Synthesis of new heterometallic complexes by tin–sulfur bond cleavage of pySSnPh₃ (pySH = pyridine-2-thiol) at triruthenium and triosmium centres

Abstract

The ruthenium–tin complex, [Ru₂(CO)₄(SnPh₃)₂(μ-pyS)₂] (1), the main product of the oxidative-addition of pySSnPh₃ to Ru₃(CO)₁₂ in refluxing benzene, is [Ru(CO)₂(pyS)(SnPh₃)] synthon. It reacts with PPh₃ to give [Ru(CO)₂(SnPh₃)(PPh₃)(κ²-pyS)] (2) and further with Ru₃(CO)₁₂ or [Os₃(CO)₁₀(NCMe)₂] to afford the butterfly clusters [MRu₃(CO)₁₂(SnPh₃)(μ₃-pyS)] (3, M=Ru; 4, M=Os). Direct addition of pySSnPh₃ to [Os₃(CO)₁₀(NCMe)₂] at 70 °C gives [Os₃(CO)₉(SnPh₃)(μ₃-pyS)] (5) as the only bimetallic compound, while with unsaturated [Os₃(CO)₈{μ₃-PPh₂CH₂P(Ph)C₆H₄}(μ-H)] the previously reported [Os₃(CO)₈(μ-pyS)(μ-H)(μ-dppm)] (6) and the new bimetallic cluster [Os₃(CO)₇(SnPh₃){μ-Ph₂PCH₂P(Ph)C₆H₄}(μ-pyS)[(μ-H)] (7) are formed at 110 °C. Compounds 1, 2, 4, 5 and 7 have been characterized by X-ray diffraction studies.

Introduction

Transition metal–tin complexes have attracted considerable interest primarily because tin can be used to modify bimetallic catalysts, improving their reactivity and product selectivity in a variety of chemical transformations [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]. Further it has recently been found that the binding of metallic nanoparticles to oxide supports can be enhanced by the incorporation of tin [10], [11], [12], [13], [14]. There are several methods for the incorporation of tin into transition metal complexes. The most widely used method is the oxidative-addition of organotin hydrides and using this methodology a number of transition metal–tin clusters with intriguing structural features have been synthesized, as exemplified by the work of Adams and coworkers [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26]. More recently other tin-element oxidative-addition reactions have been exploited, for example Gárate-Morales and Fernández-G have prepared amine-containing osmium–tin compounds via the cleavage of the nitrogen–tin bond in aminostannanes [27], [28], [29]. Our group have shown that tetraphenylthiostannane is an excellent source for the inclusion of both tin and sulfur atoms into transition metal clusters [30], reaction of Ru₃(CO)₁₂ with Ph₃Sn-SPh affording bimetallic [Ru₃(CO)₈(SnPh₃)₂(μ₃-SnPh₂)(μ-SPh)₂] resulting from both tin–sulfur and tin–carbon bond cleavage (Scheme 1) [30], [31].

If tin-containing transition metal clusters are to be used towards the synthesis of catalytically active nanoparticles then facile and high-yielding routes to these clusters is a necessity [32]. We were encouraged by the facile nature of the tin–sulfur bond cleavage (Scheme 1) but sought to limit this to a single addition rather than the multiple addition products found with Ph₃Sn-SPh. In order to do this we considered the introduction of a thiolate ligand with secondary binding sites and consequently we have investigated reactions of pyridine-2-thiolate-triphenyltin (pySSnPh₃) with triruthenium and triosmium clusters. Thus, in contrast to the phenylsulfide ligand which generally acts either as a terminal one-electron, or bridging three-electron, donor ligand, the pyridine-2-thiolate ligand (pyS) can coordinate to metal centres in a wide variety of ways (Chart 1) which in turn is expected to influence the nature of the products formed. Indeed this is the case as we have found that the presence of the coordinating nitrogen atom substantially affects the course of the reactions and we obtained a completely different set of products to the related reactions with PhS-SnPh₃. These findings are presented herein.