Selenium and tellurium derivatives of a monocarbon platinacarbaborane complex†

Abstract

The reaction between Na[Pt(PEt₃)₂(η⁵-7-CB₁₀H₁₁)] 1 and PhSeCl in thf (tetrahydrofuran) afforded a mixture containing the isomeric species [Pt(SePh)(PEt₃)(η⁵-n-SePh-7-CB₁₀H₁₀)] (n = 8 2a or 9 2b) and the compound [Pt(SePh)(PEt₃){η⁵-8-O(CH₂)₄Cl-7-CB₁₀H₁₀}] 3. The molecular structures of complexes 2a and 3 were established by X-ray crystallography. Both molecules have Pt(SePh)(PEt₃) groups with the platinum atoms pentahapto co-ordinated by nido-7-CB₁₀ cage frameworks. In 2a the cage substituted SePh group is attached to the boron atom in the α site with respect to the carbon in the CBBBB ring ligating the platinum and this is true also of the O(CH₂)₄Cl substituent in 3. The isomers 2 are also formed when PhSeSePh is used instead of PhSeCl. Treatment of the salt 1 with PhTeI in thf yielded a mixture of [Pt(PEt₃)₂{η⁵-9-Te(Ph)CH₂Cl-7-CB₁₀H₁₀}] 4 and [Pt₂(TePh)(µ-TePh)₂(PEt₃)₂(η⁵-2-CB₁₀H₁₁)] 5. Single-crystal X-ray diffraction studies were employed to establish the formulations and molecular structures of both molecules. Compound 4 is a charge-compensated platinacarbaborane with a Pt(PEt₃)₂ group and with the nido-7-CB₁₀ framework carrying a Te(Ph)CH₂Cl moiety at the boron vertex situated in the β site with respect to the carbon in the CBBBB ring ligating the platinum. Complex 5 is a diplatinum species in which Pt(TePh)(PEt₃) and Pt(PEt₃)(η⁵-2-CB₁₀H₁₁) units are bridged by two TePh groups. The X-ray study revealed that in forming compound 5 from the reagent 1 the nido-7-CB₁₀H₁₁ cage system has undergone an unusual polytopal rearrangement to a nido-2-CB₁₀H₁₁ framework.