Julie A. Francis

Sterically crowded aryloxides of aluminum: intramolecular coordination of bidentate ligands

Reactions of (BHT) 2 Al(H)(Et 2 O) (BHT-H=HOC 6 H 2 -2,6- t Bu 2 -4-Me) with HOCH 2 CH 2 EMe x (E=O, S, x =1; E=N, x =2) yield dimeric species, [(BHT)Al(H)(μ-OCH 2 CH 2 NMe 2 )] 2 ( 2 ), [(BHT)Al(H)(μ-OCH 2 CH 2 OMe)] 2 ( 3 ), [(BHT)Al(H)(μ-OCH 2 CH 2 SMe)] 2 ( 4 ), respectively or [(BHT)Al(OCH 2 CH 2 NMe 2 )(μ-OCH 2 CH 2 NMe 2 )] 2 ( 5 ), [(BHT)Al(OCH 2 CH 2 OMe)(μ-OCH 2 CH 2 OMe)] 2 ( 6 ) and [(BHT)Al(OCH 2 CH 2 SMe)(μ-OCH 2 CH 2 SMe)] 2 ( 7 ), respectively, depending on the stoichiometry of the reaction. The non-bridged donor atoms interact intramolecularly to form five-coordinate aluminum centers. A mixture of (BHT)Li(Et 2 O) and (BHT) 2 Al(H)(Et 2 O), formed from the reaction of LiAlH 4 and BHT-H, reacts with the aforementioned alcohols to yield the monomeric structures (BHT) 2 Al(μ-OCH 2 CH 2 NMe 2 ) 2 Li ( 8 ), (BHT) 2 Al(μ-OCH 2 CH 2 OMe) 2 Li ( 9 ), (BHT) 2 Al(μ-OCH 2 CH 2 SMe) 2 Li ( 10 ), respectively. If the reaction is carried out with an excess of HOCH 2 CH 2 SMe, the solvate of compound 10 is formed, (BHT) 2 Al(μ-OCH 2 CH 2 SMe) 2 Li(HOCH 2 CH 2 SMe) ( 11 ). The lithium cation in compounds 8 – 11 is stabilized in the structure by formation of bonds with both the anionic oxygens as well as the neutral donor ligands. The bond valencies have been calculated for Al and Li in compounds 8 and 11 .

1,3-diphenylamidine and methylaminopyridine compounds of gallium

Abstract Reaction of Ga ( t Bu ) 3 with the 1,3-diphenylamidine [PhN(H)C(H)NPh, H-dpam] yields monomeric ( t Bu ) 2 Ga ( dpam ) (1). The partial hydrolysis of 1 results in the isolation of ( t Bu ) 2 Ga (μ- dpam )(μ- OH ) Ga ( t Bu ) 2 (2), whose structure consists of a gallium dimer in which the amidine and hydroxide ligands bridge two Ga ( t Bu ) 2 moieties. Reaction of [Me2Ga(μ-Cl)]2 with H-dpam results in the complex [H2-dpam] [Me2GaCl2] (3). The solid state structure of 3 indicates the presence of a hydrogen bonded cation-anion complex, in which the core has a twisted eight-membered ring configuration. The versatility of amidines as both chelating and bridging ligands to gallium is discussed with respect to the predominance of bridging and chelating modes of coordination of carboxylates and triazenides, respectively. Reaction of 2-(methylamino)pyridine (H-map) with Ga ( t Bu ) 3 allows for the isolation of ( t Bu ) 2 Ga ( map ) (4). In contrast, reaction with [( t Bu ) 2 Ga (μ- Cl )] 2 and [Me2Ga(μ-Cl)]2 yields the Lewis acid base adducts, ( t Bu ) 2 GaCl ( H-map ) (5) and Me2GaCl(H-map) (6), respectively. Reaction of compound 6 with nPrNH2 does not result in the deprotonation of the H-map ligand, but ligand metathesis and the formation of ( t Bu ) 2 GaCl ( NH 2 n Pr ) (7). The structures of 2, 3, 6, and 7 have been determined by X-ray crystallography.

Are intramolecularly stabilized compounds of aluminum suitable structural models of the SN2 transition state? Molecular structure of [(tBu)2Al(μ-OC6H4-2-OMe)]2

Abstract The synthesis and crystallographic characterization of [( t Bu) 2 Al(μ-OC 6 H 4 -2-OMe)] 2 , when combined with the previously reported methyl, ethyl and iso -butyl analogs, allows for the structural comparison of the homologous series [R 2 Al(μ-OC 6 H 4 -2-OMe)] 2 with the ideal structural changes that occur during the S N 2-like cleavage of an aluminum alkoxide dimer with an intramolecular Lewis base. Ab initio calculations on the model system, [H 2 Al(μ-OCH 2 CH 2 OH)] 2 , confirm that in the absence of steric effects, intramolecularly stabilized compounds of aluminum are suitable structural models of the S N 2 transition state. However, real compounds are not good models since the bond distances are controlled by the steric bulk of the alkyl substituents on adjacent aluminum centers rather than the extent of coordination of the fifth ligand.

Molecular structure of [(tBu)2Al(μ-Cl)]2

The molecular structure of [(tBu)2Al(μ-OPh)]2 has been determined. The intramolecular steric interaction between the phenyl groups and thetert-butyl ligands results in the geometry about aluminum being significantly distorted from tetrahedral, with the AlC2 planes are pitched 62° with respect to the Al2O2 plane. The greater distortion from tetrahedral about aluminum, and the orientation of the phenoxide ring more nearly perpendicular to the M2O2 core as compared to that in [(tBu)2Ga(μ-OPh)]2 are all consistent with increasedtBu...Ph steric interaction as a consequence of the smaller M2O2 core for [(tBu)2Al(μ-OPh)]2. Crystal data: tetragonal, I41/acd,a=16.44(1),c=21.41(1) Å,V=5788(7) Å3,Z=8,R=0.047,Rw=0.045.

Hydroalumination of H2C==CHCH2SMe: Synthesis and Molecular Structure of (tBu)2Al(CH2CH2CH2SMe)

Hydroalumination of H2C=CHCH2SMe with [(tBu)2Al(μ-H)]3 yields the monomeric thioether compound . The molecular structure of consists of discreet monomers in which the thioether-alkyl ligand acts as a chelate ligand with an Al-S interaction [2.511(2) A] that is significantly shorter than observed for other intra-molecular coordination compounds, 2.78–2.95 A. The coordination about aluminum is highly distorted from tetrahedral and is therefore best described as capped trigonal planar or trigonal bipyramidal with a vacant coordination site. Crystal data: monoclinic, P21/n (No. 14), a = 6.6357(5), b = 13.630(1), c = 16.959(1) A, β = 95.416(6)°. V = 1527.0(2) A3, Z = 4, R = 0.0412, Rw = 0.0503.

Hydroalumination of H2C=CHCH2 SMe: Synthesis and Molecular Structure of

Hydroalumination of H2C=CHCH2SMe with [(tBu)2Al(μ-H)]3 yields the monomeric thioether compound . The molecular structure of consists of discreet monomers in which the thioether-alkyl ligand acts as a chelate ligand with an Al-S interaction [2.511(2) A] that is significantly shorter than observed for other intra-molecular coordination compounds, 2.78–2.95 A. The coordination about aluminum is highly distorted from tetrahedral and is therefore best described as capped trigonal planar or trigonal bipyramidal with a vacant coordination site. Crystal data: monoclinic, P21/n (No. 14), a = 6.6357(5), b = 13.630(1), c = 16.959(1) A, β = 95.416(6)°. V = 1527.0(2) A3, Z = 4, R = 0.0412, Rw = 0.0503.

Hydroalumination of H2C=CHCH2SMe: Synthesis and Molecular Structure of

Hydroalumination of H2C=CHCH2SMe with [(tBu)2Al(μ-H)]3 yields the monomeric thioether compound . The molecular structure of consists of discreet monomers in which the thioether-alkyl ligand acts as a chelate ligand with an Al-S interaction [2.511(2) A] that is significantly shorter than observed for other intra-molecular coordination compounds, 2.78–2.95 A. The coordination about aluminum is highly distorted from tetrahedral and is therefore best described as capped trigonal planar or trigonal bipyramidal with a vacant coordination site. Crystal data: monoclinic, P21/n (No. 14), a = 6.6357(5), b = 13.630(1), c = 16.959(1) A, β = 95.416(6)°. V = 1527.0(2) A3, Z = 4, R = 0.0412, Rw = 0.0503.