Note Adventitious formation of a new oxopentadienyl Mn(I) tricarbonyl complex: Structural study and bonding investigation of (h 5 -CH 2 C(Fc)CHC(Fc)O)Mn(CO) 3 Jean-Pierre Djukic * , Christophe Michon 1 , Michel Pfeffer, Nathalie Gruber-Kyritsakas, André de Cian Institut de Chimie, UMR 7177 CNRS, Université de Strasbourg, 4 rue Blaise Pascal, F-67000 Strasbourg, France article info Article history: Received 19 April 2011 Received in revised form 5 June 2011 Accepted 9 June 2011 Keywords: Manganese Aldol condensation Insertion X-ray diffraction DFT abstract A Mn(I) tricarbonyl complex of a 1,3-diferrocenyl-1-oxopentadienyl ligand was synthesised adventi- tiously by what seems to be an in-situ aldol-like condensation of two acetylferrocene units promoted by benzyl-Mn(CO) 5 . X-ray structural analysis of this unexpected product confirms the h 5 coordination of the 1,3-diferrocenyl-1-oxopentadienyl ligand to the Mn(CO) 3 moiety. The nature of the metal-ligand bonding relationship was studied by theoretical calculations; it outlines the charge unbalance (polarisation) at the oxopentadienyl moiety as well as the lack of ketone character of the latter Mn-bound ligand. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Heteropentadienyl-transition metal complexes have been extensively studied during the past 30 years and several reviews of this subject have appeared. Indeed, Ernst [1a], Oshima [1b], Bleeke [1c], Paz-Sandoval [1d,1f] and Omae [1e] underlined the various bonding modes (i.e h 5 , h 3 or h 1 ) offered by the heteropentadienyl ligands, leading to various reactivities for transmetalation, inser- tion, coupling, addition and oxidative addition along with activation of various bonds and molecules. Following our past and continuous interest on the synthesis and the reactivity of cyclometallated compounds [2,3], and particularly Mn(I) compounds [3], we report herein the adventitious synthesis of a new heteropentadienyl Mn(I) tricarbonyl complex and the study of the bonding mode of the ligand to the Mn(I) metal centre by DFT methods. 2. Results and discussion 2.1. Synthesis and cyclomanganation of 1,3-diferrocenyl-butan-1- one ligand with (h 1 -PhCH 2 )Mn(CO) 5 Along our research efforts for the synthesis of ligand-appended cymantrenes [3c,d], we initially aimed to synthesise new (h 5 - fluorenyl)Mn(CO) 3 complex 4 (Scheme 1). Acetyl-ferrocene 1 was allowed to react with 1.1 equivalent of (h 1 -benzyl)pentacarbo- nylmanganese in a refluxing heptane-toluene (1/1) mixture for 12 h. Due to the known air and moisture sensitivity of the expected intermediate 2 [4], the resulting crude mixture was immediately evaporated under vacuum and subsequently treated without further purification with 6 equivalents of 9-diazofluorene in a refluxing 4:1 mixture of n-hexane and toluene. After 3 h of reaction, the resulting mixture was purified by flash chromatog- raphy leading to 3 in 24% yield whereas a large amount (corre- sponding to nearly quantitative yield) of bis[9-(9H)-fluorenyliden] azine 5 [5] was formed by decomposition of 9-diazofluorene. A large amount of starting material was also recovered. It was clear that the heteropentadienyl Mn(I) tricarbonyl complex 3 was the result of an in-situ aldol condensation of two acetylferrocene units promoted by (h 1 -benzyl)Mn(CO) 5 . To the best of our knowledge, the mode of action of (h 1 -benzyl)Mn(CO) 5 under thermolytic conditions has long been a matter of debate, being poised as nucleophilic [6], electrophilic [7] or radical [8] in various cases [9]. Noteworthy, such one-pot aldol condensation was already observed for acetylferrocene by Bruce [10] using MeMn(CO) 5 as well as by Woodgate [11] for [h 6 -(phenyl)-ethanone]Cr(CO) 3 6 using (h 1 -benzyl)Mn(CO) 5 . Moreover, Wu [12] and Sorensen [13] reported separately the preparation of the 1,3-diferrocenyl-buten- 1-one ligand 7 through aldol condensation under conventional conditions. The case reported by Bruce [10] resembles the one dealt with herein: in the formation of 3 the putative “aldol” condensation of 1 should result formally only in the loss of water and the * Corresponding author. Tel.: þ33 368851523; fax: þ33 390245001. E-mail address: djukic@unistra.fr (J.-P. Djukic). 1 Present address: Université Lille Nord de FranceeUniversité Lille 1, UCCS UMR 8181 CNRS, ENSCL, CCCF, (Chimie-C7) BP 90108, 59652 Villeneuve d’Ascq Cedex, France. Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem 0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2011.06.011 Journal of Organometallic Chemistry 696 (2011) 3268e3273