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RESEARCH PRODUCT

A Discrete P⋅⋅⋅II⋅⋅⋅P Assembly: The Large Influence of Weak Interactions on the31P NMR Spectra of Phosphane–Diiodine Complexes

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Thioethers, except derivatives of [7-R-7,8-C2B9H11] , are more weakly coordinating ligands than phosphanes. This difference is evidenced by the I I distances in the spokeshaped charge-transfer (CT) complexes R2S·I2 and R3P·I2 (Figure 1). The I I distance is sensitive to the strength of the interaction between the s* LUMO orbital on I2 and the HOMO orbital of the donor atom: the stronger the donor, the longer the I I distance. In these spoke CT complexes, the I I distance varies from 3.2 0.2 7 in R3P·I2 adducts [5] to 2.80 0.05 7 in R2S·I2 adducts, [6] indicating the weaker donor character of the thioether group. Whereas extended I2 arrays, spoke adducts of I2, polyiodides, and other structural configurations involving I2 molecules are well described, examples of discrete assemblies incorporating an I2 molecule bridging to two donor atoms are limited. The P···I I···P assembly is unknown, and only a few examples of the S···I I···S motif have been reported. As thioethers are weaker donors than phosphanes, we predicted that R3P·I2·PR3 adducts could be generated by using a very weakly coordinating phosphane ligand. By using the carboranyl phosphane (Mecarb)iPr2P (Mecarb= 1-(2Me-1,2-C2B10H10)), the complex (Mecarb)iPr2P·I2 containing the shortest I I distance observed in a spoke adduct was produced. A weaker donor ligand than (Mecarb)iPr2P can be obtained by replacing the isopropyl fragments by electronwithdrawing phenyl groups, as in (Mecarb)Ph2P (1). [10] Use of ligand 1 allowed the formation of the desired complex 1·I2·1 (2), which was isolated as red-brown crystals from a solution of 1 and I2 (1:1) in CH2Cl2 after 2 months at 4 8C. Single-crystal X-ray diffraction confirmed that the structure of 2 consists of one I2 molecule bridging two molecules of 1 (Figure 2). A nearly linear P···I I···P arrangement is observed, in which the P···I and I I distances