High-Spin Organocobalt(II) Complexes in a Thioether Coordination Environment

Abstract

A series of electronically and coordinatively unsaturated four-coordinate organocobalt(II) complexes, [PhTt tBu ]Co(R) ([PhTt tBu ] ) phenyltris((tert-butylthio)methyl)borate; R ) Me, Et, Ph, Bn) have been prepared by reaction of [PhTt tBu ]CoCl with the corresponding R 2 Mg reagent. These high-spin, S ) 3/2, complexes have been characterized spectroscopically and several of their structures determined by X-ray diffraction. The R ) allyl derivative, [PhTt tBu ]Co(η 3 -allyl), is low spin. Reaction of [PhTt tBu ]Co(R) with CO yielded the acyl adducts [PhTt tBu ]Co(CO)C(O)R when R ) Me, Et, Ph. These five-coordinate, lowspin complexes possess square pyramidal stereochemistry with a thioether occupying the apical position. In contrast, [PhTt tBu ]Co(R), R ) Bn or allyl, reacted with CO generating the brown cobalt(I) dicarbonyl [PhTt tBu ]Co(CO) 2 . The latter reaction is proposed to proceed via CO-promoted Co-C bond homolysis. The Ni complex [κ 2 -PhTt tBu ]Ni(η 3 -allyl) shows no reactivity with CO under similar conditions. Each of the [PhTt tBu ]Co(R) species reacts with NO, generating brown [κ 2 -PhTt tBu ]Co(NO) 2 in good yield.

Mild and Homogeneous Cobalt‐Catalyzed Hydrogenation of CC, CO, and CN Bonds

“…In the solid state, paramagnetic complex 1 has a square-planar geometry, and solution-state magnetic-moment measurements are also consistent with a square-planar low-spin d 7 configuration (m eff = 2.2 m B ). [21,22] The solution-state magnetic moment of complex 1 is quite similar to that of the related square-planar complex [(N(SiMe 2 CH 2 PPh 2 ) 2 )Co(CH 2 SiMe 3 )] (2.…”

Coordination chemistry of poly(thioether)borate ligands

“…Carbonylation of [PhTt tBu ]Co(R), R = Me, Et, Ph, results in a rapid color change from green to red signaling formation of low-spin [PhTt tBu ]Co(CO)(C(O)R). Alternatively, [PhTt tBu ]Co(Bn) and [PhTt tBu ]Co(η 3 -allyl) are reduced to the monovalent [PhTt tBu ]Co(CO) 2 by CO. We have further found that this dicarbonyl adduct is in equilibrium with the high-spin monocarbonyl, [PhTt tBu ]Co(CO) [68]. For comparison, CO addition to [Tp tBu ]Co(Me) yielded [Tp tBu ]Co(CO) [64] and the smaller [Tp iPr2 ]Co(R), R = allyl, p -methylbenzyl, converted to [Tp iPr2 ]Co(CO)(C(O)R) [63].…”

“…The R = Me and Bn derivatives of Fe and Co were characterized by X-ray diffraction analyses [68,69]; the Bn derivatives feature η 1 -benzyl ligation. The complexes exhibit magnetic moments consistent with high-spin states, S = 3/2 for Co and S = 2 for Fe.…”

“…Further, this complex displays unusual magnetic characteristics, namely, a negative and large zero-field splitting ( D = −33(3)cm −1 ) and a large uniaxial orbital hyperfine component [71] (coincident with the Fe–C vector). The η 3 -allyl complexes of Co and Ni have been synthesized similarly and are five- and four-coordinate respectively, by virtue of κ 3 - and κ 2 -[PhTt tBu ] ligation [68]. In contrast to square planar [κ 2 -PhTt tBu ]Ni(η 3 -allyl), [Tp iPr2 ]Ni(η 3 -allyl) [63] is square pyramidal with one pyrazole occupying an apical site.…”

“…For example, [PhBP iPr 3 ]Fe(R) complexes are susceptible to rapid hydrogenolysis with H 2 [72]. The organo-iron [69] and organo-cobalt [68] complexes herein undergo facile reaction with CO yielding several different products depending upon the identity of the alkyl/aryl group (Scheme 5). Carbonylation of [PhTt tBu ]Co(R), R = Me, Et, Ph, results in a rapid color change from green to red signaling formation of low-spin [PhTt tBu ]Co(CO)(C(O)R).…”