear clusters RuOs3(μ-H)2(CO)12(EPh3) (E=P, As, Sb)

“…Ligand migration involving triorganophosphine (PR 3 ) ligands has sometimes been invoked in the fluxional behaviour of organometallic compounds [1][2][3]. However, there are very few examples in the literature in which activation parameters and standard free energy values for PR 3 migration are available.…”

“…However, there are very few examples in the literature in which activation parameters and standard free energy values for PR 3 migration are available. To our knowledge, only two examples have been reported; these are: (i) a series of diruthenium dihydrido complexes, [Cp*Ru] 2 (PR 3 )(l-H) 2 (R = Me, Et, i-Pr, Cy, Bz, OMe, OPh), in which the PR 3 ligand migrated between the two Ru centres (no new isomer was produced) [2], and (ii) the heterometallic clusters PtRu 5 (CO) 16 (l 6 -C)(PMe 2 Ph) and PtRu 5 (CO) 16 (l 6 -C)(PMe 3 ), in which the phosphine ligand migrated between the Pt (major isomer) and the Ru (minor isomer) vertices of an octahedron, with a concomitant CO shift [3]. We have recently reported that the heteronuclear cluster RuOs 3 (l-H) 2 (CO) 13 (1) undergoes facile substitution with PPh 3 under trimethylamine N-oxide activation, to afford the mono-and disubstituted derivatives RuOs 3 (l-H) 2 (CO) 13Àn (PPh 3 ) n (n = 1 (2a) or 2 (3a)).…”