Journal article
Iridium Dihydroxybipyridine Complexes Show That Ligand Deprotonation Dramatically Speeds Rates of Catalytic Water Oxidation
Inorganic chemistry, v 52(16), pp 9175-9183
19 Aug 2013
PMID: 23387353
Featured in Collection : UN Sustainable Development Goals @ Drexel
Abstract
We report highly active iridium precatalysts, [Cp*Ir(N,N)Cl]Cl (1-4), for water oxidation that are supported by recently designed dihydroxybipyridine (dhbp) ligands. These ligands can readily be deprotonated in situ to alter the electronic properties at the metal; thus, these catalyst precursors have switchable properties that are pH-dependent. The pK(a) values in water of the iridium complexes are 4.6(1) and 4.4(2) with (N,N) = 6,6'-dhbp and 4,4'-dhbp, respectively, as measured by UV-vis spectroscopy. For homogeneous water oxidation catalysis, the sacrificial oxidant NaIO4 was found to be superior (relative to CAN) and allowed for catalysis to occur at higher pH values. With NaIO4 as the oxidant at pH 5.6, water oxidation occurred most rapidly with (N,N) = 4,4'-dhbp, and activity decreased in the order 4,4'-dhbp (3) > 6,6'-dhbp (2) >> 4,4'-dimethoxybipyridine (4) > bipy (1). Furthermore, initial rate studies at pH 3-6 showed that the rate enhancement with dhbp complexes at high pH is due to ligand deprotonation rather than the pH alone accelerating water oxidation. Thus, the protic groups in dhbp improve the catalytic activity by tuning the complexes' electronic properties upon deprotonation. Mechanistic studies show that the rate law is first-order in an iridium precatalyst, and dynamic light scattering studies indicate that catalysis appears to be homogeneous. It appears that a higher pH facilitates oxidation of precatalysts 2 and 3 and their [B(Ar-F)(4)](-) salt analogues 5 and 6. Both 2 and 5 were crystallographically characterized.
Metrics
Details
- Title
- Iridium Dihydroxybipyridine Complexes Show That Ligand Deprotonation Dramatically Speeds Rates of Catalytic Water Oxidation
- Creators
- Joseph DePasquale - Drexel UniversityIsmael Nieto - Drexel Univ, Dept Chem, Philadelphia, PA 19104 USALauren E. Reuther - Drexel Univ, Dept Chem, Philadelphia, PA 19104 USACorey J. Herbst-Gervasoni - Drexel Univ, Dept Chem, Philadelphia, PA 19104 USAJared J. Paul - Villanova UniversityVadym Mochalin - Drexel Univ, Dept Mat Sci & Engn, Philadelphia, PA 19104 USAMatthias Zeller - Youngstown State UniversityChristine M. Thomas - Brandeis UniversityAnthony W. Addison - Drexel UniversityElizabeth T. Papish - Drexel Univ, Dept Chem, Philadelphia, PA 19104 USA
- Publication Details
- Inorganic chemistry, v 52(16), pp 9175-9183
- Publisher
- American Chemical Society; Washington, DC
- Number of pages
- 9
- Grant note
- 0087210 / NSF; National Science Foundation (NSF) Villanova University CHE-0846383 / NSF CAREER; National Science Foundation (NSF); NSF - Office of the Director (OD) CAP-491 / Ohio Board of Regents Youngstown State University 0846383 / Direct For Mathematical & Physical Scien; National Science Foundation (NSF); NSF - Directorate for Mathematical & Physical Sciences (MPS) Drexel University
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Chemistry
- Web of Science ID
- WOS:000323460800005
- Scopus ID
- 2-s2.0-84882638897
- Other Identifier
- 991019168517604721
UN Sustainable Development Goals (SDGs)
This publication has contributed to the advancement of the following goals:
InCites Highlights
Data related to this publication, from InCites Benchmarking & Analytics tool:
- Collaboration types
- Domestic collaboration
- Web of Science research areas
- Chemistry, Inorganic & Nuclear