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Half-Sandwich Ruthenium-Phosphine Complexes with Pentadienyl and Oxo- and Azapentadienyl Ligands

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posted on 22.10.2012, 00:00 authored by Amira Reyna-Madrigal, Anabel Moreno-Gurrola, Odilia Perez-Camacho, M. Elena Navarro-Clemente, Patricia Juárez-Saavedra, Marco A. Leyva-Ramirez, Atta M. Arif, Richard D. Ernst, M. Angeles Paz-Sandoval
Treatment of RuCl2(PPh3)3 and RuHCl­(PPh3)3 with the tin compound CH2C­(Me)­CHC­(Me)­CH2SnMe3 gives the corresponding acyclic pentadienyl half-sandwich (η5-CH2C­(Me)­CHC­(Me)­CH2)­RuX­(PPh3)2 [X = Cl, (2); H, (3)]. The steric congestion in 2 is most effectively relieved by formation of the cyclometalated complex (η5-CH2C­(Me)­CHC­(Me)­CH2)­Ru(C6H4PPh2)­(PPh3) (4). Addition of 1 equiv of PHPh2 to (η5-CH2CHCHCHCH2)­RuCl­(PPh3)2 (1) affords the chiral complex (η5-CH2CHCHCHCH2)­RuCl­(PPh3)­(PHPh2) (5), while compound (η5-CH2C­(Me)­CHC­(Me)­CH2)­RuCl­(PPh3)­(PHPh2)] (6) is directly obtained from the reaction of RuCl2(PPh3)3 with CH2C­(Me)­CHC­(Me)­CH2Sn­(Me)3 and PHPh2. Treatment of RuCl2(PPh3)3 with the corresponding Me3SnCH2CHCHCHNR (R = Cy, t-Bu) affords (1-3,5-η-CH2CHCHCHNCy)­RuCl­(PPh3)2 (7) and [1-3,5-η-CH2CHCHCHN­(t-Bu)]RuCl­(PPh3)2 (8). The hydrolysis of 7, on a silica gel chromatography column, allows the isolation of RuCl­(η5-CH2CHCHCHO)­(PPh3)2 (9). The azapentadienyl complex 7 reacts with 1 equiv of PHPh2 to afford [1-3,5-η-CH2CHCHCHN­(Cy)]­RuCl­(PPh3)­(PHPh2) (10), while the corresponding product [1-3,5-η-CH2CHCHCHN­(t-Bu)]­RuCl­(PPh3)­(PHPh2) (11) from 8 is only observed through 1H and 31P NMR spectroscopy as a mixture of isomers. Two equivalents of PHPh2 gives spectroscopic evidence of [η3-CH2CHCHCHN­(t-Bu)]­RuCl­(PHPh2)3. A mixture of products [η5-CH2C­(Me)­CHC­(Me)­O]­RuCl­(PPh3)2 (12) and [η5-CH2C­(Me)­CHC­(Me)­O]­RuH­(PPh3)2 (13) is obtained from reaction of RuCl2(PPh3)3 with Li­[CH2C­(Me)­CHC­(Me)­O]. In contrast, the oxopentadienyl compound 13 is cleanly formed from RuHCl­(PPh3)3 and Li­[CH2C­(Me)­CHC­(Me)­O]. An attempt to separate compounds 12 and 13 by crystallization gives an orthometalated product [η5-CH2C­(Me)­CHC­(Me)­O]­Ru­(C6H4PPh2)­(PPh3) (14), which is the oxopentadienyl analogue to 4. The bulky [1-3,5-η-CH2C­(t-Bu)­CHC­(t-Bu)­O]­RuH­(PPh3)2 (15) analogue to 13 has also been prepared from RuHCl­(PPh3)3 and Li­[CH2C­(t-Bu)­CHC­(t-Bu)­O]. Compounds 3, 5, 6, 7, and 1215 have been structurally characterized. The preferred heteropentadienyl orientations and the relative positions of the H, Cl, PPh3, and PHPh2 ligands have been established in the piano-stool structures for all compounds, and it can be definitively surmised that the chemistry involved in the heteropentadienyl half-sandwich compounds studied is dominated by steric effects.