Structural and Electronic Differences of Copper(I) Complexes with Tris(pyrazolyl)methane and Hydrotris(pyrazolyl)borate Ligands

Abstract

Copper(I) complexes with tripodal nitrogen-containing neutral ligands such as tris(3,5-diisopropyl-1-pyrazolyl)methane (L1') and tris(3-tertiary-butyl-5-isopropyl-1-pyrazolyl)methane (L3'), and with corresponding anionic ligands such as hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (L1-) and hydrotris(3-tertiary-butyl-5-isopropyl-1-pyrazolyl)borate (L3-) were synthesized and structurally characterized. Copper(I) complexes [Cu(L1')Cl] (1), [Cu(L1')(OClO3)] (2), [Cu(L1')(NCMe)](PF6) (3a), [Cu(L1')(NCMe)](ClO4) (3b), [Cu(L1')(CO)](PF6) (4a), and [Cu(L1')(CO)](ClO4) (4b) were prepared using the ligand L1'. Copper(I) complexes [Cu(L3')Cl] (5) and [Cu(L3')(NCMe)](PF6) (6) with the ligand L3' were also synthesized. Copper(I) complexes [Cu(L1)(NCMe)] (7) and [Cu(L1)(CO)] (8) were prepared using the anionic ligand L1-. Finally, copper(I) complexes with anionic ligand L3- and acetonitrile (9) and carbon monoxide (10) were synthesized. The complexes obtained were fully characterized by IR, far-IR, 1H NMR, and 13C NMR spectroscopy. The structures of both ligands, L1' and L3', and of complexes 1, 2, 3a, 3b, 4a, 4b, 5, 6, 7, and 10 were determined by X-ray crystallography. The effects of the differences in (a) the fourth ligand and the counteranion, (b) the steric hindrance at the third position of the pyrazolyl rings, and most importantly, (c) the charge of the N3 type ligands, on the structures, spectroscopic properties, and reactivities of the copper(I) complexes are discussed. The observed differences in the reactivities toward O2 of the copper(I) acetonitrile complexes are traced back to differences in the oxidation potentials determined by cyclic voltammetry. A special focus is set on the carbonyl complexes, where the 13C NMR and vibrational data are presented. Density functional theory (DFT) calculations are used to shed light on the differences in CO bonding in the compounds with neutral and anionic N3 ligands. In correlation with the vibrational and electrochemical data of these complexes, it is demonstrated that the C-O stretching vibration is a sensitive probe for the "electron richness" of copper(I) in these compounds.

An Extremely Bulky Tris(pyrazolyl)methanide: A Tridentate Ligand for the Synthesis of Heteroleptic Magnesium(II) and Ytterbium(II) Alkyl, Hydride, and Iodide Complexes

“…In both, the pyrazolyl moieties are seemingly arranged in such a fashion as to minimize steric interactions between the bulky adamantyl groups. Similar structures have been reported for other bulky tris(pyrazolyl)methanes, for example, HC(3-tBu-5-iPrpz) 3 [11] and HC(3-Mespz) 2 (5- Mespz) (Mes = mesityl), [12] which display NÀC and CÀC distances that are comparable to those in 1 and 2. Only poor-quality X-ray crystallographic data could be obtained for compound 3.…”

Copper Complexes with Neutral N4 Tripodal Ligands: Influence of the Number of Nitrogen Donors on Their Structures, Properties, and Reactivity

“…[Cu(CH 3 CN) 4 ](ClO 4 ), [59] 3,5-diisopropylpyrazole, [53] and tris(pyrazol-1-ylmethyl)amine [39] were synthesized according to published methods. The reported copper(I) complexes [Cu{HC(3,5-iPr 2 pz) 3 }(PPh 3 )](ClO 4 ) [{Cu(L1Ј)(PPh 3 )}(ClO 4 )], [20] [Cu{HC(3,5-iPr 2 pz) 3 }(CO)](PF 6 ) [{Cu(L1Ј)(CO)}(PF 6 )], [12] [Cu-{H 2 C(3,5-iPr 2 pz) 2 }] 2 (ClO 4 ) 2 [{Cu(L1ЈЈ)} 2 (ClO 4 ) 2 ], [20] and [Cu-{H 2 C(3,5-iPr 2 pz) 2 }(PPh 3 )](ClO 4 ) [{Cu(L1ЈЈ)(PPh 3 )}(ClO 4 )] [20] were prepared by published methods.…”

“…[23] [Cu(tpa)(CH 3 CN)](ClO 4 ) 2.00 [23] [Cu(Me 1 tpa)](ClO 4 ) [51] [Cu(Me 2 tpa)](PF 6 ) [51] [Cu(Me 3 tpa)](BF 4 ) [51] [Cu(L1ЈЈ)(CH 3 CN)](PF 6 ) 2.31 [20] [Cu(L1Ј)(CH 3 CN)](PF 6 ) 2.34 [12] [Cu(L1Ј)(CH 3 CN)](ClO 4 ) 2.29 [12] www.eurjic. The 31 P NMR spectrum of the copper(I) triphenylphosphane complex 8 shows a single resonance for PPh 3 , as shown in Figure 8.…”

“…The tpzb and tpzm ligands with identical side chains are therefore expected to have different nucleophilicity and different electron donating properties to metal centers due to their different overall charges. [12] In contrast, bis(pyrazolyl)methane (bpzm) ligands (e.g. L1ЈЈ in Figure 1) act as neutral bidentate ligands and many complexes containing these ligands have been synthesized.…”

“…Thus, whereas the Cu I CO complex with L1Ј is mononuclear, the analogous complex with L1ЈЈ is binuclear with one bridging ClO 4 -anion. [12,20] In addition, the 31 P NMR spectrum of the Cu I PPh 3 complex of L1ЈЈ shows a narrower signal than that of the corresponding complex with L1Ј. [20] These differences between tpzm (N3 donor set) and bpzm (N2 donor set) have led to renewed interest in their complexes.…”