Synthesis and characterisation of NHC copper boryl complexes [(NHC)Cu–Bneop] and their decomposition to low-valent copper clusters.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A series of five unsymmetrical platinum(ii) bis-boryl complexes, bearing two distinct boryl ligands, are obtained by the oxidative addition reaction of unsymmetrical diborane(4) derivatives, bearing either two different dialkoxy or one dialkoxy and one diamino boryl moiety, with [(Ph3P)2Pt(C2H4)]. All five complexes were structurally and spectroscopically characterised. The bis-boryl platinum(ii) complexes exhibit slightly distorted square-planar cis-boryl structures with acute B-Pt-B angles, short B⋯B distances of 2.44-2.55 Å and relatively long trans-boryl P-Pt distances around 2.34 Å. The 31P-195Pt NMR coupling constants are indicative for the strongly donating/trans-influencing boryl ligands. Despite the structural and spectroscopic data at hand no finally conclusive order of the donor properties/trans-influence of the boryl ligands can be deduced on the basis of these data. This may be explained by an (residual) interaction of two boryl ligands.
A novel, versatile and modular route to unsymmetrical diborane(4) derivatives bearing either two different diol moieties or one diol and one diamine moiety is presented. Utilising the very basic approach of reacting a boron nucleophile with a boron electrophile to establish the B-B bond allows a simple variation of the two individual boron moieties. The copper(i) boryl complexes used as nucleophilic boron sources are readily accessible from commercially available symmetrical diborane(4) derivatives, whilst equally readily available boron halide derivatives are used as electrophiles. Seven previously inaccessible diborane(4) derivatives were obtained and fully characterised, including single crystal X-ray structure determinations, illustrating the broad scope of the method.
Five novel NHC copper(I) boryl complexes were synthesized by B-B activation via sigma-bond metathesis of symmetrical tetraalkoxy and unsymmetrical dialkoxy diamino diborane(4) derivatives. Despite their low stability, the NHC copper boryl complexes were thoroughly characterized spectroscopically and structurally. Variation of the NHC ligand (ItBu or Me(2)IiPr) as well as of the boryl ligand (Bpin, Bdmab, or BiPrEn) allowed, for the first time systematically, a study in such complexes of the dependence on steric encumbrance. For sterically more demanding ligand combinations, mononuclear linear complexes were obtained, while with less demanding ligand combinations, dimeric dinuclear complexes with two bridging mu-boryl ligands were obtained, exhibiting extremely short Cu center dot center dot center dot Cu distances (<2.26 angstrom). The decomposition of all these complexes was found to proceed via a common pathway, leading ultimately to elemental copper, the free NHC ligand, and the respective symmetrical diborane(4) derivative. The rate of decomposition depended strongly on the steric encumbrance of the individual complex. Two apparently low-valent copper clusters were observed and suggested to be relevant species with respect to the reductive decomposition of the copper(I) boryl complexes.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
We report the first isolation of phosphine copper boryl complexes-species pivotal to numerous copper-catalyzed borylation reactions. The reaction of diboron(4) derivatives with copper terf-butoxide complexes of phosphine ligands allows the isolation of the dimeric mu-boryl-bridged Cu(l) complexes [(iPr(3)P)Cu-Bdmab](2)(4) and [(C6H4(Ph2P)(2))Cu-Bpin](2) (6) with Cu center dot center dot center dot Cu distances of 2.24-2.27 A (dmab = (NMe)(2)C6H4, pin = (OCMe2)(2))). A slightly more sterically demanding boryl ligand furnishes the unprecedented multinuclear copper boryl complex [(iPr(3)P)(2)Cu-8(B(iPrEn))(3)(OrBu)(3)] (5), a potential intermediate of the decomposition of an initial Cu(l) boryl complex (iPrEn = (NiPr)(2)C2H4). All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy; and elemental analysis. DFT computations support the nature of these unique complexes and give insight into their electronic structures.
Since its introduction in 2010 by Suginome et al., pinB–Bdan [pin = OCMe 2 CMe 2 O, dan = (NH) 2 (C 10 H 6 )] has become a valuable reagent in various regioselective (bis-)borylation reactions, and related unsymmetrical diborane(4) derivatives have been used as versatile precursors for diaminoboryl complexes. However, the unsymmetrical diborane(4) derivatives employed show little variation of the diol and diamine moieties. The present study expands this class of compounds and reports the synthesis of unsymmetrical diborane(4) derivatives [C 2 H 4 ( t BuN) 2 ]B–B(NMe 2 ) 2 and [C 2 H 4 ( t BuN) 2 ]B–B(NMe 2 )Cl, bearing a sterically demanding non-aromatic diamine moiety, as well as [C 6 H 4 (HN) 2 ]B–B(O 2 C 5 H 10 ), [C 6 H 4 (HN) 2 ]B–B(O 2 C 2 H 4 ), and [C 6 H 4 (HN) 2 ]B–B[O 2 C 6 H 2 (C 2 H 9 ) 2 ], which illustrate the variability of the diol moiety. Fully characterization of all compounds including single-crystal X-ray diffraction studies allows for the first time a comparative discussion of the spectroscopic and structural properties of this class of compounds.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The unsymmetrical diborane(4) pinB-B((RN)2(C6H4)) (R = Me, Bn) reacts with [(Me3P)4Rh-X] (X = Me, OtBu) giving predominantly either [(Me3P)4Rh-Bpin] or [(Me3P)3Rh-B((RN)2(C6H4))] depending on X. At low temperatures in the presence of excess PMe3 the unprecedented equatorial boryl complex [(Me3P)4Rh-B((MeN)2(C6H4))] is formed.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Diaminoboryl ligands are currently intensively investigated because of their unique coordination chemical properties, for example, as part of pincer ligands. Owing to synthetic restrictions, however, access to diaminoboryl complexes is limited. Unsymmetrical diborane(4) derivatives comprising a dialkoxy- and a diaminoboron moiety provide efficient access to diaminoboryl complexes either by oxidative addition or by σ-bond metathesis reactions. Especially, the latter is complementary to existing methods and overcomes the existing limitations. This is illustrated by the modular synthesis of four unsymmetrical diborane(4) derivatives and their application in the selective preparation of unprecedented unsymmetrical diboryl PtII complexes as well as sterically little encumbered diaminoboryl CuI complexes.
