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.