Luminescent Low-Valent Rhenium Complexes with 1,2-Bis(dialkylphosphino)ethane Ligands. Synthesis and X-ray Crystallographic, Electrochemical, and Spectroscopic Characterization

Abstract

A series of low-valent rhenium phosphine complexes with the general formula [Re(dmpe)(3-x)(depe)(x)](2+/+) (x = 0-3), where dmpe is 1,2-bis(dimethylphosphino)ethane and depe is 1,2-bis(diethylphosphino)ethane, were synthesized and characterized. The reaction of [Re(benzil)(PPh(3))Cl(3)] with the appropriate phosphine yielded the homoleptic tris complexes [Re(dmpe)(3)](+) and [Re(depe)(3)](2+), while the mixed-ligand complexes [Re(dmpe)(2)(depe)](+) and [Re(dmpe)(depe)(2)](2+) were prepared from [Re(dmpe)(2)Cl(2)](+) and [Re(depe)(2)Cl(2)](+), respectively. The oxidation state of the final product strongly depends on the donating properties of the ligand. Each complex, however, exhibits a diffusion-controlled, reversible one-electron transfer between Re(I) and Re(II) with formal reduction potentials, E degrees ', ranging from -0.09 to -0.28 V versus a ferrocene external standard. Subsequent oxidation to Re(III) was found to be chemically irreversible. UV-vis and luminescence spectroelectrochemical techniques were used to study the spectral properties of the Re(I) and Re(II) forms. The Re(II) complexes are red in color and exhibit absorption features from 350 to 600 nm; the lowest-energy transition was assigned as a sigma(P) to dpi(Re) ligand-to-metal charge-transfer (LMCT) transition. Excitation into the lowest-energy absorption band revealed rare examples of luminescent (Phi approximately 0.07) LMCT excited states from d(5) transition-metal complexes in a room temperature solution. Structural characterization of salts of both oxidation states of [Re(dmpe)(2)(depe)](2+/+) was also performed.

Synthesis, structure, photophysics and electrochemiluminescence of Re(i) tricarbonyl complexes with cationic 2,2-bipyridyl ligands

“…Mark Wrighton firstly reported the visible-light metal-to-ligand charge-transfer (MLCT) transitions and the long-lived MLCT phosphorescence in the room temperature fluid solution of Re(I) tricarbonyl diimine complexes [Re(N-N)(CO) 3 X] (N-N = diimine) in 1974. 1 In the last three decades, tremendous attention has been paid to investigate the properties and the applications of Re(I) tricarbonyl diimine complexes, [2][3][4][5][6] and various types of Re(I) tricarbonyl complexes have been designed and synthesized. The characteristic MLCT excited state and its luminescence features can be utilized for a wide range of applications, such as the emissive layer for light-emitting devices, [5][6][7][8] photosensitizers, [9][10][11] photocatalysts, [12][13][14] biological receptors [15][16][17][18][19] and electrochemiluminescence.…”

Homoleptic Tris-Diphosphine Re(I) and Re(II) Complexes and Re(II) Photophysics and Photochemistry

“…16−19 Very few simple homoleptic Re II complexes are known: [(bpy) 3 Re] 2+ (bpy = 2,2′b i p y r i d i n e ) , 2 0 , 2 1 [ ( 2 , 2 ′ -a z o b i p y r i d i n e ) 3 R e ] 2 + , 2 2 [(dmpe) 3 Re] 2+ , 23,24 and most recently the mixed diphosphine chelate systems [(depe) 3−x (dmpe) x Re] 2+ (x = 0−3). 25 [(dmpe) 3 Re] 2+ and its congener [(dmpe) 3 Tc] 2+ exhibit unique luminescence properties in solution, with higher quantum efficiencies (Φ em ) than [(bpy) 3 Ru] 2+ . 26,27 In addition, this class of complexes has been highlighted as potentially useful since their excited states are strongly oxidizing; they have been labeled as highly oxidizing excited states (HOES).…”

“…Besides [(dmpe) 3 Re] 2+ , the only modest extension of this class has been to the series [(dmpe) 3−x (depe) x Re] 2+ . 25 Diphosphines have good flexibility in terms of pendant group and phosphinelinker modifications and have a considerable potential for tuning ground state and emission properties. Here we report the extension of [(PP) 3 Re] + systems to a broader range of trischelate compounds and their associated Re II analogues, [(PP) 3 Re] 2+ .…”

Photophysical properties of metal complexes

“…69 Complexes of the form [Re(dmpe) 3Àn (depe) n ] 2+ (dmpe = bis(dimethylphosphino)ethane, depe = bis(diethylphosphino)ethane) exhibit rare examples of luminescent ligand to metal charge transfer (LMCT) states (f = B0.07) for d 5 transition metal complexes in solution at room temperature. 70 The complex [Re 2 (dppm) 2 (p-O 2 CC 4 H 6 NO 2 ) 2 Cl 2 ] (dppm = bis(diphenylphosphino)methane) has a 1 MLCT absorption at much higher energy to similar quadruply bonded Mo 2 and W 2 complexes, and holds less promise for panchromatic photovoltaic applications. 71 The first emission studies of Tc 2 X 8 2À (X = Cl, Br) have been carried out and show luminescence from the 1 d-d* state with shorter lifetimes than their rhenium analogues.…”