Search

The oxidation of alkanes by various peroxides ((t)BuOOH, H2O2, PhCH2C(CH3)2OOH) is efficiently catalyzed by [Os(VI)(N)Cl4](-)/Lewis acid (FeCl3 or Sc(OTf)3) in CH2Cl2/CH3CO2H to give alcohols and ketones. Oxidations occur rapidly at ambient conditions, and excellent yields and turnover numbers of over 7500 and 1000 can be achieved in the oxidation of cyclohexane with (t)BuOOH and H2O2, respectively. In particular, this catalytic system can utilize PhCH2C(CH3)2OOH (MPPH) efficiently as the terminal oxidant; good yields of cyclohexanol and cyclohexanone (>70%) and MPPOH (>90%) are obtained in the oxidation of cyclohexane. This suggests that the mechanism does not involve alkoxy radicals derived from homolytic cleavage of MPPH but is consistent with heterolytic cleavage of MPPH to produce a metal-based active intermediate. The following evidence also shows that no free alkyl radicals are produced in the catalytic oxidation of alkanes: (1) The product yields and distributions are only slightly affected by the presence of O2. (2) Addition of BrCCl3 does not affect the yields of cyclohexanol and cyclohexanone in the oxidation of cyclohexane. (3) A complete retention of stereochemistry occurs in the hydroxylation of cis- and trans-1,2-dimethylcyclohexane. The proposed mechanism involves initial O-atom transfer from ROOH to [Os(VI)(N)Cl4](-)/Lewis acid to generate [Os(VIII)(N)(O)Cl4](-)/Lewis acid, which then oxidizes alkanes via H-atom abstraction.

Systematic investigations on the reactions between cis‐[M(dppm)2Cl2] (M=Ru/Os; dppm=1,1‐bis(diphenylphosphino)methane) and pyridine/quinoline substituted homopropargylic alcohols uncovered the diverse Ru(II)/Os(II)‐induced alkyne activation pathways. The alkynes underwent cyclization on M via a "non‐vinylidene" pathway at lower temperatures, resulting in alkenyl intermediates which might further metallacyclize to give metallapyrroloindolizines. Conversely, reactions at higher temperatures induced alkyne cyclization on M via a "vinylidene" pathway, affording cyclic oxacarbene complexes. Additionally, a rare decyclization mechanism was observed during the transformation of a metallacyclization‐resistant alkenyl complex into a cyclic oxacarbene complex. DFT calculations were employed to validate the experimental findings. Overall, these results not only provide insights into controlling alkyne activation pathways, but also offer new strategies for preparing metalated heterocyclic and metallacyclic complexes. [ABSTRACT FROM AUTHOR]

Two types of unexpected quinolizinium complexes were obtained from the reactions between pyridine-functionalized propargylic alcohol HC≡CC(OH)(Ph)(CH2(2-py)) (L1) and cis-[M(L^L)2Cl2] (M = Ru, Os; L^L = 1,1-bis(diphenylphosphino)methane (dppm), 2,2′-bipyridine (bpy)). Their molecular structures revealed that L1 can be activated by Ru and Os via the conventional "vinylidene-involving" or unconventional "non-vinylidene-involving" pathways. [ABSTRACT FROM AUTHOR]

Metallafuran complexes with a fused five‐membered phosphonium ring were synthesized from reactions between terminal ynones HC≡C(C=O)R and cis‐[Ru/Os(dppm)2Cl2] (dppm=1,1‐bis(diphenylphosphino)methane). A metal–vinylidene‐involving pathway was found to be an energetically feasible formation mechanism for these complexes. These phosphonium‐containing metallafurans, like many phosphonium‐functionalized drugs, have the ability to induce mitochondrial dysfunction. They also exhibit stronger cytotoxicity against several human cancer cell lines in comparison with their metal precursors and the classic anticancer drug cisplatin. Overall, this work provides structural and mechanistic insights for the rational design of functional metallacycles via activation of alkynes by RuII and OsII centers. [ABSTRACT FROM AUTHOR]

The OsVI nitrido complex, OsVI(N)(quin)2(OTs) ( 1, quin=2-quinaldinate, OTs=tosylate), is a highly selective and efficient catalyst for the ring hydroxylation of alkylbenzenes with H2O2 at room temperature. Oxidation of various alkylbenzenes occurs with ring/chain oxidation ratios ranging from 96.7/3.3 to 99.9/0.1, and total product yields from 93 % to 98 %. Moreover, turnover numbers up to 6360, 5670, and 3880 can be achieved for the oxidation of p-xylene, ethylbenzene, and mesitylene, respectively. Density functional theory calculations suggest that the active intermediate is an OsVIII nitrido oxo species. [ABSTRACT FROM AUTHOR]

Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group8 metal-oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy=2,2′:6′,2″:6″,2‴-quaterpyridine, pic=4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os=O distance of 1.7375 Å. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C–H bond dissociation energy as high as 90 kcalmol-1. This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species. [ABSTRACT FROM AUTHOR]

Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group 8 metal-oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy = 2,2':6',2'':6'',2'''-quaterpyridine, pic = 4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os=O distance of1.7375 A. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C--H bond dissociation energy as high as 90kcalmol--1. This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species. [ABSTRACT FROM AUTHOR]

Highlights from the article: Keywords: alkyne activation; metallacycles; osmium; ruthenium B Reactions between terminal ynones b and ruthenium(II)/osmium(II) precursors with a 1,1-bis(diphenylphosphino)methane (dppm) auxiliary ligand produced metallafuran complexes with a fused five-membered phosphonium ring. Alkyne activation, metallacycles, osmium, ruthenium.

Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group8 metal-oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy=2,2′:6′,2″:6″,2‴-quaterpyridine, pic=4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os=O distance of 1.7375 Å. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C–H bond dissociation energy as high as 90 kcalmol-1. This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species. [ABSTRACT FROM AUTHOR]

Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group 8 metal-oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy = 2,2':6',2'':6'',2'''-quaterpyridine, pic = 4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os=O distance of1.7375 A. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C--H bond dissociation energy as high as 90kcalmol--1. This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species. [ABSTRACT FROM AUTHOR]