Manganese Silylene Hydride Complexes: Synthesis and Reactivity with Ethylene to Afford Silene Hydride Complexes

Abstract

Reaction of the ethylene hydride complex trans-[(dmpe) MnH(C H )] (1) with Et SiH at 20 °C afforded the silylene hydride [(dmpe) MnH(=SiEt )] (2 a) as the trans-isomer. By contrast, reaction of 1 with Ph SiH at 60 °C afforded [(dmpe) MnH(=SiPh )] (2 b) as a mixture of the cis (major) and trans (minor) isomers, featuring a Mn-H-Si interaction in the former. The reaction to form 2 b also yielded [(dmpe) MnH (SiHPh )] (3 b); [(dmpe) MnH (SiHR )] (R=Et (3 a) and Ph (3 b)) were accessed cleanly by reaction of 2 a and 2 b with H , and the analogous reactions with D afforded [(dmpe) MnD (SiHR )] exclusively. Both 2 a and 2 b engaged in unique reactivity with ethylene, generating the silene hydride complexes cis-[(dmpe) MnH(R Si=CHMe)] (R=Et (4 a), Ph (4 b)). Compounds trans-2 a, cis-2 b, 3 b, and 4 b were crystallographically characterized, and bonding in 2 a, 2 b, 4 a, and 4 b was probed computationally.

Interconversion and reactivity of manganese silyl, silylene, and silene complexes

“…This reaction mirrors the reactions of silylene hydride complexes 3 R2 with ethylene (vide supra: Scheme 1). 32 Moreover, complexes 6 R,H reacted with a second equivalent of ethylene to form silene hydride complexes with two hydrocarbyl groups on Si, [(dmpe) 2 MnH(REtSi]CHMe)] (6 Ph,Et : R ¼ Ph, 6 Bu,Et : R ¼ n Bu); the products of apparent ethylene insertion into the Si-H bond (Scheme 3 and Fig. 2).…”

“…We recently communicated the synthesis (Scheme 1) of the rst unstabilized terminal silylene complexes of a group 7 metal, [(dmpe) 2 MnH(]SiR 2 )] (3 Ph2 : R ¼ Ph, 3 Et2 : R ¼ Et), by the reaction of [(dmpe) 2 MnH(C 2 H 4 )] (1) 31 with secondary hydrosilanes (H 2 SiR 2 ). 32 In the solid state, the silylene and hydride ligands are cis (diphenyl analogue 3 Ph2 ) or trans (diethyl analogue 3 Et2 ) disposed, in the former case with an Si-H interligand interaction. Silylene hydride complexes with interligand Si-H interactions were rst reported in 2004 by the Tobita 21 ([(C 5 Me 4 Et)(OC) 2 WH(]SiH{C(SiMe 3 ) 3 })]) and Tilley 22 ([Cp*(dmpe)MoH(]SiEt 2 )]) 33 groups, and since that time, W, Fe, Ru, and Ni examples have been reported.…”

“…(1) with primary and secondary hydrosilanes to generate silylene-hydride (3 R2 ) and disilyl hydride (4 R ) complexes respectively, reactions of the latter two complexes with H 2 to generate isostructural silyl dihydride complexes (5 R2 or 5 R respectively), and reaction of silylene hydride complexes 3 R2 with ethylene to generate silene hydride complexes (6 R2 ). 32,35,36 Only one isomer is shown for 2, 5, and A. Scheme 2 Reported reactions capable of converting between silylene, silyl, silene and alkyl isomers.…”

“…generate silyl dihydride complexes [(dmpe) 2 MnH 2 (SiHRR 0 )] (5 Ph2 : R ¼ R 0 ¼ Ph; 5 Et2 : R ¼ R 0 ¼ Et; 5 Ph : R ¼ Ph, R 0 ¼ H; 5 Bu : R ¼ n Bu, R 0 ¼ H), suggesting the accessibility of a common lowcoordinate silyl intermediate, [(dmpe) 2 Mn(SiHRR 0 )] (2). 32,36 Therefore, disilyl hydride complexes 4 R could potentially react as sources of manganese silylene hydride complexes with an SiH substituent, and exposure of 4 R to ethylene may provide a route to silene complexes bearing an SiH substituent.…”

“…40 In this regard, manganese mediated hydrosilylation of polar unsaturated bonds has been well studied, 41 but only a handful of manganese catalysts have been reported for alkene hydrosilylation. 32,42 The typical mechanism for alkene hydrosilylation (Chalk-Harrod mechanism) involves oxidative addition of a hydrosilane to generate a silyl hydride complex, followed by alkene coordination, C-H bond-forming 1,2-insertion, and nally Si-C bond-forming reductive elimination. However, in some cases alkene coordination is followed by C-Si bond-forming 1,2insertion and then C-H bond-forming reductive elimination (modied Chalk-Harrod mechanism).…”