Computational Investigation on the Role of Disilene Substituents Toward N₂O Activation

Abstract

The effect of substituents in disilene mediated NO 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 (I) in the presence of four different substituents (-NMe, -Cl, -Me, -SiMe) is addressed in this investigation. We primarily propose two plausible mechanistic routes: Pathway I featuring disilene → silylene decomposition followed by NO coordination and Pathway II constituting the NO attack without Si-Si bond cleavage. Depending on the fashion of NO 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 (-NMe, -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 NO attack. In the absence of any lone-pair influence from substituents (-Me, -SiMe), 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 NO 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 NO 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 NO 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.

Precise Activation of Ammonia and Carbon Dioxide by an Iminodisilene

“…Surprisingly,t his compound isomerized quickly (within 4h)and quantitatively to the thermodynamically more stable trans-isomer 4-t (DE = 5.8 kcal mol À1 ), which was isolated as ayellowish solid in 76 % yield. In contrast to the oxygenation of Jutzis( E)-disilene [Cp*(TMS) 2 NSi] 2 with N 2 Or ecently reported by Roesky et al,w hich gave an isolable mixture of cis-a nd transdioxadisiletanes, [17] as econd oxygenation step to the transisomer of 5-c was only observed upon heating aC 6 D 6 solution of 4-t to 50 8 8CinN 2 Oatmosphere for 16 h. This result agrees with acalculated high energy barrier of 20.4 kcal mol À1 for the second oxygenation process and ah igh-lying and sterically protected LUMO of 4-t that hinders the subsequent nucleophilic N 2 Oa ttack (Supporting Information, Figure S50). Quite the opposite picture was found for the HOMO with ac onsiderable amount of accessible p-electron density in between the SiÀSi bond.…”

“…In contrast to the oxygenation of Jutzis( E)-disilene [Cp*(TMS) 2 NSi] 2 with N 2 Or ecently reported by Roesky et al,w hich gave an isolable mixture of cis-a nd transdioxadisiletanes, [17] as econd oxygenation step to the transisomer of 5-c was only observed upon heating aC 6 D 6 solution of 4-t to 50 8 8CinN 2 Oatmosphere for 16 h. This result agrees with acalculated high energy barrier of 20.4 kcal mol À1 for the second oxygenation process and ah igh-lying and sterically protected LUMO of 4-t that hinders the subsequent nucleophilic N 2 Oa ttack (Supporting Information, Figure S50). Exposure of 1 in C 6 D 6 to one atmosphere of N 2 Oatroom temperature gave an instant yellow solution that was monitored by 1 Ha nd 29 Si NMR spectroscopy.A sc onfirmed by matching GIAO-DFT NMR shifts (SiO exp.…”

“…In analogy to the stereospecific hydrogenation, the crystallographic data of 2a ( Figure 1) elucidated aracemic mixture of (RR/SS)-1-aminodisilane with at ypical SiÀSi single bond length (Si1ÀSi6 2.3984(6) )t hat is slightly shorter than that of the respective hydrogen activation product (2.4142- (7) ). [13a] Both silanes exhibit short SiÀN NHI bond lengths (2a Si1 À N1 1.6694 (15) ,S i6 À N4 1.6605 (16) ; 2b Si1 À N1 1.6350 (17) )and quite obtuse SiN NHI Cangles (2aSi1-N1-C1 177.51(14)8 8,S i6-N4-C21 167.43(15)8 8; 2b Si1-N1-C1 177.51-(15)8 8), indicating an increased s-character of the orbital on the nitrogen centers. [14] TheS i ÀNH 2 bonds (2a Si1ÀN7 1.7497-(18) , 2b Si1ÀN4 1.702(4) )are,however, within the range of typical SiÀNb ond lengths of related compounds (I' ' 1.772(3) , IIb' ' 1.7237 (10) ).…”

Recent advances of group 14 dimetallenes and dimetallynes in bond activation and catalysis

“…Depending on the attached ligands, three reaction pathways of the addition of N 2 O to a Si Si bond likely take place according to a recent theoretical study. 128 The first one, starting with dissociation of the double bond into silylene monomers followed by a nucleophilic attack of N 2 O and concluding with the dimerization of the resulted silanone intermediates, affords cis - and trans -products. This pathway is favored by substituents without a lone pair of electrons, leading to a more unstable disilene and therefore facilitating the subsequent attack of N 2 O. Alternatively, N 2 O reacts directly with the double bond either as a nucleophile or an electrophile.…”

“…Nucleophilic N 2 O leads to an end-on attack whereas electrophilic N 2 O interacts with the disilene in a side-on fashion. 128 Within dimetallyne chemistry the activation of N 2 O is reported with several outcomes. For bisgermylene 13a , the reaction proceeds with a simple oxygen transfer that breaks and inserts into the Ge–Ge bond ( Scheme 17 ).…”