2-Adamantanol

OH-stretching red shifts in bulky hydrogen-bonded alcohols: jet spectroscopy and modeling.[Pubmed:16898684]

J Phys Chem A. 2006 Aug 17;110(32):9839-48.

The available database for OH-stretching bands of jet-cooled aliphatic alcohol dimers is extended to systems including 1-adamantanol and 2-Adamantanol, using a heated pulsed nozzle coupled to an FTIR spectrometer. This database is used to simplify and parametrize the standard Wang et al. AMBER/parm99.dat force field for the prediction of hydrogen-bond-induced red shifts, as it avoids complications due to mode coupling and cooperativity. Apart from subtle chiral recognition effects, the performance of the simple model in describing steric, electronic, and conformational influences on the red shifts is remarkable, as exemplified by predictions for mixed-alcohol dimers. The resulting semiempirical approach can complement quantum chemical calculations, in particular for larger systems, although the good performance is rather specific to red shift predictions.

Bioconversion of 1-adamantanol to 1,3-adamantanediol using Streptomyces sp. SA8 oxidation system.[Pubmed:20471592]

J Biosci Bioeng. 2010 Jun;109(6):550-3.

To efficiently produce 1,3-adamantanediol (1,3-ad(OH)(2)) from 1-adamantanol (1-adOH), our stocks of culture strains and soil microorganisms were surveyed for hydroxylation activity towards 1-adOH. Among them, the soil actinomycete SA8 showing the highest hydroxylation activity was identified as Streptomyces sp. based on 16S ribosomal DNA sequence analysis. The reaction products were purified by silica gel column chromatography, and from NMR and MS analyses, they were identified as 1,3-ad(OH)(2) and 1,4-ad(OH)(2). Streptomyces sp. SA8 produced 5.9 g l(-1) 1,3-ad(OH)(2)from 6.2 g l(-1) 1-adOH in culture broth after 120 h at 25 degrees C. Using resting cells, 2.3 g l(-1) 1,3-ad(OH)(2) was produced after 96 h of incubation at a 69% conversion rate. In both cases, 1,4-ad(OH)(2) was formed as a byproduct at a rate of about 15%. Strain SA8 also hydroxylated 2-Adamantanol and 2-methyl-2-Adamantanol.

Non-heme mu-Oxo- and bis(mu-carboxylato)-bridged diiron(iii) complexes of a 3N ligand as catalysts for alkane hydroxylation: stereoelectronic factors of carboxylate bridges determine the catalytic efficiency.[Pubmed:27336757]

Dalton Trans. 2016 Jul 28;45(28):11422-36.

A series of non-heme (mu-oxo)bis(mu-dicarboxylato)-bridged diiron(iii) complexes, [Fe2(O)(OOCH)2(L)2](2+)1, [Fe2(O)(OAc)2(L)2](2+)2, [Fe2(O)(Me3AcO)2(L)2](2+)3, [Fe2(O)(OBz)2(L)2](2+)4, [Fe2(O)(Ph2AcO)2(L)2](2+)5 and [Fe2(O)(Ph3AcO)3(L)2](2+)6, where L = N,N-dimethyl-N'-(pyrid-2-ylmethyl)ethylenediamine, OAc(-) = acetate, Me3AcO(-) = trimethylacetate, OBz(-) = benzoate, Ph2AcO(-) = diphenylacetate and Ph3AcO(-) = triphenylacetate, have been isolated and characterized using elemental analysis and spectral and electrochemical techniques. They have been studied as catalysts for the selective oxidation of alkanes using m-chloroperbenzoic acid (m-CPBA) as the oxidant. Complexes 2, 3, and 4 possess a distorted bioctahedral geometry in which each iron atom is coordinated to an oxygen atom of the mu-oxo bridge, two oxygen atoms of the mu-carboxylate bridge and three nitrogen atoms of the 3N ligand. In an acetonitrile/dichloromethane solvent mixture all the complexes display a d-d band characteristic of the triply bridged diiron(iii) core, revealing that they retain their identity in solution. Upon replacing electron-donating substituents on the bridging carboxylates by electron-withdrawing ones the E1/2 value of the one-electron Fe(III)Fe(III)--> Fe(III)Fe(II) reduction becomes less negative. On adding one equivalent of Et3N to a mixture of one equivalent of the complex and an excess of m-CPBA in the acetonitrile/dichloromethane solvent mixture an intense absorption band (lambdamax, 680-720 nm) appears, which corresponds to the formation of a mixture of complex species. All the complexes act as efficient catalysts for the hydroxylation of cyclohexane with 380-500 total turnover numbers and good alcohol selectivity (A/K, 6.0-10.1). Adamantane is selectively oxidized to 1-adamantanol and 2-Adamantanol (3 degrees /2 degrees , 12.9-17.1) along with a small amount of 2-adamantanone (total TON, 381-476), and interestingly, the sterically demanding trimethylacetate bridge around the diiron(iii) centre leads to high 3 degrees /2 degrees bond selectivity; on the other hand, the sterically demanding triphenylacetate bridge gives a lower 3 degrees /2 degrees bond selectivity. A remarkable linear correlation between the pKa of the bridging carboxylate and TON for both cyclohexane and adamantane oxidation is observed, illustrating the highest catalytic activity for 3 with strongly electron-releasing trimethylacetate bridges.

Novel nickel(ii) complexes of sterically modified linear N4 ligands: effect of ligand stereoelectronic factors and solvent of coordination on nickel(ii) spin-state and catalytic alkane hydroxylation.[Pubmed:28418046]

Dalton Trans. 2017 Jun 6;46(22):7181-7193.

A series of Ni(ii) complexes of the types [Ni(L)(CH3CN)2](BPh4)21-3, 5 and [Ni(L4)](BPh4)24, where L = N,N'-bis(2-pyrid-2-ylmethyl)-1,4-diazepane (L1), N-(6-methylpyrid-2-ylmethyl)-N'-(pyrid-2-ylmethyl)-1,4-diazepane (L2), N,N'-bis(6-methyl-2-pyridylmethyl)-1,4-diazepane (L3), N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethylenediamine (L5) and L4 = N,N'-bis((1-methyl-1H-imidazole-2-yl)methyl)-1,4-diazepane, have been isolated and characterized. The complex cations of 1 and 4 possess, respectively, distorted octahedral and low-spin square planar coordination geometries in which nickel(ii) is meridionally coordinated to all four nitrogen atoms of L1 and L4. DFT studies reveal that L5 with the ethylenediamine backbone coordinates in the cis-beta mode in [Ni(L5)(CH3CN)2](2+)5, but in the cis-alpha mode in [Ni(L5)(H2O)2](2+). Also, they illustrate the role of ligand donor atom type, diazacyclo backbone and steric hindrance to coordination of pyridyl nitrogen in conferring novel coordination geometries on Ni(ii). All these complexes catalyse the oxidation of cyclohexane in the presence of m-CPBA as the oxidant up to 600 turnover numbers (TON) with relatively good alcohol selectivity (A/K, 5.6-7.2). Adamantane is oxidized to 1-adamantanol, 2-Adamantanol and 2-adamantanone with high bond selectivity (3 degrees /2 degrees , 8.7-11.7). The incorporation of methyl substituent(s) on one (2) or both (3) of the pyridyl rings and the replacement of both the pyridylmethyl arms in 1 by imidazolylmethyl arms to give 4 decrease the catalytic efficiency. Interestingly, 5 with the cis-beta mode of coordination provides two labile cis coordination sites for oxidant binding, leading to higher total TON and product/bond selectivity.

Nickel(II) complexes of tripodal 4N ligands as catalysts for alkane oxidation using m-CPBA as oxidant: ligand stereoelectronic effects on catalysis.[Pubmed:21850329]

Dalton Trans. 2011 Oct 7;40(37):9413-24.

Several mononuclear Ni(II) complexes of the type [Ni(L)(CH(3)CN)(2)](BPh(4))(2) 1-7, where L is a tetradentate tripodal 4N ligand such as N,N-dimethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L1), N,N-diethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L2), N,N-dimethyl-N'-(1-methyl-1H-imidazol-2-ylmethyl)-N'-(pyrid-2-ylmethyl)ethane-1,2 -diamine (L3), N,N-dimethyl-N',N'-bis(1-methyl-1H-imidazol-2-ylmethyl)ethane-1,2-diamine (L4), N,N-dimethyl-N',N'-bis(quinolin-2-ylmethyl)ethane-1,2-diamine (L5), tris(benzimidazol-2-ylmethyl)amine (L6) and tris(pyrid-2-ylmethyl)amine (L7), have been isolated and characterized using CHN analysis, UV-Visible spectroscopy and mass spectrometry. The single-crystal X-ray structures of the complexes [Ni(L1)(CH(3)CN)(H(2)O)](ClO(4))(2) 1a, [Ni(L2)(CH(3)CN)(2)](BPh(4))(2) 2, [Ni(L3)(CH(3)CN)(2)](BPh(4))(2) 3 and [Ni(L4)(CH(3)CN)(2)](BPh(4))(2) 4 have been determined. All these complexes possess a distorted octahedral coordination geometry in which Ni(II) is coordinated to four nitrogen atoms of the tetradentate ligands and two CH(3)CN (2, 3, 4) or one H(2)O and one CH(3)CN (1a) are located in cis positions. The Ni-N(py) bond distances (2.054(2)-2.078(3) A) in 1a, 2 and 3 are shorter than the Ni-N(amine) bonds (2.127(2)-2.196(3) A) because of sp(2) and sp(3) hybridizations of the pyridyl and tertiary amine nitrogens respectively. In 3 the Ni-N(im) bond (2.040(5) A) is shorter than the Ni-N(py) bond (2.074(4) A) due to the stronger coordination of imidazole compared with the pyridine donor. In dichloromethane/acetonitrile solvent mixture, all the Ni(ii) complexes possess an octahedral coordination geometry, as revealed by the characteristic ligand field bands in the visible region. They efficiently catalyze the hydroxylation of alkanes when m-CPBA is used as oxidant with turnover number (TON) in the range of 340-620 and good alcohol selectivity for cyclohexane (A/K, 5-9). By replacing one of the pyridyl donors in TPA by a weakly coordinating -NMe(2) or -NEt(2) donor nitrogen atom the catalytic activity decreases slightly with no change in the selectivity. In contrast, upon replacing the pyridyl nitrogen donor by the strongly sigma-bonding imidazolyl or sterically demanding quinolyl/benzimidazolyl nitrogen donor, both the catalytic activity and selectivity decrease, possibly due to destabilization of the intermediate [(4N)(CH(3)CN)Ni-O ](+) radical species. Adamantane is selectively (3 degrees /2 degrees , 12-17) oxidized to 1-adamantanol, 2-Adamantanol and 2-adamantanone while cumene is selectively oxidized to 2-phenyl-2-propanol. In contrast to cyclohexane oxidation, the incorporation of sterically hindering quinolyl/benzimidazolyl donors around Ni(ii) leads to a high 3 degrees /2 degrees bond selectivity for adamantane oxidation. A linear correlation between the metal-ligand covalency parameter (beta) and the turnover number has been observed.

Chemoselective and biomimetic hydroxylation of hydrocarbons by non-heme micro-oxo-bridged diiron(III) catalysts using m-CPBA as oxidant.[Pubmed:19562169]

Dalton Trans. 2009 Jul 14;(26):5101-14.

Three novel non-heme micro-oxo-bridged diiron(III) complexes [Fe2(micro-O)(L1)2] 2, where H2(L1) is N,N'-o-phenylenebis(salicylideneimine), [Fe2(micro-O)(L2)2].2H2O 4, where H2(L2) is N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), and [Fe2(micro-O)(L3)2] 6, where H2(L3)=1,4-bis(2-hydroxybenzyl)-1,4-diazepane, have been isolated and studied as catalysts for the selective oxidative transformation of alkanes into alcohols using m-choloroperbenzoic acid (m-CPBA) as co-oxidant. The mononuclear iron(III) complexes [Fe(L1)Cl] 1 and [Fe(L4)Cl] 7, where H2(L4)=1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane, have been also isolated and those corresponding to the dimeric complexes 4 and 6 have been generated in CH3CN solution and characterized as [Fe(L2)Cl] 3 and [Fe(L3)Cl] 5 by using ESI-MS, absorption and EPR spectral and electrochemical methods. The molecular structures of 4 and 6 have been successfully determined by single crystal X-ray diffraction. Both 4 and 6 possess the Fe-O-Fe structural motif with each iron atom possessing a distorted square pyramidal coordination geometry. The steric constraint at the iron(III) center in 6 is higher than that in 4 as understood from the values of the trigonality structural index (tau: 4, 0.226, 0.273; 6, 0.449) due to the higher steric congestion built by the diazapane back bone. The micro-oxo-to-Fe(III) LMCT band for 4 is observed around 622 nm (epsilon, 1830 M(-1) cm(-1)) in methanol but is not observed in CH3CN solution and it is blue-shifted to around 485 nm (epsilon, 5760 M(-1) cm(-1)) in 6, possibly due to the higher Fe-O-Fe bond angle in the latter (4, 177.4; 6, 180 degrees). The Fe(III)/Fe(II) redox potentials of the dinuclear complexes (E1/2: 2, -0.606; 4, -0.329; 6, -0.889 V) are more negative than those for their corresponding mononuclear complexes (E1/2: 1, -0.300 V; 3, -0.269; 5, -0.289 V) due to O2- coordination. Interestingly, upon addition of peroxides (H2O2, t-BuOOH) and the peracid m-CPBA, the intensity of the phenolate-to-Fe(III) LMCT band for 2 and 6 decreases but does not exhibit any appreciable change for 4. In the presence of m-CPBA cyclohexane is selectively (A/K, 12.2) oxidized by the dimeric complex to cyclohexanol (A, CyOH) and a small amount of the further oxidized product cyclohexanone (K, CyO). However, interestingly, the corresponding monomeric complex affords enhanced yields of both CyOH and CyO but with a lower selectivity (A/K=1.7) and also 1-chlorocyclohexane via oxidative ligand transfer (OLT). The oxidation of adamantane by 4 affords exclusively 1-adamantanol (50.5%) and 2-Adamantanol (9.5%) with enhanced yields over 12 h. In contrast, 3 provides 1-adamantanol (32.4%) and 2-Adamantanol (14.8%) and adamantanone (14.6%) in addition to 1-chloroadamantane (14.1%) as the OLT product. The secondary C-H bond of ethylbenzene is randomly activated by both 3 and 4 to give 1-phenylethanol and acetophenone. Also, oxidation of cumene with tertiary C-H bonds to give 2-phenyl-2-propanol and the further oxidized product acetophenone is illustrated by invoking the iron-phenoxyl radical species as invoked for metalloporphyrin-catalyzed systems. The strong chemoselectivity in C-H bond activation of alkanes by 4has been illustrated by invoking the involvement of a high-valent iron-oxo intermediate generated by using m-CPBA rather than the conventional oxidants H2O2 and t-BuOOH. In contrast to 4, the complexes 2 and 6 fail to effect the oxidation of hydrocarbons in the presence of H2O2, t-BuOOH and m-CPBA as the co-oxidant.

Nickel(II) complexes of pentadentate N5 ligands as catalysts for alkane hydroxylation by using m-CPBA as oxidant: a combined experimental and computational study.[Pubmed:25100547]

Chemistry. 2014 Sep 1;20(36):11346-61.

A new family of nickel(II) complexes of the type [Ni(L)(CH(3)CN)](BPh(4))(2), where L=N-methyl-N,N',N'-tris(pyrid-2-ylmethyl)-ethylenediamine (L1, 1), N-benzyl-N,N',N'-tris(pyrid-2-yl-methyl)-ethylenediamine (L2, 2), N-methyl-N,N'-bis(pyrid-2-ylmethyl)-N'-(6-methyl-pyrid-2-yl-methyl)-ethylenediami ne (L3, 3), N-methyl-N,N'-bis(pyrid-2-ylmethyl)-N'-(quinolin-2-ylmethyl)-ethylenediamine (L4, 4), and N-methyl-N,N'-bis(pyrid-2-ylmethyl)-N'-imidazole-2-ylmethyl)-ethylenediamine (L5, 5), has been isolated and characterized by means of elemental analysis, mass spectrometry, UV/Vis spectroscopy, and electrochemistry. The single-crystal X-ray structure of [Ni(L(3))(CH(3)CN)](BPh(4))(2) reveals that the nickel(II) center is located in a distorted octahedral coordination geometry constituted by all the five nitrogen atoms of the pentadentate ligand and an acetonitrile molecule. In a dichloromethane/acetonitrile solvent mixture, all the complexes show ligand field bands in the visible region characteristic of an octahedral coordination geometry. They exhibit a one-electron oxidation corresponding to the Ni(II) /Ni(III) redox couple the potential of which depends upon the ligand donor functionalities. The new complexes catalyze the oxidation of cyclohexane in the presence of m-CPBA as oxidant up to a turnover number of 530 with good alcohol selectivity (A/K, 7.1-10.6, A=alcohol, K=ketone). Upon replacing the pyridylmethyl arm in [Ni(L1)(CH(3)CN)](BPh(4))(2) by the strongly sigma-bonding but weakly pi-bonding imidazolylmethyl arm as in [Ni(L5)(CH(3)CN)](BPh(4))(2) or the sterically demanding 6-methylpyridylmethyl ([Ni(L3)(CH(3)CN)](BPh(4))(2) and the quinolylmethyl arms ([Ni(L4)(CH(3)CN)](BPh(4))(2), both the catalytic activity and the selectivity decrease. DFT studies performed on cyclohexane oxidation by complexes 1 and 5 demonstrate the two spin-state reactivity for the high-spin [(N5)Ni(II)-O(.)] intermediate (ts1(hs), ts2(doublet)), which has a low-spin state located closely in energy to the high-spin state. The lower catalytic activity of complex 5 is mainly due to the formation of thermodynamically less accessible m-CPBA-coordinated precursor of [Ni(II) (L5)(OOCOC(6)H(4)Cl)](+) (5 a). Adamantane is oxidized to 1-adamantanol, 2-Adamantanol, and 2-adamantanone (3 degrees /2 degrees , 10.6-11.5), and cumene is selectively oxidized to 2-phenyl-2-propanol. The incorporation of sterically hindering pyridylmethyl and quinolylmethyl donor ligands around the Ni(II) leads to a high 3 degrees /2 degrees bond selectivity for adamantane oxidation, which is in contrast to the lower cyclohexane oxidation activities of the complexes.