Rearrangement and Scission of Terminal Alkynes in Dimolybdenum Complexes on Reaction with Ruthenium Carbonyl:  Formation of Trinuclear Vinylidene and Hexanuclear Bis(alkylidyne) Clusters

Abstract

The reaction of the dimolybdenum alkyne complexes Mo 2 (CO) 4 (µ-R 1 CtCR 2 )Cp 2 (Cp ) η-C 5 H 5 ; R 1) H, R 2 ) H, Me, Ph, CO 2 Me; 1a-d) with Ru 3 (CO) 12 in refluxing toluene or heptane affords reasonable yields of the orange µ 3 -vinylidene clusters [Mo 2 Ru(µ 3 -CdCHR 2 )(CO) 7 Cp 2 ] (2a-d). The crystal structure of Mo 2 Ru(µ 3 -CdCHMe)(CO) 7 Cp 2 (2b) has been determined and shows that the metal triangle is capped by a vinylidene ligand which is formally σ-bound to the two molybdenum atoms and π-bound to the ruthenium. Low to moderate yields of the blue-turquoise hexanuclear bis(alkylidyne) clusters Mo 2 Ru 4 (µ 3 -CR 1 )(µ 3 -CR 2 )(CO) 12 Cp 2 (3a-d) are formed in addition to the vinylidene clusters, especially if the reaction is carried out in heptane. The synthesis of 3a is particularly noteworthy, as it represents the first example of the scission of ethyne into two methylidyne fragments on a metal cluster. The disubstituted alkyne complex 1e (R 1) R 2 ) Me) leads to the corresponding hexanuclear cluster 3e in either solvent, but complexes of bulkier disubstituted alkynes 1f and 1g (R 1 ) R 2) Et, CO 2 Me) do not give analogous products. The X-ray crystal structure of the cluster Mo 2 Ru 4 (µ 3 -CMe) 2 (CO) 12 Cp 2 ‚CH 2 Cl 2 (3e‚CH 2 Cl 2 ) reveals an octahedral metal core in which the two MoCp fragments occupy adjacent positions, with the two alkylidyne groups formed by scission of the alkyne ligand capping the two Mo 2 Ru faces. Unusually for octahedral clusters, complexes of type 3 have 84 cluster valence electrons.

Dithiolene transfer from nickel to a dimolybdenum centre: the first dithiolene alkyne complex

“…Elemental analyses were carried out by the Microanalytical Service of the Department of Chemistry. Complex 1 was prepared by a slight adaptation of the literature procedure [10,19].…”

Site-selective substitution and vinylidene–alkylidyne–vinylidene interconversion in dimolybdenum–ruthenium clusters

“…As expected, the structure is very similar to that of 1b which we reported previously. 6 The two Mo᎐Ru bonds in 2b are slightly longer than in 1b but the Mo᎐Mo bond is if anything slightly shorter, while the geometry of the vinylidene ligand itself is, within experimental error, identical in both compounds. The phosphine ligand occupies a position essentially trans to one of the Mo᎐Ru bonds.…”

“…Recently we reported that the readily available complexes [Mo 2 (µ-HC᎐ ᎐ ᎐ CR)(CO) 4 (η-C 5 H 5 ) 2 ] undergo rearrangement of the alkyne ligand on reaction with [Ru 3 (CO) 12 ] to give the trinuclear vinylidene clusters [Mo 2 Ru(µ 3 -C᎐ ᎐ CHR)(CO) 7 -(η-C 5 H 5 ) 2 ] (R = H 1a, Me 1b, Ph 1c or CO 2 Me 1d) in reasonable yields (typically 45%). 5, 6 We have now examined the reactivity of these clusters towards phosphines, and here report that they undergo site-selective substitution of a ruthenium-bound CO ligand by PPh 2 Me, and also react with PPh 2 H to give monoand bis-phosphido-bridged clusters. This latter reaction also involves the sequential conversion of the vinylidene ligand first into an alkylidyne and then back to a vinylidene.…”

[μ-3-(8-Quinolyloxy)propanediyl]bis[dicarbonyl(η5-methoxycarbonylcyclopentadienyl)molybdenum(III)]

“…For general background to dimolybdenum alkyne complexes, see: Conole et al (1989Conole et al ( , 1990; Adams et al (1995Adams et al ( , 1996; Muetterties (1980); Gibson et al (1991); Brady & Pettit (1980); Sappa et al (1983Sappa et al ( , 1985; Raithby & Rosales (1985). For semibridging CO ligands, see: ; Klingler et al (1978).…”

“…Financial support from the National Natural Science Foundation of China (No. 20572064) The dimolybdenum alkyne complexes have been extensively examined (Conole et al, 1989(Conole et al, , 1990Adams et al, 1995Adams et al, , 1996 due to their potential applications in catalysis and materials (Muetterties, 1980;Gibson et al, 1991;Brady & Pettit, 1980). Moreover, such complexes can be used as precursors for constructing higher-nuclearity alkyne clusters (Sappa et al, 1983(Sappa et al, , 1985Raithby & Rosales, 1985).…”