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

Unexpected Vulnerability of DPEphos to C-O Activation in the Presence of Nucleophilic Metal Hydrides

C-O bond activation of DPEphos occurs upon mild heating in the presence of [Ru(NHC)2 (PPh3 )2 H2 ] (NHC=N-heterocyclic carbene) to form phosphinophenolate products. When NHC=IEt2 Me2 , C-O activation is accompanied by C-N activation of an NHC ligand to yield a coordinated N-phosphino-functionalised carbene. DFT calculations define a nucleophilic mechanism in which a hydride ligand attacks the aryl carbon of the DPEphos C-O bond. This is promoted by the strongly donating NHC ligands which render a trans dihydride intermediate featuring highly nucleophilic hydride ligands accessible. C-O bond activation also occurs upon heating cis-[Ru(DPEphos)2 H2 ]. DFT calculations suggest this reaction is promoted by the steric encumbrance associated with two bulky DPEphos ligands. Our observations that facile degradation of the DPEphos ligand via C-O bond activation is possible under relatively mild reaction conditions has potential ramifications for the use of this ligand in high-temperature catalysis.

P-C-Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine-Boranes

{Rh(xantphos)}-based phosphido dimers form by P-C activation of xantphos (4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) in the presence of amine-boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H2 BNMeH]n from H3 B⋅NMeH2 and dimeric [H2 BNMe2 ]2 from H3 B⋅NMe2 H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine-borane dehydropolymerization.

Oxidation of germa- and stanna-closo-dodecaborate

The oxidation of closo-heteroborates [GeB11H11](2-) and [SnB11H11](2-) is presented. Upon oxidation germa-closo-dodecaborate yields a symmetrical dimer exhibiting a Ge-Ge bond between two clusters. This dimer shows sulphur insertion into the Ge-Ge bond at room temperature. In contrast, oxidation of the homologous tin cluster results in an unsymmetrical dimer bearing an Sn-B bond between two clusters. The Sn-B dimer is also the product of the hydride abstraction reaction. In the presence of the donor ligand 2,2'-bipyridine, the oxidation of closo-cluster [SnB11H11](2-) leads to the Sn(IV)-half sandwich coordination compound [bipy-SnB11H11] which dissolves in DMSO to give the Sn(IV)-adduct [bipy(DMSO)-SnB11H11].

Dinuclear copper complexes: coordination of Group 14 heteroborates

The dinuclear copper(i) complex [Cu₂(μ-dmapm)(CH₃CN)₂][BF₄]₂ was reacted with Group 14 heteroborates. Four different coordination motives have been characterized.