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, (<b>2</b>); H, (<b>3</b>)]. The steric congestion in <b>2</b> is most effectively relieved by formation of the cyclometalated complex (η⁵-CH₂C­(Me)­CHC­(Me)­CH₂)­Ru(C₆H₄PPh₂)­(PPh₃) (<b>4</b>). Addition of 1 equiv of PHPh₂ to (η⁵-CH₂CHCHCHCH₂)­RuCl­(PPh₃)₂ (<b>1</b>) affords the chiral complex (η⁵-CH₂CHCHCHCH₂)­RuCl­(PPh₃)­(PHPh₂) (<b>5</b>), while compound (η⁵-CH₂C­(Me)­CHC­(Me)­CH₂)­RuCl­(PPh₃)­(PHPh₂)] (<b>6</b>) 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, <i>t-</i>Bu) affords (1-3,5-η-CH₂CHCHCHNCy)­RuCl­(PPh₃)₂ (<b>7</b>) and [1-3,5-η-CH₂CHCHCHN­(<i>t</i>-Bu)]RuCl­(PPh₃)₂ (<b>8</b>). The hydrolysis of <b>7</b>, on a silica gel chromatography column, allows the isolation of RuCl­(η⁵-CH₂CHCHCHO)­(PPh₃)₂ (<b>9</b>). The azapentadienyl complex <b>7</b> reacts with 1 equiv of PHPh₂ to afford [1-3,5-η-CH₂CHCHCHN­(Cy)]­RuCl­(PPh₃)­(PHPh₂) (<b>10</b>), while the corresponding product [1-3,5-η-CH₂CHCHCHN­(<i>t</i>-Bu)]­RuCl­(PPh₃)­(PHPh₂) (<b>11</b>) from <b>8</b> is only observed through ¹H and ³¹P NMR spectroscopy as a mixture of isomers. Two equivalents of PHPh₂ gives spectroscopic evidence of [η³-CH₂CHCHCHN­(<i>t</i>-Bu)]­RuCl­(PHPh₂)₃. A mixture of products [η⁵-CH₂C­(Me)­CHC­(Me)­O]­RuCl­(PPh₃)₂ (<b>12</b>) and [η⁵-CH₂C­(Me)­CHC­(Me)­O]­RuH­(PPh₃)₂ (<b>13</b>) is obtained from reaction of RuCl₂(PPh₃)₃ with Li­[CH₂C­(Me)­CHC­(Me)­O]. In contrast, the oxopentadienyl compound <b>13</b> is cleanly formed from RuHCl­(PPh₃)₃ and Li­[CH₂C­(Me)­CHC­(Me)­O]. An attempt to separate compounds <b>12</b> and <b>13</b> by crystallization gives an orthometalated product [η⁵-CH₂C­(Me)­CHC­(Me)­O]­Ru­(C₆H₄PPh₂)­(PPh₃) (<b>14</b>), which is the oxopentadienyl analogue to <b>4</b>. The bulky [1-3,5-η-CH₂C­(<i>t</i>-Bu)­CHC­(<i>t</i>-Bu)­O]­RuH­(PPh₃)₂ (<b>15</b>) analogue to <b>13</b> has also been prepared from RuHCl­(PPh₃)₃ and Li­[CH₂C­(<i>t</i>-Bu)­CHC­(<i>t</i>-Bu)­O]. Compounds <b>3</b>, <b>5</b>, <b>6</b>, <b>7</b>, and <b>12</b>–<b>15</b> 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