Germa- and Stanna-closo-dodecaborate in Reaction with [PdCl₂(Xantphos)]: P–C and B–H Bond Activation

Abstract

The two nucleophilic heteroborates germa-closo-dodecaborate and stanna-closo-dodecaborate show different reactivity toward the electrophile [PdCl2(Xantphos)]: In the case of the germanium ligand we found straightforward substitution of one chloride ligand and formation of a Ge–Pd bond. The tin ligand also reacts to give the substitution products [PdCl(SnB11H11)(Xantphos)]− and [Pd(SnB11H11)(Xantphos)], but the complexes exhibit a subsequent reaction under activation of a B–H and P–C bond. A dinuclear Pd(I)–Pd(I) complex featuring a P–B bond was characterized, and during its formation the evolution of benzene was detected. The respective germanium derivative does not show an activation reaction even at elevated temperature.

Synthesis and Coordination Chemistry of a Chelating P–Sn Ligand Based on Stanna‐closo‐dodecaborate

“…Inspired by our palladium‐based B–H activation and P–B bond‐formation reaction, we started to investigate palladium‐based coupling procedures between xantphos and the tributylammonium salt of stanna‐ closo ‐dodecaborate 1 (Scheme ) . Although the stoichiometric coupling reaction proceeds at room temperature with formation of the palladium complexes A and B , 22 mol‐% of [Pd(OAc) 2 ] and higher temperatures are necessary for the coupling of xantphos and heteroborate 1 in a catalytic reaction.…”

“…coupling procedures between xantphos and the tributylammonium salt of stanna-closo-dodecaborate 1 (Scheme 1). [7] Although the stoichiometric coupling reaction proceeds at room temperature with formation of the palladium complexes A and B, 22 mol-% of [Pd(OAc) 2 ] and higher temperatures are necessary for the coupling of xantphos and heteroborate 1 in a catalytic reaction. The reaction of xantphos with [SnB 11 H 11 ] 2-(Scheme 1) was monitored by means of 31 P{ 1 H} NMR spectroscopy.…”

“…A couple of years ago, we studied the coordination chemistry of the germa‐ and stanna‐ closo ‐dodecaborate nucleophiles at a palladium xantphos electrophile . In these reactions, we found a difference in reactivity between the germanium and tin ligands.…”

“…[6] A couple of years ago, we studied the coordination chemistry of the germa-and stanna-closo-dodecaborate nucleophiles at a palladium xantphos electrophile. [7] In these reactions, we found a difference in reactivity between the germanium and tin ligands. The germanium-based nucleophile exhibits well-established η 1 -coordination through the germanium atom at the pal-phosphine moiety.…”

“…Characterized coupling products between xantphos and [SnB 11 H 11 ] 2-. [7] Consequently, we aimed to develop a rational synthesis for the chelating P-Sn ligand found in the palladium coordination chemistry in A (Figure 1). In this manuscript, we present a synthetic procedure for the synthesis of a stanna-closo-dodecaborate-based bidentate P-Sn ligand, along with the first reactions of this tin and phosphorus donor with electrophiles.…”