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

Abstract

Two pyridyl ligands containing redox-active ferrocenyl groups [Fe(η⁵-C₅H₅)(η-⁵C₅H₄C₆H₄R)][R = C₅H₄N 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-CNC₅H₄R′)][R′= C₆H₄(η⁵-C₅H₄)Fe(η⁵-C₅H₅)1, R′= CHNC₆H₄(η⁵-C₅H₄)Fe(η⁵-C₅H₅)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 [Os₃(µ-H)₂(CO)₉{µ₃-CPPh₂(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.