C. Niamh McMahon

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.

ALCOHOL AND SECONDARY AMINE COMPLEXES OF TRI-TERT-BUTYLALUMINIUM : ENHANCED STABILITY THROUGH INTRAMOLECULAR HYDROGEN BONDING

Reaction of Al(Bu t ) 3 with between 1 and 2 equivalents of HOCH 2 CH 2 CH 2 NMe 2 allows for the isolation of the Lewis acid–base complex, (Bu t ) 3 Al[O(H)CH 2 CH 2 CH 2 NMe 2 ] 1, which undergoes alkane elimination above 45 °C to yield [(Bu t ) 2 Al(µ-OCH 2 CH 2 CH 2 NMe 2 )] 2 2. Compound 2 is also formed directly when 2 equivalents of Al(Bu t ) 3 react with 1 equivalent of HOCH 2 CH 2 CH 2 NMe 2 . The molecular structure of 1 shows an Al–O bond distance comparable to that found in the bridging alkoxide compounds 2 and [(Bu t ) 2 Al(µ-OPr n )] 2 3, suggesting that the Al–O · · · H unit may be considered analogous to a bridging alkoxide unit, Al(µ-OR)Al, as a consequence of a significant contribution from the zwitterionic alkoxide - /ammonium + form made possible by a strong intraligand hydrogen bond. The kinetics of the conversion of 1 into 2 have been studied. A large activation energy and positive deuterium isotope effect are consistent with breaking of the hydrogen bond during the transition state. The reaction of (Bu t ) 3 Al(NMe 3 ) 4 with ethanol yields [(Bu t ) 2 Al(µ-OEt)] 2 5. The reaction of Al(Bu t ) 3 with HN(Me)(CH 2 ) n NMe 2 (n = 3 or 2) yields the stable Lewis acid–base adducts (Bu t ) 3 Al[NH(Me)CH 2 CH 2 CH 2 NMe 2 ] 6 and (Bu t ) 3 Al[NH(Me)CH 2 CH 2 NMe 2 ] 7, respectively. The molecular structures of compounds 1–3, 6 and 7 have been confirmed by X-ray crystallography. The implications of the structures and stabilities of compounds 1, 6 and 7 are discussed with respect to the protonolysis reaction of aluminium alkyls with Bronsted acids (HX) and a new intermolecular elimination mechanism is proposed.

Observation of an unusual amine oxidation reaction during the oxidation and hydrolysis of [: molecular structures of [ and (OPPh3) ☆

Abstract Reaction of [(tBu)2Ga(μ-Cl)]2 with Li(o-C6H4NMe2) yields [ ( t Bu ) 2 Ga (o- C 6 H 4 NMe 2 )] 2 (1). The atmospheric oxidation/hydrolysis of 1 results in the isolation of ( t Bu ) 2 Ga (o- C 6 H 4 Me 2 ] (2). The structure of compound 2 (as determined by X-ray crystallography) consists of a gallium dimer in which one of the ortho-(dimethylamino)phenyl ligands is oxidized and the other exhibits strong intramolecular O3·N hydrogen bonding ( ΔG ‡ = 57.3 kJ mol −1 ) to the hydroxide bridge. A pathway for the formation of 2 is proposed. Reaction of compound 1 with OPPh3 results in the formation of the Lewis acid-base complex [ ( t Bu ) 2 Ga (o- C 6 H 4 NMe 2 )(OPPh3) (3), whose structure has been confirmed by X-ray crystallography.

Molecular structure of (tBu)3AlP(nPr)3

The crystal and molecular structure of (tBu)3AlP(nPr)3 has been determined. The Al(1)−P(1) bond distance [2.594(3) Å] is slightly longer than other aluminum-phosphine complexes; however, the geometry about aluminum is similar to that of the [AlCl(tBu)3]− anion, suggesting that the geometry about the aluminum in tri-tert-butylaluminum complexes is defined by the size of thetert-butyl ligands and not as a consequence of the steric bulk of the Lewis base. Crystal data: Monoclinic,P2t,a=8.932(2),b=16.832(3),c=9.328(2), Å, β=114.36(3)°,V=1277.6(6) Å3,Z=4,R.=0.055,Rw=0.053.

Synthesis of a base-stabilized alumoxane: preferential hydrolysis of an aluminium–amido over an aluminium–alkyl

The preferential hydrolytic cleavage of an A1-N versus an A1-C bond allows for isolation of the base stabilized alkylalumoxane,[(tBu)2A1{NH(Me)CH2CH2NMe2}]2(µ-O), from the hydrolysisof the intra-molecularly stabilized amino-amide compound, (tBu)2A1[N(Me)CH2CH2NMe2], providing a possible general route to alkylalumoxanes.

Steric Effects in Aluminum Compounds Containing Monoanionic Potentially Bidentate Ligands: Effect of the Steric Bulk at the α-Carbon

Reaction of [(iBu)2AlH]2 with l-ephedrine yields [(iBu)2Al{μ-OC(H)(Ph)CH(Me)N(H)Me}]2 (1). Reaction of Al(tBu)3 with (2S,3R)-(+)-4-(dimethylamino)-1,2-diphenyl-3-methyl-2-butanol (ChiraldR) yields (tBu)2Al[OC(CH2Ph)(Ph)CH(Me)CH2NMe2] (2). The molecular structures of compounds 1 and 2 have been determined by X-ray crystallography. Compound 2 is monomeric with a six membered chelate heterocyclic ring. In contrast, compound 1 exists as a bridged dimer. The formation of monomeric chelate species for compound 2, rather than the alkoxide bridged dimer as is found for 1 is found to be due to the steric bulk of the aluminum alkyl and substitution at the ligands α-carbon. Crystal data: (1) orthorhombic, P212121, a = 10.987(2), b = 18.795(4), c = 19.270(4) A, V = 3979(1) A3, Z = 4, R = 0.1056, R w = 0.2454. (2) tetragonal, I4, a = 22.236(3), c = 10.784(1) A, V = 5332.0(5) A3, Z = 8, R = 0.0485, R w = 0.0537.

New complexes of platinum(0) with cyclopropenes

New cyclopropene complexes of platinum have been synthesised with a variety of bulky substituents on all positions of the cyclopropene ring. Two of these novel complexes, [Pt(3,3-Ph 3 C 3 H 2 )(PPh 3 ) 2 ] and [Pt(1,2-Ph 2 C 3 H 2 )(PPh 3 ) 2 ], have been structurally characterised by X-ray analysis. Both contain a cyclopropene ring which has remained intact upon complexation. The bond lengths within the complexes are remarkably independent of the substituents. The structural characteristics and the 31 P NMR spectra of these complexes are discussed in detail.