Lewis acidity trends of aluminum and gallium halides have been considered on the basis of joint X-ray and density functional theory studies. Structures of complexes of heavier group 13 element trihalides MX(3) (M = Al, Ga; X = Cl, Br, I) with monodentate nitrogen-containing donors Py, pip, and NEt(3) as well as the structure of the AlCl(3)·PPh(3) adduct have been established for the first time by X-ray diffraction studies. Extensive theoretical studies (B3LYP/TZVP level of theory) of structurally characterized complexes between MX(3) and nitrogen-, phosphorus-, arsenic-, and oxygen-containing donor ligands have allowed us to establish the Lewis acidity trends Al > Ga, Cl ≈ Br > I. Analysis of the experimental and theoretical results points out that the solid state masks the Lewis acidity trend of aluminum halides. The difference in the Al-N bond distances between AlCl(3)·D and AlBr(3)·D complexes in the gas phase is small, while in the condensed phase, shorter Al-N distances for AlBr(3)·D complexes are observed with 9-fluorenone, mdta, and NEt(3) donors. The model based on intermolecular (H···X) interactions in solid adducts is proposed to explain this phenomenon. Thus, the donor-acceptor bond distance in the solid complexes cannot always be used as a criterion of Lewis acidity.

The synthesis and characterization of the first parent phosphanylalane and phosphanylgallane stabilized only by a Lewis base (LB) are reported. The corresponding substituted compounds, such as IDipp⋅GaH2PCy2 (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene) were obtained by the reaction of LiPCy2 with IDipp⋅GaH2Cl. However, the LB‐stabilized parent compounds IDipp⋅GaH2PH2 (3) and IDipp⋅AlH2PH2 (4) were prepared via a salt metathesis of LiPH2⋅DME with IDipp⋅E′H2Cl (E′=Ga, Al) or by H2‐elimination reactions of IDipp⋅E′H3 (E′=Ga, Al) and PH3, respectively. The compounds could be isolated as crystalline solids and completely characterized. Supporting DFT computations gave insight into the reaction pathways as well as into the stability of these compounds with respect to their decomposition behavior.

Donor-acceptor complexes of borazine (BZ) and its substituted derivatives with Lewis acids (A = MCl(3), MBr(3); M = B, Al, Ga) and Lewis bases (D = NH(3), Py) have been theoretically studied at the B3LYP/TZVP level of theory. The calculations showed that complexes with Lewis bases only are unstable with respect to dissociation into their components, while complexes with Lewis acids only (such as aluminum and gallium trihalides) are stable. It was shown that formation of ternary D→BZ→A complexes may be achieved by subsequent introduction of the Lewis acid (acceptor A) and the Lewis base (donor D) to borazine. The nature of substituents in the borazine ring, their number, and position were shown to have only minor influence on the stability of ternary D→BZ→A complexes due to the compensation effect. Much weaker acceptor properties of borazine are explained in terms of large endothermic pyramidalization energy of the boron center in the borazine ring. In contrast to borazine, binary complexes of the isoelectronic benzene were predicted to be weakly bound even in the case of very strong Lewis acids; ternary DA complexes of benzene were predicted to be unbound. The donor-acceptor complex formation was predicted to significantly reduce both the endothermicity (by 70-95 kJ mol(-1)) and the activation energy (by 40-70 kJ mol(-1)) for the borazine hydrogenation. Thus, activation of the borazine ring by Lewis acids may be a facile way for the hydrogenation of borazines and polyborazines.

The complexes of group 13 element trispentafluorophenyl derivatives E(C6F5)3 (E = B, Al, Ga, In) with diethyl ether of 1:1 composition have been synthesized and structurally characterized. All compounds are isostructural. Thermal stability studies reveal that at elevated temperatures all complexes decompose with pentafluorobenzene evolution. The geometries and thermodynamic characteristics for the dissociation reactions of the compounds have been computed using three DFT methods. The 1H NMR α‐proton chemical shifts for the coordinated ether in deuteriobenzene and in CD2Cl2 solutions correlate with gas phase dissociation enthalpies of the complexes. Potentially high Lewis acidity of B(C6F5)3 is hindered by the large pyramidalization energy of the acceptor moiety.

Solid state structures of group 13 metal halide complexes with pyrazine ( pyz) of 2 : 1 and 1 : 1 composition have been established by X-ray structural analysis. Complexes of 2 : 1 composition adopt molecular structures MX 3 ·pyz·MX 3 with tetrahedral geometry of group 13 metals. Complexes of AlBr 3 and GaCl 3 of 1 : 1 composition are 1D polymers (MX 3 ·pyz) ∞ with trigonal bipyramidal geometry of the group 13 metal, while the weaker Lewis acid GaI 3 forms the monomeric molecular complex GaI 3 ·pyz, which is isostructural to its pyridine analog GaI 3 ·py. Tensimetry studies of vaporization and thermal dissociation of AlBr 3 ·pyz and AlBr 3 ·pyz·AlBr 3 complexes have been carried out using the static method with a glass membrane null-manometer. Thermodynamic characteristics of vaporization and equilibrium gas phase dissociation of the AlBr 3 ·pyz complex have been determined. Comprehensive theoretical studies of (MX 3 ) n ·( pyz) m complexes (M = Al, Ga; X = Cl, Br, I; n = 1, 2; m = 1-3) have been carried out at the B3LYP/ TZVP level of theory. Donor-acceptor bond energies were obtained taking into account reorganization energies of the fragments. Computational data indicate that the formation of (MX 3 ·pyz) ∞ polymers with coordination number 5 is only slightly more energetically favorable than the formation of molecular complexes of type MX 3 ·pyz for X = Cl, Br. It is expected that on melting (MX 3 ·pyz) ∞ polymers dissociate into individual MX 3 ·pyz molecules. This dovetails with low melting enthalpies of the (MX 3 ·pyz) ∞ complexes.Polymer stability decreases in the order AlCl 3 > AlBr 3 > GaCl 3 > AlI 3 > GaBr 3 > GaI 3 . For MI 3 ·pyz complexes computations predict that the monomeric structure motif is more energetically favorable compared to the catena polymer. These theoretical predictions agree well with the experimentally observed monomeric complex GaI 3 ·pyz in the solid state. Thus, the Lewis acidity of the group 13 halides may play a decisive role in the formation of 1D polymeric networks.

Mechanisms of initial stages of gas phase reactions between trimethylaluminum and ammonia have been explored by DFT studies. Subsequent substitution of CH3 groups in AlMe3 by amido groups and substitution of hydrogen atoms in ammonia by AlMe2 groups have been considered. Structures of Al(CH3)x(NH2)3-x, NHx(Al(CH3)2)3-x (x = 0-3) and related donor-acceptor complexes, dimerization products, and reaction pathways for the methane elimination have been obtained. The transition state for the first methane elimination from Al(CH3)3NH3 adduct is the highest point on the reaction pathway; subsequent processes are exothermic and do not require additional activation energy. In excess ammonia, subsequent methane elimination reactions may lead to formation of [Al(NH2)3]2, while in excess trimethylaluminum, formation of N(AlMe2)3 is feasible. Formation of [AlMe2NH2]2 dimer is very favorable thermodynamically. Studies on model reactions between AlH3 and NH3 indicate that reaction barriers obtained for hydrogen-substituted species may serve as an upper estimate in studying the reactivity of methyl-substituted analogues in more complex systems.

Complexes formed by interaction of E(C6F5)3 (E = B, Al, Ga, In) with excess of acetonitrile (AN) were structurally characterized. Quantum chemical computations indicate that for Al(C6F5)3 and In(C6F5)3 the formation of a complex of 1:2 composition is more advantageous than for B(C6F5)3 and Ga(C6F5)3, in line with experimental observations. Formation of the solvate [Al(C6F5)3·2AN]·AN is in agreement with predicted thermodynamic instability of [Al(C6F5)3·3AN]. Tensimetry study of B(C6F5)3·CH3CN reveals its stability in the solid state up to 197 °C. With the temperature increase, the complex undergoes irreversible thermal decomposition with pentafluorobenzene formation.

Structures of two new molecular complexes of antimony pentafluoride with pyridine (Py) and acetonitrile (AN), SbF5•Py and Sb2F10•AN, as well as a molecular complex of antimony trifluoride Sb2F6•Py and its...