219823-00-4Relevant academic research and scientific papers
1,1′-diphosphaferrocene derivatives for labeling of molecules of biological interest. The X-ray molecular structures of 4-oxo-4-(3,3′,4, 4′-tetramethyl-1,1′-diphosphaferrocen-2-yl)butanoic acid and its bis-W(CO)5 complex
Zakrzewski, Janusz,K?ys, Arkadiusz,Bukowska-Strzyzewska, Maria,Tosik, Anita
, p. 5880 - 5886 (1998)
3,3′,4,4′-Tetramethyl-1,1′-diphosphaferrocene (1) reacts with succinic anhydride in the presence of AlCl3 to give 4-oxo- 4-(3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocen-2-yl)butanoic acid (2) in 80% yield. This complex treated with 1 equiv of W(CO) 5(THF) gave a mixture of the products in which the W(CO)5 moiety is coordinated to P(1′) (3a) and to P(1) (3b) in the ratio ～ 7:1. With two equiv of W(CO)5(THF) the bis-W(CO)5 adduct (4) was obtained and transformed into the corresponding N-succinimidyl ester (5) by treatment with N-hydroxysuccinimide in dichloromethane in the presence of DCC (dicyclohexylcarbodiimide). This activated ester reacts with benzylamine and glycine methyl ester to give the corresponding amides in good yields. The crystal structures of 2 and 4 have been determined by X-ray diffraction. Both structures show unexpected conformations with short intramolecular P- - -P distances, indicating secondary bonding between phosphorus atoms. This contrasts with the X-ray structure of 1 displaying longer P- - -P distance (no secondary bonding) and theoretical calculations showing destabilizing, repulsive P- - -P interactions in the 1,1′-diphosphaferrocene system (Ashe, A. J., III; Al-Ahmad, S. Adv. Organomet. Chem 1996, 39, 325, and references therein). Apparently, conformational preferences of 1,1′-diphosphaferrocenes are small, since they are so easily changed by small changes in the substitution. Furthermore, the structure of 2 shows intermolecular P- - -P secondary bonding, giving rise to the formation of stacking columns along the z axis. The structural differences between 2 and 4 and between the W(CO)5 moiety in 4 and this moiety coordinated to nitrogen in W(CO)5-(azaferrocene) complexes have also been analyzed.
