Computational Investigation on the Role of Disilene Substituents Toward N 2 O Activation.

The effect of substituents in disilene mediated N2 O activation was studied at the M06-2X/QZVP//ωB97xD/TZVP level of theory. The relationship between structural diversity and the corresponding reactivity of six disilenes (IA-F t ) in the presence of four different substituents (-NMe2 , -Cl, -Me, -SiMe3 ) is addressed in this investigation. We primarily propose two plausible mechanistic routes: Pathway I featuring disilene → silylene decomposition followed by N2 O coordination and Pathway II constituting the N2 O attack without Si-Si bond cleavage. Depending on the fashion of N2 O approach the latter route was further differentiated into Pathway IIa and Pathway IIb detailing the "end-on" and "side-on" attack to the disilene scaffold. Interestingly, the lone pair containing substituents (-NMe2 , -Cl,) facilitates disilene → silylene dissociation; on the contrary it reduces the electrophilicity at Si center in silylene, a feature manifested with higher activation barrier during N2 O attack. In the absence of any lone-pair influence from substituents (-Me, -SiMe3 ), the decomposition of disilenes is considerably endothermic. Therefore, Pathway I appears to be the less preferred route for both types of substituents. In Pathway IIa, the N2 O moiety uniformly approaches via O-end to both the silicon centers in disilenes. However, the calculations reveal that Pathway IIa, although not operational for all disilenes, is unlikely to be a viable route due to the predominantly higher transition barrier (ca. 36 kcal/mol). The most feasible route in this current study accompanying moderately low activation barriers (∼19-26 kcal/mol) is Pathway IIb, which involves successive addition of two N2 O units proceeding via terminal N, O toward the Si centers and is applicable for all disilenes. The reactivity of substituted disilenes can be estimated in terms of the first activation barrier of N2 O attack. Surprisingly, in Pathway IIb, the initial activation barrier and hence the reactivity shows negligible correlation with Si-Si bond strength, indicating toward the versatility of the reaction route.