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

The addition of Et 2 O·BF 3 or Me 2 S·BCl 3 to the BNBN-cumulene-bridged Pt(II) A-frame complexes [(μ-1,1-BNBN(TMS) 2 )(μ-dmpm) 2 Pt 2 X 2 ] (TMS = SiMe 3 , dmpm = CH 2 (PMe 2 ) 2 , X = Br 1 Br , I 1 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 2 (complex 2 Br -F ) or BCl 2 (complexes 2 Br -Cl and 2 I -Cl ) moiety, respectively. X-ray crystallographic and multinuclear NMR-spectroscopic data show that the Pt→BF 2 interaction in 2 Br -F is very weak and merely electrostatic, while the Pt→BCl 2 interaction in 2 Br -Cl and 2 I -Cl is a stronger donor-acceptor bond. In contrast, the reaction of Me 2 S·BBr 3 with 1 Br yielded a ca. 3:2 mixture of the analogous B-Br addition product to the iminoborane, 2 Br -Br , and the product of a subsequent oxidative addition of one B-Br bond of the chelating BBr 2 moiety to the adjacent platinum center, the mixed-valence boranediyl-bridged, Pt(II)-Pt(IV)-bromoboryl complex 3-Br 5 . The analogous reactions of Me 2 S·BI 3 with 1 Br and Me 2 S·BBr 3 with 1 I yielded complex product mixtures of Pt(II)-Pt(II)-borane ( 2 Br -I and 2 I -Br , respectively) and Pt(II)-Pt(IV)-boryl complexes ( 3-Br n I 5- n , n = 1-3) analogous to 2 X -Y and 3-Br 5 , 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 BBr 2 Ar (Ar = 2,4,6-Me 3 C 6 H 2 (Mes), 2,3,5,6-Me 4 C 6 H (Dur)) with 1 Br , which yielded the cationic Pt(II)-Pt(II)-borenium analogues of 2 Br -Br , the complexes 4 Br -Ar , 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.