A computational study to determine whether substituents make E[triple bond, length as m-dash]nitrogen (E = B, Al, Ga, In, and Tl) triple bonds synthetically accessible.

This study theoretically determines the effect of substituents on the stability of the triple-bonded L-E[triple bond, length as m-dash]N-L (E = B, Al, Ga, In, and Tl) compound using the M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp levels of theory. Five small substituents (F, OH, H, CH and SiH) and four large substituents (SiMe(SiBu), SiPrDis, Tbt ([double bond, length as m-dash] CH-2,4,6-{CH(SiMe)}) and Ar* ([double bond, length as m-dash]CH-2,6-(CH-2,4,6-i-Pr))) are used. Unlike other triply bonded L-E[triple bond, length as m-dash]P-L, L-E[triple bond, length as m-dash]As-L, L-E[triple bond, length as m-dash]Sb-L and L-E[triple bond, length as m-dash]Bi-L molecules that have been studied, the theoretical findings for this study show that both small (but electropositive) ligands and bulky substituents can effectively stabilize the central E[triple bond, length as m-dash]N triple bond. Nevertheless, these theoretical observations using the natural bond orbital and the natural resonance theory show that the central E[triple bond, length as m-dash]N triple bond in these acetylene analogues must be weak, since these E[triple bond, length as m-dash]N compounds with various ligands do not have a real triple bond.