Al-X Bond Research Articles

Theoretical assessment of donor–acceptor complexes [X(PPh3)2 → AlH2]+ (X = C–Pb): structures and bonding

Quantum chemical investigations at the BP86/def2-SVP, BP86/def2-TZVPP and BP86/TZ2P+ levels of theory have been done for the series of AlH2+ complexes that carry carbodiphosphorane and analogues called tetrylones [X(PPh3)2–AlH2]+ (Al-XPPh) (X = C–Pb) using charge and partitioning methods. The most stable structures of Al-XPPh have been found for carbone CPPh as a mildly side-on style in carbone complex Al-CPPh, while the heavier tetrylone adducts Al-SiPPh−Al-PbPPh have significantly different side-on fashions SiPPh−PbPPh, which exhibit the more acute bending angles in tilted forms linked to AlH2+ fragment. Bond dissociation energies (BDEs), De (kcal/mol), slightly decrease from the strongest bonded carbone, Al-CPPh, to the weaker bonded heavier homologues. The bulky tetrylone ligands XPPh have significantly influenced to the Al-X bond strength in complexes Al-XPPh when calculating BDEs with dispersion interaction. The NBO analysis revealed that the [X(PPh3)2 → AlH2]+ donation comes mainly from the σ- and π-contributions of the ligands. The EDA–NOCV calculations showed that the bond sturdiness of the Al–X bond results from the decrease in [X(PPh3)2 → AlH2]+ donation and electrostatic attraction. The EDA–NOCV data also indicated that AlH2+–tetrylone complexes exhibit not only (PPh3)2X → AlH2+ strong σ-donors and weak π-donors but also (PPh3)2X ← AlH2+ weak π-back donation as π–π electrons shared in complexes.

A quantum chemical study of alkoxy derivatives of three-coordinate aluminum

DFT and HF methods using the PC GAMESS-Firefly program are employed to calculate the spatial and electronic structures of molecules: alkoxy derivatives of aluminum. By NBO and AIM methods the main characteristics of Al-O, C-O, and Al-X bonds in these molecules are determined. It is shown that Al and O atoms interact with each other as atoms with closed shells. The C-O bonds are close to covalent, whereas the Al-X bonds are the intermediate type bonds.

C Al 4 X (XSi,Ge): Molecules with simultaneous planar tetracoordinate carbon, aluminum, and silicon/germanium

The authors report the first theoretical study on the hexa-atomic molecules CAl(4)X (X=Si,Ge) at the B3LYP/6-311++G(2d), MP2/6-311++G(2d), and CCSD(T)/6-311++G(3df) (single point) levels. Three low-lying isomers (within 2.0 kcal/mol) can be formally viewed as constructed by one Al+ interacting with the planar CAl3X- at the side Al-X bond (X-1), side Al-Al bond (X-2), and central C atom (X-3). The isomers X-1 and X-2 both have planar structures that include the planar tetracoordinate carbon, aluminum, and silicon/germanium, while the three-dimensional isomer X-3 has the pentacoordinate carbon. The planarity of X-1 and X-2 is ascribed to the ligand five-center two-electron bonding molecular orbital, similar to the orbital responsible for the planarity of CAl3X- (X=Si,Ge). Kinetically, the two planar structures X-1 and X-2 can be easily interconverted to each other via the intermediate X-3, indicative of their coexistence. Of particular interest, isomer X-1 represents the first example that simultaneously contains three types of planar centers in a single molecule, to the best of our knowledge. The three low-lying and structurally interesting isomers X-1, X-2, and X-3 await future experimental verification. The present results could enrich the planar chemistry.

Conversion of a (sp3)C–F bond of alkyl fluorides to (sp3)C–X (X = Cl, C, H, O, S, Se, Te, N) bonds using organoaluminium reagents

A simple method for the conversion of (sp(3))C-F bonds of alkyl fluorides to (sp(3))C-X (X = Cl, C, H, O, S, Se, Te, N) bonds has been achieved by the use of a hexane solution of organoaluminum reagents having Al-X bonds.

Theoretical study of aluminide clusters Al13X, Al13X−, and Al13X 2 − (X=H, Hal, OH, NH2, CH3, and C6H5)

The structural, electronic, energy, and vibrational characteristics of the Al13X− and Al13X 2 − clusters, with an aluminum-centered (Alc) icosahedral cage Al13 and with one or two outer-sphere ligands X=H, F, Cl, Br, OH, NH2, CH3, C6H5, have been calculated within the B3LYP approximation of the density functional theory using the 6-31G* and 6-311+G* basis sets. In all Al13X− radicals, the unpaired electron is localized at the cage atom Al* located opposite the Al-X bond. This Al* atom is the most favorable site for attaching the second X ligand of any nature (trans-addition rule). According to the previously suggested molecular model of the valence state of the [Al 13 − ] “superatom,” the calculated energies D 1(Al 13 − -X) of addition of the first ligand to the Al 13 − anion are about 1 eV lower than the corresponding energies of addition of the second ligand D 2(XAl 13 − -X). The structure of the Al13 cage depends on the nature of the nature of the substituent X and can radically change in going from anions to their neutral congeners. In the lowest-lying Al13X isomer with electronegative substituents X (Hal, OH, NH2, CH3, etc.), the aluminum cage has a marquee structure (1, symmetry C s) with a hexagonal base and a pentagonal “roof.” For Al13X analogues with electropositive ligands X (Al, Li, Na), a tridentate isomer (T, C 3v ) with the X substituent coordinated to a face of the Al13 icosahedron is preferable. In the case of moderately electronegative X ligands (of the H type), the marquee (1) and icosahedral (T) isomers are close in energy. The stretching vibration frequencies of isomers 1 and T differ significantly in magnitude and intensity so that vibrational spectroscopy methods can be especially applicable to their experimental identification.

Concerning the mechanism of the ring opening of propylene oxide in the copolymerization of propylene oxide and carbon dioxide to give poly(propylene carbonate).

The reactions between (TPP)AlX, where TPP = tetraphenylporphyrin and X = Cl, O(CH(2))(9)CH(3), and O(2)C(CH(2))(6)CH(3), and propylene oxide, PO, have been studied in CDCl(3) and have been shown to give (TPP)AlOCHMeCH(2)X and (TPP)AlOCH(2)CHMeX compounds. The relative rates of ring opening of PO follow the order Cl > OR > O(2)CR, but in the presence of added 4-(dimethylamino)pyridine, DMAP (1 equiv), the order is changed to O(2)CR > OR. From studies of kinetics, the ring opening of PO is shown to be first order in [Al]. Carbon dioxide inserts reversibly into the Al-OR bond to give the compound (TPP)AlO(2)COR, and this reaction is promoted by the addition of DMAP. The coordination of DMAP to (TPP)AlX is favored in the order O(2)C(CH(2))(6)CH(3) > O(2)CO(CH(2))(9)CH(3) >> O(CH(2))(9)CH(3). The microstructure of the poly(propylene carbonate), PPC, formed in the reactions between (TPP)AlCl/DMAP and (R,R-salen)CrCl and rac-PO/S-PO/R-PO and CO(2), has been investigated by (13)C [(1)H] NMR spectroscopy. The ring opening of PO is shown to proceed via competitive attack on the methine and methylene carbon atoms, and furthermore attack at the methine carbon occurs with both retention and inversion of stereochemistry. On the basis of these results, the reaction pathway leading to ring opening of PO can be traced to an interchange associative mechanism, wherein coordination of PO to the electrophilic aluminum atom occurs within the vicinity of the Al-X bond (X = Cl, OR, O(2)CR, or O(2)COR). The role of DMAP is two-fold: (i) to labilize the trans Al-X bond toward heterolytic behavior, and (ii) to promote the insertion of CO(2) into the Al-OR bond.

DFT study on the reed diethylaluminum cation-like system: structure and bonding in Et(2)Al(CB(11)H(6)X(6)) (X = Cl, Br).

Electronic and molecular structure has been investigated in the diethylaluminum cation-like system Et(2)Al(CB(11)H(6)X(6)) (1, X = Cl; 2, X = Br) and neutral compounds AlX(3) (X = Cl, Br, Me, C(6)H(5)) with DFT B3LYP and BP86 levels of theory. The calculated geometries of Et(2)Al(CB(11)H(6)X(6)) (1, X = Cl; 2, X = Br) are in excellent agreement with those determined experimentally by X-ray crystallography. The Al-X bond distances 2.442, 2.445 A in 1 and 2.579, 2.589 A in 2 are longer than those expected for single bonds based on covalent radius predictions (Al-Cl = 2.15 A and Al-Br = 2.32 A) and those observed for bridged Al-X-Al bonds (2.21 A in Al(2)Cl(6), 2.33 A in Al(2)Br(6)) and are close to sum of ionic radii of Al(3+) and X(-) (Al-Cl = 2.35 A and Al-Br = 2.50 A). The optimized geometries of the neutral compounds AlX(3) (X = Cl, Br, Me(3), C(6)H(5)) at BP86/TZ2P show Al-Cl = 2.088 A in AlCl(3), Al-Br = 2.234 A in AlBr(3), Al-C = 1.973 A in AlMe(3), Al-C = 2.255 A in Al(C(6)F(5))(3). These bond distances are similar to those expected for single bonds based on covalent radius predictions. The calculated charge distribution indicates that the aluminum atom carries a significant positive charge while the ethyl and carborane groups are negatively charged. The Cl and Br atoms in compounds 1 and 2 are slightly positive while, in neutral compounds AlX(3) (X = Cl, Br, Me(3), C(6)H(5)), X is negatively charged. Energy decomposition analysis of Et(2)Al(delta)(+)(carborane)(delta)(-) shows that the bonding between the fragments is more than half electrostatic. The ionic character of the Al...Cl bonds in compound 1(59.8%) is greater than the Al.Br bonds in the compound 2 (57.9%). This quantifies and gives legitimacy to the designation of these types of compounds as "ion-like". The Al-X bonding in AlX(3) is mainly covalent with percentage ionic character 28.2% in AlCl(3), 31.5% in AlBr(3), 25.6% in AlMe(3), 18.4% in Al(C(6)F(5))(3).

Les composes de coordination des halogenures d'aluminium: mise au point sur leurs proprietes structurales et les methodes d'analyses

Les composes de coordination des halogenures d'aluminium: mise au point sur leurs proprietes structurales et les methodes d'analyses

Bond length-bond energy term correlations for bonds in Al2X6 compounds

Published thermochemical data are used to calculate bond energy terms for the bridging and terminal Al-X bonds of some representative Al2X6 compounds.