The carbene transfer to strong Lewis acids: copper is better than silver.

A new convenient approach to the synthesis of useful N-heterocyclic carbene complexes of group 13 metals was successfully developed. We demonstrate that air-stable copper(i) diaminocarbene complexes are excellent carbene transfer reagents for the synthesis of (IMes or IPr)MCl3 with high yields (M = Al, Ga). Use of this simple method allowed for the first time to obtain (IPr)AlCl3, inaccessible via a free carbene route. In contrast to copper complexes, under the same conditions the more commonly used silver analog (IPr)AgCl reacts with MCl3 (M = Al, Ga, In) yielding only the homoleptic cationic complexes [(IPr)2Ag]+MCl4-.

Versatile structures of group 13 metal halide complexes with 4,4'-bipy: from 1D coordination polymers to 2D and 3D metal-organic frameworks.

A systematic structural study of complexes formed by aluminium and gallium trihalides with 4,4'-bipyridine (bipy) in 2 : 1, 1 : 1, and 1 : 2 stoichiometric ratios has been performed. Molecular structures of 11 complexes in the solid state have been determined for the first time. Complexes of 2 : 1 composition are molecular, while complexes of 1 : 1 composition form metal-organic frameworks of different kinds: an ionic 3D network (three interpenetrated lvt nets for AlCl3bipy), an ionic 2D network for AlBr3bipy and GaBr3bipy and a 1D coordination polymer in the case of GaCl3bipy. Thus, the nature of the Lewis acid plays a critical role in the structural type of the complex in the solid state. Incorporation of excess bipy molecules into (GaCl3bipy)∞ (formation of crystallosolvate) leads to an unprecedented change of the molecular structure from a non-ionic 1D coordination polymer to an ionic 2D metal organic framework [GaCl2bipy2](+)[GaCl4](-)·2bipy. As indicated by the temperature-dependent XRD study, removal of bipy by heating in a vacuum restores the non-ionic 1D structure. Quantum chemical computations for simple cluster model systems (up to eight Al and Ga atoms) reveal that ionic forms are slightly favourable, although the energy differences between the ionic and non-ionic structures are not large. These theoretical predictions are in good agreement with experimental findings. Thus, even relatively simple cluster models may be used to indicate the structural preferences in the solid state. Both experimental and computational IR frequency shifts of the in-plane ring bending mode of bipy upon complexation correlate well with the M-N bond distances in the complexes.

Masking of Lewis acidity trends in the solid-state structures of trichlorido- and tribromido(2,2':6',2''-terpyridine-κ(3)N,N',N'')gallium(III).

The molecular structures of trichlorido(2,2':6',2''-terpyridine-κ(3)N,N',N'')gallium(III), [GaCl3(C15H11N3)], and tribromido(2,2':6',2''-terpyridine-κ(3)N,N',N'')gallium(III), [GaBr3(C15H11N3)], are isostructural, with the Ga(III) atom displaying an octahedral geometry. It is shown that the Ga-N distances in the two complexes are the same within experimental error, in contrast to expected bond lengthening in the bromide complex due to the lower Lewis acidity of GaBr3. Thus, masking of the Lewis acidity trends in the solid state is observed not only for complexes of group 13 metal halides with monodentate ligands but for complexes with the polydentate 2,2':6',2''-terpyridine donor as well.

Structures and stability of molecular InBr3Py(x) (x = 1-3) complexes: unexpected solid state stabilization of dimeric In2Br6Py4 as compared to valence-isoelectronic group 15 and 17 halogen bridging dimers.

Molecular structures of series of InBr3Py(x) complexes (x = 1-3) in the solid state have been determined by single crystal structure analysis. For x = 2, an unexpected dimeric In2Br6Py4 structure, which features a nearly planar In2Br6 unit, has been established. This structure completes the series of known valence-isoelectronic dimeric molecules of group 17 (I2Cl6) and group 15 elements (As2Cl6·2PMe3). Theoretical studies at the B3LYP/def2-TZVP level of theory reveal that all gaseous M2X6Py4 dimers (M = Al, Ga, In, Tl; X = Cl, Br) are energetically unstable with respect to dissociation into MX3Py2 monomers. This finding is in stark contrast to the valence-isoelectronic group 17 and 15 analogs, which are predicted to be energetically stable with respect to dissociation. Thus, additional interactions in the solid state play a crucial role in stabilization of the experimentally observed dimeric In2Br6Py4. Thermal stability and volatility of InBr3Py(x) complexes have been studied by tensimetry and mass spectrometry methods. Mass spectrometry data indicate that, in contrast to the lighter group 13 element halides, species with two In atoms, such as In2Br6Py2, are present in the gas phase. Thermodynamic characteristics for the heterogeneous dissociation processes of InBr3Py(x) (x = 2, 3) complexes with Py evolution have been determined.

Fast H/D exchange of B,B',B''-tribromoborazine in C6D6 in the presence of aluminum tribromide: first evidence for an electrophilic substitution reaction of borazines in solution.

A solution of B,B',B''-tribromoborazine (BrBNH)(3) in excess C(6)D(6) in a sealed NMR tube shows no changes for over 14 months at room temperature but undergoes fast (within minutes) H/D exchange in the presence of AlBr(3) as a Lewis acid, as evidenced by (1)H, (2)H, (11)B, and (27)Al NMR spectroscopy. The proposed electrophilic exchange mechanism is in agreement with the results of DFT computations. To our knowledge, this is the first example of the electrophilic substitution reaction of borazines in solution.