Synthesis of rhenium-platinum complexes bearing carbaborane ligands and their unusual dynamic behavior

摘要

Treatment of Cs[3,3,3-(CO)(3)-closo-3,1,2-ReC2B9H11] 1 with [Pt(NCMe)(2){Ph2P(CH2)(2)PPh2}][BF4](2) yielded [3,3,3-(CO)(3)-3,8-(Pt{Ph2P(CH2)(2)PPh2})-8-(mu-H)-closo-3,1,2-ReC2B9H10][ BF4] 2b as the sole product. The cation of salt 2b is a bimetallic species with a Re-Pt bond bridged by a nido-7,8-C2B9H11 ligand pentahapto coordinated to the rhenium and with the beta-B-H bond in the ligating CCBB ring of the carbaborane cage forming a 3-centre 2-electron B-H-->Pt bond. Deprotonation of 2b with strong bases gives an isomeric mixture of the complexes [3,3,3-(CO)(3)-3,n-(Pt{Ph2P(CH2)(2)PPh2})-closo-3,1,2-ReC2B9H10] 3a (n=4), 3b (n=8). The isomers are readily separated and the proportion of 3a to 3b formed is solvent- as well as base-dependent. In THF solutions of 2b afford a 1:3:1 equilibrium mixture of 2b, 3a, and 3b. Refluxing THF solutions of 1 with [Pt(H)(THF)(PEt3)(2)][BF4] for several days yields a separable mixture of the isomers [3,3,3-(CO)(3)-3,n-{Pt(PEt3)(2)}-closo-3,1,2-ReC2B9H10] 4a (n=4), 4b (n=8). The same reactants, when stirred together in CH2Cl2 at ambient temperatures, give 4a and [3,3,3-(CO)(3)-3,8-{Pt(H)(PEt3)}-8-(mu-H)-closo-3,1,2-ReC2B9H10] 5. Complex 4a, not 5, is the precursor to 4b, the interconversion occurring at elevated temperatures in solution by an intramolecular exchange of B-Pt sigma bonds between alpha-B and beta-B vertices in the coordinating CCBBB face of the cage. Treatment of 1 with [Pt(Me)(THF)(PMe2Ph)(2)][BF4] at room temperature initially gives [3,3,3-(CO)(3)-3,4-{Pt(PMe2Ph)(2)}-closo-3,1,2-ReC2B9H10] 6a. However, 6a isomerizes in CH2Cl2 solutions at ambient temperatures to give a 1:1 mixture of 6a and [3,3,3-(CO)(3)-3,8-{Pt(PMe2Ph)(2)}-closo-3,1,2-ReC2B9H10] 6b. The NMR data (H-1, C-13, B-11 and P-31) for the new complexes are discussed. [References: 34]