Synthesis, Structures,\nand Photophysical Properties\nof Ruthenium(II) Quinolinolato Complexes

Abstract

Reaction of [Ru^II(PR₃)₃Cl₂] with 2-methyl<b>-</b>8-quinolinolate (MeQ)\nin the\npresence of Et₃N in MeOH produced the neutral carbonyl\nhydrido complexes [Ru^II(MeQ)­(PR₃)₂(CO)­(H)] (R = Ph (<b>1</b>), MeC₆H₄ (<b>2</b>), MeOC₆H₄ (<b>3</b>)). An analogous\nreaction occurs between [Ru^II(PPh₃)₃Cl₂] and MeQH in ethanol to give [Ru^II(MeQ)­(PPh₃)₂(CO)­(CH₃)] (<b>4</b>). The carbonyl,\nhydride, and methyl ligands of these complexes are most likely derived\nfrom the decarbonylation of ROH. Reaction of [Ru^II(PPh₃)₃(CO)­(H)₂] with 5-substituted quinolinolato\nligands (XQ, X = H, Cl, Ph) produced the neutral complexes [Ru^II(XQ)­(PPh₃)₂(CO)­(H)] (XQ = Q (<b>5</b>), ClQ (<b>6</b>), PhQ (<b>7</b>)). Treatment\nof <b>1</b> and <b>5</b>–<b>7</b> with excess\nKCN in MeOH following by metathesis with PPh₄Cl afforded\nPPh₄⁺ salts of the anionic carbonyl dicyano\ncomplexes [Ru^II(XQ)­(CO)­(CN)₂(PPh₃)]⁻ (XQ = MeQ (<b>8</b>), Q (<b>9</b>) ClQ (<b>10</b>), PhQ (<b>11</b>)). Under similar conditions,\nreaction of <b>1</b> with excess CyNC in the presence of NH₄PF₆ afforded [Ru^II(MeQ)­(CyNC)₂(CO)­(PPh₃)]⁺ (<b>12</b>). All complexes\nhave been characterized by IR, ESI/MS, ¹H NMR and elemental\nanalysis. The crystal structures of complexes <b>3</b>, <b>4</b>, <b>8</b>, and <b>12</b> have been determined\nby X-ray crystallography. The UV and emission spectra of these complexes\nhave also been investigated. All complexes exhibit short-lived quinolinolate-based\nLC fluorescence in solution at room temperature and dual emissions\nderived from LC fluorescence and phosphorescence at 77 K glassy medium.\nThese emissions are relatively insensitive to the nature of the ancillary\nligands but are readily tunable by varying the substituents on the\nquinolinolato ligand.