Synthesis and Molecular Structural Studies of a Series of Orthometalated Dimers [RAlN(t-Bu)-μ-(CH₂C₆H₄)]₂, where R = Me, Et, n-Pr, n-Bu, i-Bu

Abstract

The orthometalated aluminum-nitrogen dimer series [RAlN(t-Bu)-µ-(CH 2 C 6 H 4 )] 2 (R ) Me, 1; Et, 2; n-Pr, 3; n-Bu, 4; i-Bu, 5) was synthesized by thermolysis of 1:1 mixtures of R 3 Al with HN(t-Bu)CH 2 Ph. The reaction times and temperatures required for orthometalation, the molecular structural data, and the 1 H and 13 C NMR spectral parameters of the dimers are compared with the reported data for the series [RAlN-(CH 2 Ph)-µ-(CH 2 C 6 H 4 )] 2 .

Synthesis and Molecular Structure Studies of [Me2AlN(i-Pr)CH2Ph]2 and the Related Orthometalated Dimers [RAlN(i-Pr)-μ-(CH2C6H4)]2, where R = Me, n-Pr, n-Bu, i-Bu

“…Reaction of ( i -Bu) 3 Al with HN( i -Pr)CH 2 Ph leads initially to dimer formation, [( i -Bu) 2 AlN( i -Pr)CH 2 Ph] 2 , but its decomposition occurs before the reactants are consumed. The reaction conditions for formation of [R 2 AlN( i -Pr)CH 2 Ph] 2 are similar to those for the series [R 2 AlN(CH 2 Ph) 2 ] 2 , but for the latter all five dimers were isolated and characterized. − However, the thermolysis reactions of 1:1 mixtures of R 3 Al with HN( t -Bu)CH 2 Ph at 100 °C are similar to the reaction of ( i -Bu) 3 Al with HN( i -Pr)CH 2 Ph in that the reactions are facile and the dimers formed are subject to further alkane elimination . The role of R and R‘ in influencing the reaction sequence 2R 3 Al + HNR‘ 2 → 2R 3 Al·HNR‘ 2 → [R 2 AlNR‘ 2 ] 2 + 2RH has been discussed in terms of the steric and electronic effects of the R and R‘ groups .…”

“…Orthometalated dimer formation is complete for 2 after heating for 6 days at 150 °C followed by 4 days at 175 °C, whereas compounds 3 − 5 require less heating (6 days at 155 °C) . The synthesis of [RAlN(CH 2 Ph)-μ-(CH 2 C 6 H 4 )] 2 requires heating of the R 3 Al/HN(CH 2 Ph) 2 mixtures at 150−155 °C for three weeks, independent of R; however, the reaction conditions for the formation of [RAlN( t- Bu)-μ-(CH 2 C 6 H 4 )] 2 from thermolysis of R 3 Al/HN( t -Bu)CH 2 Ph are more moderate (120 °C, 1−4 days, with R = Me requiring heating for the longest time) …”

“…Therefore, our systematic study of the formation of the aluminum−nitrogen dimers [R 2 AlN(R‘)CH 2 Ph] 2 (where R‘ = Me; benzyl, isopropyl, tert -butyl) and the requirements for formation of their respective orthometalated dimers [RAlN(R‘)-μ-(CH 2 C 6 H 4 )] 2 have established that aluminum−nitrogen dimer stability and the subsequent ease of orthometalation depend to a significant degree on the steric nature of the group on the nitrogen atom of the amine, R‘, and are affected only slightly by the alkyl group R. These findings are in agreement with reactivity studies involving the formation of orthometalated palladium complexes from dibenzylamine or similar aromatic amines …”

“…Recently, there have been several reports discussing the influence that bulky substituents have on the formation of orthometalated palladium complexes . Also, we have reported the synthesis and characterization of two series of orthometalated aluminum−nitrogen dimers from the thermolysis of R 3 Al (R = Me, Et, n -Pr, n -Bu, i -Bu) with dibenzylamine and with tert -butylbenzylamine. − Therein, the effects of the steric bulk of the organic substituents on the nitrogen and aluminum atoms were investigated in terms of the ease of the formation of the orthometalated dimers and their spectral and structural properties. The reactions of R 3 Al and HN(CH 2 Ph) 2 lead to the formation of [R 2 AlN(CH 2 Ph) 2 ] 2 at 120 °C, − but the orthometalated dimers are obtained only after heating at 150 °C for three weeks.…”

“…The reactions of R 3 Al and HN(CH 2 Ph) 2 lead to the formation of [R 2 AlN(CH 2 Ph) 2 ] 2 at 120 °C, − but the orthometalated dimers are obtained only after heating at 150 °C for three weeks. The thermolysis reactions of mixtures of R 3 Al and HN( t- Bu)CH 2 Ph proceed more readily, and the orthometalated dimers [RAlN( t- Bu)-μ-(CH 2 C 6 H 4 )] 2 are obtained at lower temperatures, with much shorter reaction times, and in higher yields. In fact, the orthometalation reactions are so facile that they proceed before the initial reactants are consumed and dimer formation, [R 2 AlN( t- Bu)CH 2 Ph] 2 , is complete; as a consequence, no dimers were isolated for the tert -butylbenzylamine reaction system.…”