Alcohol Decarbonylation Research Articles

Cationic, Neutral, and Anionic Hydrides of Iridium with PSiP Pincers

This work describes synthetic routes from the known precursor [IrClH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (1) to new hydride and polyhydride derivatives. Substituting the chloride ligand with triflate leads to the five-coordinate complex [IrH{κO-O3S(CF3)}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (2), which can undergo reversible coordination of water (H2O) or dihydrogen (H2) to generate respectively the cationic derivative [IrH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(OH2)2](CF3SO3) (3) or the neutral trans-hydride-dihydrogen [IrH{κO-O3S(CF3)}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(η2-H2)] (6) in equilibrium. The use of acetonitrile or carbon monoxide (CO) excess instead of water produces stable analogues of 3 (complexes 4 or 5, respectively). The reaction between 1 and NaBH4 affords the tetrahydroborate derivative [IrH{κ2H-H2BH2}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (7), which can be protonated with triflic acid to form 2 or with HBF4 to give the dinuclear cationic derivative [(μ:κ2H,κ2H-BH4)[IrH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]2](BF4) (8). The reactions of 7 with alcohols afford either the dihydride-carbonyl [IrH2{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(CO)] (9) or the known tetrahydride [IrH4{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (10), depending on the ease of alcohol decarbonylation. NMR observations and density functional theory calculations on the fluxional behavior of 10 indicate that the spatial contour of the mer PSiP framework conditions hydride-ligand exchanges. Complex 10 reacts with NaH in tetrahydrofuran to form the anionic trihydride [IrH3{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]Na (11), which exists as a mixture of fac and mer isomers in equilibrium.

On the Importance of Decarbonylation as a Side‐Reaction in the Ruthenium‐Catalysed Dehydrogenation of Alcohols: A Combined Experimental and Density Functional Study

We report a density functional study (B97-D2 level) of the mechanism(s) operating in the alcohol decarbonylation that occurs as an important side-reaction during dehydrogenation catalysed by [RuH2(H2)(PPh3)3]. By using MeOH as the substrate, three distinct pathways have been fully characterised involving either neutral tris- or bis-phosphines or anionic bis-phosphine complexes after deprotonation. α-Agostic formaldehyde and formyl complexes are key intermediates, and the computed rate-limiting barriers are similar between the various decarbonylation and dehydrogenation paths. The key steps have also been studied for reactions involving EtOH and iPrOH as substrates, rationalising the known resistance of the latter towards decarbonylation. Kinetic isotope effects (KIEs) were predicted computationally for all pathways and studied experimentally for one specific decarbonylation path designed to start from [RuH(OCH3)(PPh3)3]. From the good agreement between computed and experimental KIEs (observed kH/kD =4), the rate-limiting step for methanol decarbonylation has been ascribed to the formation of the first agostic intermediate from a transient formaldehyde complex.

Acceptorless Photocatalytic Dehydrogenation for Alcohol Decarbonylation and Imine Synthesis

Die metallorganisch katalysierte photokatalytische dehydrierende Decarbonylierung von primären Alkoholen zu Alkanen, CO und H2 wird mit Blick auf die Umsetzung hochoxygenierter Materialien neuerlich untersucht (siehe Schema). Methanol, Ethanol, Benzylalkohol und Cyclohexanmethanol werden einfach decarbonyliert. Die Photokatalysatoren sind auch in der Dehydrierung von Aminen aktiv und liefern N-Alkylaldimine und H2.

Acceptorless Photocatalytic Dehydrogenation for Alcohol Decarbonylation and Imine Synthesis

It has come to light: Renewed interest in conversions of highly oxygenated materials has motivated studies of the organometallic-catalyzed photocatalytic dehydrogenative decarbonylation of primary alcohols into alkanes, CO, and H(2). Methanol, ethanol, benzyl alcohol, and cyclohexanemethanol are readily decarbonylated. The photocatalysts are also active for amine dehydrogenation to give N-alkyl aldimines and H(2).

Access to Ruthenium(0) Carbonyl Complexes via Dehydrogenation of a Tricyclopentylphosphine Ligand and Decarbonylation of Alcohols

The carbonylruthenium(0) complex Ru(CO){PCyp2(η2-C5H7)}2 (4) has been prepared by reaction of RuH2{PCyp2(η2-C5H7)}2 (3) with an excess of tert-butylethylene in the presence of ethanol. Decarbonylation of ethanol is also observed when reacting the bis(dihydrogen) complex RuH2(η2-H2)2(PCyp3)2 (1) with 2 equiv of ethanol. The reaction results formally in the substitution of one dihydrogen ligand by a carbonyl, and the corresponding complex RuH2(η2-H2)(CO)(PCyp3)2 (5) was isolated. An excess of tert-butylethylene reacted with 5 to give RuH2(CO){PCyp2(η2-C5H7)}(PCyp3) (6), which corresponds to the formal loss of 2 equiv of dihydrogen: loss of the dihydrogen ligand and dehydrogenation of one cyclopentyl ring. The dihydride 6 can be dehydrogenated further by reaction with ethylene, affording the ruthenium(0) complex Ru(η2-C2H4)(CO){PCyp2(η2-C5H7)}(PCyp3) (7). Finally, the dicarbonyl complex RuH2(CO)2(PCyp3)2 (8) was isolated by exposing 1 to 3 bar of CO. 8 and the new complexes 4−7, resulting from partial dehydrogenation of one or two cyclopentyl rings of the tricyclopentylphosphines and/or decarbonylation of alcohol, were characterized by multinuclear NMR, IR, elemental analysis, and X-ray diffraction.

Epoxides as probes of oxametallacycle chemistry on Rh(111)

Temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS) were used to investigate the reactions of ethylene oxide and propylene oxide on the clean Rh(111) surface. This study was performed to determine the reaction pathways and intermediates involved during decomposition of epoxides as a means of understanding the divergence of alcohol and aldehyde decomposition on Rh(111). Ethylene oxide decomposed via C-O scission of the ring. Decarbonylation was observed to have begun by 221 K to release adsorbed carbon monoxide and hydrocarbon fragments. Volatile carbon monoxide and di-hydrogen were the only desorbing products detected. Carbon was also deposited on the Rh(111) surface during ethylene oxide decarbonylation. Similar behavior was observed during propylene oxide decarbonylation. Decarbonylation of the adsorbed species began by 232 K. Again surface carbon was detected as well as volatile carbon monoxide and di-hydrogen. No volatile hydrocarbon products were observed during the decomposition of either epoxide. The reaction pathways and products observed are quite consistent with those observed for ethanol and 1-propanol, but not for the aldehyde isomers of these epoxides. The results of this study support the hypothesis that alcohol decarbonylation occurs via oxametallacycle intermediates on Rh(111), since the chemistry of the epoxides mimics that of the alcohols rather than that of the aldehydes. However, these intermediates were insufficiently stable to permit their isolation and spectroscopic verification by HREELS.

Amidinato complexes of the platinum metals and an avid carbonyl abstraction reaction

Platinum metal hydrido and trifluoroacetato complexes react with N,N′-diphenylamidines, PhNC(R)NHPh (R = H, Me, Et, Ph), giving the amidinato derivatives Ru{PhNC(R)NPh} 2(CO)(PPh 3), MX{PhNC(R)NPh}(CO)(PPh 3) 2 and IrX 2{PhNC(R)NPh}(PPh 3) 2 (M = Ru, Os; X = H, Cl; X 2 = H 2, Cl 2 or HCl). The reactions of RuH 2(PPh 3) 4 and OsH 4(PPh 3) 3 with amidines are accompanied by an avid alcohol decarbonylation reaction to form the carbonyls MH{PhNC(R)NPh}(CO)(PPh 3) 2.

The reactions of chlorohydrido- and dichloro-tris(triphenylphosphine)ruthenium(II) with alkali hydroxides and alkoxides. Hydridohydroxobis(triphenylphosphine)ruthenium(II) monosolvates, their reactions and related compounds

The interaction of chlorohydridotris(triphenylphosphine)ruthenium(II) with NaOH or KOH in tetrahydrofuran, acetone, or t-butyl alcohol leads, depending on conditions, first to red, five-co-ordinate complexes RuH(OH)(PPh3)2(sol)(sol = thf or H2O) secondly to hydroxo-bridged dimers, (PPh3)2H(sol)Ru(µ-OH)2Ru(sol)H(PPh3)2(sol = Me2CO, H2O, or ButOH) and thirdly to a tetranuclear complex of stoicheiometry Ru4H4(OH)2(PPh2)2(CO)2(PPh3)6(Me2CO)2.Interaction of dichlorotris(triphenylphosphine)ruthenium(II) with KOH gives similar compounds, RuCl(OH)(PPh3)2(sol)2 and {RuCl(OH)(PPh3)2(sol)}2(sol = H2O or thf) as well as {RuH(OH)(PPh3)2(thf)}2.The interaction of RuHCl(PPh3)3 with sodium methoxide gives rise to two compounds that are formulated, respectively as having Ru–CHO and Ru–OCH2 groups, The mechanism of decarbonylation of alcohols is discussed and the compounds RuH2(CO)(PPh3)2·ROH (R = Me or Et) are synthesised.I.r. and 1H and 31P n.m.r. spectra of the various complexes are given and structures for the compounds proposed on this basis.

ChemInform Abstract: THE FORMATION OF THE RHODIUM CARBONYL COMPLEXES FROM CHLOROTRIS(TRIPHENYLPHOSPHINE)RHODIUM WITH ALCOHOLS IN THE PRESENCE OF DIENE AND OLEFIN

The decarbonylation of alcohols using chlorotris[triphenylphosphine]rhodium in the presence of diene or olefin occurs with the formation of the rhodium carbonyl complex and a hydrocarbon originatin...

The Formation of the Rhodium Carbonyl Complexes from Chlorotris-[triphenylphosphine]rhodium with Alcohols in the Presence of Diene and Olefin

Abstract The decarbonylation of alcohols using chlorotris[triphenylphosphine]rhodium in the presence of diene or olefin occurs with the formation of the rhodium carbonyl complex and a hydrocarbon originating from the alcohol. The most suitable reaction system is rhodium compound/methanol/butadiene. The results suggest catalysis by a rhodium species.

Reactions of complexes of ruthenium and osmium halides with ammonia, amines, and hydrazine

Ammonia and primary amines (am) react with [MX3(PR3)3](M = Ru or Os, X = Cl or Br, and PR3= tertiary phosphine) in ethanol at 20° to form M(II) complexes, mer-[MX2am(PR3)3], and acetaldehyde. Secondary and tertiary amines with [MX3(PMe2Ph)3] also cause reduction, but the product is an alcohol complex [MX2(C2H5OH)(PMe2Ph)3]. The reduction may occur through a hydride complex intermediate because some hydrogen is produced in all the above reactions. The alcohol complexes are probably formed for steric reasons because the least sterically hindered secondary amine, piperidine, forms a piperidine complex.When the alcohol contains a small amount of water di-n-alkylamines (CnH2n+ 1)2NH are dealkylated to form the corresponding primary amine complexes [MX2 am (PR3)3](cf. similar decarbonylation of alcohol and aldehydes). The cleaved alkyl group generally appears as Cn–1H2n and all the lower n-alkanes down to methane, but from dimethylamine higher hydrocarbons are obtained and from diethylamine a little propane.Hydrazine in limited amounts forms mononuclear complexes [MCl2(N2H4)(PMe2Ph)3] or more commonly hydrazine-bridged complexes [M2X4(N2H4)2(PR3)4]. Nitrogen, hydrogen, and hydrazine hydrochloride are also produced. Under more vigorous reaction conditions [Ru(NH3)5N2]2+ is formed.

Rhodium(I) and rhodium(III) carbonyl complexes containing tertiary phosphines or tertiary arsines and halogen formed by the decarbonylation of alcohols and by the direct use of carbon monoxide

Convenient syntheses of many new rhodium(I) and rhodium(III) complexes of types trans-[RhX(CO)L2](X = Cl, Br, I, or SCN; L = PR3 or AsR3) and [RhX3(CO)L2](X = Cl or Br; L = PR3) are described which involve treating rhodium complexes with carbon monoxide. Several of the complexes trans-[RhX(CO)(PR3)2] were also conveniently prepared by treating rhodium(III) complexes of type [RhX3(PR3)3] with a primary alcohol in the presence of a base (e.g., potassium hydroxide). The carbon monoxide ligand is derived from the alcohol, and the residual fragments from the alcohols, e.g., methane from ethanol, have been identified. Reactions of the rhodium(I) compounds described include metathesis of the halogen, addition of chlorine or acetyl halides, the action of halogen acids, and displacement of ligands by the chelating phosphine Ph2P·CH2·CH2·PPh2 to give [Rh(Ph2P·CH2·CH2·PPh2)2]Cl. The rhodium(III) complex [RhCl3(CO)(PEt2Ph)2] was reduced to the rhodium(I) complex [RhCl(CO)(PEt2Ph)2] by ethanol and potassium hydroxide. Infrared [ν(CO)] and dipole moment data are given.