skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Synthesis, structural studies, and redox chemistry of bimetallic [Mn(CO) 3 ] and [Re(CO) 3 ] complexes
Manganese ([Mn(CO) 3 ]) and rhenium tricarbonyl ([Re(CO) 3 ]) complexes represent a workhorse family of compounds with applications in a variety of fields. Here, the coordination, structural, and electrochemical properties of a family of mono- and bimetallic [Mn(CO) 3 ] and [Re(CO) 3 ] complexes are explored. In particular, a novel heterobimetallic complex featuring both [Mn(CO) 3 ] and [Re(CO) 3 ] units supported by 2,2′-bipyrimidine (bpm) has been synthesized, structurally characterized, and compared to the analogous monomeric and homobimetallic complexes. To enable a comprehensive structural analysis for the series of complexes, we have carried out new single crystal X-ray diffraction studies of seven compounds: Re(CO) 3 Cl(bpm), anti -[{Re(CO 3 )Cl} 2 (bpm)], Mn(CO) 3 Br(bpz) (bpz = 2,2′-bipyrazine), Mn(CO) 3 Br(bpm), syn - and anti -[{Mn(CO 3 )Br} 2 (bpm)], and syn -[Mn(CO 3 )Br(bpm)Re(CO) 3 Br]. Electrochemical studies reveal that the bimetallic complexes are reduced at much more positive potentials (Δ E ≥ 380 mV) compared to their monometallic analogues. This redox behavior is consistent with introduction of the second tricarbonyl unit which inductively withdraws electron density from the bridging, redox-active bpm ligand, resulting in more positive reduction potentials. [Re(CO 3 )Cl] 2 (bpm) was reduced with cobaltocene; the electron paramagnetic resonance spectrum of the product exhibits an isotropic signal (near g = 2) characteristic of a ligand-centered bpm radical. Our findings highlight the facile synthesis as well as the structural characteristics and unique electrochemical behavior of this family of complexes.  more » « less
Award ID(s):
1833087
PAR ID:
10301208
Author(s) / Creator(s):
; ; ; ; ; ; ;
Date Published:
Journal Name:
Dalton Transactions
Volume:
50
Issue:
8
ISSN:
1477-9226
Page Range / eLocation ID:
2746 to 2756
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; (, Molecules)
    null (Ed.)
    4,5-diazafluorene (daf) and 9,9’-dimethyl-4,5-diazafluorene (Me2daf) are structurally similar to the important ligand 2,2’-bipyridine (bpy), but significantly less is known about the redox and spectroscopic properties of metal complexes containing Me2daf as a ligand than those containing bpy. New complexes Mn(CO)3Br(daf) (2), Mn(CO)3Br(Me2daf) (3), and [Ru(Me2daf)3](PF6)2 (5) have been prepared and fully characterized to understand the influence of the Me2daf framework on their chemical and electrochemical properties. Structural data for 2, 3, and 5 from single-crystal X-ray diffraction analysis reveal a distinctive widening of the daf and Me2daf chelate angles in comparison to the analogous Mn(CO)3(bpy)Br (1) and [Ru(bpy)3]2+ (4) complexes. Electronic absorption data for these complexes confirm the electronic similarity of daf, Me2daf, and bpy, as spectra are dominated in each case by metal-to-ligand charge transfer bands in the visible region. However, the electrochemical properties of 2, 3, and 5 reveal that the redox-active Me2daf framework in 3 and 5 undergoes reduction at a slightly more negative potential than that of bpy in 1 and 4. Taken together, the results indicate that Me2daf could be useful for preparation of a variety of new redox-active compounds, as it retains the useful redox-active nature of bpy but lacks the acidic, benzylic C–H bonds that can induce secondary reactivity in complexes bearing daf. 
    more » « less
  2. ; ; ; ; ; (, Dalton Transactions)
    Manganese( i ) tricarbonyl complexes such as [Mn(bpy)(CO) 3 L] (L = Br, or CN) are known to be electrocatalysts for CO 2 reduction to CO. However, due to their rapid photodegradation under UV and visible light, these monomeric manganese complexes have not been considered as photocatalysts for CO 2 reduction without the use of a photosensitizer. In this paper, we report a cyanide-bridged di-manganese complex, {[Mn(bpy)(CO) 3 ] 2 (μ-CN)}ClO 4 , which is both electrocatalytic and photochemically active for CO 2 reduction to CO. Compared to the [Mn(bpy)(CO) 3 CN] electrocatalyst, our CN-bridged binuclear complex is a more efficient electrocatalyst for CO 2 reduction using H 2 O as a proton source. In addition, we report a photochemical CO 2 reduction to CO using the dimanganese complex under 395 nm irradiation. 
    more » « less
  3. ; ; (, Dalton Transactions)
    The synthesis of (PNP)Re(N)X (PNP = [2-P(CHMe 2 ) 2 -4-MeC 6 H 3 ] 2 N, X = Cl and Me) complexes is described. The methylnitridorhenium complex 3 was found to react differently with CO and isocyanides, leading to the isolation of a Re( v ) acyl complex 4 and an isocyanide adduct 6 . Two parallel pathways were observed for the reaction of 3 with CO: (1) CO inserts into the Re–Me bond to afford 4 , and (2) 3 isomerizes by distortion of the aryl backbone of the PNP ligand to afford the isomer 3′ . This is followed by the reaction of 3′ with CO to afford the tricarbonyl complex 5 , which was fully characterized. The contrasting reaction of 3 with 2,6-dimethylphenyl isocyanide lends further support for the proposed isomerization pathway. DFT (M06) calculations suggest that insertion of CNR into the Re–Me bond (27.2 kcal mol −1 ) is inaccessible at room temperature. Instead the substrate adds to the metal center via the most accessible face i.e. syn to the rhenium–nitrido bond, to afford 6 . The addition of CO to isomer 3′ is proposed to proceed with a similar mechanism to 2,6-dimethylphenyl isocyanide. 
    more » « less
  4. ; ; ; ; ; ; ; (, Inorganica Chimica Acta)
    A set of six carboxylate-stabilized rhenium(I) tricarbonyl complexes supported by a 2,2’-bipyridine (bpy) ligand, Re(O2CR)(CO)3(bpy) (R = H, CH3, CHF2, R- or S CHBrCH(CH3)2, and C5H11), were prepared by acidolysis of the complex Re(OCO2C5H11)(CO)3(bpy) with the appropriate carboxylic acid and characterized by 1H and 13C-{1H} NMR and IR spectroscopy. The crystal structure of the complex, Re[R-O2CCHBrCH(CH3)2](CO)3(bpy), was determined by X-ray crystallography. Cytotoxicity results correlate positively with the Kb value of the carboxylate ligand. Apparently, the more substitutionally inert the carboxylate-stabilized complex is in a chloride-rich environment (similar to extracellular fluid) the greater the amount of cytotoxic [Re(CO)3(bpy)(H2O)]+ that forms in the cytosol. 
    more » « less
  5. ; ; (, Dalton Transactions)
    Herein we report heteroleptic Co( ii ) diimine complexes [Co(H 2 bip) 2 Cl 2 ] ( 1 ), [Co(H 2 bip) 2 Br 2 ] ( 2 ), [Co(H 2 bip) 3 ]Br 2 ·1MeOH ( 3 ) and [Co(H 2 bip) 2 (Me 2 bpy)]Br 2 ·(MeCN) 0.5 ·(H 2 O) 0.25 ( 4 ) (H 2 bip = 2,2′-bi-1,4,5,6-tetrahydropyrimidine, bpy = 2,2′-dipyridyl, Me 2 bpy = 4,4′-Me-2,2′-dipyridyl), purposefully prepared to enable a systematic study of magnetic property changes arising from the increase of overall ligand field from σ/π-donor chlorido ( 1 ) to π-acceptor 4,4′Me-2,2′bpy ( 4 ). The presence of axial and rhombic anisotropy ( D and E ) of these compounds is sufficient to allow 1–4 to show field-induced slow relaxation of magnetization. Interestingly, we found as the effective ligand field is increased in the series, rhombicity ( E / D ) decreases, and the magnetic relaxation profile changes significantly, where relaxation of magnetization at a specific temperature becomes gradually faster. We performed mechanistic analyses of the temperature dependence of magnetic relaxation times considering Orbach relaxation processes, Raman-like relaxation and quantum tunnelling of magnetization (QTM). The effective energy barrier of the Orbach relaxation process ( U eff ) is largest in compound 1 (19.2 cm −1 ) and gradually decreases in the order 1 > 2 > 3 > 4 giving a minimum value in compound 4 (8.3 cm −1 ), where the Raman-like mechanism showed the possibility of different types of phonon activity below and above ∼2.5 K. As a precursor of 1 , the tetrahedral complex [Co(H 2 bip)Cl 2 ] ( 1a ) was also synthesized and structurally and magnetically characterized: this compound exhibits slow relaxation of magnetization under an applied dc field (1800 Oe) with a record slow relaxation time of 3.39 s at 1.8 K. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email