Metallosupramolecular cluster assemblies based on donor-acceptor type structural frameworks. Syntheses, crystal structures and spectroscopic properties of novel triosmium alkylidyne carbonyl clusters bearing remote ferrocenyl units as electron donors

Two pyridyl ligands containing redox-active ferrocenyl groups [Fe(η5-C5H5)(η-5C 5H4C6H4R)] [R = C5H 4N I or NCH(C5H4N) II] have been prepared using a palladium-catalysed aromatic cross-coupling reaction. Treatment of the cluster [Os3(μ-H)3(CO)9(μ3- CCl)] with one equivalent of 1,8-diazabicyclo[5.4.0] undec-7-ene in the presence of a ten-fold excess of the ferrocenyl ligands I and II produces the compounds [Os3(μ-H)2(CO)9(μ3-CNC 5H4R′)] [R′ = C6H 4(η5-C5H4)Fe(η5- C5H5) 1, R′ = CHNC6H4(η 5-C5H4)Fe(η5-C5H 5) 2] respectively in good yields. Both compounds 1 and 2 exhibit donor-π-acceptor structural frameworks and show considerable negative solvatochromism in their UV/VIS spectra. Unlike 1 and 2 which possess extended donor-π-acceptor nature, the ferrocenyl-phosphine cluster derivative [Os 3(μ-H)2(CO)9{μ3-CPPh 2(η5-C5H4)Fe(η5- C5H4PPh2)}] 3 has also been synthesised in moderate yield by the same synthetic route using 1,1′- bis(diphenylphosphino)ferrocene as the nucleophile. The new clusters 1-3 have all been fully characterised by both spectroscopic and crystallographic methods. Conceptually, the classification of 1-3 as supermolecules is straightforward, since molecular subunits with well defined intrinsic properties can be easily identified, thus affording a new type of covalently linked donor-acceptor system. Both structural features and spectroscopic data for compounds 1-3 are fully consistent with a zwitterionic formulation for these supramolecular species. These results suggest that a strong interaction exists between the ferrocenyl moiety and the Os3C core in their ground states.