Ruthenium complexes with ferrocene-based P,C,P pincer ligand

Abstract

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...

Ruthenium bis(phosphinite) pincer complexes

“…The IR spectra of complexes 11 and 12 contain two intense bands each attributed to CO group vibrations, which suggests cis configuration of the carbonyl groups in the complexes as in the related complexes with bis(phos phine) ligands 4, 12 .…”

“…1,2 Pincer complexes 1 3-7 and 2 8 with P,C,P and N,C,N ligands, respectively, and pincer complexes 3 8, 9 containing P,N,P ligands with an aliphatic skeleton are the most popular. In addition, re cently novel ruthenium complexes 4 10 and 5 11 containing P,N,P and P,Si,P ligands as well as ferrocene based com plexes 6 12 bearing bis(phosphine) P,C,P ligands have been described.…”

P,C,P-Pincer complexes of ruthenium based on ruthenocene and pentamethylruthenocene

“…This disorder is due to superposition in a crystal of the two symmetrically nonequivalent forms of complex 8 (whose asymmetry results from different displacement of phos phorus atoms out of the Cp ring plane) and was described in detail earlier. 10 Figure 1 shows one of the forms of complex 8. Selected bond lengths and angles in complex 8 are collected in Table 1.…”

“…This results in the distortion of the molecule´s general symmetry with respect to the pseudo plane of symmetry passing through Ru(1), C(1), Ru (2). It is noteworthy that weak agostic interaction between the chelated ruthenium atom and a C-H bond of one of the tert butyl groups at the P atom has recently been found 10 (2); in cationic complex 2, this results in the broadening of the methylene proton signal in 1 H NMR spectrum recorded at room temperature. The 1 H NMR spectra of complexes 8 and 9 recorded under similar con ditions show no evidence for significant agostic interac tion.…”

Metall‐Ligand‐Kooperation

“…Der Komplex 203 a reagiert weiter in CD 2 Cl 2 ‐Lösung bei Raumtemperatur zum Isomer 204 a , für das aus NMR‐Daten eine cisoide Anordnung der Cp‐H‐ und Ru‐H‐Wasserstoffatome ermittelt wurde. Die weitere Reaktion führt zur H 2 ‐Freisetzung und Bildung von Komplex 205 a , der letztlich in einen agostischen Komplex 206 als das Hauptprodukt (80 %) umgewandelt wird, in dem der armoatische Charakter des Cp‐Rings weitgehend wiederhergestellt ist (keine signifikante C‐C‐Bindungslängenalternanz des Cp‐Rings in der Röntgenstruktur von 206 ) 159. Die bereitwillige H 2 ‐Freisetzung wird wahrscheinlich durch die cisoide Anordnung der Ru‐H‐ und Cp‐H‐Wasserstoffatome im 205 a ermöglicht.…”