2-D Molecular Alloy Ru-M (M = Cu, Ag, and Au) Carbonyl Clusters: Synthesis, Molecular Structure, Catalysis, and Computational Studies

Abstract

The reactions of [HRu₃(CO)₁₁]^- (1) with M(I) (M = Cu, Ag, and Au) compounds such as [Cu(CH₃CN)₄][BF₄], AgNO₃, and Au(Et₂S)Cl afford the 2-D molecular alloy clusters [CuRu₆(CO)₂₂]^- (2), [AgRu₆(CO)₂₂]^- (3), and [AuRu₅(CO)₁₉]^- (4), respectively. The reactions of 2-4 with PPh₃ result in mixtures of products, among which [Cu₂Ru₈(CO)₂₆]^2- (5), Ru₄(CO)₁₂(CuPPh₃)₄ (6), Ru₄(CO)₁₂(AgPPh₃)₄ (7), Ru(CO)₃(PPh₃)₂ (8), and HRu₃(OH)(CO)₇(PPh₃)₃ (9) have been isolated and characterized. The molecular structures of 2-6 and 9 have been determined by single-crystal X-ray diffraction. The metal-metal bonding within 2-5 has been computationally investigated by density functional theory methods. In addition, the [NEt₄]⁺ salts of 2-4 have been tested as catalyst precursors for transfer hydrogenation on the model substrate 4-fluoroacetophenone using ⁱPrOH as a solvent and a hydrogen source.

Scheme 1. Synthesis of [CuRu₆(CO)₂₂]⁻ (2), [AgRu₆(CO)₂₂]⁻ (3), and [AuRu₅(CO)₁₉]⁻ (4) from [HRu₃(CO)₁₁]⁻ (1)

Figure 1

Molecular structure of [CuRu₆(CO)₂₂]⁻ (2) (orange Ru; green Cu; red O; gray C). Cu···C(O) contacts [2.49–2.87 Å] are represented as fragmented lines.

Figure 2

Molecular structure of [AgRu₆(CO)₂₂]⁻ (3) (orange Ru; cyan Ag; red O; gray C). Ag···C(O) contacts [2.74 Å] are represented as fragmented lines.

Figure 3

DFT-optimized structure of 2 (orange Ru; green Cu; red O; gray C) with M–M b.c.p.’s and corresponding ρ values (pink, a.u.).

Scheme 2. Labeling of [MRu₆(CO)₂₂]⁻ (M = Cu and Ag)

Figure 4

DFT-optimized structure of 3 (orange Ru; cyan Ag; red O; gray C) with M–M b.c.p.’s and corresponding ρ values (pink, a.u.).

Scheme 3. Proposed Mechanism for the Formation of [MRu₆(CO)₂₂]⁻

Figure 5

DFT-optimized structure of [Cu(μ-H)₂{Ru₃(CO)₁₁}₂]⁻ (orange Ru; green Cu; red O; gray C; white H) with M–M and M–H b.c.p.’s and corresponding ρ values (pink, a.u.).

Figure 6

Molecular structure of [AuRu₅(CO)₁₉]⁻ (4) (orange Ru; yellow Au; red O; gray C). Au···C(O) contacts [2.81 Å] are represented as fragmented lines.

Scheme 4. Labeling of 4

Figure 7

DFT-optimized structures of 4 and [Ru₅(CO)₁₉]^2– (orange Ru; yellow Au; red O; gray C) with M–M b.c.p.’s and corresponding ρ values (pink, a.u.) and the superposition of the {Ru₅(CO)₁₉} fragments of 4 (red tones) and [Ru₅(CO)₁₉]^2– (blue tones).

Figure 8

Selected molecular orbitals (green tones) of 4 and [Ru₅(CO)₁₉]^2–. Surface isovalue = 0.03 a.u.

Scheme 5. Reactions of 2–4 with PPh₃

Figure 9

Molecular structure of [Cu₂Ru₈(CO)₂₆]^2– (5) (orange Ru; green Cu; red O; gray C). Main bond distances (Å): Ru–Ru 2.7622(18)–2.9389(18), average 2.830(6); Ru–Cu 2.583(2)–2.731(2), average 2.654(6); Cu–Cu 2.514(3). Cu···C(O) contacts [2.33–2.74 Å] are represented as fragmented lines.

Figure 10

DFT-optimized structure of 5 (orange Ru; green Cu; red O; gray C) with M–M b.c.p.’s and corresponding ρ values (pink, a.u.).

Figure 11

Molecular structure of Ru₄(CO)₁₂(CuPPh₃)₄ (6) (orange Ru; green Cu; red O; gray C). Main bond distances (Å): Ru–Ru 2.8570(6)–2.9021(11), average 2.8715(19); Ru–Cu 2.6247(8)–2.6725(10), and average 2.638(3). Cu···C(O) contacts [2.48–2.49 Å] are represented as fragmented lines.

Figure 12

Molecular structure of HRu₃(OH)(CO)₇(PPh₃)₃ (9) (orange Ru; purple P; red O; gray C; white H).

Figure 13

Molecular structure of [Ru₃(CO)₁₀(HCO₂)]⁻ (10) (orange Ru; red O; gray C; white H).