A-Frame-Templated High-Coordinate Platinum(IV) -Bis(boryl) Complexes.

The addition of EtO·BF or MeS·BCl to the BNBN-cumulene-bridged Pt(II) A-frame complexes [(μ-1,1-BNBN(TMS))(μ-dmpm)PtX] (TMS = SiMe, dmpm = CH(PMe), X = Br , I ) resulted in the oxidative addition of one B-F or B-Cl bond, respectively, to the internal BN bond of the bridging, iminoborane-like B-N≡B-N moiety, and coordination of one Pt(II) center to the resulting adjacent BF (complex ) or BCl (complexes and ) moiety, respectively. X-ray crystallographic and multinuclear NMR-spectroscopic data show that the Pt→BF interaction in is very weak and merely electrostatic, while the Pt→BCl interaction in and is a stronger donor-acceptor bond. In contrast, the reaction of MeS·BBr with yielded a ca. 3:2 mixture of the analogous B-Br addition product to the iminoborane, , and the product of a subsequent oxidative addition of one B-Br bond of the chelating BBr moiety to the adjacent platinum center, the mixed-valence boranediyl-bridged, Pt(II)-Pt(IV)-bromoboryl complex . The analogous reactions of MeS·BI with and MeS·BBr with yielded complex product mixtures of Pt(II)-Pt(II)-borane ( and , respectively) and Pt(II)-Pt(IV)-boryl complexes (, = 1-3) analogous to and , respectively, the proportion of the latter increasing with the proportion of iodide in the precursor mixture. Both multinuclear NMR-spectroscopic and X-ray crystallographic data show evidence of complex and extensive inter- and intramolecular bromide-iodide exchanges between the soft, iodide-affine platinum centers and the harder, more bromide-affine boron centers. A clue to the mechanism of these halide exchanges is provided by the reactions of BBrAr (Ar = 2,4,6-MeCH (Mes), 2,3,5,6-MeCH (Dur)) with , which yielded the cationic Pt(II)-Pt(II)-borenium analogues of , the complexes , generated by the sterics-induced displacement of the bromide substituent from the chelating Pt→BBrAr moiety, and displaying a rare metal→borenium donor-acceptor bond.