Mononuclear and Dinuclear Copper(I) Complexes of Bis(3,5-dimethylpyrazol-1-yl)methane:  Synthesis, Structure, and Reactivity

Abstract

The synthesis and structures of a mononuclear copper(I) carbonyl complex [Cu(OClO3)(CO)(H2CPz2')] (3) and a dinuclear copper(I) carbonyl complex [{Cu(CO)(H2CPz2')}2(mu-pyrazine)](ClO4)2 (4), where H2CPz2' = bis(3,5-dimethylpyrazol-1-yl)methane, are described. These two compounds were generated by the carbonylation of the corresponding copper(I)-acetonitrile complexes, [Cu(H2CPz2')(MeCN)](ClO4) (1) and [{Cu(H2CPz2')(MeCN)}2(mu-pyrazine)](ClO4)2 (2). Alternatively, treatment of mononuclear 1 and 3, respectively, with pyrazine in a molar ratio of 2:1 produces the pyrazine-bridged dinuclear Cu(I) complexes 2 and 4. Each of the complexes 1-4 can react with PPh3 to generate a common three-coordinated copper(I) complex [Cu(PPh3)(H2CPz2')](ClO4) (5). The structures of complexes 1-5 were all confirmed by X-ray crystallography. Comparison of the Cu(I)-C(CO) bond distances and the CO stretching frequencies of 3 and 4 indicates the back-donating properties of d pi(Cu)-pi*(pyrazine) bonds in 4, and accordingly, stabilizes the mixed-valence species generated from 2. Complex 3, stabilized by the strong interaction between copper(I) ion and perchlorate counteranion (Cu(I)-O(ClO4) = 2.240(3) A), is a potential precursor for polynuclear copper(I) carbonyl complexes.

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

“…This is in agreement with the distances between the N2P least-squares plane and the copper(I) ions [0.134(1) Å for Cu1 and 0.148(1) Å of Cu2], both of which show a higher planarity. The previously reported N2-type ligands L0ЈЈ and L1ЈЈ form a trigonal planar geometry in copper(I) triphenylphosphane complexes, [16,20] and the N3-type ligand L1Ј shows a tetrahedral geometry. [20] As shown in Table 4, the average Cu-N pz distance in complex 8 (2.023 Å) is almost the same as the average value for the N2-type complexes [Cu(L1ЈЈ)(PPh 3 )]-(ClO 4 ) (2.008 Å) [20] and [Cu(L0ЈЈ)(PPh 3 )](ClO 4 ) (2.019 Å) [16] but shorter than that for the N3-type complex [Cu(L1Ј)(PPh 3 )](ClO 4 ) (2.085 Å).…”

“…The previously reported N2-type ligands L0ЈЈ and L1ЈЈ form a trigonal planar geometry in copper(I) triphenylphosphane complexes, [16,20] and the N3-type ligand L1Ј shows a tetrahedral geometry. [20] As shown in Table 4, the average Cu-N pz distance in complex 8 (2.023 Å) is almost the same as the average value for the N2-type complexes [Cu(L1ЈЈ)(PPh 3 )]-(ClO 4 ) (2.008 Å) [20] and [Cu(L0ЈЈ)(PPh 3 )](ClO 4 ) (2.019 Å) [16] but shorter than that for the N3-type complex [Cu(L1Ј)(PPh 3 )](ClO 4 ) (2.085 Å). [20] The reason for this trend is that the bulkier pyrazolyl ligands result in a stronger steric repulsion with bulky PPh 3 .…”

“…Interestingly, the Cu-P bond lengths of the related complexes [Cu(L1ЈЈ)(PPh 3 )](ClO 4 ) [2.174(2) Å], [20] [Cu(L0ЈЈ)-(PPh 3 )](ClO 4 ) (2.171 Å), [16] [20] As was also the case for complexes 1 and 2, the Cu-N(tertiary nitrogen) bond lengths in complex 8 [2.313(7) Å for Cu1 and 2.364 (7) [28] which have the same N3P-type ligand environment, thus indicating weaker interactions of the tertiary amine nitrogens with the copper(I) center in 8.…”

“…L1ЈЈ in Figure 1) act as neutral bidentate ligands and many complexes containing these ligands have been synthesized. [13][14][15][16][17][18][19][20][21] In comparison with tpzb, it is interesting to investigate how the structures and properties of complexes are influenced by the different number of coordinating nitrogen donor atoms. Thus, whereas the Cu I CO complex with L1Ј is mononuclear, the analogous complex with L1ЈЈ is binuclear with one bridging ClO 4 -anion.…”

Synthesis and characterization of copper(I) compounds incorporating pyrazole-derived ligands: A study on carbon–carbon coupling reaction

“…Not only Sonogashira reaction, there are many organic reactions were performed with copper [23]. Regarding the ligands of copper catalysts, various chelated nitrogen donor atoms have also been studied and reviewed in the past years [24,25] and some neutral and mono-anionic ligands are shown in Scheme 1. Pyrazoles are extensively used as N-donor ligands to different metal ions [26][27][28].…”