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.
Reaction of 4,5-bis(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H 2 XN 2 ) with [Zr-(NMe 2 ) 4 ], followed by crystallization from O(SiMe 3 ) 2 , yielded [(XN 2 )Zr(NMe 2 ) 2 ]•{O(SiMe 3 ) 2 } 0.5 (1•{O(SiMe 3 ) 2 } 0.5 ). The zirconium dimethyl complex [(XN 2 )ZrMe 2 ] (2) was subsequently accessed (a) by treatment of 1•(O(SiMe 3 ) 2 ) 0.5 with excess AlMe 3 or (b) via reaction of 1•(O(SiMe 3 ) 2 ) 0.5 with excess Me 3 SiCl, affording [(XN 2 )ZrCl 2 ] (3) followed by reaction of 3 with 2 equiv of MeLi. Reaction of [(XN 2 )ZrMe 2 ] (2) with one equiv of B(C 6 F 5 ) 3 or [CPh 3 ][B(C 6 F 5 ) 4 ] yielded cationic [(XN 2 )ZrMe][MeB(C 6 F 5 ) 3 ] (4) and [(XN 2 )ZrMe(arene)][B(C 6 F 5 ) 4 ] {arene = η 6 -benzene (5a), η 6 -toluene (5b), or bromobenzene (5c)}, respectively. Both 4 and 5b are active for ethylene polymerization under 1 atm of ethylene at 24 and 80 °C in toluene with activities ranging from 23.5−883 kg mol −1 atm −1 h −1 , yielding polymers with weight-average molecular weights (M w ) of 70,800−88,100 g mol −1 and polydispersities (M w /M n ) of 3.94−4.67.
Interconversions between manganese silylene and silene complexes are reported, including those involving the first spectroscopically observed silene complexes with an SiH substituent, and their involvement in ethylene hydrosilylation is discussed.
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.
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