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HN(CH2CH2PR2)2-ligated copper borohydride complexes, (RPNHP)Cu(BH4) (R = iPr, Cy, tBu), which can be prepared from (RPNHP)CuBr and NaBH4, are capable of catalyzing the hydrogenation of aldehydes in an alcoholic solvent. More active hydrogenation catalysts are (RPNHP)CuBr mixed with KOtBu, allowing various aldehydes and ketones to be efficiently reduced to alcohols except those bearing a nitro, N-unprotected pyrrole, pyridine, or an ester group, or those prone to aldol condensation (e.g., 1-heptanal). Modifying the catalyst structure by replacing the NH group in (iPrPNHP)CuBr with an NMe group results in an inferior catalyst but preserves some catalytic activity. The hexanuclear copper hydride cluster, (iPrPNHP)3Cu6H6, is also competent in catalyzing the hydrogenation of aldehydes such as benzaldehyde and N-methyl-2-pyrrolecarboxaldehyde, albeit accompanied by decomposition pathways. The catalytic performance can be enhanced through the addition of a strong base or iPrPNHP. The three catalytic systems likely share the same catalytically active species, which is proposed to be a mononuclear copper hydride (RPNHP)CuH with the NH group bound to copper.

Copper hydride clusters of the type (RPNHP)nCu2nH2n (RPNHP = HN(CH2CH2PR2)2; n = 2 and 3) have been synthesized from the reaction of (RPNHP)CuBr with KOtBu under H2 or in one pot from a 1:2:2 mixture of RPNHP, CuBr, and KOtBu under H2. With medium-sized phosphorus substituents (R = iPr and Cy), the phosphine ligands stabilize both hexanuclear and tetranuclear clusters; however, the smaller clusters are kinetic products and aggregate further over time. Use of a bulkier ligand tBuPNHP leads to the formation of only a tetranuclear cluster. Crystallographic studies reveal a distorted octahedral Cu6 unit in (iPrPNHP)3Cu6H6 (2a) and (CyPNHP)3Cu6H6 (2b), while a tetrahedral Cu4 unit exists in (CyPNHP)2Cu4H4 (2b') and (tBuPNHP)2Cu4H4 (2c'), all furnished with face-capping hydrides and bridging RPNHP ligands. The aggregations are maintained in solution, although hydrides are fluxional. These copper clusters are capable of reducing aldehydes and ketones to the corresponding copper alkoxide species. Ranking their reactivity toward N-methyl-2-pyrrolecarboxaldehyde gives 2b' > 2a, 2b ≫ 2c', which correlates inversely with the order of thermal stability (against decomposition and cluster expansion).

Copper hydride clusters of the type (

Two Fe–Cu heterobimetallic complexes have been synthesized from the reactions of the (cyclopentadienone)iron complexes {2,5-(EMe3)2-3,4-(CH2)4(η4-C4C═O)}Fe(CO)3 (E = Si, 1a; E = C, 1b) with (IPr)CuOH (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene). X-ray crystallographic studies show that these complexes adopt a structure featuring a bridging hydride which can be described by the formula {2,5-(EMe3)2-3,4-(CH2)4(η4-C4C═O)}(CO)2Fe(μ-H)Cu(IPr) (E = Si, 4a′; E = C, 4b′). When they are dissolved in toluene, THF, or cyclohexane, these complexes form a rapidly equilibrated isomeric mixture of 4a′ or 4b′ and the terminal iron hydride {2,5-(EMe3)2-3,4-(CH2)4(η5-C4COCuIPr)}Fe(CO)2H (E = Si, 4a; E = C, 4b). The solution structure for the Me3Si derivative is dominated by 4a. Both 4a and 4b/4b′ react with HCO2H to form a monometallic iron hydride and (IPr)CuOCHO. They also undergo displacement of (IPr)CuH by CO. The heterobimetallic complexes are effective catalysts for the reduction of PhCHO under water-gas shif...

[243866-64-0] C17H28FeO3Si2 (MW 392.42) InChI = 1S/C15H27OSi2.2CO.Fe.H/c1-17(2,3)14-11-9-7-8-10-12(11)15(13(14)16)18(4,5)6;2*1-2;;/h16H,7-10H2,1-6H3;;;; InChIKey = RJTMTNHNKGCJOJ-UHFFFAOYSA-N (a catalyst for hydrogenation and transfer hydrogenation of aldehydes and ketones, Oppenauer-type oxidation of alcohols, and reductive amination of aldehydes and ketones; when mixed with a chiral Bronsted acid, serves as a catalyst for enantioselective hydrogenation of imines; a precursor to a cyclopentadienone compound) Alternative Name: Knolker's complex. Physical Data: a yellow powder when freshly prepared; turns to pinkish when exposed to light for more than 1 h. Solubility: soluble in benzene, toluene, THF, diethyl ether, and CH2Cl2; insoluble in water. Preparative Methods: stirring a biphasic mixture of a THF solution of {2,5-(SiMe3)2-3,4-[(CH2)4](η4-C4CO)}Fe(CO)3 (a cyclopentadienone iron tricarbonyl complex) and a 1 M aqueous solution of NaOH under an inert atmosphere for 2.5 h, followed by acidification with H3PO4 (85 wt. % in water).1 To minimize decomposition by light, aluminum foil should be used to cover the flask throughout the reaction and workup stages. Alternatively, Knolker's complex can be generated in situ by treating the cyclopentadienone iron tricarbonyl complex with Me3NO in the presence of a hydrogen donor (H2, alcohols, or HCO2H/Et3N), or with K2CO3 and water. Handling, Storage, and Precautions: decomposes upon exposure to the air, and should be handled under an inert atmosphere; compatible with water and nonoxidizing acids; incompatible with alkyl iodides and CHCl3; slowly decomposes in the presence of ambient fluorescent lighting; its toluene solution decomposes significantly when heated at 60 °C for more than 1 h. For prolonged storage, it is recommended to keep the solid sample in an amber vial and place it in a glove box freezer (−30 °C).2