[Fp(CH4)]+, [η5-CpRu(CO)2(CH4)]+, and [η5-CpOs(CO)2(CH4)]+: A Complete Set of Group 8 Metal-Methane Complexes.

Here, we report the NMR spectroscopic analysis of the group 8 transition metal methane σ-complexes [η5-CpM(CO)2(CH4)][Al(OC(CF3)3)4] (M = Fe, Ru) at -90 °C in the weakly coordinating solvent 1,1,1,3,3,3-hexafluoropropane. The iron(II)-methane complex has a 1H resonance at δ -4.27, a 13C resonance at δ -53.0, and 1JC-H = 126 Hz for the bound methane fragment. The ruthenium(II)-methane complex has a 1H resonance at δ -2.10, a 13C resonance at δ -48.8, and a 1JC-H = 126 Hz for the bound methane fragment. DFT and ab initio calculations support these experimental observations and provide further detail on the structures of the [η5-CpM(CO)2(CH4)]+ (M = Fe, Ru) complexes of the Group 8 metals. Both the iron centered methane complex, [η5-CpFe(CO)2(CH4)][Al(OC(CF3)3)4], and the ruthenium centered methane complex, [η5-CpRu(CO)2(CH4)][Al(OC(CF3)3)4], are significantly less stable than the previously reported osmium-methane complex [η5-CpOs(CO)2(CH4)][Al(OC(CF3)3)4].

Binding methane to a metal centre.

The σ-alkane complexes of transition metals, which contain an essentially intact alkane molecule weakly bound to the metal, have been well established as crucial intermediates in the activation of the strong C-H σ-bonds found in alkanes. Methane, the simplest alkane, binds even more weakly than larger alkanes. Here we report an example of a long-lived methane complex formed by directly binding methane as an incoming ligand to a reactive organometallic complex. Photo-ejection of carbon monoxide from a cationic osmium-carbonyl complex dissolved in an inert hydrofluorocarbon solvent saturated with methane at -90 °C affords an osmium(II) complex, [η5-CpOs(CO)2(CH4)]+, containing methane bound to the metal centre. Nuclear magnetic resonance (NMR) spectroscopy confirms the identity of the σ-methane complex and shows that the four protons of the metal-bound methane are in rapid exchange with each other. The methane ligand has a characteristically shielded 1H NMR resonance (δ -2.16), and the highly shielded carbon resonance (δ -56.3) shows coupling to the four attached protons (1JC-H = 127 Hz). The methane complex has an effective half-life of about 13 hours at -90 °C.

Observation and Analysis of Large Dynamic Frequency Shifts in the 1H NMR Signals of H-D in Deuterium-Substituted Dihydrogen Complexes.

A dynamic frequency shift (DFS) in the 1H NMR resonance of the HD unit of the deuterium-labeled dihydrogen complex [Ru(D)(η2-HD)(P3P3iPr)][BPh4] [P3P3iPr = P(CH2CH2CH2PiPr2)3] has been observed and analyzed. To the best of our knowledge, this is the first demonstration of the DFS for a H-D pair. The observed DFS of the center line relative to the outside lines in the H-D triplet is large, up to ∼11 Hz, because of the short H-D distance encountered in dihydrogen complexes. Analysis of the DFS as a function of the temperature, combined with density-functional-theory-calculated or least-squares-fitted electric-field-gradient (EFG) parameters, suggests an H-D bond length of 0.92-0.94 Å. A DFS was also observed in trans-[Fe(η2-HD)(H)(dppe)2]+, suggesting the DFS will be commonplace in dihydrogen complexes if appropriate conditions are employed for its observation. Possible applications of the DFS as a probe of the bond lengths, EFGs, and molecular motion, particularly in inorganic systems, are discussed.

Dinuclear acetylide-bridged ruthenium(ii) complexes with rigid non-aromatic spacers.

Rigid dinuclear ruthenium complexes containing non-aromatic caged and polycyclic spacer groups were synthesised and characterised. The complexes, [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(µ-C[triple bond, length as m-dash]C-X-C[triple bond, length as m-dash]C)], where X = 1,4-bicyclo[2.2.2]octane (C8H12) or 1,12-p-carborane (p-C2B10H10), were formed via the metathesis of terminal organic bisacetylenes with the methylruthenium complex, [trans-Ru(dmpe)2(CH3)(C[triple bond, length as m-dash]CtBu)], under mild conditions. Electrochemical studies demonstrated electronic interactions across the non-aromatic caged and polycyclic spacers was less than in the analogous complex with an aromatic spacer group, [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(µ-C[triple bond, length as m-dash]C-p-C6H4-C[triple bond, length as m-dash]C)]. Mononuclear complexes, [trans-Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)(C[triple bond, length as m-dash]C-X-C[triple bond, length as m-dash]CH)], were also synthesised. [trans-Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)(C[triple bond, length as m-dash]C-C8H12-C[triple bond, length as m-dash]CH)] and [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(µ-C[triple bond, length as m-dash]C-p-C2B10H10-C[triple bond, length as m-dash]C)] were structurally characterised by X-ray crystallography.

Reduction of Dinitrogen to Ammonia and Hydrazine on Low-Valent Ruthenium Complexes.

The ruthenium(0) dinitrogen complexes [Ru(N2)(PP3R)] [PP3R = P(CH2CH2PR2)3; R = iPr or Cy] react with triflic acid and other strong acids to afford mixtures of ammonia and hydrazine. In this reaction, Ru(0) is oxidized to Ru(II), and depending on the solvent, Ru(II) benzene or triflate complexes are isolated and characterized from the reactions with triflic acid as the final metal-containing products from the reaction. The Ru(II) products are isolated and reduced back to Ru(0) dinitrogen complexes providing a cycle for the reduction of coordinated dinitrogen.

Nitrogen fixation revisited on iron(0) dinitrogen phosphine complexes.

A reinvestigation of the treatment of [Fe(N2)(PP)2] (PP = depe, dmpe) with acid revealed no ammonium formation. Instead, rapid protonation at the metal center to give hydride complexes was observed. Treatment of [Fe(N2)(dmpe)2] with methylating agents such as methyl triflate or methyl tosylate resulted in methylation of the metal center to afford [FeMe(N2)(dmpe)2](+). Treatment of [Fe(N2)(dmpe)2] with trimethylsilyl triflate, however, resulted in reaction at dinitrogen affording NH4(+) on subsequent treatment with acid. The side-on bound hydrazine complex [Fe(N2H4)(dmpe)2](2+) and bis(ammonia) complex [Fe(NH3)2(dmpe)2](2+) were identified by (15)N NMR spectroscopy as other species formed in the reaction mixture.

Ruthenium hydrides containing the superhindered polydentate polyphosphine ligand P(CH2CH2P(t)Bu2)3.

The complex RuH2(N2)(P(2)P3(tBu)) (1) containing the extremely bulky PP3-type ligand P(2)P3(tBu) = P(CH2CH2P(t)Bu2)3 was synthesized by reduction of RuCl2(P(2)P3(tBu)) (2) with Na/NH3 under a N2 atmosphere. Like other complexes containing the P(2)P3(tBu) ligand, only three of the four donor phosphines are coordinated, and one of the phosphines remains as a dangling pendant phosphine. Reduction of RuCl2(P(2)P3(tBu)) (2) with a range of the more usual hydride reducing agents afforded the previously unknown ruthenium hydride complexes RuHCl(P(2)P3(tBu)) (3), RuH(BH4)(P(2)P3(tBu)) (6), RuH(AlH4)(P(2)P3(tBu)) (7), and the ruthenium(II) trihydride K[Ru(H)3(P(2)P3(tBu))] (8). The ruthenium tetrahydride containing a coordinated H2 ligand RuH2(H2)(P(2)P3(tBu)) (10) was synthesized by exchange of N2 in 1 by H2. Complexes 1, 3, 6, 7, and 8 were characterized by crystallography and multinuclear NMR spectroscopy.

Low oxidation state iron(0), iron(I), and ruthenium(0) dinitrogen complexes with a very bulky neutral phosphine ligand.

The synthesis of a series of iron and ruthenium complexes with the ligand P(2)P3(Cy), P(CH2CH2PCy2)3 is described. The iron(0) and ruthenium(0) complexes Fe(N2)(P(2)P3(Cy)) (1) and Ru(N2)(P(2)P3(Cy)) (2) were synthesized by treatment of [FeCl(P(2)P3(Cy))](+) and [RuCl(P(2)P3(Cy))](+) with an excess of potassium graphite under a nitrogen atmosphere. The Fe(I) and Ru(I) species [Fe(N2)(P(2)P3(Cy))](+) (3) and RuCl(P(2)P3(Cy)) (4) were synthesized by treatment of [FeCl(P(2)P3(Cy))](+) and [RuCl(P(2)P3(Cy))](+) with 1 equiv of potassium graphite under a nitrogen atmosphere. The cationic dinitrogen species [Fe(N2)H(P(2)P3(Cy))](+) (6) and [Ru(N2)H(P(2)P3(Cy))](+) (7) were formed by treatment of 1 and 3, respectively, with 1 equiv of a weak organic acid. The iron(II) complex Fe(H)2(P(2)P3(Cy)) (5) was also synthesized and characterized. Complexes [RuCl(P(2)P3(Cy))][BPh4], 1, 2, 3[BPh4], 4, 5, 6[BF4], and 7[BF4] were characterized by X-ray crystallography. The Fe(I) and Ru(I) complexes 3 and 4 were characterized by electron paramagnetic resonance (EPR) spectroscopy, and the Fe(I) complex has an EPR spectrum typical of a metal-centered radical.

Base-induced dehydrogenation of ruthenium hydrazine complexes.

Treatment of [RuCl(PP(3)(iPr))](+)Cl(-) (PP(3)(iPr) = P(CH(2)CH(2)P(i)Pr(2))(3)) with hydrazine, phenylhydrazine, and methylhydrazine afforded side-on bound hydrazine complexes [RuCl(η(2)-H(2)N-NH(2))(η(3)-PP(3)(iPr))](+), [RuCl(η(2)-H(2)N-NHPh)(η(3)-PP(3)(iPr))](+), and [RuCl(η(2)-H(2)N-NHMe)(η(3)-PP(3)(iPr))](+). The analogous reactions of [RuCl(2)(PP(3)(Ph))] (PP(3)(Ph) = P(CH(2)CH(2)PPh(2))(3)) with hydrazine, phenylhydrazine, and methylhydrazine afforded end-on bound hydrazine complexes [RuCl(η(1)-H(2)N-NH(2))(PP(3)(Ph))](+), [RuCl(η(1)-H(2)N-NHPh)(PP(3)(Ph))](+), and [RuCl(η(1)-H(2)N-NHMe)(PP(3)(Ph))](+). Treatment of parent hydrazine complex [RuCl(N(2)H(4))(PP(3)(iPr))](+) with strong base afforded the dinitrogen and dihydride complexes [Ru(N(2))(PP(3)(iPr))] and [RuH(2)(PP(3)(iPr))]. Treatment of phenylhydrazine complex [RuCl(NH(2)NHPh)(PP(3)(iPr))](+) with strong base afforded the hydrido ruthenaindazole complex [RuH(η(2)-NH═NC(6)H(4))(η(3)-PP(3)(iPr))] while similar treatment of methylhydrazine complex [RuCl(NH(2)NHMe)(PP(3)(iPr))](+) afforded the hydrido methylenehydrazide complex [RuH(NHN═CH(2))(PP(3)(iPr))]. Treatment of the hydrazine complexes [RuCl(NH(2)NHR)(PP(3)(Ph))](+) (R = H, Ph, Me) with strong base afforded the dinitrogen complex [Ru(N(2))(PP(3)(Ph))].

Side-on bound complexes of phenyl- and methyl-diazene.

Treatment of trans-[FeCl(2)(dmpe)(2)] with phenylhydrazine and 1 equiv of base afforded the side-on bound phenylhydrazido complex cis-[Fe(η(2)-NH(2)NPh)(dmpe)(2)](+). Further deprotonation of the phenylhydrazido complex afforded the side-on bound phenyldiazene complex cis-[Fe(η(2)-HN═NPh)(dmpe)(2)] as a mixture of diastereomers. Treatment of cis-[RuCl(2)(dmpe)(2)] with phenylhydrazine or methylhydrazine afforded the end-on bound phenylhydrazine or methylhydrazine complexes cis-[RuCl(η(1)-NH(2)NHR)(dmpe)(2)](+) (R = Ph, Me). Treatment of the substituted hydrazine complexes with base afforded the side-on bound phenylhydrazido complex cis-[Ru(η(2)-NH(2)NPh)(dmpe)(2)](+) as well as the phenyldiazene and methyldiazene complexes cis-[Ru(η(2)-HN═NR)(dmpe)(2)] (R = Ph, Me). cis-[RuCl(η(1)-NH(2)NHR)(dmpe)(2)](+) (R = Ph, Me), cis-[M(η(2)-NH(2)NPh)(dmpe)(2)](+) (M = Fe, Ru) and cis-[Ru(η(2)-HN═NPh)(dmpe)(2)] were characterized structurally by X-ray crystallography. cis-[Ru(η(2)-HN═NPh)(dmpe)(2)] is the first side-on bound phenyldiazene complex to be structurally characterized. In the structure of cis-[Ru(η(2)-HN═NPh)(dmpe)(2)], the geometry of the coordinated diazene fragment is significantly nonplanar (CNNH angle 137°) suggesting that the complex is probably better described as a Ru(II) metallodiaziridine than a Ru(0) diazene π-complex.

New superhindered polydentate polyphosphine ligands P(CH2CH2P(t)Bu2)3, PhP(CH2CH2P(t)Bu2)2, P(CH2CH2CH2P(t)Bu2)3, and their ruthenium(II) chloride complexes.

The synthesis and characterization of the extremely hindered phosphine ligands, P(CH(2)CH(2)P(t)Bu(2))(3) (P(2)P(3)(tBu), 1), PhP(CH(2)CH(2)P(t)Bu(2))(2) (PhP(2)P(2)(tBu), 2), and P(CH(2)CH(2)CH(2)P(t)Bu(2))(3) (P(3)P(3)(tBu), 3) are reported, along with the synthesis and characterization of ruthenium chloro complexes RuCl(2)(P(2)P(3)(tBu)) (4), RuCl(2)(PhP(2)P(2)(tBu)) (5), and RuCl(2)(P(3)P(3)(tBu)) (6). The bulky P(2)P(3)(tBu) (1) and P(3)P(3)(tBu) (3) ligands are the most sterically encumbered PP(3)-type ligands so far synthesized, and in all cases, only three phosphorus donors are able to bind to the metal center. Complexes RuCl(2)(PhP(2)P(2)(tBu)) (5) and RuCl(2)(P(3)P(3)(tBu)) (6) were characterized by crystallography. Low temperature solution and solid state (31)P{(1)H} NMR were used to demonstrate that the structure of RuCl(2)(P(2)P(3)(tBu)) (4) is probably analogous to that of RuCl(2)(PhP(2)P(2)(tBu)) (5) which had been structurally characterized.

Ruthenium hydride complexes of the hindered phosphine ligand tris(3-diisopropylphosphinopropyl)phosphine.

The synthesis and characterization of the novel hindered tripodal phosphine ligand P(CH(2)CH(2)CH(2)P(i)Pr(2))(3) (P(3)P(3)(iPr)) (1) are reported, along with the synthesis and characterization of ruthenium chloro and hydrido complexes of 1. Complexes [RuCl(P(3)P(3)(i)Pr)][BPh(4)] (2[BPh(4)]), RuH(2)(P(3)P(3)(i)Pr) (3), and [Ru(H(2))(H)(P(3)P(3)(iPr))][BPh(4)] (4[BPh(4)]) were characterized by crystallography. Complex 2 is fluxional in solution, and low-temperature NMR spectroscopy of the complex correlates well with two dynamic processes, an exchange between stereoisomers and a faster turnstile-type exchange within one of the stereoisomers.

Synthesis and characterization of iron(II) and ruthenium(II) hydrido hydrazine complexes.

Treatment of trans-[MHCl(dmpe)(2)] (M = Fe, Ru) with hydrazine afforded the hydrido hydrazine complexes cis- and trans-[MH(N(2)H(4))(dmpe)(2)](+) which have been characterized by NMR spectroscopy ((1)H, (31)P, and (15)N). Both cis and trans isomers of the Fe complex and the trans isomer of the Ru complex were characterized by X-ray crystallography. Reactions with acid and base afforded a range of N(2)H(x) complexes, including several unstable hydrido hydrazido complexes.

Mixed-valence dinitrogen-bridged Fe(0)/Fe(II) complex.

The reactions of a dinitrogen-bridged Fe(II)/Fe(II) complex [(FeH(PP(3)))(2)(µ-N(2))](2+) (3) (PP(3) = P(CH(2)CH(2)PMe(2))(3)) with base were investigated using (15)N labeling techniques to enhance characterization. In the presence of base, 3 is initially deprotonated to the Fe(II)/Fe(0) dinitrogen-bridged complex [(FeH(PP(3)))(µ-N(2))(Fe(PP(3)))](+) (4) and then to the symmetrical Fe(0)/Fe(0) dinitrogen-bridged complex (Fe(PP(3)))(2)(µ-N(2)) (5). [(FeH(PP(3)))(µ-N(2))(Fe(PP(3)))](+) (4) exhibits unusual long-range (31)P-(31)P NMR coupling through the bridging dinitrogen ligand from the phosphines at the Fe(0) center and those at the Fe(II) center. Reaction of 4 with base under an atmosphere of argon resulted in the known dinitrogen Fe(0) complex Fe(N(2))(PP(3)) (6) and a solvent C-H activation product. Complexes 3, 4, and 5 were fully characterized by multinuclear NMR spectroscopy, and complexes 3 and 4 by X-ray crystallography.

Side-on bound diazene and hydrazine complexes of ruthenium.

The reaction of cis-[RuCl(2)(PP)(2)] (PP = depe, dmpe) with hydrazine afforded end-on bound ruthenium(II) hydrazine complexes. Treatment of the hydrazine complexes with strong base afforded the side-on bound ruthenium(0) diazene complexes cis-[Ru(eta(2)-NH=NH)(PP)(2)]. Treatment of cis-[Ru(eta(2)-NH=NH)(depe)(2)] with weak acid under chloride-free conditions afforded the side-on bound hydrazine complex cis-[Ru(eta(2)-N(2)H(4))(depe)(2)](2+). These are the first reported side-on bound diazene and hydrazine complexes of ruthenium, and they have been characterized by NMR spectroscopy ((1)H, (31)P, (15)N) and by X-ray crystallography. The interconversion between the ruthenium diazene and the ruthenium hydrazine by acid-base treatment was reversible.

Rhodium(I) and iridium(I) complexes containing bidentate phosphine-imidazolyl donor ligands as catalysts for the hydroamination and hydrothiolation of alkynes.

A series of novel cationic and neutral rhodium and iridium complexes containing bidentate phosphine-imidazolyl donor ligands of the general formulae [M(ImP)(COD)]BPh(4) (M = Rh, ImP = ImP2, 3; ImP1a, 4a; ImP1b, 4b and M = Ir, ImP = ImP2, 5; ImP1a, 6a and ImP1b, 6b), [Ir(ImP)(CO)(2)]BPh(4) (ImP = ImP2, 7; ImP1a, 8a and ImP1b, 8b), [Rh(ImP1b)(CO)(2)]BPh(4) (10b) and [M(ImP)(CO)Cl] (M = Rh, ImP = ImP2, 11; ImP1b,12 and M = Ir, ImP = ImP2, 13; ImP1b, 14 ) where COD = 1,5-cyclooctadiene, ImP2 = 1-methyl-2-[(2-(diphenylphosphino)ethyl]imidazole, 1; ImP1a = 1-methyl-2-[(diphenylphosphino)methyl]imidazole, 2a and ImP1b = 2-[(diisopropylphosphino)methyl]-1-methylimidazole, 2b were successfully synthesised. The solid state structures of 3, 6a, 11 and 12 were determined by single crystal X-ray diffraction analysis. A number of these complexes are effective as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methyl-1-pyrroline. The cationic complexes are significantly more effective than analogous neutral complexes. The cationic iridium complex 8b , containing the phosphine-imidazolyl ligand with the bulky isopropyl groups on the phosphorus donor, is more efficient than analogous complexes with the phenyl substituents on the phosphorus donor atom, 7 and 8a. The complexes 7-8b are also moderately effective in catalysing the addition of thiophenol to a range of terminal alkynes. In contrast to the hydroamination reaction, placement of the isopropyl group on the phosphorus donor leads to a decrease in the reactivity of the resulting metal complexes as catalysts for the hydrothiolation reaction.

Iron(0) and ruthenium(0) complexes of dinitrogen.

The synthesis of a series of iron and ruthenium complexes with the new ligand PP(i)(3) (1) P(CH(2)CH(2)P(i)Pr(2))(3) is described. The iron(0) and ruthenium(0) dinitrogen complexes Fe(N(2))(PP(i)(3)) (4) and Ru(N(2))(PP(i)(3)) (5) were synthesized by treatment of the iron(II) and ruthenium(II) cationic species [FeCl(PP(i)(3))](+) (2) and [RuCl(PP(i)(3))](+) (3) with potassium graphite under a nitrogen atmosphere. The cationic dinitrogen species [Fe(N(2))H(PP(i)(3))](+) (6) and [Ru(N(2))H(PP(i)(3))](+) (7) were prepared by treatment of 4 and 5, respectively, with 1 equiv of a weak organic acid. Complexes 2.[BPh(4)], 3.[BPh(4)], 4, 5, and 6.[BF(4)] were characterized by X-ray crystallography. The structural characterization of 5 is the first report for a ruthenium(0) dinitrogen complex.

Base-mediated conversion of hydrazine to diazene and dinitrogen at an iron center.

The treatment of the hydrazine complex cis-[Fe(N(2)H(4))(dmpe)(2)](2+) with base afforded the diazene complex cis-[Fe(N(2)H(2))(dmpe)(2)]. This reaction is reversed by the treatment of the diazene complex with a mild acid, while treatment of the hydrazine complex with a mixture of KOBu(t) and Bu(t)Li afforded the dinitrogen complex [Fe(N(2))(dmpe)(2)].

The first side-on bound metal complex of diazene, HN[double bond]NH.

The side-on bound metal complex of diazene cis-[Fe(NH[double bond]NH)(dmpe)(2)] was synthesised by reaction of [Fe(dmpe)(2)Cl(2)] with hydrazine in the presence of potassium graphite and characterised by (15)N NMR spectroscopy and X-ray crystallography.