Molybdenum and Tungsten Nitrosyl Complexes in Hydrogen Activation

Dybov, Alexander; Blacque, Olivier; Berke, Heinz

doi:10.1002/ejic.201000301

Cited by 12 publications

(8 citation statements)

References 45 publications

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“…The Mo−N distance of 1.780(10) Å in the linear Mo(NO) unit is similar to the distances found in the series of Mo-NO complexes in which phosphines stabilize the low-valent molybdenum, and the NO is assigned as NO + . 20,21 The N− O distance within the Mo 0 -NO + unit is 1.186(12) Å, slightly (but barely statistically significant) longer than the N−O distance within the Co III -NO − unit [1.161(15) Å].…”

Section: ■ Results and Discussionmentioning

confidence: 94%

Linear and Bent Nitric Oxide Ligand Binding in an Asymmetric Butterfly Complex: CoMoCo′

et al. 2021

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Two synthetic approaches to install metallodithiolate ligands on molybdenum centers using the synthons [Mo 2 (CH 3 CN) 10 ] 4+ and (N 2 S 2 )Co(NO) [N 2 S 2 = N,N-bis(2-mercaptoethyl)-1,4-diazacycloheptane and NO = nitric oxide], or [Mo(NO) 2 (CH 3 CN) 4 ] 2+ (CH 3 CN = acetonitrile) and [(N 2 S 2 )Co] 2 lead to a bisnitrosylated, trimetallic dication, CoMoCo′. This unique asymmetric butterfly complex, with S = 1, has a bent NO within the small {Co(NO)} 8 wing (denoted as Co), reflecting Co III (NO − ), and is S-bridged to a linear {Mo(NO)} 6 diamagnetic unit. The latter is further S-bridged to a pentacoordinate (N 2 S 2 )Co III (CH 3 CN) donor in the larger wing and is the origin of the two unpaired electrons, denoted as Co′. The asymmetry in Mo−Co distances, 3.33 Å in the Co wing and 2.73 Å in the Co′ wing, indicated a Mo−Co′ bonding interaction. The transfer of NO from (N 2 S 2 )Co(NO) in the former path is needed to cleave the strong quadruple bond in [Mo≣Mo] 4+ , with the energetic cost compensated for via a one-electron bond between Mo and Co′, as indicated by natural bonding orbital analysis.

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Section: ■ Results and Discussionmentioning

confidence: 94%

Linear and Bent Nitric Oxide Ligand Binding in an Asymmetric Butterfly Complex: CoMoCo′

et al. 2021

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“…of LiBH 4 in Et 3 N at room temperature resulted in the formation of the hydride complex 2a (Scheme 1). [25] (Figure 2). Similar to the chloride compound 1a, the hydride compound 2a displays a pseudo-octahedral coordination geometry with the phosphorus atoms of the dippp ligand and the two carbonyl ligands in-plane with the metal centre and the hydride ligand located trans to the nitrosyl group.…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

“…In isoelectronic cationic bis(diphosphane)nitrosylmolybdenum and -tungsten complexes the H 2 ligand adds oxidatively to form dihydride complexes. [25] H 2 complexes are normally more acidic than the corresponding dihydride complexes. Therefore the former species are preferably involved in heterolytic splitting by deprotonation and the latter foster catalyses of the Wilkinson type.…”

Section: Introductionmentioning

confidence: 99%

Molybdenum Nitrosyl Complexes and Their Application in Catalytic Imine Hydrogenation Reactions

2010

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The reaction between [Mo(CO)4(NO)(ClAlCl3)] and the sterically hindered diphosphanes (P∩P) 1,3‐bis(diisopropylphosphanyl)propane (dippp, a), 1,2‐bis(diisopropylphosphanyl)ethane (dippe, b), 1,1′‐bis(diisopropylphosphanyl)ferrocene (dippf, c) and 1,2‐bis(dicyclohexylphosphanyl)ethane (dcype, d) produced the chlorides [Mo(P∩P)(CO)2(NO)Cl] (1a–1d), which were transformed into the corresponding hydrides [Mo(P∩P)(CO)2(NO)H] (2a–2d) by reaction with LiBH4 in Et3N at room temperature. The molybdenum–THF complex [Mo(dippp)(CO)2(NO)(THF)][BArF4] [3a; ArF = 3,5‐(CF3)2C6H3], obtained by the reaction of 2a with [H(Et2O)2][BArF4], was exemplarily tested in the hydrogenation of the imine PhCH=N(α‐naphthyl). Replacement of the [BArF4]– counterion by the more stable [B(C6F5)4]– anion greatly increased the catalytic activity. The use of in situ mixtures of the hydrides 2a–2d and [H(Et2O)2][B(C6F5)4] improved the hydrogenation activity. The hydride 2b in combination with [H(Et2O)2][B(C6F5)4] exhibited the highest TOF value of 123 h–1 in the reduction of PhCH=N(α‐naphthyl). The hydrogenation of the imines PhCH=NPh, p‐ClC6H4CH=NPh, p‐ClC6H4CH=N‐p‐C6H4Cl, PhCH=NCH(Ph)2 and PhCH=NMes showed TOF values of 34, 74, 41, 18 and 84 h–1 at room temperatureand a H2 pressure of 30 bar. A mechanism for the ionic hydrogenation with “proton‐before‐hydride transfer” is anticipated.

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“…THF coordination to the metal center was confirmed by 1D NOE experiments, which additionally established the exchange of the coordinated THF with free THF in solution. Our group has previously reported that the protonation of a Mo(dippe) 2 (NO)H complex with [H(Et 2 O) 2 ][BAr F 4 ] produced the 16 e − cationic complex [Mo(dippe) 2 (NO)][BAr F 4 ] stabilized by an agostic interaction of one of the H Me atoms of the dippe ligand with the metal center 23. However, for 4 a( syn ) evidence for an agostic stabilization by H methyl atoms of the etp i p ligand could not be provided, since the proton‐coupled 13 C DEPT experiment showed no reduction of the J (C,H) coupling constants of the C Me atoms.…”

Section: Resultsmentioning

confidence: 99%

“…A satisfactory elemental analysis of 4 b( syn ) supported the composition of [W(NO)(CO)(mer‐etp i p)(THF)][B(C 6 F 5 ) 4 ]. As an alternative reaction mode, one could envisage formation of a cationic dihydrogen or dihydride complex, [W(NO)(CO)(H 2 )(etp i p)][B(C 6 F 5 ) 4 ] or [W(NO)(CO)(H) 2 (etp i p)][B(C 6 F 5 ) 4 ], respectively, via protonation of 2 b( syn ) at the hydride site to form an H 2 ligand and subsequent oxidative addition 23. However, this possibility was excluded since signals of dihydrogen or dihydride ligands could not be observed in the 1 H NMR spectra or in the 31 P– 1 H correlation spectra.…”

Section: Resultsmentioning

confidence: 99%

Hydrogenation of Imines Catalyzed by Trisphosphine‐Substituted Molybdenum and Tungsten Nitrosyl Hydrides and Co‐Catalytic Acid

Chakraborty

Blacque

Fox

et al. 2014

Chemistry An Asian Journal

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Hydride complexes Mo,W(CO)(NO)H(mer-etp(i)p) (iPr2PCH2CH2)2PPh=etp(i)p) (2 a,b(syn), syn and anti of NO and Ph(etp(i)p) orientions) were prepared and probed in imine hydrogenations together with co-catalytic [H(Et2O)2][B(C6F5)4] (140 °C, 60 bar H2). 2 a,b(syn) were obtained via reduction of syn/anti-Mo,W(NO)Cl3(mer-etp(i)p) and syn,anti-Mo,W(NO)(CO)Cl(mer-etp(i)p). [H(Et2O)2][B(C6F5)4] in THF converted the hydrides into THF complexes syn-[Mo,W(NO)(CO)(etp(i)p)(THF)][B(C6F5)4]. Combinations of the p-substituents of aryl imines p-R(1)C6H4CH=N-p-C6H4R(2) (R(1),R(2)=H,F,Cl,OMe,α-Np) were hydrogenated to amines (maximum initial TOFs of 1960 h(-1) (2 a(syn)) and 740 h(-1) (2 b(syn)) for N-(4-methoxybenzylidene)aniline). An 'ionic hydrogenation' mechanism based on linear Hammett plots (ρ=-10.5, p-substitution on the C-side and ρ=0.86, p-substitution on the N-side), iminium intermediates, linear P(H2) dependence, and DKIE=1.38 is proposed. Heterolytic splitting of H2 followed by 'proton before hydride' transfers are the steps in the ionic mechanism where H2 ligand addition is rate limiting.

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Molybdenum and Tungsten Nitrosyl Complexes in Hydrogen Activation

Cited by 12 publications

References 45 publications

Linear and Bent Nitric Oxide Ligand Binding in an Asymmetric Butterfly Complex: CoMoCo′

Linear and Bent Nitric Oxide Ligand Binding in an Asymmetric Butterfly Complex: CoMoCo′

Molybdenum Nitrosyl Complexes and Their Application in Catalytic Imine Hydrogenation Reactions

Hydrogenation of Imines Catalyzed by Trisphosphine‐Substituted Molybdenum and Tungsten Nitrosyl Hydrides and Co‐Catalytic Acid

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