Cu+aq forms stable complexes with carbon monoxide in aqueous solutions. Furthermore it reacts very fast with aliphatic radicals. The reaction of Cu(CO)+naq with methyl radicals, *CH3, was studied using the pulse-radiolysis technique. The results point out that methyl radicals react with Cu(CO)+aq to form an unstable intermediate with a CuII-C σ bond identified as (CO)CuII-CH3+, k=(1.1 ± 0.2) × 109 M-1 s-1. This intermediate has a strong LMCT charge transfer band (λmax=385 nm, εmax=2500 M-1 cm-1) which is similar to the absorption bands of other transient complexes with CuII-alkyl σ bonds. The coordinated carbon monoxide in (CO) CuII-CH3+ inserts into the copper-carbon bond (or rather the coordinated methyl migrates to the coordinated carbon monoxide ligand) at a rate of (3.0 ± 0.8) × 102 s-1 to form the copper-acetyl complex, (CO)mCuII-C(CH3)=O+ (λmax=480 nm, εmax=2100 M-1 cm-1). The rate of formation of (CO)CuII-CH3+ and of the insertion reaction are pH independent. The complex (CO)mCuII-C(CH3)=O+ is also unstable and decomposes heterolytically to yield acetaldehyde and Cu2+aq as the final stable products. This reaction is slightly pH dependent. The same reactivity pattern has been observed for the Cu(CO)+naq complexes (n=2 or 3). The results clearly point out that CO remains coordinated to transient complexes of the type CuII-alkyl.
Bibliographical noteFunding Information:
This study was supported in part by the Israel Science Foundation administered by The Israel Academy of Sciences and Humanities and by a grant from the Budgeting and Planning Committee of The Council of Higher Education and the Israel Atomic Energy Commission. D.M. wishes to express his thanks to Mrs Irene Evens for her ongoing interest and support.
- Carbonyl complexes
- Copper complexes
- Kinetics and mechanism
- Methyl complexes
- Methyl migration