656812-68-9Relevant academic research and scientific papers
Reactivity of 2-pyridine-aldehyde and 2-acetyl-pyridine coordinated to [Re(CO)3]+ with alcohols and amines: Metal mediated Schiff base formation and dimerization
Wang, Wenwu,Spingler, Bernhard,Alberto, Roger
, p. 386 - 393 (2003)
The coordination of an aldehyde or a ketone to Lewis acidic metal centers activates the carbonyl carbon atom towards nucleophilic attack. We studied the coordination chemistry of [ReBr3(CO)3]2- (1) in water and in organic solvents with 2-acetyl-pyridine (2) and 2-pyridine-aldehyde (3) and investigated its reactivity towards aromatic and aliphatic amines. Rapid imine formation in water between coordinated organic carbonyls and pendant amine groups of biomolecules is useful to directly link the latter with the fac-[Re(CO)3]+ or fac-[ 99mTc(CO)3]+ moiety. The reaction of [ReBr 3(CO)3]2- with 2 in methanol produced the mononuclear complex [ReBr(CO)3(C5H4NCOCH 3)] (4), in which the carbonyl group is coordinated to the Re(I) center. The reaction of 1 with 3 is different and gave the dinuclear complex [Re2(μ-OCH(OCH3)C5H4N) 2(CO)6] (5) in which a semiacetal is formed. The coordinated aldehyde in the mononuclear complex [ReBr(CO)3(C 5H4NCHO)] (6) is highly electrophilic and reacts with methanol to form the dinuclear complex 5. The reaction of 4 with aniline affords very rapid formation of [ReBr(CO)3(C5H 4NC(CH3)NC6H5)] (7). In situ preparation of 6 and reaction with aniline or 1-aminopropane gave the corresponding Schiff base complexes [ReBr(CO)3(C5H 4NCHNC6H5)] (8) and [ReBr(CO) 3(C5H4NCHNCH2CH2CH 3)] (9), respectively. Compounds 4, 5, 8 and 9 are characterized by X-ray structure analysis. The Schiff base formation occurs in water at a very high rate. The rate constant for the formation of 7 was determined at -50°C in methanol. The rate law is second-order with k=1.36±0.19×10 -2 M-1 s-1. In the absence of rhenium, no formation of Schiff base is observed at 20°C over the same time period. The formation of the 99mTc analogues of complexes 8 and 9 was confirmed by HPLC comparison with the corresponding Re complexes.
