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. 2014 Nov 10;33(21):6132-6140.
doi: 10.1021/om5007769. Epub 2014 Oct 9.

Synthesis and Reactivity of Four- and Five-Coordinate Low-Spin Cobalt(II) PCP Pincer Complexes and Some Nickel(II) Analogues

Sathiyamoorthy Murugesan  1 , Berthold Stöger  1 , Maria Deus Carvalho  2 , Liliana P Ferreira  3 , Ernst Pittenauer  1 , Günter Allmaier  1 , Luis F Veiros  4 , Karl Kirchner  1
Affiliations

Synthesis and Reactivity of Four- and Five-Coordinate Low-Spin Cobalt(II) PCP Pincer Complexes and Some Nickel(II) Analogues

Sathiyamoorthy Murugesan et al. Organometallics. .

Abstract

Anhydrous CoCl2 or [NiCl2(DME)] reacts with the ligand PCPMe-iPr (1) in the presence of nBuLi to afford the 15e and 16e square planar complexes [Co(PCPMe-iPr)Cl] (2) and [Ni(PCPMe-iPr)Cl] (3), respectively. Complex 2 is a paramagnetic d7 low-spin complex, which is a useful precursor for a series of Co(I), Co(II), and Co(III) PCP complexes. Complex 2 reacts readily with CO and pyridine to afford the five-coordinate square-pyramidal 17e complexes [Co(PCPMe-iPr)(CO)Cl] (4) and [Co(PCPMe-iPr)(py)Cl] (5), respectively, while in the presence of Ag+ and CO the cationic complex [Co(PCPMe-iPr)(CO)2]+ (6) is afforded. The effective magnetic moments μeff of all Co(II) complexes were derived from the temperature dependence of the inverse molar magnetic susceptibility by SQUID measurements and are in the range 1.9 to 2.4 μB. This is consistent with a d7 low-spin configuration with some degree of spin-orbit coupling. Oxidation of 2 with CuCl2 affords the paramagnetic Co(III) PCP complex [Co(PCPMe-iPr)Cl2] (7), while the synthesis of the diamagnetic Co(I) complex [Co(PCPMe-iPr)(CO)2] (8) was achieved by stirring 2 in toluene with KC8 in the presence of CO. Finally, the cationic 16e Ni(II) PCP complex [Ni(PCPMe-iPr)(CO)]+ (10) was obtained by reacting complex 3 with 1 equiv of AgSbF6 in the presence of CO. The reactivity of CO addition to Co(I), Co(II), and Ni(II) PCP square planar complexes of the type [M(PCPMe-iPr)(CO)] n (n = +1, 0) was investigated by DFT calculations, showing that formation of the Co species, 6 and 8, is thermodynamically favorable, while Ni(II) maintains the 16e configuration since CO addition is unfavorable in this case. X-ray structures of most complexes are provided and discussed. A structural feature of interest is that the apical CO ligand in 4 deviates significantly from linearity, with a Co-C-O angle of 170.0(1)°. The DFT-calculated value is 172°, clearly showing that this is not a packing but an electronic effect.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Overview of Co PCP Complexes Reported in the Literature
Scheme 2
Scheme 2. Synthesis of Complexes [Co(PCPMe-iPr)Cl] (2) and [Ni(PCPMe-iPr)Cl] (3)
Figure 1
Figure 1
Optimized B3LYP geometries of the low-spin (left) and high-spin (right) isomers [Co(PCPMe-iPr)Cl] (2). Hydrogen atoms are omitted for clarity.
Figure 2
Figure 2
Structural view of [Co(PCPMe-iPr)Cl] (2) showing 50% thermal ellipsoids (H atoms and a second independent complex are omitted for clarity).
Figure 3
Figure 3
Structural view of [Ni(PCPMe-iPr)Cl] (3) showing 50% thermal ellipsoids (H atoms and three other independent complexes are omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Ni1–P1 2.1811(5), Ni1–P2 2.1800(5), Ni1–C1 1.915(2), Ni1–Cl1 1.785(2), P1–Ni1–P2 165.79(2), C1–Ni1–Cl1 175.30(7).
Scheme 3
Scheme 3. Synthesis of Co(I), Co(II), and Co(III) PCP Complexes Based on [Co(PCPMe-iPr)Cl] (2)
Figure 4
Figure 4
(a) Structural view of [Co(PCPMe-iPr)(CO)Cl] (4) showing 50% thermal ellipsoids (H atoms omitted for clarity). (b) Inner part of 4 showing the square pyramidal structure as well as the significant bending of the apical CO ligand.
Figure 5
Figure 5
Structural view of [Co(PCPMe-iPr)(py)Cl] (5) showing 50% thermal ellipsoids (H atoms are omitted for clarity).
Figure 6
Figure 6
(a) DFT-computed frontier orbitals (d-splitting) and (b) spin density for [Co(PCPMe-iPr)Cl] (2) (left) and for [Co(PCPMe-iPr)(CO)Cl] (4) (right).
Figure 7
Figure 7
Structural view of [Co(PCPMe-iPr)(CO)2]SbF6 (6) showing 50% thermal ellipsoids (H atoms and SbF6– counterion are omitted for clarity).
Scheme 4
Scheme 4. Synthesis of [Co(PCPMe-iPr)(CH3CN)3]2+ (9)
Figure 8
Figure 8
Structural view of [Co(PCPMe-iPr)Cl2] (7) showing 50% thermal ellipsoids (H atoms are omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Co1–P1 2.2549(4), Co1–P2 2.2602(4), Co1–C1 1.937(1), Co1–Cl1 2.2635(4), Co1–Cl2 2.2918(3), P1–Co1–P2 161.16(1), C1–Co1–Cl1 148.87(3), C1–Co1–Cl2 106.77(3), Cl1–Co1–Cl2 104.36(1).
Figure 9
Figure 9
Structural view of [Co(PCPMe-iPr)(CO)2] (8) showing 50% thermal ellipsoids (H atoms and a second independent complex are omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Co1–P1 2.1710(5), Co1–P2 2.1740(5), Co1–C1 1.998(2), Co1–C21 1.799(2), Co1–C22 1.743(2), P1–Co1–P2 147.69(2), C1–Co1–C21 99.94(8), C1–Co1–C22 154.76(7), C21–Co1–C22 105.28(8), Co1–C21–O1 175.1(2), Co1–C22–O2 178.0(1).
Scheme 5
Scheme 5. Synthesis of [Ni(PCPMe-iPr)(CO)]+ (10)
Scheme 6
Scheme 6. Free Energies (kcal/mol) Calculated for the Addition of CO to the 15e and 16e Square Planar Complexes [Co(PCPMe-iPr)(CO)]n (n = +1, 0) and [Ni(PCPMe-iPr)(CO)]+
Figure 10
Figure 10
Structural view of [Ni(PCPMe-iPr)(CO)]SbF6 (10) showing 50% thermal ellipsoids (H atoms, a second independent complex, and SbF6– counterion are omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Ni1–P1 2.1811(5), Ni1–P2 2.1800(5), Ni1–C1 1.915(2), Ni1–C21 1.785(2), P1–Ni1–P2 165.79(2), C1–Ni1–C21 175.30(7), Ni1–C21–O1 176.5(2).
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References

    1. For reviews on pincer complexes, see:

    2. Albrecht M.; van Koten G. Angew. Chem., Int. Ed. 2001, 40, 3750–3781. - PubMed
    3. van der Boom M. E.; Milstein D. Chem. Rev. 2003, 103, 1759–1792. - PubMed
    4. Singleton J. T. Tetrahedron 2003, 59, 1837.
    5. Bhattacharya P.; Guan H. Comment Inorg. Chem. 2011, 32, 88.
    6. Schneider S.; Meiners J.; Askevold B. Eur. J. Inorg. Chem. 2012, 412–429.
    7. Morales-Morales D.; Jensen C. M., Eds. The Chemistry of Pincer Compounds; Elsevier: Amsterdam, 2007.
    8. van Koten G., Milstein D., Eds.; Organometallic Pincer Chemistry; Topics in Organometallic Chemistry Vol. 40; Springer: Berlin, 2013.
    1. Benito-Garagorri D.; Kirchner K. Acc. Chem. Res. 2008, 41, 201–213. - PubMed
    1. Benito-Garagorri D.; Bocokić V.; Mereiter K.; Kirchner K. Organometallics 2006, 25, 3817–3823.

    1. For recent examples of Fe PNP complexes based on the 2,6-diaminopyridine scaffold see:

    2. Bichler B.; Holzhacker C.; Stöger B.; Puchberger M.; Veiros L. F.; Kirchner K. Organometallics 2013, 32, 4114–4121. - PMC - PubMed
    3. Benito-Garagorri D.; Alves L. G.; Veiros L. F.; Standfest-Hauser C. M.; Tanaka S.; Mereiter K.; Kirchner K. Organometallics 2010, 29, 4932–4942.
    4. Benito-Garagorri D.; Puchberger M.; Mereiter K.; Kirchner K. Angew. Chem., Int. Ed. 2008, 47, 9142–9145. - PubMed

    1. For recent examples of Mo PNP complexes based on the 2,6-diaminopyridine scaffold see:

    2. Öztopcu Ö.; Holzhacker C.; Puchberger M.; Weil M.; Mereiter K.; Veiros L. F.; Kirchner K. Organometallics 2013, 32, 3042–3052. - PMC - PubMed
    3. de Aguiar S. R. M. M.; Stöger B.; Pittenauer E.; Allmaier G.; Puchberger M.; Veiros L. F.; Kirchner K. J. Organomet. Chem. 2014, 760, 74–83. - PMC - PubMed

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