- آخرین فایل ها
- پرفروشترین فایل ها
- پربازدیدترین فایل ها
In the course of developing a new class of strained sandwich species for ring-opening polymerization, we discovered that the outcome of the common salt-metathesis approach strongly depends on the substituent on nitrogen. While the first azaphosphaferrocenophanes could be prepared for R = SiMe3, other cases unexpectedly gave unstrained structural isomers. Experimental results, complemented by DFT calculations, are discussed.
The in situ prepared dilithio derivative of the known species 1-bromo-1′-(trimethylsilylamino)ferrocene (1) reacted with tBuPCl2 to form the first example of a ferrocenophane (FCP) bridged by nitrogen and phosphorus (2). Sulfurization of 2 followed by column chromatography on silica gel gave the expected FCP with a tBu(S)PN(SiMe3) bridging moiety (3a) and its desilylated counterpart with a tBu(S)PNH bridging moiety (3b). The molecular structure of 3b was determined by single-crystal X-ray analysis (α = 18.40(11)°). Using a common synthetic methodology, two new 1-amino-1′-bromoferrocene derivatives were prepared, one species with a PhCH2 (6a) and another with a tBuCH2 group (6b) on nitrogen. Dilithiation of 6a followed by addition of tBuPCl2 gave a mixture of three constitutional isomers: the targeted FCP (7a), the 1,1′-disubstituted ferrocene derivative (tBuPH)(PhCH═N)fc (8a), and the FCP bridged by a (NH)(CHPh)PtBu moiety (9a). NMR spectroscopy revealed that 8a is the precursor for 9a. The salt-metathesis reaction of the dilithio derivative of 6b with tBuPCl2 exclusively gave the 1,1′-disubstituted ferrocene derivative (tBuPH)(tBuCH═N)fc (8b), which does not isomerize to the respective FCP. DFT calculations at the M06/6-311+G(d,p) level were used to better rationalize these unexpected results.
|حجم فایل||966 B|