Hydrido Copper Clusters Supported by Dithiocarbamates: Oxidative Hydride Removal and Neutron Diffraction Analysis of [Cu₇(H){S₂C(aza-15-crown-5)}₆]

Abstract

Reactions of Cu(I) salts with Na(S(2)CR) (R = N(n)Pr(2), NEt(2), aza-15-crown-5), and (Bu(4)N)(BH(4)) in an 8:6:1 ratio in CH(3)CN solution at room temperature yield the monocationic hydride-centered octanuclear Cu(I) clusters, [Cu(8)(H){S(2)CR}(6)](PF(6)) (R = N(n)Pr(2), 1(H); NEt(2), 2(H); aza-15-crown-5, 3(H)). Further reactions of [Cu(8)(H){S(2)CR}(6)](PF(6)) with 1 equiv of (Bu(4)N)(BH(4)) produced neutral heptanuclear copper clusters, [Cu(7)(H){S(2)CR}(6)] (R = N(n)Pr(2), 4(H); NEt(2), 5(H); aza-15-crown-5, 6(H)) and clusters 4-6 can also be generated from the reaction of Cu(BF(4))(2), Na(S(2)CR), and (Bu(4)N)(BH(4)) in a 7:6:8 molar ratio in CH(3)CN. Reformation of cationic Cu(I)(8) clusters by adding 1 equiv of Cu(I) salt to the neutral Cu(7) clusters in solution is observed. Intriguingly, the central hydride in [Cu(8)(H){S(2)CN(n)Pr(2)}(6)](PF(6)) can be oxidatively removed as H(2) by Ce(NO(3))(6)(2-) to yield [Cu(II)(S(2)CN(n)Pr(2))(2)] exploiting the redox-tolerant nature of dithiocarbamates. Regeneration of hydride-centered octanuclear copper clusters from the [Cu(II)(S(2)CN(n)Pr(2))(2)] can be achieved by reaction with Cu(I) ions and borohydride. The hydride release and regeneration of Cu(I)(8) was monitored by UV-visible titration experiments. To our knowledge, this is the first time that hydride encapsulated within a copper cluster can be released as H(2) via chemical means. All complexes have been fully characterized by (1)H NMR, FT-IR, UV-vis, and elemental analysis, and molecular structures of 1(H), 2(H), and 6(H) were clearly established by single-crystal X-ray diffraction. Both 1(H) and 2(H) exhibit a tetracapped tetrahedral Cu(8) skeleton, which is inscribed within a S(12) icosahedron constituted by six dialkyl dithiocarbamate ligands in a tetrametallic-tetraconnective (μ(2), μ(2)) bonding mode. The copper framework of 6(H) is a tricapped distorted tetrahedron in which the four-coordinate hydride is demonstrated to occupy the central site by single crystal neutron diffraction. Compounds 1-3 exhibit a yellow emission in both the solid state and in solution under UV irradiation at 77 K, and the structureless emission is assigned as a (3)metal to ligand charge transfer (MLCT) excited state. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations on model compounds match the experimental structures and provide rationalization of their bonding and optical properties.

Copper(i) diselenocarbamate clusters: synthesis, structures and single-source precursors for Cu and Se composite materials

“…The 1 H NMR spectra of compounds 2 H and 3 H besides the resonances of alkyl groups show a broad peak at δ 3.05 and 3.01 ppm, respectively, the chemical shift of an encapsulated hydride, which was further corroborated by 2 H NMR spectra of their analogous deuterium species (2 D, and 3 D ) at δ 3.03 and 3.07 ppm ( Figure S1-S4). 27 Since similar results in the positive ESI-mass spectrum were also identified on their sulfur analogues, 27 these provide an important lesson: the formulation of a molecular composition by using the mass spectrometry must be very cautious not to assign an adduct ion as the actual composition of a species, which is indeed neutral. Thus, the positions of hydride resonance in the reduced products display a slightly downfield shift, which is contrast to chemical shifts of sulfur analogues [Cu 8 (H){S 2 CNR 2 } 6 ] + (R = n Pr at 7.05 ppm, Et at 7.02 ppm), and [Cu 7 (H){S 2 CNR 2 } 6 ] (R = n Pr at 6.55 ppm, Et at 6.49 ppm).…”

“…The spectral characteristics for both complexes are almost identical and only those of complex 2 H are depicted in Figure 4. 27 These compounds exhibit an orange emission in both the solid state and solution under UV−irradiation at 77 K. In the frozen state (CH 2 Cl 2 ) of 2 H , the emission band is centered at 606 nm (Figure 4c), which is red-shifted about ~36 nm compared to the emission from the solid state (570 nm). 35 Additionally, a less intense absorption peak is also detected at 367 (ε = 23000 cm −1 M −1 ) and 362 (ε = (24000) cm −1 M −1 ) nm, which can be reasonably assigned as the metal to ligand charge transfer (MLCT) transition due to the presence of an almost identical pattern of their dithiocarbamates analogous.…”

“…The 1 H NMR spectrum of each compound reveals a single type of resonances for alkyl (propyl and ethyl) groups of diselenocarbamates to postulate the identical electronic environment around all ligands. 27 which suggested the potential re-formation of [Cu 8 (H)(Se 2 CNR 2 ) 6 ] + in the gas phase during ESI-mass analysis conditions. In a similar way, the presence of hydride in the reduced products 4 H and 5 H of 2 H and 3 H , respectively, was also defined at δ 3.32 and 3.21 ppm ( Figure S5-S8).…”

“…Additionally, the avg. 27 The average of Cu v ···Cu v distances (2.888(8) Å) are slightly longer than the sum of the van der Waals radii for two copper atoms, 2.8 Å, whereas, the average of (7)-3.2899 (7); Cu-Se-Cu, 61.28(6)-66.47(5), Se-C-Se 120.4(2)-121.6(2). three Cu atoms, each capping on the triangular face of tetrahedron to generate a tricapped tetrahedral geometry of Cu 7 core (Figure 3).…”

Mixed-metal cluster chemistry. 35. Syntheses and structural studies of Mo 3 Ir 3 (μ 3 -O)(μ-CO) 3 (CO) 8 ( η 5 -C 5 H 5 ) 3 , Mo 4 Ir 4 (μ-CO) 4 (CO) 9 ( η 5 -C 5 H 5 ) 4 and Mo 3 Ir 5 (μ-CO) 3 (Cl)(CO) 6 ( η 5 -C 5 H 5 ) 3 ( η 5 -C 5 HMe 4 )

“…Tetracapped tetrahedral core geometries are uncommon, previous examples being Ni 8 (m 4 -Se) 6 (PPr i 3 ) 4 [28], Os 4 Pd 4 (CO) 12 (PBu t 3 ) 4 [29], [Ag 8 (m 4 -H){m 4 -k 2 (S,S 0 )-S 2 P(OR) 2 } 6 ](PF 6 ) (R ¼ Et [30], Et, Pr i [31]), [Cu 8 (m 4 -H){m 4 -k 2 (S,S 0 )-S 2 CNR 2 } 6 ](PF 6 ) (R ¼ Et, Pr n [32]). Thus, as with 2, the literature precedents are group 10 or group 11 metal-rich, emphasizing the unusual nature of cluster growth in the group 6-group 9 mixed-metal system for which cluster buildup at core tetrahedra rather than octahedra has thus far been seen [6,19,20,33,34].…”