Solvothermal synthesis of cobalt PCP pincer complexes from [Co2(CO)8]

Abstract

Treatment of [Co₂(CO)₈] with the ipso-substituted P(C-X)P^Y ligands (X = Br, Cl; R = iPr, tBu) bearing Y = NH and CH₂ linkers under solvothermal conditions affords the five-coordinate Co(I) and Co(III) complexes [Co^I(PCP^Y-R)(CO)₂] and [Co^III(PCP^Y-R)X₂]. The later are paramagnetic exhibiting a solution magnetic moment in the range of 3.0-3.3 μ_B which is consistent with a d⁶ intermediate spin system corresponding to two unpaired electrons. In the case of P(C-X)P^Y ligands (X = Br, Cl; R = tBu; Y = NH) the formation of the square planar Co(II) complex [Co(PCP^NH-tBu)X] was favored. This complex gives rise to a magnetic moment of 1.8 μ_B being consistent with a d⁷ low spin system corresponding to one unpaired electron. All complexes are characterized by means of spectroscopic techniques (NMR, IR), HR-MS. Representative complexes were also characterized by X-ray crystallography.

Supplementary information: The online version contains supplementary material available at 10.1007/s00706-023-03123-x.

Keywords: Cobalt; Oxidative addition; Pincer complexes; Transmetalation.

Fig. 1

Structural view of [Co(PCP^NH-iPr)(CO)₂] (4) showing 50% thermal ellipsoids (most H atoms omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Co1-C1 2.022(3), Co1-P1 2.1807(7), Co1-P4 2.1827(6), Co1-C19 1.752(3), Co1-C20 1.782(2), P1-Co1-P4 153.46(3), C19-Co1-C20 108.4(1), C1-Co1-C19 141.1(1), C1-Co1-C20 110.5(1)

Fig. 2

DFT calculated structure of [Co(PCP^NH-iPr)(Cl)₂] (6a) in the triplet state (S = 1). Selected bond lengths (Å) and bond angles (deg): Co-C1 1.911, Co-P1 2.258, Co-P2 2.2251, Co-Cl1 2.273, Co-Cl2 2.294, P1-Co-P2 164.7, Cl1-Co-Cl2 108.7

Fig. 3

Structural view of [Co(PCP^NH-tBu)Br]⋅CH₃CN (7d⋅CH₃CN) showing 50% thermal ellipsoids (most H atoms and solvent omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Co1-C1 1.930(2), Co1-P1 2.2393(7), Co1-P2 2.2332(7), Co1-Br1 2.3686(6), N1-HN1 0.85(2), P1-Co1-P2 165.22(3), C1-Co1-Br1 179.87(5)

Fig. 4

Structural view of [Co(PCP^CH2-iPr)(CO)₂] (8) showing 50% ellipsoids (most H atoms omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Co1-C2 2.013(1), Co1-P1 2.1942(6), Co1-P2 2.1919(7), Co1-C22 1.756(2), Co1-C23 1.794(2), C22-O1 1.167(3), C23-O2 1.148(2), P1-Co1-P2 144.83(2), C2-Co1-C22 164.75(8), C2-Co1-C23 91.38(6), C22-Co1-C23 103.87(8)

Fig. 5

Structural view of [Co(PCP^CH2-tBu)(CO)₂] (9) showing 50% ellipsoids (H atoms omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Co1-C1 1.995(3), Co1-P1 2.2365(9), Co1-P2 2.2444(9), Co1-C25 1.748(3), Co1-C26 1.785(3), C25-O1 1.157(5), C26-O2 1.150(3), P1-Co1-P2 146.53(4), C1-Co1-C25 166.3(1), C1-Co1-C26 88.7(1), C25-Co1-C26 105.0(1)