Synthesis and Characterization of Palladium and Platinum Iminoboryl Complexes

Abstract

The presence of a triple bond between boron and nitrogen renders iminoboranes, XÀBNÀR, isoelectronic to alkynes, XÀCCÀR. This relationship stimulated intense experimental [1, 2] and theoretical [3] studies on these compounds. Indeed, their chemistry was extensively investigated for more than two decades, particularly in the research groups led by Paetzold [1] and Nöth. [2] Despite strong similarities in the structural properties of iminoboranes and alkynes, the polarity and relative weakness of the BN linkage [3] leads to its increased reactivity in comparison to that of the CC triple bond, and to the thermodynamic instability of iminoboranes towards cyclooligomerization.[1, 2] Low temperature, high dilution, and the presence of sterically demanding substituents on either side of the triple bond are generally necessary to hinder the otherwise favorable cyclization process and allow for the isolation of monomeric compounds.Among the numerous reactions of iminoboranes, 1,2-additions of polar reagents across the BN multiple bond were thoroughly investigated.[ [4b] afforded examples of transition-metal-bound iminoborane ligands. A coordination mode akin to that of side-on-bound alkynes was observed, with a varying degree of BN multiple bonding retained in the final compounds. Cyclodimerization of iminoboranes within the coordination sphere of different transition metals was also reported, yielding h 4 -coordinated diazadiboretidines. [1, 5a,c] [2+2] Cycloadditions of different XÀ BNÀR compounds with the short-lived complex [Cp 2 Ti= CH 2 ] yielded 1-aza-2-bora-4-titanacyclobutanes.[5b] However, in contrast to the wealth of reported transition-metal alkynyl complexes [L n M À C C À R], [6] corresponding iminoboryl compounds [L n MÀBNÀR] are unknown.We recently described the synthesis of trans-[(Cy 3 P) 2 Pt(Br){B (

Oxidative Addition at a Carbene Center: Synthesis of an Iminoboryl–CAAC Adduct

“…Interestingly, all of the geometric parameters are very similar to those observed for complex A 1 (Scheme 1). [5] Indeed, the geometry around boron [ 16] In addition, the BÀC distance [1.543(3) ] is slightly shorter than a typical BÀC single bond (1.59 ). [17] Interestingly, the 11 B{ 1 H} NMR spectrum shows a broad singlet at + 6.5 ppm, in the range expected for the iodoiminoborane 3 c (3 a: 17.4 ppm; 3 b: 12.4 ppm), and thus we wondered whether the iminoborylium structure of 4 I was retained in solution.…”

“…Similarly, the addition of two equivalents of 1 to a benzene solution of (Me 3 Si) 2 NBBr 2 2 b resulted in the isolation of compound 3 b as a yellow solid in 95 % yield (Scheme 2). [5] A single-crystal X-ray diffraction study shows that the boron center of 3 b is in a planar environment, and the B-N-Si angle [133.3(2)8] indicates that the lone pair on nitrogen is accessible (Figure 1). [15] The BÀC distance is 1.606(4) and the BÀBr and BÀN distances are 2.078(3) and 1.304(3) , respectively.…”

“…[3] Despite the large number of known transition metal alkynyl complexes [L n MÀCCÀR], [4] it was only as recently as 2006 that Braunschweig and co-workers reported the isolation of transition metal iminoboryl complexes A (Scheme 1). [5] The trans-[(Br)(PCy 3 ) 2 M(BNÀSiMe 3 )] (M = Pd, Pt) complexes were obtained upon oxidative addition of the BÀBr bond in (Me 3 Si) 2 NBBr 2 to [M(PCy 3 ) 2 ] and subsequent facile intramolecular elimination of Me 3 SiBr at room temperature. Notably, the transition metal iminoboryl systems were found to be stable against oligomerization, yet reactive towards a variety of substrates.…”

Synthesis and Hydroboration of a Mixed‐Donor Iminoboryl Complex of Platinum

“…[3] Transition metal iminoboryl complexes (L n MBϵNR, II and III; Figure 1), discovered in 2006 in our laboratories, are essentially transition metal derivatives of iminoboranes, containinganM-Bsinglebond. [4] Anumberofreactivitypatternsof iminoboryl complexes have been reported, including substitution of the halide ligand of complexes of the form III by an acetylide, [4c] formation of Lewis adducts through the Lewis-basic iminoboryl nitrogen atom with the Lewis acid AlCl 3 , [4b] and 1,2-dipolar additions (with water, methanol, hydrogen bromide-diethyl ether, aniline and 1,4-diaminobenzene) in which the hydrogen atom is ultimately found on the nitrogen atom. [4b,4c] chemistry was observed in 1,2-dipolar additions using catecholborane and the ditopic borane HBO 2 (1,2,4,5-C 6 H 2 )-O 2 BH.…”

“…[4] Herein, we prepare the first iminoboryl complex bearing mixed-donor ligands, and subject this complex to hydroboration.…”