Synthesis, reactivity and X-ray crystal structure of an uncomplexed 1-phosphabarrelene: application to the synthesis of 1,1 '-bis(dimethylsilylphosphinine)ferrocenes
S. Welfele et al., Synthesis, reactivity and X-ray crystal structure of an uncomplexed 1-phosphabarrelene: application to the synthesis of 1,1 '-bis(dimethylsilylphosphinine)ferrocenes, NEW J CHEM, 25(10), 2001, pp. 1264-1268
The 5,6-diphenyl-3-tertiobutyl-1,2-azaphosphinine 3 reacts with bis(phenyle
thynyldimethylsilyl)ferrocene, 2, to afford a mixture of the phosphinine 4,
resulting from the cycloaddition of 3 with one alkynyl group of 2, and 1-p
hosphabarrelene, 5, whose formation results from an intramolecular [4 + 2]
cycloaddition between the remaining alkynyl group of the ferrocenyl ligand
and the 1,4-phosphabutadienic system of 4. The X-ray structure of compound
5 was obtained and shows no particular strain in the molecule. Competitive
experiments have shown that, at high temperature, phosphinine 4 equilibrate
s with barrelene 5. Synthesis of a bidentate ligand 6, incorporating two di
methylsilyl-substituted phosphinines, was achieved by reacting the azaphosp
hinine 3 with half an equivalent of the ferrocene derivative 2. The mixed l
igand 8, incorporating two different phosphinine subunits, was also prepare
d using a two-step sequence by reacting a mixture of 4 and 5 with diazaphos
phinine 1. This reaction first produced an intermediate azaphosphinine-phos
phinine ligand 7, which was then trapped with trimethylsilylacetylene to af
ford ligand 8.