Synthesis, Structures, and Transformations of Bridging and Terminally-Coordinated Trimethylammonioalkenyl Ligands in Zwitterionic Pentaruthenium Carbido Carbonyl Complexes

Highly Reduced Ruthenium Carbide Carbonyl Clusters: Synthesis, Molecular Structure, Reactivity, Electrochemistry, and Computational Investigation of [Ru6C(CO)15]4

The reaction of [Ru6C(CO)16]2- (1) with NaOH in DMSO resulted in the formation of a highly reduced [Ru6C(CO)15]4- (2), which was readily protonated by acids, such as HBF4·Et2O, to [HRu6C(CO)15]3- (3). Oxidation of 2 with [Cp2Fe][PF6] or [C7H7][BF4] in CH3CN resulted in [Ru6C(CO)15(CH3CN)]2- (5), which was quantitatively converted into 1 after exposure to CO atmosphere. The reaction of 2 with a mild methylating agent such as CH3,I afforded the purported [Ru6C(CO)14(COCH3)]3- (6). By employing a stronger reagent, that is, CF3SO3CH3, a mixture of [HRu6C(CO)16]- (4), [H3Ru6C(CO)15]- (7), and [Ru6C(CO)15(CH3CNCH3)]- (8) was obtained. The molecular structures of 2-5, 7, and 8 were determined by single-crystal X-ray diffraction as their [NEt4]4[2]·CH3CN, [NEt4]3[3], [NEt4][4], [NEt4]2[5], [NEt4][7], and [NEt4][8]·solv salts. The carbyne-carbide cluster 6 was partially characterized by IR spectroscopy and ESI-MS, and its structure was computationally predicted using DFT methods. The redox behavior of 2 and 3 was investigated by electrochemical and IR spectroelectrochemical methods. Computational studies were performed in order to unravel structural and thermodynamic aspects of these octahedral Ru-carbide carbonyl clusters displaying miscellaneous ligands and charges in comparison with related iron derivatives.

Synthesis and Chemistry of Ammonioethenyl and Phosphonioethenyl Ligands in Zwitterionic Dirhenium Carbonyl Complexes

New zwitterionic dirhenium carbonyl complexes containing ammonioethenyl and phosphonioethenyl ligands have been synthesized and studied. The reaction of Re₂(CO)₁₀ with C₂H₂ and Me₃NO yielded the dirhenium complex Re₂(CO)₉(NMe₃) (6) and the new zwitterionic complex Re₂(CO)₉[η¹-E-2-CH═CH(NMe₃)] (7). Compound 6 was characterized structurally and was found to have a NMe₃ ligand in an equatorial coordination site cis to a long Re-Re single bond, Re-Re = 3.0938(2) Å. Compound 7 can be obtained from the reaction of 6 with ethyne (C₂H₂) formally by the insertion of ethyne into the Re-N bond to the NMe₃ ligand. Compound 7 contains a 2-trimethylammonioethenyl ligand, ^-CH═CH(⁺NMe₃), that is formally a zwitterion having a positive charge on the nitrogen atom and a negative charge on the terminal carbon atom. When coordinated to rhenium by the terminal ethenyl carbon atom, the negative charge on the ^-CH═CH(⁺NMe₃) carbon atom is formally transferred to the rhenium atom. The reaction of Re₂(CO)₁₀ with C₂H₂ and NEt₃ in the presence of Me₃NO yielded the new dirhenium complex Re₂(CO)₉[η¹-E-2-CH═CH(NEt₃)] (8) together with some 6 and 7. Compound 8 is structurally similar to 7, but it contains a NEt₃ group in the ammonioethenyl ligand in the place of the NMe₃ group in 7. Reactions of 7 with PMePh₂ and PPh₃ yielded the zwitterionic 2-arylphosphonioethenyl-coordinated dirhenium carbonyl complexes, Re₂(CO)₉[η¹-E-2-CH═CH(PPh₂Me)] (9a) and Re₂(CO)₉[η¹-E-2-CH═CH(PPh₃)] (9b), and the zwitterionic 1-phosphonioethenyl ligand in the dirhenium carbonyl complexes, Re₂(CO)₉[η¹-1-C(PPh₂Me)(═CH₂)] (10a), Re₂(CO)₈[μ-η²-1-C(PPh₂Me)(═CH₂)] (11a), and Re₂(CO)₈[[μ-η²-1-C(PPh₃)(CH₂)] (11b). Compound 10a was converted to 11a and the new compound Re₂(CO)₇(μ-H)[μ-η²-1-(CH₂C)P(Ph)(Me)(o-C₆H₄)], (12) by decarbonylation using Me₃NO. Compound 12 contains an ortho-metalated phenyl ring. The new products 6,7, 8, 9b, 10a, 11a, 11b and 12 were characterized structurally by single-crystal X-ray diffraction analyses.

Structure-Property Relationships of Inorganic-Organic Hybrid Semiconducting Se-Fe-Cu-CO Polymers

A novel family of inorganic-organic-hybrid SeFe₃(CO)₉-dipyridyl two- and one-dimensional Cu polymers was synthesized via the three-component liquid-assisted grinding (LAG) of [Cu(MeCN)₄]⁺, inorganic cluster [SeFe₃(CO)₉]^2- (1), and rigid conjugated dipyridyls 4,4'-dipyridyl (dpy) and 1,2-bis(4-pyridyl)ethylene (bpee) or flexible conjugation-interrupted dipyridyls 1,2-bis(4-pyridyl)ethane (bpea) and 1,3-bis(4-pyridyl)propane (bpp). They included a cluster-linked 2D polymer, [(μ₄-Se)Fe₃(CO)₉Cu₂(MeCN)(dpy)_1.5]_n (1-dpy-2D), a cluster-pendant 1D chain, [(μ₃-Se)Fe₃(CO)₉Cu₂(dpy)₃]_n (1-dpy-1D), cluster-blocked 1D polymers, [(μ₃-Se)Fe₃(CO)₉Cu₂(L)]_n (1-L-1D, L = bpee, bpea), and a cluster-linked 2D polymer, [(μ₄-Se)Fe₃(CO)₉Cu₂(bpp)₂]_n (1-bpp-2D). The reversible dimensionality transformations of these three types of polymers accompanied by the change in coordination modes of 1 were achieved by the LAG addition of 1/[Cu(MeCN)₄]⁺ or dipyridyl ligands. These polymers were found to possess tunable low-energy gaps (1.49-1.72 eV) that increased in the order regarding their structural features: cluster-linked 1-dpy-2D and 1-bpp-2D, cluster-blocked 1-bpea-1D and 1-bpee-1D, and cluster-pendant 1-dpy-1D and [(μ₃-Se)Fe₃(CO)₉Cu₂(L)_2.5]_n (L = bpee, 1-bpee-2D; bpea, 1-bpea-2D), indicative of the importance of the participation of cluster 1. The measured electrical conductivities of 1-bpp-2D, 1-bpea-1D, and 1-dpy-1D were 3.13 × 10^-7, 2.92 × 10^-7, and 2.30 × 10^-7 S·cm^-1, respectively, which were parallel for the trend in their energy gaps, revealing semiconducting behaviors, supported by XPS, XANES, and DFT calculations. The surprising semiconductivity of the conjugation-interrupted bpp-linked 1-bpp-2D was mainly ascribed to electron transport via C-H···O(carbonyl) hydrogen bonds and aromatic C-H···π contacts within its closely packed 2D layers. Water-/light-stable polymers 1-bpp-2D, 1-bpea-2D, and 1-dpy-1D were also demonstrated to exhibit excellent pseudo-first-order photodegradation toward nitroaromatics and organic dyes, where cluster-linked polymer 1-bpp-2D performed the best, as predicted by its structural features and narrow energy gap.