An evaluation of monovalent osmium supported by the PNP ligand environment

Tsvetkov, Nikolay P.; Fan, Hongjun; Caulton, Kenneth G.

doi:10.1039/c0dt00989j

Cited by 16 publications

(5 citation statements)

References 40 publications

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“…The Schneider group has prepared the five-coordinate bridging d 5 –d 5 complex [( tBu PNP)ReCl] 2 (μ-N 2 ) ( 7 -Re in Scheme ) which undergoes a facile cleavage of the bridging N 2 ligand at room temperature. , No terminal N 2 complex was detected in this system. In contrast, terminal N 2 bonding has been observed in five coordinate d 6 -Tc I and d 6 -Os II PNP pincer complexes. , [ 7 -Re] 2 (μ-N 2 ) has two unpaired electrons in 3π μ * ; therefore, for eq , ΔBO eq π = 1, and according to the above discussion the bridging M–N 2 bonds are expected to be stronger than the terminal M–N 2 ones. Consistently, for 7 -Re, Δ E eq v and Δ G eq ° are computed to be quite negative: −10.8 and −6.9 kcal/mol, respectively.…”

Section: Resultsmentioning

confidence: 92%

“…In contrast, terminal N 2 bonding has been observed in five coordinate d 6 -Tc I and d 6 -Os II PNP pincer complexes. 43,44 [7-Re] 2 (μ-N 2 ) has two unpaired electrons in 3π μ *; therefore, for eq 1, ΔBO eq π = 1, and according to the above discussion the bridging M−N 2 bonds are expected to be stronger than the terminal M−N 2 ones. 3 and 4) Complexes described in Scheme 7.…”

Section: Journal Of Thementioning

confidence: 91%

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Understanding Terminal versus Bridging End-on N₂ Coordination in Transition Metal Complexes

et al. 2021

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Terminal and bridging end-on coordination of N 2 to transition metal complexes offer possibilities for distinct pathways in ammonia synthesis and N 2 functionalization. Here we elucidate the fundamental factors controlling the two binding modes and determining which is favored for a given metal−ligand system, using both quantitative density functional theory (DFT) and qualitative molecular orbital (MO) analyses. The Gibbs free energy for converting two terminal MN 2 complexes into a bridging MNNM complex and a free N 2 molecule (2ΔG eq °) is examined through systematic variations of the metal and ligands; values of ΔG eq °range between +9.1 and −24.0 kcal/mol per M−N 2 bond. We propose a model that accounts for these broad variations by assigning a fixed π-bond order (BO π ) to the triatomic terminal MNN moiety that is equal to that of the free N 2 molecule, and a variable BO π to the bridging complexes based on the character (bonding or antibonding) and occupancy of the π-MOs in the tetratomic MNNM core. When the conversion from terminal to bridging coordination and free N 2 is associated with an increase in the number of π-bonds (ΔBO eq π > 0), the bridging mode is greatly favored; this condition is satisfied when each metal provides 1, 2, or 3 electrons to the π-MOs of the MNNM core. When each metal in the bridging complex provides 4 electrons to the MNNM π-MOs, ΔBO eq π = 0; the equilibrium in this case is approximately ergoneutral and the direction can be shifted by dispersion interactions.

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Section: Resultsmentioning

confidence: 92%

Section: Journal Of Thementioning

confidence: 91%

Understanding Terminal versus Bridging End-on N₂ Coordination in Transition Metal Complexes

et al. 2021

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“…Tridentate “pincer” ligands by now represent a ligand archetype in transition-metal chemistry . Metal complexes of these robust, tunable scaffolds have been used as platforms for studies of bond activation, in the identification of transient intermediates, and to support unusual chemical transformations at both highly electron-rich , and electron-deficient transition-metal centers. We are interested in the construction of bridged, binucleating ligands based on pincer frameworks to explore cooperativity between metal centers .…”

Section: Introductionmentioning

confidence: 99%

Binuclear Palladium Complexes Supported by Bridged Pincer Ligands

Herbert

Ozerov

2011

Organometallics

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A series of binucleating ligands each containing two tridentate pincer sites based on a central, monoanionic aryl (C) donor flanked by neutral phosphinito (P) and imino (N) donors, [(PCN)-(CH2) n -(PCN)] (1), or a central, monoanionic amido (N) flanked by neutral phosphine (P) and imino donors (N), [(PNN)-(CH2) n -(PNN)] (4), are presented. The metalating sites were linked through the condensation of two equivalents of m-hydroxybenzaldehyde or the purposively built asymmetric diarylamine [(H)N(2-C(O)H-4-Me-C6H3)(2-P(iPr)2-4-Me-C6H3)] (3) with primary α,ω-diamines (1,2-diaminoethane, n = 2; 1,4-diaminobutane, n = 4), which simultaneously constructed the imino arms and bridged the pincer cores. Ligands 1 and 4 were then used in the synthesis of neutral, square-planar palladium(II) complexes 5 and 6, [(PCN-C n )Pd2X2, (PNN-C n )Pd2X2; n = 2, 4; X = Cl, OAc, OTf]. The difference in the trans influence of the central donor was demonstrated through X-ray crystal structures of 5b-Cl, (PCN-C4)Pd2Cl2, and 6b-Cl, (PNN-C4)Pd2Cl2. The (PNN-C n )Pd2X2 complexes (6) proved to be redox-active, presumably via oxidation of the ligand, and cyclic voltammetry illustrated the extent to which electronic communication between the two pincer sites is mediated by the length of the bridge between them. (PCN-C n )Pd2OTf2 (5-OTf) and (PNN-C n )Pd2OTf2 (6-OTf) complexes reacted with hydride donors such as Et3SiH or β-hydride-containing alkoxides such as NaOiPr to generate bridging-hydride monocations [(PCN)Pd-H-Pd(PCN)-C n ][OTf] (5-H, n = 2, 4) and [(PNN)Pd-H-Pd(PNN)-C2][OTf] (6a-H), where the supported Pd–Pd separation was also found to be affected by the bridge length. In the case of the (CH2)4-bridged (PNN-C4)PdOTf (6b-OTf), a bridging-hydride monocation was not observed. Instead, the formation of [(PN(H)N)Pd-Pd(PNN)-C4][OTf] (6b-H), protonated at the amido N of the ligand with a direct Pd(I)–Pd(I) bond, was recorded.

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“…The chemistry of the osmium-pincer has been mainly focused on a few PCP complexes reported by the groups of Gusev, Jia, and Milstein and PNP compounds described by the groups of Caulton, Gusev, and Jia along with some CCC, CNC, CNN, CNO, and NNN derivatives. In the search for more rigid and robust skeletons than our usual starting fragment trans -Os(P i Pr 3 ) 2 , , three years ago we synthesized the ligands 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene (xant(P i Pr 2 ) 2 ) and 4,6-bis(diisopropylphosphino)dibenzofuran (dbf(P i Pr 2 ) 2 ), which were used to prepare the corresponding osmium(III) complexes OsCl 3 (POP) .…”

Section: Introductionmentioning

confidence: 99%

POP-Pincer Osmium-Polyhydrides: Head-to-Head (Z)-Dimerization of Terminal Alkynes

et al. 2013

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A wide range of osmium-polyhydride complexes stabilized by the POP-pincer ligand xant(P(i)Pr2)2 (9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) have been synthesized through cis-OsCl2{κ-S-(DMSO)4} (1, DMSO = dimethyl sulfoxide). Treatment of toluene solutions of this adduct with the diphosphine, under reflux, leads to OsCl2{xant(P(i)Pr2)2}(κ-S-DMSO) (2). The reaction of 2 with H2 in the presence of Et3N affords OsH3Cl{xant(P(i)Pr2)2} (3), which can be also prepared by addition of xant(P(i)Pr2)2 to toluene solutions of the unsaturated d(4)-trihydride OsH3Cl(P(i)Pr3)2 (5). Complex 3 reductively eliminates H2 in toluene at 90 °C. In the presence of dimethyl sulfoxide, the resulting monohydride is trapped by the S-donor molecule to give OsHCl{xant(P(i)Pr2)2}(κ-S-DMSO) (6). The reaction of 2 with H2 is sensible to the Brønsted base. Thus, in contrast to Et3N, NaH removes both chloride ligands and the hexahydride OsH6{xant(P(i)Pr2)2} (7), containing a κ(2)-P-binding diphosphine, is formed under 3 atm of hydrogen at 50 °C. Complex 7 releases a H2 molecule to yield the tetrahydride OsH4{xant(P(i)Pr2)2} (8), which can be also prepared by reaction of OsH6(P(i)Pr3)2 (9) with xant(P(i)Pr2)2. Complex 8 reduces H(+) to give, in addition to H2, the oxidized OsH4-species [OsH4(OTf){xant(P(i)Pr2)2}](+) (10, OTf = trifluoromethanesulfonate). The redox process occurs in two stages via the OsH5-cation [OsH5{xant(P(i)Pr2)2}](+) (11). The metal oxidation state four can be recovered. The addition of acetonitrile to 10 leads to [OsH2(η(2)-H2)(CH3CN){xant(P(i)Pr2)2}](2+) (12). The deprotonation of 12 yields the osmium(IV) trihydride [OsH3(CH3CN){xant(P(i)Pr2)2}](+) (13), which is also formed by addition of HOTf to the acetonitrile solutions of 8. The latter is further an efficient catalyst precursor for the head-to-head (Z)-dimerization of phenylacetylene and tert-butylacetylene. During the activation process of the tetrahydride, the bis(alkynyl)vinylidene derivatives Os(C≡CR)2(=C═CHR){xant(P(i)Pr2)2} (R = Ph (14), (t)Bu (15)) are formed.

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An evaluation of monovalent osmium supported by the PNP ligand environment

Cited by 16 publications

References 40 publications

Understanding Terminal versus Bridging End-on N₂ Coordination in Transition Metal Complexes

Understanding Terminal versus Bridging End-on N₂ Coordination in Transition Metal Complexes

Binuclear Palladium Complexes Supported by Bridged Pincer Ligands

POP-Pincer Osmium-Polyhydrides: Head-to-Head (Z)-Dimerization of Terminal Alkynes

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An evaluation of monovalent osmium supported by the PNP ligand environment

Cited by 16 publications

References 40 publications

Understanding Terminal versus Bridging End-on N2 Coordination in Transition Metal Complexes

Understanding Terminal versus Bridging End-on N2 Coordination in Transition Metal Complexes

Binuclear Palladium Complexes Supported by Bridged Pincer Ligands

POP-Pincer Osmium-Polyhydrides: Head-to-Head (Z)-Dimerization of Terminal Alkynes

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Understanding Terminal versus Bridging End-on N₂ Coordination in Transition Metal Complexes

Understanding Terminal versus Bridging End-on N₂ Coordination in Transition Metal Complexes