The reaction of ( p-FC 6H 4) 3PE (E = Se, S) with diiodine: The single crystal X-ray structures of ( p-FC 6H 4) 3PSe, ( p-FC 6H 4) 3PS, ( p-FC 6H 4) 3PSeI 2, and ( p-FC 6H 4) 3PSI 2

Abstract

The reactions of the tris( p-fluorophenyl)phosphine chalcogenides ( p-FC 6H 4) 3PE (E = Se ( 1), E = S ( 2)) with diiodine have been performed. The products of these reactions are the 1:1 charge-transfer compounds ( p-FC 6H 4) 3PSeI 2 ( 3), and ( p-FC 6H 4) 3PSI 2 ( 4), which feature a linear E–I–I motif typical of these types of spoke or “molecular dart” adducts. The I–I bonds in 3 [I–I: 2.8888(12)/2.8950(11) Å] and 4 [I–I: 2.8042(17)/2.835(2) Å] are lengthened with respect to diiodine in the solid-state, which is consistent with donation of electron density from the chalcogen atom to the σ ∗ antibonding orbital of the diiodine molecule. The elongation of the I–I bonds is considerably lower in magnitude than is observed for many CT adducts of diiodine as a result of the relatively poor donating capability of the phosphine chalogenides 1 and 2. A comparison with the non-fluorinated analogues Ph 3PEI 2 (E = S and Se) shows that the fluorine atom has little apparent effect upon the strength of the CT adduct formed, and that the I–I bond lengths appear to be more influenced by steric effects. The P–E–I angles in 3 and 4 are more acute than in the non-fluorinated Ph 3PEI 2 analogues, and as a result the steric influence of the aryl rings may be more strongly felt. This steric effect may act in competition with the electronic effect which would otherwise result in a more pronounced shortening of the I–I bond, compared to analogous Ph 3PEI 2 (E = S and Se) systems, although the differences are relatively small, and may also be due to packing effects.