Tungsten Dinitrogen Complexes Research Articles

Boron Insertion into the N≡N Bond of a Tungsten Dinitrogen Complex.

The 1,3-addition of 1,2-diaryl-1,2-dibromodiboranes (B2Br2Ar2) to trans-[W(N2)2(dppe)2] (dppe = κ2-(Ph2PCH2)2), which is accompanied by a Br-Ar substituent exchange between the two boron atoms, is followed by a spontaneous rearrangement of the resulting tungsten diboranyldiazenido complex to a 2-aza-1,3-diboraallenylimido complex displaying a linear, cumulenic B=N=B moiety. This rearrangement involves the splitting of both the B-B and N=N bonds of the N2B2 ligand, formal insertion of a BAr boranediyl moiety into the N=N bond, and coordination of the remaining BArBr boryl moiety to the terminal nitrogen atom. Density functional theory calculations show that the reaction proceeds via a cyclic NB2 intermediate, followed by dissociation into a tungsten nitrido complex and a linear boryliminoborane, which recombine by adduct formation between the nitrido ligand and the electron-deficient iminoborane boron atom. The linear B=N=B moiety also undergoes facile 1,2-addition of Brønsted acids (HY = HOPh, HSPh, and H2NPh) with concomitant Y-Br substituent exchange at the terminal boron atom, yielding cationic (borylamino)borylimido tungsten complexes.

Tungsten and molybdenum dinitrogen complexes supported by a pentadentate tetrapodal phosphine ligand: comparative spectroscopic, electrochemical and reactivity studies.

The tungsten dinitrogen complex [W(N2)(PMe2PPPh2)] (2) (PMe2PPPh2 = [2-({bis[3-(diphenylphosphino)propyl]-phosphino}methyl)-2-methylpropane-1,3-diyl]bis(dimethylphosphine)) is synthesized and characterized by X-ray diffraction as well as IR and NMR spectroscopies, showing strong analogies to its molybdenum analogue [Mo(N2)(PMe2PPPh2)] (1). Whereas cyclic voltammetry studies indicate very similar redox potentials, detailed electrochemical and IR-spectroelectrochemical investigations reveal characteristic differences between 1 and 2 upon electrochemical oxidation in THF. Protonation of 2 with HBArF (BArF = tetrakis(3,5-bis(trifluoromethyl)-phenyl)borate) leads to the hydrazido(2-) derivative 3 which is spectroscopically characterized as well. In the presence of SmI2/H2O slightly overstoichiometric conversion of N2 to ammonia (2.75 equiv.) is observed. Although this is far below the activity of the Mo-complex 1, it renders 2 the first W complex to produce more than 2 equivalents of NH3 from N2 upon addition of protons and reductant.

Protonation Studies of a Tungsten Dinitrogen Complex Supported by a Diphosphine Ligand Containing a Pendant Amine

Treatment of trans-[W(N2)2(dppe)(PEtNMePEt)] (dppe = Ph2PCH2CH2PPh2; PEtNMePEt = Et2PCH2N(Me)CH2PEt2) with 3 equiv of tetrafluoroboric acid (HBF4·Et2O) at −78 °C generated the seven-coordinate tungsten hydride trans-[W(N2)2(H)(dppe)(PEtNMePEt)][BF4]. At higher temperatures, protonation of a pendant amine is also observed, affording trans-[W(N2)2(H)(dppe)(PEtNMe(H)PEt)][BF4]2, with formation of the hydrazido complex [W(NNH2)(dppe)(PEtNMe(H)PEt)][BF4]2 as a minor product. A similar product mixture was obtained using triflic acid (HOTf). The protonated products are thermally sensitive and do not persist at ambient temperature. Upon acid addition to the carbonyl analogue cis-[W(CO)2(dppe)(PEtNMePEt)], the seven-coordinate carbonyl hydride complex trans-[W(CO)2(H)(dppe)(PEtNMe(H)PEt)][OTf]2 was generated. A mixed diphosphine complex without the pendant amine in the ligand backbone, trans-[W(N2)2(dppe)(depp)] (depp = Et2P(CH2)3PEt2), was synthesized and treated with HOTf, selectively generating a hydrazido complex, [W(NNH2)(OTf)(dppe)(depp)][OTf]. Computational analysis probed the proton affinity of three sites of protonation in these complexes: the metal, pendant amine, and N2 ligand. Room-temperature reactions with 100 equiv of HOTf produced NH4+ from reduction of the N2 ligand (electrons come from W). The addition of 100 equiv of HOTf to trans-[W(N2)2(dppe)(PEtNMePEt)] afforded 0.81 equiv of NH4+, while 0.40 equiv of NH4+ was formed upon treatment of trans-[W(N2)2(dppe)(depp)] with HOTf, showing that the complexes containing proton relays produce more products of reduction of N2.

Efficient Carbene and Carbyne Formation in Molybdenum(0) and Tungsten(0) Dinitrogen Complexes

Zerovalent group 6 dinitrogen phosphine complexes react with 3,3-diphenylcyclopropene to give vinylcarbyne hydride complexes that have been characterized crystallographically. Computational studies indicate that the observed products resulted from the α-migration and rearrangement of an initially formed vinylcarbene.

Synthesis and Protonation of Molybdenum– and Tungsten–Dinitrogen Complexes Bearing PNP-Type Pincer Ligands

Novel molybdenum– and tungsten–dinitrogen complexes bearing PNP-type pincer ligands are prepared and characterized by X-ray analysis. Reactions of these molybdenum– and tungsten–dinitrogen complexes with an excess amount of sulfuric acid in THF at room temperature afford ammonia and hydrazine in good yields.

Research inspired by the chemistry of nitrogenase — Novel metal complexes and their reactivity toward dinitrogen, nitriles, and alkynes

Summarized here are our continuous studies of the last three decades concerning syntheses of new types of complexes learned from nitrogenase and their reactivites toward dinitrogen, nitriles, and alkynes. For Mo and W dinitrogen complexes with tertiary phosphine coligands, a variety of their intriguing reactivities have been demonstrated, and novel transformations of the N2 ligands into numerous nitrogen-containing ligands and compounds have been developed. The C≡N bond cleavage of certain nitriles also proceeds on the Mo site surrounded by tertiary phosphines. Stimulated by the sophisticated structure of the active site of nitrogenase, multinuclear metal–sulfur complexes have been synthesized in rational ways. New types of stoichiometric and catalytic reactions of alkynes have been found by using the thiolato-bridged diruthenium complexes and some cubane-type sulfido clusters containing a noble metal.Key words: nitrogen fixation, molybdenum and tungsten dinitrogen complexes, ruthenium thiolato complexes, metal sulfido clusters, nitriles, alkynes.

A Personal Account of Some Dinitrogen and Organometallic Chemistry Research at the University of Sussex

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mo/WN2 and N2H2 complexes with trans nitrile ligands: electronic structure, spectroscopic properties and relevance to nitrogen fixation

Molybdenum and tungsten dinitrogen complexes with trans nitrile groups are of significant interest to synthetic nitrogen fixation as they can be protonated to the corresponding N2H2 complexes with retention of the trans ligand. This is in contrast to their bis(dinitrogen) counterparts where one N2 group is exchanged by a ligand X deriving from the acid used for protonation (X=Hal−, HSO4− etc.). Here the first crystal structure of a tungsten(0) dinitrogen nitrile complex having a P4 ligand set is presented. The electronic and vibrational properties of this and analogous N2 and N2H2 systems with trans nitrile ligands are investigated using IR and Raman spectroscopies coupled to DFT calculations. Force constants are evaluated from experimental frequencies and isotope shifts by the QCA–NCA procedure developed earlier [N. Lehnert, F. Tuczek, Inorg. Chem. 38 (1999) 1659]. The resulting electronic structure descriptions are compared with those obtained earlier for the bis(dinitrogen) and trans fluoro N2H2 complexes, respectively [N. Lehnert, F. Tuczek, Inorg. Chem. 38 (1999) 1671]. Importantly, the N2 ligand is found to be activated to a higher degree in the trans nitrilo as compared with the corresponding bis(dinitrogen) system. On the other hand, the N2H2 ligand is less activated in the trans nitrilo than in the analogous trans fluoro complexes. Further, bonding of the nitrile group becomes labile at the N2H2 stage of N2 reduction. These results are interpreted based on the electronic donor/acceptor properties of the respective trans ligands, and the consequences regarding the reactivity of these systems towards further protonation and their potential use for synthetic nitrogen fixation are discussed.

Synthesis and Structures of p-tert-Butyltetrathiacalix[4]arene-dihydrides of Mo(IV) and W(IV)

Abstract The reaction of zero-valent molybdenum and tungsten dinitrogen complexes cis-[M(N2)2(PMe2Ph)4] (M = Mo, W) with 1 equiv of p-tert-butyltetrathiacalix[4]arene (TC4A(OH)4) gave novel dihydrido complexes [TC4A(OH)2(O2MH2 (PMe2Ph)3)] (M = Mo, W). The structures were determined by X-ray crystallography.

Synthesis, structure, and electrochemical studies of molybdenum and tungsten dinitrogen, diazenido, and hydrazido complexes that contain aryl-substituted triamidoamine ligands.

One-electron reduction of [ArN(3)N]MoCl complexes (Ar = C(6)H(5), 4-FC(6)H(4), 4-t-BuC(6)H(4), 3,5-Me(2)C(6)H(3)) yields complexes of the type [ArN(3)N]Mo-N=N-Mo[ArN(3)N], while two-electron reduction yields ([ArN(3)N]Mo-N=N)(-) derivatives (Ar = C(6)H(5), 4-FC(6)H(4), 4-t-BuC(6)H(4), 3,5-Me(2)C(6)H(3), 3,5-Ph(2)C(6)H(3), and 3,5-(4-t-BuC(6)H(4))(2)C(6)H(3)). Compounds that were crystallographically characterized include ([t-BuC(6)H(4)N(3)N]Mo)(2)(N(2)), Na(THF)(6)([PhN(3)N]Mo-N=N)(2)Na(THF)(3), [t-BuC(6)H(4)N(3)N]Mo-N=N-Na(15-crown-5), and ([Ph(2)C(6)H(3)N(3)N]MoNN)(2)Mg(DME)(2). Compounds of the type [ArN(3)N]Mo-N=N-Mo[ArN(3)N] do not appear to form when Ar = 3,5-Ph(2)C(6)H(3) or 3,5-(4-t-BuC(6)H(4))(2)C(6)H(3), presumably for steric reasons. Treatment of diazenido complexes (e.g., [ArN(3)N]Mo-N=N-Na(THF)(x)) with electrophiles such as Me(3)SiCl or MeOTf yielded [ArN(3)N]Mo-N=NR complexes (R = SiMe(3) or Me). These species react further to yield ([ArN(3)N]Mo-N=NMe(2))(+) species in the presence of methylating agents. Addition of anionic methyl reagents to ([ArN(3)N]Mo-N=NMe(2))(+) species yielded [ArN(3)N]Mo(N=NMe(2))(Me) complexes. Reduction of [4-t-BuC(6)H(4)N(3)N]WCl under dinitrogen leads to a rare ([t-BuC(6)H(4)N(3)N]W)(2)(N(2)) species that can be oxidized by two electrons to give a stable dication (as its BPh(4)(-) salt). Reduction of hydrazido species leads to formation of Mo=N in low yields, and only dimethylamine could be identified among the many products. Electrochemical studies revealed expected trends in oxidation and reduction potentials, but also provided evidence for stable neutral dinitrogen complexes of the type [ArN(3)N]Mo(N(2)) when Ar is a relatively bulky terphenyl substituent.

Protonation of coordinated N2 on tungsten with H2 mediated by sulfido-bridged dinuclear molybdenum complexes.

Reaction of tungsten dinitrogen complexes [W(N2)2L4] (L = PMe2Ph, PMePh2) and 10 equiv of sulfido-bridges molybdenum complexes [Cp‘Mo(μ2-S2CH2)(μ-S)(μ-SR)MoCp‘]OTf (Cp‘ = η5-C5H5, η5-C5H4Me; R = H, Me; OTf = OSO2CF3) under 1 atm of H2 afforded NH3 in moderate (33−52%) yields based on the tungsten atom.

Preparation of Sulfide-Bridged Di- or Trinuclear Pyrrolylimido and Diazoalkane Complexes Derived from a Tungsten Dinitrogen Complex

Abstract Tungsten pyrrolylimido and diazoalkane complexes, cis,mer-[WCl2(NNC4H4)(PMe2Ph)3] and cis,mer-[WCl2(NN=CRR′)(PMe2Ph)3], which are readily derived from the dinitrogen complex cis-[W(N2)2(PMe2Ph)4], reacted with [PPh4]2[WS4] to give the sulfide-bridged di- or trinuclear pyrrolylimido and diazoalkane complexes, [PPh4][WCl(NNC4H4)(PMe2Ph)2(μ-S)2WS2] (4) and [PPh4][WCl(NN=CRR′)(PMe2Ph)2(μ-S)2WS2] (R = R′ = Me (5a); R = Me, R′ = Ph; R = H, R′ = p-MeC6H4), or [{WCl(NNC4H4)(PMe2Ph)2(μ-S)2}2W] (7) and [{WCl(NN=CMePh)(PMe2Ph)2(μ-S)2}2W]. Treatment of 4 or 5a with tetraalkylthiuram disulfide resulted in the formation of sulfide-dithiocarbamate complexes: [W(NNC4H4)(PMe2Ph)(S2CNR2)(μ-S)2WS(S2CNR2)] (R = Et, Pri (9b)) and [W(NN=CMe2)(PMe2Ph)(S2CNEt2)(μ-S)2WS(S2CNEt2)]. On the other hand, replacement of two PMe2Ph ligands in 4 and 5 by Ph2PCH2CH2PPh2 (dppe) afforded [PPh4][WCl(NNC4H4)(dppe)(μ-S)2WS2] and [PPh4][WCl(NN=CRR′)(dppe)(μ-S)2WS2] (R = R′ = Me; R = Me, R′ = Ph (12b)), where 12b has been shown to react further with [RhCl(cod)]2 (cod = 1,5-cyclooctadiene) to give a bimetallic trinuclear complex [WCl(NN=CMePh)(dppe)(μ-S)2W(μ-S)2Rh(cod)] (13). Detailed structures have been determined by X-ray analyses for 4, 5a, 7, 9b, and 13.

ChemInform Abstract: Preparation and Properties of Molybdenum and Tungsten Dinitrogen Complexes. Part 60. Syntheses of Tungsten Diazoalkane Complexes from a Dinitrogen Complex and Diketones. Conversion of Molecular Nitrogen into Pyrazoles via the Diazoalkane Complexes as Intermediates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Selective N–N and W–N Bond Cleavage of Tungsten Pyrrolylimido Complexes Derived from Tungsten Dinitrogen Complex

Abstract Treatment of the pyrrolylimido complexes cis,trans-( [WX2(NNCH=CHCH=CH)(L)(PMe2Ph)2] ) (X = Cl, Br, I; L = PMe2Ph (6), CNBut, CO, PhC≡CH, PhCHO, Br) with LiAlH4or KOH produced pyrrole, 1-aminopyrrole, and ammonia, where both the reaction conditions and the nature of the ligand L showed significant effects on the pyrrole/1-aminopyrrole selectivity. Thus, reduction of cis,trans-( [WBr2(NNCH=CHCH=CH)(CNBut)(PMe2Ph)2] ) with LiAlH4 followed by methanolysis gave pyrrole and ammonia in almost quantitative yields. On the other hand, 1-aminopyrrole was quantitatively produced from the complexes by the reaction of KOH in alcohol when L = CO, PhC≡CH, or PhCHO. While analogous treatment of 6 with KOH in ethanol afforded both pyrrole and 1-aminopyrrole with low selectivity under N2 atmosphere, 1-aminopyrrole was produced from 6 in excellent yield under 1 atm of CO. On the contrary, pyrrole and ammonia were selectively formed from the reaction of 6b (X = Br) with KOH/18-crown-6 ether in THF. Replacement of one of the PMe2Ph ligands in the diazoalkane complex cis,mer-[WBr2(NN=CMeCH2CH2COMe)(PMe2Ph)3] (12) by CO or CNBut facilitated the cyclization of the diazoalkane ligand to provide the (2,5-dimethylpyrrolyl)imido complexes cis,trans-( [WBr2(NNCMe=CHCH=CMe)(L)(PMe2Ph)2] ) (L = CO 14; L = CNBut 15), although complex 12 failed to undergo the ring closure by aqueous HBr. 2,5-Dimethylpyrrole and 1-amino-2,5-dimethylpyrrole were selectively obtained by LiAlH4 reduction of 15 and by treatment of 14 with KOH in EtOH, respectively.

Synthesis and structures of tungsten ferrocenyldiazoalkane complexes derived from a dinitrogen complex.: Part 58. Preparation and properties of molybdenum and tungsten dinitrogen complexes

Reaction of the hydrazido(2-) complex cis, mer-[WCl 2(NNH 2)(PMe 2Ph) 3], derived from a dinitrogen complex cis-[W(N 2) 2(PMe 2Ph) 4], with formylferrocene or acetylferrocene gave ferrocenyldiazoalkane complexes cis, mer-[WCl 2(NNCRFc)(PMe 2Ph) 3] ( 2: R = H, Me; Fc = (η 5-C 5H 4)Fe(η 5-C 5H 5)). Treatment of 2 with π-acceptor ligands L such as CO, CH 2CH 2, p-MeC 6H 4CHO, p-MeC 6H 4CCH and Bu tNC afforded a series of ferrocenyldiazoalkane complexes cis, trans-[WCl 2(NNCRFc)(L)(PMe 2Ph) 2] ( 4), while upon treatment with CH 2Cl 2 2 gave the W(V) complexes mer, trans-[WCl 3(NNCRFc)(PMe 2Ph) 2] ( 5). The X-ray analyses have been undertaken to determine the detailed structures for 2a (R = H) and 5b (R = Me).

Synthesis of Boryldiazenido Complexes from Tungsten Dinitrogen Complexes

Abstract The anionic tungsten dinitrogen complex trans-[NBu4][W(NCS)(N2)(dppe)2] reacted with primary and secondary boranes to give the corresponding boryldiazenido complexes, among which trans-[W(NCS)(N=NBHCMe2CHMe2)(dppe)2] was structurally determined. A related boryldiazenido complex was also obtained by the reaction of trans-[W(N2)2(dppe)2] with 9-borabicyclo[3.3.1]nonyl trifluoromethanesulfonate. These reactions provide the first examples of boration of coordinated dinitrogen.

タングステンの窒素錯体から誘導されるアシルヒドラジド(2-)錯体のX線構造

タングステンの窒素錯体から誘導されるアシルヒドラジド(2-)錯体のX線構造

Preparation and properties of molybdenum and tungsten dinitrogen complexes: XLII. Preparation and characterization of W(V) diazoalkane complexes mer,trans-[WX 3(NNCMeR)(PMe 2Ph) 2] (X  Br, I; R  Me, Ph) and hydrazido(2-) complex [WI 3(NNH 2)(PMe 2Ph) 2]. X-ray structure of mer,trans-[WBr 3(NNCMePh)(PMe 2Ph) 2

Reactions of W(IV) diazoalkane complexes cis,mer-[WX 2(NNCMeR)(PMe 2Ph) 3] (X  Br, I; R  Me, Ph) and hydrazido(2-) complex cis,mer-[WI 2(NNH 2)(PMe 2Ph) 3] with five equivalents of CH 2X 2 in toluene at 80°C gave paramagnetic W(V) complexes, mer,trans-[WX 3(NNCMeR)(PMe 2Ph) 2] and [WI 3(NNH 2)(PMe 2Ph) 2] respectively. The latter complex was also obtained upon hydrolysis of a W(V) disilylhydrazido(2-) complex mer,trans-[WI 3(N NSiMe 2CH 2CH 2S iMe 2)(PMe 2Ph) 2] and was converted into mer,trans-[WI 3(NNCMeR)(PMe 2Ph) 2] by the subsequent condensation with RMeCO. The structure of mer,trans-[WBr 3(NNCMePh)(PMe 2Ph) 2] ( 6d) was determined by X-ray analysis. Crystal data for 6d are as follows: monoclinic, space group P2 1/ n with a = 9.900(3) Å, b = 21.029(4) Å, c = 13.950(2) Å, β = 96.80(2)°, V = 2883.9(11) Å 3, Z = 4 and R = 0.060 for 4567 reflections.

Preparation and properties of molybdenum and tungsten dinitrogen complexes. 39. Alkenyldiazenido complexes of molybdenum and tungsten derived from dinitrogen complexes: their synthesis, characterization, and novel reactivities

α-Deprotonation of molybdenum or tungsten diazoalkane complexes trans-[MF(NN=CR 1 CHR 2 R 3 ) (dpe) 2 ] [BF 4 ] (1, M=Mo or W, dpe=Ph 2 PCH 2 CH 2 PPh 2 ) by LDA (lithium diisopropylamide) or NaN(SiMe 3 ) 2 provides a general route to alkenyldiazenido complexes trans-[MF(NNCR 1 =CR 2 R 3 ) (dpe) 2 ].

Preparation and properties of molybdenum and tungsten dinitrogen complexes. 38. Hydrido-carbonato, hydrido-carbamato, and carbon dioxide complexes of tungsten derived from the carbonyl-dinitrogen complex trans-[W(CO)(N2)(Ph2PCH2CH2PPh2)2

Reaction of trans-[W(CO)(N 2 )(dppe) 2 ] (dppe=Ph 2 PCH 2 CH 2 PPh 2 ) with excess MeOH or HNR 2 (R=Me, ES, R 2 =(CH 2 ) 4 , (CH 2 ) 2 , (CH 2 ) 2 O(CH 2 ) 2 ) under CO 2 afforded a hydrido-arbonato complex [WH(η 1 -OCO 2 Me)(CO)(dppe) 2 ].