Syntheses, X-ray crystallographic, spectroscopic and electrochemical characterizations of three and five coordinate SNS copper(I) and (II) complexes: Effect of pincer ligand on coordination geometry

John R. Miecznikowski*, Christine E. Villa, Nicholas A. Bernier, Margaret Siu, Camile D. Gomes, Kilee A. Bayne, Jerry P. Jasinskib, Wayne Loc, Eric Reinheimerd, Daniel Bake, Mekhala Patie

Fairfield University, Department of Chemistry & Biochemistry, 1073 North Benson Road, Fairfield, CT 06824. U.S.A. bDepartment of Chemistry, Keene State College, 229 Main Street, Keene, NH 03435. U.S.A.

cDepartment of Chemistry, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02467. U.S.A. dDepartment of Chemistry, California State Polytechnic University Pomona, 3801 West Temple Avenue, Pomona, CA. 91768. U.S.A.

eDepartment of Chemistry, Molecular Biology, Cell Biology, and Biochemistry, Boston University 24 Cummington Street, Boston, MA, 02215. U.S.A. Introduction

Recently, we have developed and synthesized a series of tridentate pincer ligands, each possessing two sulfur- and one nitrogen-donor functionalities (SNS), based on bis-imidazole or bis-triazole precursors. The tridentate SNS ligands incorporate thione-substituted imidazole or triazole functionalities. We have prepared somewhat rigid ligand systems through the use of 2,6-dibromopyridine as a ligand precursor. In addition, we have prepared more flexible ligand systems by employing the starting material 2,6-(dibromomethyl)pyridine to introduce a methylene linker into the pincer ligand. We have metallated these ligand precursors to form zinc(II) complexes containing these tridentate ligands. These zinc complexes are functional models for LADH. In an effort to learn about the reactivity of the SNS ligand precursors with other metal salts, we have metallated these ligand precursors to form copper (I) and (II) complexes. We are interested in characterizing these complexes using a variety of techniques. One of our ultimate goals is to react the formed copper complexes with oxygen atom donors. This is significant because we have copper proteins in our body (copper enzymes) that facilitate the transfer of oxygen from one molecule to another. From these reactivity studies, we will learn more about oxygen atom transfer that happens in Nature.

Questions and Goals: 1.  Can we prepare and characterize a series of SNS Cu (I) and

(II) tridentate pincer complexes, which vary in electronic and conformational properties (R-groups)? Characterization techniques: X-ray crystallography, UV-Vis spectroscopy, ESI-MS, ATR-IR spectroscopy, EPR Spectroscopy, elemental analyses.

References

•  Miecznikowski, J.R.; Lo, W.; Lynn, M.A.; O’Loughlin, B.E.; DiMarzio, A.P.; Martinez, A.M.; Lampe, L.; Foley, K.M.; Keilich, L.C.; Lisi, G.P.; Kwiecien, D.J.; Pires, C.M.; Kelly, W.J.; Kloczko, N.F.; Morio, K.N. Inorganica Chimica Acta, 2011, 376, 515-524.

•  Miecznikowski, J.R.; Lo, W.; Lynn, M.A.; Jain, S.; Keilich, L.C.; Kloczko, N.F.; O’Loughlin, B.E.; DiMarzio, A.P.; Foley, K.M.; Keilich, L.C.; Lisi, G.P.; Kwiecien, D.J.; Butrick, E.E.; Powers, E..; Al-Abbasee, R. Inorganica Chimica Acta, 2012, 387, 25-36.

•  Miecznikowski, J.R.; Jasinski, J.P.; Lynn, M.A.; Jain, S.; Butrick, E.E.; Drozdoski, A.R.; Archer, K.A.; Panarra, J.T.; Inorganica Chimica Acta, 2013, 394, 310-321.

•  Miecznikowski, J.R.; Lynn, M.A.; Jasinski, J.P.; Reinheimer, E.; Bak, D.W.; Pati, M.; Butrick, E.E.; Drozdoski, A.E.R.; Archer, K.A.; Villa, C.E.; Lemons, E.G.; Powers, E.; Siu, M.; Gomes, C.D.; Morio, K.N.; Journal of Coordination Chemistry, 2014, 67, 29-44..

•  Miecznikowski, J.R.; Lynn, M.A.; Jasinski, J.P.; Lo, W.; Bak, D.W.; Pati, M.; Butrick, E.E.; Drozdoski, A.E.R.; Archer, K.A.; Villa, C.E.; Lemons, E.G.; Powers, E.; Siu, M.; Gomes, C.D.; Bernier, N.A.; Morio, K.N.; Polyhedron, 2014; 80, 157-165.

Acknowledgements •  Fairfield University Start-up Funding •  Fairfield University Research Grants •  Fairfield University Science Institute •  Fairfield University Summer Research Kuck Fund •  Fairfield University Chemistry & Biochemistry

Department •  E. Gerald Corrigan ‘63 Scholarship •  Yale University •  NSF cCWCS Workshop: Crystallography for

Chemists (June 2011) •  NSF – MRI Grant No. CHE1039027 and NSF–

MRI Grant No. CHE08539

Syntheses Crystal Structures of SNS Copper Pincer Complexes

Bond Lengths: Cu(1)-N(1) = 2.3385(18) Å Cu(1)-Cl(1) = 2.2797(6) Å Cu(1)-Cl(2) = 2.3032(6) Å Cu(1)-S(2) = 2.3292(7) Å Cu(1)-S(1) = 2.3163(7)Å S(1)-C(6) = 1.708(2) Å S(2)-C(13) = 1.703(2) Å Bond Angles (degrees): N(1)-Cu(1)-Cl(1) = 113.65(5) N(1)-Cu(1)-S(1) = 84.65(5) Cl(1)-Cu(1)-S(2) = 94.11(2) S(1)-Cu(1)-S(2) = 168.53(2) Cl(1)-Cu(1)-Cl(2) = 141.15(3) S(1)-Cu(1)-Cl(2) = 95.16(2)

R = nButyl [3]

R = isopropyl [7] Bond Lengths: Cu(1)-S(1) = 2.1989(17) Å Cu(1)-S(2) = 2.2003(17) Å Cu(1)-N(4) = 2.2123(16) Å S(1)-C(4) = 1.695(6) Å S(2)-C(14) = 1.696(5) Å Cu(3)-Cl(1) = 2.2343(17) Å Cu(3)-Cl(2) = 2.2606(16) Å Cu(3)-Cl(3) = 2.2750(15) Å Cu(3)-Cl(4) = 2.2507(16) Å Bond Angles (degrees): S(1)-Cu(1)-S(2) = 123.63(7) S(1)-Cu(1)-N(4) = 118.86(15) S(2)-Cu(1)-N(4) = 117.49(15)

Low Temperature (10K) X-band EPR Spectra and Simulation of 3

UV-Visible Spectroscopy

Bond Lengths: Cu(1)-S(1) = 2.198(2) Å Cu(1)-S(2) = 2.225(2) Å Cu(1)-N(4) = 2.012(6) Å S(1)-C(1) = 1.702(8) Å S(2)-C(10) = 1.714(8) Å Cu(3)-Cl(1) = 2.219(2) Å Cu(3)-Cl(2) = 2.293(2) Å Cu(3)-Cl(3) = 2.235(2) Å Cu(3)-Cl(4) = 2.255(2) Å Bond Angles (degrees): S(1)-Cu(1)-S(2) = 119.92(9) S(1)-Cu(1)-N(4) = 120.54(19) S(2)-Cu(1)-N(4) = 119.51(18)

R = nButyl [9]

!

!

!!

λ max ε (M-1cm-1) 571.00 396

403.16 (sh) 647 310.00 8.10 x 103

266.90 (sh) 17900 249.46 (sh) 20700 229.55 (sh) 23100

215 25800

!

!

Cyclic Voltammetry

-250

-200

-150

-100

-50

0

50

-3000 -2000 -1000 0 1000 2000 3000

Cu

rren

t (u

A)

Potential (mV)

Conclusions:

•  Added ferrocene as internal standard (reversible process,

Eo = 400 mV, ΔEp = 98 mV)

•  Reversible Process (verified with scan rate study) •  Eo = 1576 mV, 1709

mV, (oxidation) •  Eo = 1526, -509 mV

(reduction •  Ligand Precursor

Potentials •  Eo = 1289 mV

(oxidation) •  Eo = -2376mV

(reduction)

λ max ε (M-1cm-1) 461.00 1.22 x 103

299.31 (sh) 5.07 x 103

258.00 3.39 x 104

EPR spectra were measured at 9.24GHz. The g⊥ experimental value was 2.08 and the gǁ‖ experimental value was 2.43. The experimentally determined hyperfine splitting (Aǁ‖) of the gǁ‖ signal was 114 G. The g values are consistent with axial electronic structure of the Cu(II) center.

3

7

3

R = isopropyl [1] Bond Lengths: Cu(1A)-N(1) = 2.289(2) Å Cu(1A)-Cl(1) = 2.3352(7) Å Cu(1A)-Cl(2) = 2.3113(7) Å Cu(1A)-S(2) = 2.3094(8) Å Cu(1A)-S(1) = 2.3274(8)Å S(1)-C(9) = 1.701(3) Å S(2)-C(8) = 1.708(3) Å Bond Angles (degrees): N(1)-Cu(1A)-Cl(1) = 104.39(6) N(1)-Cu(1A)-S(1) = 84.95(6) Cl(1)-Cu(1A)-S(2) = 95.38(3) S(1)-Cu(1A)-S(2) = 170.97(3) Cl(1)-Cu(1A)-Cl(2) = 148.79(3) S(1)-Cu(1A)-Cl(1) = 96.96(3)