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.

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The molecule (η5-Me2Pdl)Mn(CO)3 (η5-Me2Pdl = 2,4-dimethyl-η5-pentadienyl) has been prepared by a new method and used as a starting material to prepare the molecules (η5-Me2Pdl)Mn(CO) n (PMe3)3–n (n = 2, 1) by phosphine substitution for carbonyls. The first carbonyl substitution is achieved thermally in refluxing cyclohexane, and the second carbonyl substitution requires photolysis. At room temperature in benzene the associative intermediate (η3-Me2Pdl)Mn(CO)3(PMe3) that precedes the initial loss of carbonyl is observed. Single-crystal structures are reported for all complexes, including the associative intermediate of the first substitution in which the pentadienyl ligand has slipped to the η3 bonding mode. These molecules offer an opportunity to examine fundamental principles of the interactions between metals and pentadienyl ligands in comparison to the well-developed chemistry of metal cyclopentadienyl (Cp) complexes as a function of electron richness at the metal center. Photoelectron spectra of these molecules show that the Me2Pdl ligand has π ionizations at energy lower than that for the analogous Cp ligand and donates more strongly to the metal than the Cp ligand, making the metal more electron rich. Phosphine substitutions for carbonyls further increase the electron richness at the metal center. Density functional calculations provide further insight into the electronic structures and bonding of the molecules, revealing the energetics and role of the pentadienyl slip from η5 to η3 bonding in the early stages of the associative substitution mechanism. Computational comparison with dissociative ligand substitution mechanisms reveals the roles of dispersion interaction energies and the entropic free energies in the ligand substitution reactions. An alternative scheme for evaluating the computational translational and rotational entropy of a dissociative mechanism in solution is offered.

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An addition reaction of dinuclear [(η6‐C6Me6)Ru(η3, 1‐exo‐syn‐CH2CHCHCHO)]2(BF4)2 (1) with different Lewis bases in acetone results in the formation of mononuclear [(η6‐C6Me6)Ru(η3‐exo‐syn‐CH2CHCHCHO)(L)](BF4) (L = PMe3, 2; PPh3, 3; PHPh2, 4; Ph2PEtPy, 6; CO, 7) and dinuclear [{(η6‐C6Me6)Ru(η3‐exo‐syn‐CH2CHCHCHO)}2(μ2‐dppe)](BF4)2 (5). The addition of Ph2PCH2CH2PPh2 to the dinuclear product 1 affords 5 which show a bridging phosphine between two ruthenium centers. A comparative study of the new cationic arene derivatives and the corresponding isoelectronic Cp*Ru(heteropentadienyl) is established. All compounds were characterized by IR spectroscopy, high resolution mass spectrometry, NMR spectroscopy and the crystal structures of 2 and 3 are also described.