Ruthenium Dihydrogen Complexes Research Articles

The effect of the counteranion on the loss of hydrogen from cationic ruthenium dihydrogen complexes in the solid state

The loss of the dihydrogen ligand from trans-[Ru(H2)H(dppe)2]+ cations (dppe = PPh2CH2CH2PPh2) in the solid state was investigated using 31P CP/MAS NMR spectroscopy and single crystal X-ray diffraction. While facile dihydrogen loss was observed at room temperature from crystalline samples with the large counteranions BPh4− and B(ArF)4−, ArF = 3,5-C6H3(CF3)2, it only occurred upon heating from complexes with the smaller anions BF4− and PF6−, resulting in the loss of crystallinity. Single crystal X-ray diffraction studies of the new complexes [RuH(dppe)2]BPh4 and trans-[Ru(H2)H(dppe)2]BArF4 are reported. A comparison of the crystal structures of square pyramidal [RuH(dppe)2]BPh4 and octahedral [Ru(H2)H(dppe)2]BPh4 shows that only minor structural changes occur upon loss of H2 from the crystal.

Temperature-dependent elongation of the H[sbnd]H bond in dihydrogen complexes of Ru(II) bearing an NHC ligand: Effect of the NHC and trans ligands

Ruthenium hydride complexes bearing an N-heterocyclic carbene ligand [RuHCl(CO)(IMes)(PPh3)(L/L′)] (L = py, 2; 4Mepy, 3; L′ = MeCN, 4; Me3CCN, 5) have been synthesized in high-yields via reaction of [RuHCl(CO)(IMes)(PPh3)] (1) with pyridyl ligands L (L = py and 4Mepy) or nitrile ligands L′ (L′ = MeCN and Me3CCN). The ligands L/L′ are labile in all the ruthenium hydride complexes; they can be easily replaced by Lewis bases. The X-ray structures of complexes 2 and 3 show intramolecular π-π interactions between the aromatic ring of PPh3, IMes, and pyridyl ligands. The protonation reaction of 2–5 gives the corresponding dihydrogen complexes of the type [RuCl(η2-H2)(CO)(IMes)(PPh3)(L/L′)][OTf] complexes (L = py, 6; 4Mepy, 7; L′ = MeCN, 8; Me3CCN, 9). In all the dihydrogen complexes, HH bond distances of η2-H2 ligand is temperature-dependent: 0.98 Å to 0.93 Å in the temperature range of 183–233 K. Attempts to synthesize analogous ruthenium hydride complexes bearing phosphine ligands resulted in a mixture of cis and trans-[RuHCl(CO)(PPh3)2(L)] [L = py, 10/11 (transHCl/cisHCl); 4Mepy, 12/13 (transHCl/cisHCl)] complexes. A comparative study has been done to get an insight into the temperature-dependent HH bond distances in complexes 6–8 by synthesizing analogous ruthenium dihydrogen complexes, [RuCl(η2-H2)(CO)(PPh3)2(L)](OTf) (L = py, 15; 4Mepy, 17). All the complexes have been characterized using NMR spectroscopy. The X-ray crystal structures of complexes 2, 3, and 12 have also been determined.

Homobimetallic hydride and dihydrogen complexes of ruthenium bearing N-heterocyclic carbene ligands

A series of new homobimetallic hydride complexes of ruthenium bearing N-heterocyclic carbene ligand of the type [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (4,4’-bpy = 4,4’-bipyridine) (2), [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyen)] (4,4’-dpyen = 1,2-bis(4-pyridyl)ethylene) (4), and [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyan)] (4,4’-dpyan = 1,2-bis(4-pyridyl)ethane) (5) has been synthesized and characterized starting from [RuHCl(IMes)(PPh3)(CO)] (1). The pyridyl-based ligands, (4,4’-bpy), (4,4’-dpyen), and (4,4’-dpyan) in these complexes act as the bridging ligands between the two ruthenium fragments. The bridging ligand in these bimetallic complexes is very labile. Reaction of these complexes with PMe3 led to extensive substitution of not only the bridging ligand but also the PPh3 ligands. Reaction of complexes 2, 4, and 5 with HOTf at low temperatures result in the formation of the corresponding dihydrogen complexes, [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-bpy)][OTf]2 (9), [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyen)][OTf]2 (10), and [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyan)][OTf]2 (11), respectively. These are the first examples of homobimetallic ruthenium dihydrogen complexes bearing NHC ligands. The intact nature of the H–H bond in these derivatives was established by variable temperature 1H (400 MHz) spin-lattice relaxation time (T1, ms) measurements and from the H, D coupling constants of the corresponding HD isotopomers. The H–H distances (dHH) in these complexes fall in the range 0.95–0.98 Å. Hydrogen evolution takes place upon warming the dihydrogen complexes generated at low temperatures, indicating the labile nature of the H2 ligand in these complexes. The X-ray crystal structure of [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] complex (2) has been determined.

Synthesis and characterisation of ruthenium dihydrogen complexes and their reactivity towards B–H bonds

In this paper the synthesis and characterisation of ruthenium dihydrogen complexes bearing rigid aliphatic PNP pincer-type ligands are described. As one result hydride complexes were synthesised in good to high yields by a one-pot direct hydrogenation reaction. As another finding the dihydrogen complex, stabilised with a N-Me group in the ligand frame, can be converted with dimethylamine borane into a rare σ-boron complex [RuH2(BH3)(Me-PNP)] with rapid B-N decoupling. Additionally, we present the first mass spectrometric analysis of the synthesised σ-complexes via liquid injection field desorption/ionisation technique (LIFDI-MS).

Influence of the Electronics of the Phosphine Ligands on the H−H Bond Elongation in Dihydrogen Complexes

Five new monocationic dihydrogen complexes of ruthenium of the type trans-[RuCl(eta(2)-H(2))(PP)(2)][BF(4)] (PP = bis-1,2(diarylphosphino)ethane, aryl = p-fluorobenzyl, 1a, benzyl, 2a, m-methylbenzyl, 3a, p-methylbenzyl, 4a, p-isopropylbenzyl, 5a) have been prepared by protonating the precursor hydride complexes trans-[RuCl(H)(PP)(2)] using HBF(4).OEt(2). The dihydrogen complexes are quite stable and have been isolated in the solid state. The intact nature of the H-H bond in these derivatives has been established from the short spin-lattice relaxation times (T1, ms) and observation of substantial H, D couplings in the HD isotopomers. The H-H bond distances (dHH, A) increase systematically from 0.97 to 1.03 A as the electron-donor ability of the substituent on the diphosphine ligand increases from the p-fluorobenzyl to the p-isopropylbenzyl moiety. The d(HH) in trans-[Ru(eta(2)-H(2))(Cl)((C(6)H(5)CH(2))(2)PCH(2)CH(2)P(CH(2)C(6)H(5))(2))(2)][BF(4)], 2a, was found to be 1.08(5) A by X-ray crystallography. In addition, two new 16-electron dicationic dihydrogen complexes of the type [Ru(eta(2)-H(2))(PP)(2)][OTf](2) (PP = (ArCH(2))(2)PCH(2)CH(2)P(CH(2)Ar)(2), Ar = m-CH(3)C(6)H(4-), 6a, p-CH(3)C(6)H(4)-, 7a) have also been prepared and characterized. These derivatives were found to possess elongated dihydrogen ligands.

Synthesis and Characterization of New Dicationic Dihydrogen Complexes of Ruthenium

A series of new dicationic dihydrogen complexes of the type trans‐[Ru(η2‐H2)(L)(dppm)2][X]2 (L=CH3CN, CH2˭CHCN, C6H5CN, C6H5NC, CO; X=BF4, OTf; dppm=Ph2PCH2PPh2) have been prepared by protonating the precursor hydrides using either HBF4 · Et2O or HOTf. The variable temperature spin‐lattice relaxation times (T 1, ms) and the H, D coupling constants of the η2‐HD isotopomers indicate the intact nature of the H‐H bond in these derivatives. The H‐H distances of the dihydrogen complexes bearing trans‐nitrile ligands are not significantly affected by the sterics and the electronics of the nitrile. On the other hand, the H‐H distances of the dihydrogen complexes bearing either isonitrile or CO ligand are comparable to those possessing chelating diphosphine ligands of greater bite angle. Also, the thermal stabilities of these complexes are significantly less than those bearing diphosphines of greater bite angle. The trans‐[Ru(H)(CH3CN)(dppm)2][BF4] complex has been characterized by X‐ray crystallography.

H/D Exchange at Aromatic and Heteroaromatic Hydrocarbons Using D2O as the Deuterium Source and Ruthenium Dihydrogen Complexes as the Catalyst

Getting heavy: At temperatures as low as 50 °C, D2O can serve as a cheap and readily available deuterium source for the efficient deuteration of aromatic and heteroaromatic substrates if nonclassical ruthenium hydride complexes are used as catalysts (see scheme). DFT calculations support a catalytic cycle comprising σ-bond metathesis as the key step for the exchange processes. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2007/z603677_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

H/D Exchange at Aromatic and Heteroaromatic Hydrocarbons Using D2O as the Deuterium Source and Ruthenium Dihydrogen Complexes as the Catalyst

H/D Exchange at Aromatic and Heteroaromatic Hydrocarbons Using D₂O as the Deuterium Source and Ruthenium Dihydrogen Complexes as the Catalyst

An acidity scale of phosphonium tetraphenylborate salts and ruthenium dihydrogen complexes in dichloromethane

Equilibrium constants (KDM) for reactions between acids and bases of the title compounds in CD2Cl2 (DM) have been determined by 31P and 1H NMR spectroscopy at room temperature. [HPCy3]BPh4 and [HPCy3]BF4, with pKDM assigned by literature convention to 9.7, have been used as the anchor compounds for the pKDM determinations. A continuous scale of pKDM values covering the range 9.7 to 5.7 is created with the acidic compounds [HPR3]BPh4. Those acids with pKDM greater than 6 are stable, while those with more acidic cations HPR3+ protonate BPh4– to produce R3PBPh3 and benzene. The literature pKTHF values reported for [HPBu2Ph]BPh4, [HPMePh2]BPh4, and [HPEtPh2]BPh4 are questionable because of this protonation reaction. NOE and PGSE 1H NMR techniques are used to show that [HPCy2Ph]BPh4 in DM exists as ion pairs and higher aggregates up to quadrupoles at the concentrations used in the acid–base studies. The new dihydrogen complexes [Ru(H2)Cl(PPh3)2(dach)]BF4 (dach = (1R,2R)-(–)-diaminocyclohexane) and [Ru(H2)Cl{tmeP2(NH)2}]BF4 (tmeP2(NH)2 = PPh2C6H4CH2NHCMe2CMe2NHCH2C6H4PPh2) were prepared by reaction of RuHCl(PPh3)2(dach) and RuHCl{tmeP2(NH)2} with HBF4. Their crystal structures are reported, and the pKDM values of their BPh4– salts were determined to be 8.6 and 6.9, respectively.Key words: acidity, dihydrogen complex, hydride, phosphonium, dichloromethane.

Synthesis and reactivity of hydride and dihydrogen complexes of ruthenium with tris(pyrazolyl)borate and phosphite ligands

Chloro phosphite complexes RuClTpL(PPh 3) ( 1a, 1b) [L = P(OEt) 3, PPh(OEt) 2] and RuClTp[P(OEt) 3] 2 ( 1c) [Tp = hydridotris(pyrazolyl)borate] were prepared by allowing RuClTp(PPh 3) 2 to react with an excess of phosphite. Treatment of the chloro complexes 1 with NaBH 4 in ethanol yielded the hydride RuHTpL(PPh 3) ( 2a, 2b) and RuHTp[P(OEt) 3] 2 ( 2c) derivatives. Protonation reaction of 2 with Brønsted acids was studied and led to thermally unstable (above 10 °C) dihydrogen [Ru(η 2- H 2)TpL(PPh 3)] + ( 3a, 3b) and [Ru(η 2-H 2)Tp{P(OEt) 3} 2] + ( 3c) complexes. The presence of the η 2-H 2 ligand is indicated by short T 1 min values and J HD measurements of the partially deuterated derivatives. Aquo [RuTp(H 2O)L(PPh 3)]BPh 4 ( 4), carbonyl [RuTp(CO)L(PPh 3)]BPh 4 ( 5), and nitrile [RuTp(CH 3CN)L(PPh 3)]BPh 4 ( 6) derivatives [L = P(OEt) 3] were prepared by substituting H 2 in the η 2-H 2 derivatives 3. Vinylidene [RuTp{ C C(H)R}L(PPh 3)]BPh 4 ( 7, 8) (R = Ph, t Bu) and allenylidene [RuTp( C C CR1R2)L(PPh 3)]BPh 4 ( 9– 11) complexes (R1 = R2 = Ph, R1 = Ph R2 = Me) were also prepared by allowing dihydrogen complexes 3 to react with the appropriate HC CR and HC CC(OH)R1R2 alkynes. Deprotonation of vinylidene complexes 7, 8 with NEt 3 was studied and led to acetylide Ru(C CR)TpL(PPh 3) ( 12, 13) derivatives. The trichlorostannyl Ru(SnCl 3)TpL(PPh 3) ( 14) compound was also prepared by allowing the chloro complex RuClTpL(PPh 3) to react with SnCl 2 · 2H 2O in CH 2Cl 2.

Synthesis and Characterization of the First Examples of Dicationic Dihydrogen Complexes of Iron and Ruthenium with the PF3 Ligand

AbstractNew dicationic dihydrogen complexes of the type trans‐[M(η2‐H2)(PF3)(diphosphane)2]2+ [M = Ru, diphosphane = dppm (Ph2PCH2PPh2); M = Fe, Ru, diphosphane = dppe (Ph2PCH2CH2PPh2)] have been prepared from the precursor hydrides trans‐[M(H)(PF3)(diphosphane)2]+ upon reaction with HOTf. In the case of dppm, in addition to the trans‐dihydrogen complex cis‐[Ru(η2‐H2)(PF3)(dppm)2]2+ was also obtained in the protonation reaction. The intact nature of the H−H bond in these derivatives has been established using the spin−lattice relaxation time measurements (short T1 values) and the large JH,D coupling constant of the H−D isotopomers. The H−H bond lengths and the stabilities of the dihydrogen complexes are discussed in terms of the π‐acidity of the PF3 ligand and compared with other systems possessing trans CO and CNH ligands. The trans‐[Ru(η2‐H2)(PF3)(dppe)2]2+ complex was found to be remarkably stable with respect to the loss of bound H2 for a period of about 16 h. The H−D isotopomer of this complex exhibits small temperature variations in the JH,D coupling constant. The X‐ray crystal structure of trans‐[Ru(H)(PF3)(dppm)2][BF4] has been determined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Novel catalytic hydrogenolysis of silyl enol ethers by the use of acidic ruthenium dihydrogen complexes

Treatment of 1-trimethylsilyloxy-1-cyclohexene ( 1a) in the presence of a catalytic amount of the acidic dihydrogen complex [RuCl(η 2-H 2)(dppe) 2]OTf ( 4a) [dppe=1,2-bis(diphenylphosphino)ethane, OTf=OSO 2CF 3] (10 mol.%) under 1 atm of H 2 in anhydrous ClCD 2CD 2Cl at 50 °C for 8 h afforded cyclohexanone ( 3a) and Me 3SiH in quantitative NMR yields. Silyl enol ethers such as 1-triethylsilyloxy-1-cyclohexene ( 1b), 1- t-butyldimethylsilyloxy-1-cyclohexene ( 1c), and other trimethylsilylethers ( 1d, 1e, and 1f) reacted similarly with H 2 to afford the corresponding ketones and trialkylsilanes. The direct proton transfer from H 2 to the trimethylsilyl enol ethers ( 1a and 1d– 1f) was confirmed by the experiments employing D 2 gas, where α-monodeuterated ketones ( 3a′ and 3d′– 3f′) were obtained in high yields. The enantioselective protonation of prochiral silyl enol ethers with 1 atm of H 2 by employing [RuCl(η 2-H 2)(( S)-BINAP) 2]OTf ( 4e) [BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl] and [RuCl(η 2-H 2)(( R, R)-CHIRAPHOS) 2]OTf ( 4f) [CHIRAPHOS=2,3-bis(diphenylphosphino)butane] showed that no enantioselectivity was observed in either catalytic or stoichiometric protonation reactions under various reaction conditions. The reaction of [RuHCl(dppe) 2] ( 5a) with one equivalent of Me 3SiOTf under 1 atm of H 2 produced rapidly 4a, concurrent with the formation of Me 3SiH. Based on these studies, the mechanism for this novel hydrogenolysis of silyl enol ethers is proposed which involves heterolytic cleavage of the coordinated H 2 on the ruthenium atom caused by the nucleophilic attack of the oxygen atom of enol ethers to give ketones and Me 3SiOTf, and the subsequent reaction of the resultant complex 5a with Me 3SiOTf under 1 atm of H 2 to regenerate the original dihydrogen complex 4a. On the other hand, the stoichiometric reaction of a lithium enolate 6e with one equivalent of 4e at −78 °C in CH 2Cl 2 under 1 atm of H 2 afforded 2-methyl-1-tetralone ( 3e) with 75% ee ( S) in >95% yield, together with the formation of [RuHCl(( S)-BINAP) 2] ( 5e).

Ruthenium dihydrogen complexes with wide bite angle diphosphines.

The wide bite angle diphosphines homoxantphos (10,11-dihydro-4,5,-bis(diphenylphosphino)dibenzo[b,f]oxepine), sixantphos (4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin), and thixantphos (2,8-dimethyl-4,6-bis(diphenylphosphino)phenoxathiin) were used to prepare cis[MH(2)(diphosphine)(2)] complexes (1a-f) by reaction of [Ru(cod)(cot)] (cod = cyclo-octa-1,5-diene, cot = cyclo-octa-1,3,5-triene) with 2 equiv of the diphosphine under dihydrogen pressure. The electronic properties of the thixantphos ligand were varied. Complexes 1a-f can be protonated with HBF(4) or CF(3)COOH to yield hydrido(dihydrogen) complexes cis[MH(H(2))(diphosphine)(2)](+) (2a-f), which were characterized by VT (variable temperature) NMR and T(1) measurements. These complexes show fast hydrogen atom exchange between the eta(2)-H(2) and the terminal hydride at all temperatures studied. They are thermally unstable toward dihydrogen loss yielding the cationic monohydride complexes cis[MH(diphosphine)(2)](+) (3a-f). Coordination of the eta(2)-H(2) is dominated by sigma --> d donation, and hence, the H-H distance is hardly influenced by the electronic properties of the ligands.

Chemistry of dihydrogen complexes containing only phosphorus co-ligands

A series of new dicationic dihydrogen complexes of ruthenium of the typecis-[(dppm)2Ru(η2-H2)(L)][BF4]2 (dppm = Ph2PCH2PPh2; L = phosphite) have been prepared by protonating the precursor hydride complexescis-[(dppm)2Ru(H)(L)][BF4] using HBF4•Et2O. The precursor hydride complexes have been obtained fromtrans-[(dppm)2Ru(H)(L)][BF4] (L = phosphite) via a rare acid-catalysed isomerization reaction in six coordinate species. Thetrans-[(dppm)2Ru(H)(L)][BF4] complexes (L = phosphine) upon protonation gave the isomerized derivatives, however, further addition of acid resulted in a five-coordinate species, [(dppm)2RuCl]+ presumably via an intermediate phosphine dihydrogen complex. The electronic as well as the steric properties of the co-ligands seem to strongly influence the structure-reactivity behaviour of this series of complexes.

Synthesis and spectroscopic properties of elongated ruthenium dihydrogen complexes: temperature and isotope dependence of H-H distances.

Several dihydrogen complexes of ruthenium of the form [Cp/Cp*Ru(P-P)H(2)](+) (P-P = chelating diphosphine ligand) have been prepared by reaction of the corresponding neutral chloride complexes with H(2) in the presence of NaB(ArF)(4). Treatment with D(2) or T(2) gas leads to incorporation of deuterium or tritium in the dihydrogen ligand. Measurement of the resulting H-D and H-T couplings as a function of the temperature and magnetic field gives results consistent with computational studies which predict that the H-H bond distance will increase with temperature and will be significantly shortened by isotopic substitution. The degree of the observed temperature dependence is found to be a critical function of the ancillary ligand set.

Some New Dicationic Dihydrogen Complexes of Ruthenium

A series of new dicationic dihydrogen complexes of ruthenium of the type trans-[(dppe)2Ru(η2-H2)(RCN)][BF4]2 [dppe = Ph2PCH2CH2PPh2; R = CH3, CH3CH2, CH3CH2CH2, CH2=CH, p-CH3−C6H4−CH2, C6H5, and (CH3)2N] have been prepared by the protonation reaction of the precursor hydrides, trans-[(dppe)2Ru(H)(RCN)][BF4] using HBF4·OEt2. The variable temperature spin-lattice relaxation times (T1, ms) and the H, D coupling constants of the η2-HD isotopomers indicate the intact nature of the H−H bond in these complexes. It was found that the spectroscopic and chemical properties of these derivatives are not very sensitive to the change in the trans nitrile ligand. The pKa values of the dihydrogen complexes have been determined using the equilibrium: trans-[(dppe)2Ru(H)(RCN)][BF4] + HBF4·OEt2 ⇄ trans-[(dppe)2Ru(η2-H2)(RCN)][BF4]2 + Et2O by 1H NMR spectroscopy.

Formation of ammonia in the reactions of a tungsten dinitrogen with ruthenium dihydrogen complexes under mild reaction conditions.

Treatment of cis-[W(N2)2(PMe2Ph)4] (5) with an equilibrium mixture of trans-[RuCl(eta 2-H2)(dppp)2]X (3) with pKa = 4.4 and [RuCl(dppp)2]X (4) [X = PF6, BF4, or OTf; dppp = 1,3-bis(diphenylphosphino)propane] containing 10 equiv of the Ru atom based on tungsten in benzene-dichloroethane at 55 degrees C for 24 h under 1 atm of H2 gave NH3 in 45-55% total yields based on tungsten, together with the formation of trans-[RuHCl(dppp)2] (6). Free NH3 in 9-16% yields was observed in the reaction mixture, and further NH3 in 36-45% yields was released after base distillation. Detailed studies on the reaction of 5 with numerous Ru(eta 2-H2) complexes showed that the yield of NH3 produced critically depended upon the pKa value of the employed Ru(eta 2-H2) complexes. When 5 was treated with 10 equiv of trans-[RuCl(eta 2-H2)(dppe)2]X (8) with pKa = 6.0 [X = PF6, BF4, or OTf; dppe = 1,2-bis(diphenylphosphino)ethane] under 1 atm of H2, NH3 was formed in higher yields (up to 79% total yield) compared with the reaction with an equilibrium mixture of 3 and 4. If the pKa value of a Ru(eta 2-H2) complex was increased up to about 10, the yield of NH3 was remarkably decreased. In these reactions, heterolytic cleavage of H2 seems to occur at the Ru center via nucleophilic attack of the coordinated N2 on the coordinated H2 where a proton (H+) is used for the protonation of the coordinated N2 and a hydride (H-) remains at the Ru atom. Treatment of 5, trans-[W(N2)2(PMePh2)4] (14), or trans-[M(N2)2(dppe)2] [M = Mo (1), W (2)] with Ru(eta 2-H2) complexes at room temperature led to isolation of intermediate hydrazido(2-) complexes such as trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf (19), trans-[W(OTf)(NNH2)(PMePh2)4]OTf (20), and trans-[WX(NNH2)(dppe)2]+ [X = OTf (15), F (16)]. The molecular structure of 19 was determined by X-ray analysis. Further ruthenium-assisted protonation of hydrazido(2-) intermediates such as 19 with H2 at 55 degrees C was considered to result in the formation of NH3, concurrent with the generation of W(VI) species. All of the electrons required for the reduction of N2 are provided by the zerovalent tungsten.

Influence of the Cone Angles and the π-Acceptor Properties of Phosphorus-Containing Ligands in the Chemistry of Dihydrogen Complexes of Ruthenium

A series of new dicationic dihydrogen complexes of ruthenium of the type trans-[(dppe)2Ru(η2-H2)(L‘)][BF4]2 (dppe = Ph2PCH2CH2PPh2; L‘ = PF(OMe)2, PF(OEt)2, PF(OiPr)2) have been prepared by protona...

Synthesis, Characterization, and Acidity of Ruthenium Dihydrogen Complexes with 1,4,7-Triazacyclononane, 1,4,7-Trimethyl-1,4,7-triazacyclononane, and Hydrotris(pyrazolyl)borato Ligands

Protonation of [RCnRuH(L)(L‘)]+ (RCn = 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane; L,L‘ = (PPh3)2, dppe, and CO,PPh3) produced the corresponding dicationic dihydrogen complexes [RCnRu(H2)(L)(L‘)]2+. Protonation of TpRuH(dppe) (Tp = hydrotris(pyrazolyl)borato) yielded the new monocationic dihydrogen complex [TpRu(H2)(dppe)]+. The acidity of the dihydrogen complexes [RCnRu(H2)(L)(L‘)]2+ and monocationic dihydrogen complexes [TpRu(H2)(L)(L‘)]+ (L,L‘ = dppe, (PPh3)2, CH3CN,PPh3, and CO,PPh3) has been studied. It was found that the dicationic complexes are more acidic than their monocationic Tp and Cp counterparts. [MeCnRu(H2)(CO)(PPh3)]2+ was found to be more acidic than [HCnRu(H2)(CO)(PPh3)]2+, probably due to the stronger H−H interaction in the latter complex. It is also noted that triazacyclononane and hydrotris(pyrazolyl)borato dihydrogen complexes with pseudo aqueous pKa values well above that of H3O+ can be deprotonated by H2O to form the corresponding monohydride complexes in organic/aqueous mixed solvents. It is believed that deprotonation of the dihydrogen ligands in these complexes is assisted by strong solvation of H+ by H2O.

Synthesis, Characterization, and Reactivity of Dicationic Dihydrogen Complexes of Osmium and Ruthenium.

The dicationic complexes [Os(H(2))(PR(3))(2)(bpy)(CO)](2+) [PR(3) = PPh(3), PMePh(2) (2a,b)], [Os(H(2))(PPh(3))(2)(phen)(CO)](2+) (2c), and [Ru(H(2))(PPh(3))(2)(bpy)(CO)](2+) (4) (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline) have been prepared by the protonation of the corresponding monocationic hydrides using an excess of trifluoromethanesulfonic acid. The presence of a bound dihydrogen ligand is indicated by short T(1) minimum values consistent with H-H distances of 0.92-1.04 Å. For the partially deuterated derivatives, J(HD) values of 25.1-31.0 Hz were observed. The dicationic complexes are strong acids, indicating that the bound H(2) is substantially activated toward heterolytic cleavage. The H(2) ligand is tightly bound to the metal center and does not undergo exchange with D(2) over the course of several weeks. The complex [Os(H(2))(PPh(3))(2)(bpy)(CO)](2+) (2a) has been shown to be very stable in solution at room temperature. In contrast, the ruthenium analogue, [Ru(H(2))(PPh(3))(2)(bpy)(CO)](2+) (4), decomposes in solution at room temperature but is relatively stable at temperatures less than 245 K.