It
was recently discovered that (Ph2PPrPDI)Mn (PDI =
pyridine diimine) exists as a superposition of low-spin Mn(II) that
is supported by a PDI dianion and intermediate-spin Mn(II) that is
antiferromagnetically coupled to a triplet PDI dianion, a finding
that encouraged the synthesis and electronic structure evaluation
of late first row metal variants that feature the same chelate. The
addition of Ph2PPrPDI to FeBr2 resulted in bromide
dissociation and the formation of [(Ph2PPrPDI)FeBr][Br].
Reduction of this precursor using excess sodium amalgam afforded (Ph2PPrPDI)Fe, which possesses an Fe(II) center that is supported
by a dianionic PDI ligand. Similarly, reduction of a premixed solution
of Ph2PPrPDI and CoCl2 yielded the cobalt analog,
(Ph2PPrPDI)Co. EPR spectroscopy and density functional
theory calculations revealed that this compound features a high-spin
Co(I) center that is antiferromagnetically coupled to a PDI radical
anion. The addition of Ph2PPrPDI to Ni(COD)2 resulted in ligand displacement and the formation of (Ph2PPrPDI)Ni, which was found to possess a pendent phosphine group. Single-crystal
X-ray diffraction, CASSCF calculations, and EPR spectroscopy indicate
that (Ph2PPrPDI)Ni is best described as having a Ni(II)-PDI2– configuration. The electronic differences between
these compounds are highlighted, and a computational analysis of Ph2PPrPDI denticity has revealed the thermodynamic penalties
associated with phosphine dissociation from 5-coordinate (Ph2PPrPDI)Mn, (Ph2PPrPDI)Fe, and (Ph2PPrPDI)Co.
Through the application of a redox-innocent aryl diimine chelate, the discovery and utilization of a cobalt catalyst, (Ph2PPrADI)Co, that exhibits carbonyl hydrosilylation turnover frequencies of up to 330 s–1 is...
The preparation of redox-active ligand supported manganese, iron, cobalt, and nickel compounds that feature hemilabile phosphine moieties has allowed for highly efficient hydrosilylation catalysis.
The phosphine-substituted aryl diimine cobalt catalyst, ( Ph2PPr ADI)Co, has been found to mediate the dehydrocoupling of diamines or polyamines to poly(methylhydrosiloxane) (PMHS) to generate hydrogen and crosslinked solids in an atom-efficient fashion. The resulting siloxane diamine and siloxane polyamine networks persist in the presence of air or water at room temperature and can tolerate temperatures of up to 1600 °C. Upon lowering the catalyst loading to 0.01 mol %, ( Ph2PPr ADI)Co was found to catalyze the dehydrocoupling of 1,3-propanediamine and PMHS (m = 35) to generate a siloxane diamine foam with a turnover frequency of 157 s −1 relative to diamine consumption, the highest activity ever reported for Si−N dehydrocoupling. Furthermore, upon systematically reducing the number of potential branch points, the ( Ph2PPr ADI)Co-catalyzed dehydrocoupling of diamines with hydride-terminated poly(dimethylsiloxane) (PDMS) was found to yield linear siloxane diamine polymers with molecular weights of up to 47,300 g/mol.
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