This is the peer reviewed version of the following article: [[(IMes)2Pt(H)( Barnes, Guillaume Bélanger-Chabot, Laurent Maron, Philippe Berrouard, Pierre Audet, and Frédéric-Georges Fontaine  Since the first report of a metallaboratrane by Hill in 1999, [1] there has been a quest for transition metal complexes containing a dative interaction with group XIII Lewis acids. In a recent report, Braunschweig demonstrated that [(PCy3)2Pt 0 ] interacts with alanes to form Lewis adducts [(PCy3)2Pt(AlX3)], [2] which are rare examples of well characterized alane (M→AlR3) complexes. [3][4] However, the analogous reaction with haloboranes does not yield Lewis adducts, but instead forms platinum boryl complexes, [5] a class of anionic boron containing species with numerous examples reported to date.[6] The only compounds having an M→B dative interaction with boron are supported by ambiphilic ligands. [7][8][9] While metallaboratranes having bis-or tris(methimazolyl)boranes have the borane coordinating the transition metal selectively, [10] the Lewis acid moiety of phosphinoboranes, prepared by Bourissou, [11] in addition to interacting with a transition metal can interact with an anionic ligand within the coordination sphere, depending on the nature of the transition metal and the ambiphilic ligand. Such an interaction is seldom observed with Lewis acids and is supported by ambiphilic ligands, [12] with the exception of BF4 adducts and halocarboranes where the Lewis acidity of the boron can no be longer considered. [13] []A. Languérand, S. S. Barnes, G. While borabenzene adducts are the subject of continuing interest, mainly for their electronic properties, [14] the coordination modes of these heterocyclic molecules with transition metals are quite limited.A common feature of borabenzenes (where L is a neutral Lewis base) [15] and boratabenzenes, [16] the analogue with anionic nucleophiles, is their coordination via the aromatic ring in a η 6 fashion, analogous to arene and cyclopentadienyl ligands, respectively.[17] The exception is a phosphidoboratabenzene which binds transition metals by the phosphine moiety.[18] Using the efficient and general strategy of forming borabenzene organic adducts from boracyclohexadiene by the elimination of Me3SiCl, first developed by Fu (Scheme 1), [19] we examined the possibility of using a nucleophilic transition metal complex as a group to stabilize the Lewis acidic boron orbital on borabenzene. By applying this strategy, the isolation of an η 1 -borabenzene transition metal adduct, and consequently of an unchelated borane having a dative interaction with a transition metal, could be possible. During these investigations, we observed that the B-Cl oxidative addition of the boracyclohexadiene with Pt 0 does not occur, contrary to what was previously observed with haloboranes. Instead, formation of an μ-η 1 -Cl-borabenzene adduct, which is a peculiar bonding mode for an unchelated Lewis acid, was observed. Scheme 1. General scheme for formation of borabenzene adducts from b...

2 Table of Contents GraphicAbstract The bonding properties of borabenzene with various neutral Lewis bases have been investigated. 1-Chloro-4-isopropyl-2-trimethylsilyl-2,4-boracyclohexadiene reacts with a number of Lewis bases -notably pyridine, PMe3, PCy3 and PPh3 -to afford 4-isopropylborabenzene-base adducts.These adducts can undergo ligand exchange to afford new borabenzene complexes. The scope and mechanism of the reaction, as well as the steric and electronic properties of different adducts were studied experimentally and computationally.4

Eine Pt‐Cl‐B‐Wechselwirkung entsteht bei der Reaktion eines Borabenzolderivats und einer Platin(0)‐Vorstufe mit sperrigen N‐heterocyclischen Carbenliganden. Der resultierende Platin(II)‐Komplex (siehe Bild; Pt rot, N blau, Cl grün, B rosa, Si gelb) zeigt einen neuen Bindungsmodus für Borabenzol, das sich gewöhnlich als η6‐Ligand an Übergangsmetalle anlagert.