The reaction of (p-FC6H4)3PE (E = Se, S) with diiodine: The single crystal X-ray structures of (p-FC6H4)3PSe, (p-FC6H4)3PS, (p-FC6H4)3PSeI2, and (p-FC6H4)3PSI2

The reactions of the tris(p-fluorophenyl)phosphine chalcogenides (p-FC6H4)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-FC6H4)3PSeI2 (3), and (p-FC6H4)3PSI2 (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 Ph3PEI2 (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 Ph3PEI2 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 Ph3PEI2 (E = S and Se) systems, although the differences are relatively small, and may also be due to packing effects. © 2007 Elsevier Ltd. All rights reserved.