10.1021/acs.organomet.7b00423.s001
Tufan
K. Mukhopadhyay
Tufan
K.
Mukhopadhyay
Chandrani Ghosh
Chandrani
Ghosh
Marco Flores
Marco
Flores
Thomas L. Groy
Thomas L.
Groy
Ryan J. Trovitch
Ryan J.
Trovitch
Hydrosilylation of Aldehydes and Formates Using a
Dimeric Manganese Precatalyst
American Chemical Society
2017
turnover frequency
Dimeric Manganese Precatalyst
imine coordination
2PEt
ambient temperature
propylene-bridged variant
Mn catalyst
Ojima mechanism
Mn center
κ 4
η 2
electron PDI reduction
Ph
PDI chelate
dimer dissociation
donor functionalities
carboxylate hydrosilylation
turnover frequencies
EPR spectroscopic analysis
2017-09-13 13:18:49
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Hydrosilylation_of_Aldehydes_and_Formates_Using_a_Dimeric_Manganese_Precatalyst/5402014
The
formally zero-valent Mn dimer [(<sup>Ph2PEt</sup>PDI)Mn]<sub>2</sub> has been synthesized upon reducing (<sup>Ph2PEt</sup>PDI)MnCl<sub>2</sub> with excess Na/Hg. Single crystal X-ray diffraction analysis
has revealed that [(<sup>Ph2PEt</sup>PDI)Mn]<sub>2</sub> possesses
a κ<sup>4</sup>-PDI chelate about each Mn center, as well as
η<sup>2</sup>-imine coordination across the dimer. The chelate
metrical parameters suggest single electron PDI reduction and EPR
spectroscopic analysis afforded a signal consistent with two weakly
interacting <i>S</i> = <sup>1</sup>/<sub>2</sub> Mn centers.
At ambient temperature in
the absence of solvent, [(<sup>Ph2PEt</sup>PDI)Mn]<sub>2</sub> has
been found to catalyze the hydrosilylation of aldehydes at loadings
as low as 0.005 mol % (0.01 mol % relative to Mn) with a maximum turnover
frequency of 9,900 min<sup>–1</sup> (4,950 min<sup>–1</sup> per Mn). Moreover, the [(<sup>Ph2PEt</sup>PDI)Mn]<sub>2</sub>-catalyzed
dihydrosilylation of formates has been found to proceed with turnover
frequencies of up to 330 min<sup>–1</sup> (165 min<sup>–1</sup> relative to Mn). These metrics are comparable to those described
for the leading Mn catalyst for this transformation, the propylene-bridged
variant (<sup>Ph2PPr</sup>PDI)Mn; however, [(<sup>Ph2PEt</sup>PDI)Mn]<sub>2</sub> is more easily inhibited by donor functionalities. Carbonyl
and carboxylate hydrosilylation is believed to proceed through a modified
Ojima mechanism following dimer dissociation.