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

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 12–15 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.