First ruthenium complexes with a ferrocene based pincer ligand were synthesized. The cyclometallation of 1,3 bis[(di tert butylphosphino)methyl]ferrocene with RuCl 2 (DMSO) 4 in 2 methoxyethanol afforded the RuCl(CO)[{2,5 (Bu t 2 PCH 2 ) 2 C 5 H 2 }Fe(C 5 H 5 )] (RuCl(CO)[ Bu t P,C,P Fe ]) complex (5). Complex 5 reversibly binds CO to form the RuCl(CO) 2 [ Bu t P,C,P Fe ] complex (6). The analogous reaction in the presence of NaBAr´4 (Ar´ = 3,5 (CF 3 ) 2 C 6 H 3 ) produced the cationic complex {Ru(CO) 2 [ Bu t P,C,P Fe ]}BAr´4 (7). The structures of complexes 5 and 7 were established by single crystal X ray diffraction. The X ray diffraction study revealed an agostic interaction between one of the C-H bonds of the axial (exo oriented with respect to the ferrocene iron atom) tert butyl group and the Ru atom in complexes 5 and 7.Organometallic complexes with tridentate mono anionic aryl ligands, so called pincer complexes, have been extensively studied in recent years. 1,2 These com plexes have attracted interest due to their high stability and ability of catalyzing various organic reactions.Recently, we have studied a new type of pincer complexes, viz., metallocene based bimetallic pincer complexes. 3 The availability of these complexes was ex emplified by the cyclometallation of 1,3 bis[(dialkyl phosphino)methyl]ferrocene 3,4 and bis[(dialkylphos phino)methyl]ruthenocene. 4 Platinum metal com plexes with metallocene based pincer ligands 2-7 proved to be as stable as their benzene analogs. Recently, we have demonstrated 8 that the iridium complexes IrH 2 [{2,5 (Bu t 2 PCH 2 ) 2 C 5 H 2 }M(C 5 H 5 )] (M = Fe or Ru) are the most active of all the known homogeneous cata lysts for alkane dehydrogenation.The sandwich nature of metallocene pincer ligands provides new possibilities for fine controlling the steric and electronic effects of chelated metal atoms serving as the catalytic centers, for example, by introducing sub stituents into the unmetallated cyclopentadienyl ring 9 (not only the electron density on the chelated metal atom but also the steric accessibility of this atom for the substrate can be controlled), varying the nature of the central atom of the metallocene moiety 8 and its redox state, 7,8 and constructing planar chiral structures. The synthesis of metallocene based rhodium, 3,10 iridium, 4,8 and palla dium 5-7,9 pincer complexes was documented. However, related ruthenium complexes have not been described in the literature. The properties of ruthenium complexes as excellent catalysts for the hydrogenation of carbonyl com pounds 11 and olefin metathesis 12 are well known.In the present study, we report the synthesis and prop erties of first ferrocene based ruthenium pincer complexes.
Results and Discussion
Synthesis of ruthenium complexesAs mentioned earlier, the choice of the cyclo metallating agent can play a decisive role in the synthesis of metal pincer complexes. Our first attempt, as well as attempts of other researchers, 10 to use the RuCl 2 (PPh 3 ) 3 complex as the starting reagent for the cyc...
