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

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, nBu)
at 60 °C afforded ethane and the disilyl hydride manganese complexes
[(dmpe)2MnH­(SiH2R)2] (4a, R = Ph; 4b, R = nBu).
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 = tBu, o-xylyl) afforded the
manganese­(I) ethyl complexes [(dmpe)2MnEt­(CNR)] (6a, R = tBu; 6b,
R = o-xylyl). Ethyl complex 6a did not
react further with CNtBu 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.