[(dmpe)₂MnH(C₂H₄)] as a Source of a Low-Coordinate Ethyl Manganese(I) Species: Reactions with Primary Silanes, H₂, and Isonitriles

Abstract

Wilkinson’s manganese­(I) ethylene hydride complex trans-[(dmpe)2MnH­(C2H4)] (1) reacts as a source of a low-coordinate manganese­(I) ethyl complex. This is illustrated in the reactivity of 1 toward a variety of reagents. Reactions of 1 with primary silanes RSiH3 (R = Ph, n Bu) at 60 °C afforded ethane and the disilyl hydride manganese complexes [(dmpe)2MnH­(SiH2R)2] (4a, R = Ph; 4b, R = n Bu). Additionally, reaction with H2 at 60 °C afforded ethane and the dihydrogen hydride complex [(dmpe)2MnH­(H2)] (5), which has previously been prepared by an alternate route. The proposed low-coordinate intermediate, [(dmpe)2MnEt], was not observed spectroscopically but could be trapped using isonitrile ligands; reaction of 1 with CNR (R = t Bu, o-xylyl) afforded the manganese­(I) ethyl complexes [(dmpe)2MnEt­(CNR)] (6a, R = t Bu; 6b, R = o-xylyl). Ethyl complex 6a did not react further with CN t Bu at 80 °C. In contrast, complex 6b reacted with excess o-xylyl isonitrile to form 1,1-insertion products, including the iminoacyl complex [(dmpe)­Mn­(CNXyl)3{C­(NXyl)­CEt­(NXyl)}] (7, Xyl = o-xylyl). Complexes 4a, 6a,b, and 7, as well as the previously reported 1 and 5, have been crystallographically characterized, and DFT calculations have been employed to probe the accessibility of cis ethylene hydride and ethyl isomers of 1.

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

“…Isomerization of 6 Bu,H to 3 Bu,Et has been observed in the absence of ethylene and hydrosilanes (Scheme 4), and this pathway is also thought to be involved in the reactions of [ MnH] (A), which can re-enter the proposed catalytic cycle (vide infra) as shown in Scheme 8. This reactivity bears resemblance to that of '(dmpe) 2 MnEt' (an isomer of 1) 35 with H 2 SiPh 2 to afford a 1 : 1 mixture of (a) [(dmpe) 2 MnH(]SiPh 2 )] (3 Ph2 ) and ethane, the products of C-H bond-forming oxidative addition/reductive elimination (or s-bond metathesis) followed by a-hydride elimination, and (b) [(dmpe) 2 MnH 2 (SiHPh 2 )] (5 Ph2 ) and Ph 2 -SiEtH, the products of C-Si bond-forming oxidative addition/ reductive elimination (or s-bond metathesis) to form [(dmpe) 2 MnH] (A), followed by oxidative addition of a second equivalent of H 2 SiPh 2 . 32 Pathways 'a', 'b' and 'c' described above (green reaction arrows in Scheme 8) generate the observed disilyl hydride (4 R ), silylene hydride (3) and silene hydride (6) complexes.…”

“…In contrast to the reactions of 1 with secondary hydrosilanes, reactions with primary hydrosilanes (H 3 SiR) yielded disilyl hydride complexes [(dmpe) 2 MnH(SiH 2 R) 2 ] (4 Ph : R ¼ Ph, 4 Bu : R ¼ n Bu; Scheme 1). 35 The syntheses of both silylene hydride complexes 3 R2 and disilyl hydride complexes 4 R from 1 were proposed to proceed via a 5-coordinate silyl intermediate [(dmpe) 2 Mn(SiHRR 0 )] (2 Ph2 : R ¼ R 0 ¼ Ph; 2 Et2 : R ¼ R 0 ¼ Et; 2 Ph : R ¼ Ph, R 0 ¼ H; 2 Bu : R ¼ n Bu, R 0 ¼ H), which undergoes a-hydride elimination to generate 3 R2 , or oxidative addition of a second equivalent of hydrosilane to afford 4 R (Scheme 1).…”

“…(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.…”

Reactions of Manganese Silyl and Silylene Complexes with CO2 and C(NiPr)2: Synthesis of Mn(I) Formate and Amidinylsilyl Complexes

“…Argon was purchased from PraxAir. [(dmpe) 2 MnH­(C 2 H 4 )], [(dmpe) 2 MnH­(SiH 2 Ph) 2 ] ( 1 Ph ), [(dmpe) 2 MnH­(SiH 2 n Bu) 2 ] ( 1 Bu ), [(dmpe) 2 MnH­(SiPh 2 )] ( 2 Ph2 ), and [(dmpe) 2 MnH­(SiEt 2 )] ( 2 Et2 ) were prepared using literature procedures. Compound 2 Ph2 was obtained in a mixture with the reaction byproduct [(dmpe) 2 MnH 2 (SiHPh 2 )]; in multiple repetitions of this reaction, recrystallization yielded mixtures with 2 Ph2 contents ranging from 26–83%.…”

“…Our group has recently reported the manganese disilyl hydride complexes [(dmpe) 2 MnH­(SiH 2 R) 2 ] ( 1 Ph : R = Ph, 1 Bu : R = n Bu) and silylene hydride complexes [(dmpe) 2 MnH­(SiR 2 )] ( 2 Ph2 : R = Ph, 2 Et2 : R = Et). , Exposure of either set of complexes to ethylene resulted in an unprecedented transformation to afford manganese silene hydride complexes [(dmpe) 2 MnH­(RR′SiCHMe)] (Scheme ). , Reaction schemes were proposed for this transform­ation involving either a 5-coordinate silyl complex ( A ; formed from 1 R by hydrosilane elimination, or from 2 R2 by 1,1-insertion) or a silylene hydride complex (formed from 1 R by hydrosilane elimination to form A , followed by α-hydride elimination); Scheme .…”