closo-Monocarbaboranes as ligands for transition metals: synthesis and reactivity of exo-diphosphineplatinum-closo-monocarbaborane complexes; structure of [Pt{But2P(CH2)2PBut2}(closo-CB11H12)][CB11H12]

Abstract

Protonation of the complexes [PtR₂(L–L)][R = Me, L–L =(C₆H₁₁)₂P(CH₂)₃P(C₆H₁₁)₂1a; Bu^t₂P(CH₂)₃PBu^t₂, 1b; Bu^t₂P(CH₂)₂PBu^t₂1c; or Bu^t₂PCH₂C₆H₄CH₂PBu^t₂, 1d; R = CH₂Bu^t, L–L =(C₆H₁₁)₂P(CH₂)₃P(C₆H₁₁)₂, 2a; Bu^t₂P(CH₂)₃PBu^t₂, 2b; or Bu^t₂P(CH₂)₂PBu^t₂, 2c] with the monocarbaborane acid HCB₁₁H₁₂ in diethyl ether at 0 °C affords the exo-diphosphineplatinum-closo-monocarbaborane complexes [Pt(L–L)(closo-CB₁₁H₁₂)][CB₁₁H₁₂][L–L =(C₆H₁₁)₂P(CH₂)₃P(C₆H₁₁)₂, 3a, Bu^t₂P(CH₂)₃PBu^t₂, 3b; Bu^t₂P(CH₂)₂PBu^t₂3c; or Bu^t₂PCH₂C₆H₄CH₂PBu^t₂, 3d] in which the co-ordinated closo-CB₁₁H₁₂ ligand is strongly bond to platinum via two exo-polyhedral three-centre two-electron (Pt ⋯ H ⋯ B) bridges. These complexes are fluxional in solution at room temperature. A single-crystal X-ray diffraction study of 3c confirmed the bonding mode of the dodecarboraneligand. Complex 3c crystallizes in the monoclinic space group C2/c, a= 16.199(4), b= 16.564(5), c= 14.896(3)Å, β= 93.64(2)° and Z= 4. The final discrepancy index was R= 0.043, R′= 0.050 for 2838 independent reflections. The geometry around the platinum centre is distorted square planar with µ-H–Pt 1.90(8), Pt–B 2.342(8) and B-µ–H 1.23(8)Å. In contrast when the solvent is changed from ether to tetrahydrofuran (thf), complex 1b on protonation is converted into [PtMe(thf){Bu^t₂P-P(CH₂)₃PBu^t₂}][CB₁₁H₁₂]5. Complexes 3b-3d react with acetonitrile to yield [Pt(NCMe)₂(L–L)][CB₁₁H₁₂]₂[L–L = Bu^t₂P(CH₂)₃PBu^t₂, 6b; Bu^t₂P(CH₂)₂PBu^t₂, 6c; or Bu^t₂CH₂C₆H₄CH₂Bu^t₂, 6d]. Likewise 3b reacts with pyridine affording [Pt(NC₅H₅)₂{Bu^t₂P(CH₂)₃PBu^t₂}][CB₁₁H₁₂]₂7. However C₂H₄, CO and PPh₃ do not react readily with these complexes. The thf complex 5 reacts with deuteriated acetonitrile to form [PtMe(NCCD₃){Bu^t₂P(CH₂)₃PBu^t₂}][CB₁₁H₁₂]8. Spectroscopic data for the new complexes are presented and discussed.