T. Adrian George

Reactions of coordinated dinitrogen. 16. New mono-dinitrogen complexes of molybdenum that produce ammonia and hydrazine

Preparation des complexes Mo(N 2 )(triphos)L 2 (L 2 =2 PPhMe 2 ; Me 2 PCH 2 PMe 2 , 1,2-(Me 2 As) 2 C 6 H 4 , Ph 2 PCH 2 PPh 2 , Ph 2 PCH 2 CH 2 PPh 2 ). Les reactions avec HBr dans CH 2 Cl 2 donnent NH 3 , hydrazine et N 2

The addition of carbon monoxide to certain binuclear organometalllic compounds of iron, molybdenum and tungsten containing bridging thiolate ligands. The formation fo mononuclear species

Abstract The reaction of carbon monoxide wiht [Fe(CO)(C 5 H 5 (RS)] 2 and [M9CO) 2 (C 5 H 5 )(RS)] 2 (where M = Mo or W, and R = p -CH 3 C 6 H 4 ) in tetrahydrofuran results in (a) the cleavage of the bridging sulfur  metal bond, (b) the uptake of carbon monoxide, and (c) the formation of the mononuclear species; Fe(CO) 2 (C 5 H 5 )(RS) and M(CO) 3 (C 5 H 5 (RS). The relative stabilities of the two isomers of [Fe(CO)(C 5 H 5 (RS)] 2 are discussed.

The protonation of alkyldiazenido derivatives of molybdenum. The crystal and molecular structure of the benzene solvate of iodo-N-octylhydrazidobis[1,2-bis(diphenylphosphino)ethane] molybdenum iodide

Abstract The monoprotonation of MoI(N 2 C 8 H 17 )(dppe) 2 (I, where dppe = 1,2-bis(diphenylphosphino)ethane) by anhydrous HX (where X = Cl, Br, and I) to give [MoI(NNHC 8 H 17 )(dppe) 2 ] X is reported. The crystal and molecular structure of the benzene solvate of [MoI(NNHC 8 H 17 )(dppe) 2 ] I has been determined and the unique hydrogen atom located.

Reactions of coordinated dinitrogen—XXII. Synthesis, characterization and reactions of hydrazido(2-) complexes of molybdenum. Crystal structures of two hydrazido(2-) complexes ☆

Abstract The reactions of anhydrous HX (X = Br, Cl) with trans-Mo(N2)2(triphos) (PPh3) (1) where triphos = PhP(CH2CH2PPh2)2, yield [MoX(NNH2)(triphos)(PPh3)]X as a mixture of isomers: 1A(X) and 1B(X). In solution, PPh3 dissociates rapidly from the B isomer. Addition of PPh3 to a mixture of 1A(X) and 1B(X) enabled the separation of the isomers by fractional crystallization. Addition of PPh2Me to a mixture of 1A(X) and 1B(X) led to the isolation of 1A(X) and [MoX(NNH2)(triphos)(PPh2Me)]X [2B(X)]. Amber 1A(Cl) crystallizes with one molecule of toluene in the monoclinic space group P21 with a = 13.714(2), b = 13.924(2), c = 14.279(3) A, β = 102.44(1)°, and Z = 2. Olive-green 2B(Cl) crystallizes with two molecules of salvation; one each of pentane and toluene, in the triclinic space group P 1 with a = 12.922(2), b = 13.552(3), c = 18.067(4) A, α = 106.04(1), β = 107.65(1), γ = 97.22(1)°, and Z = 2. Loss of PPh3 from 1B(X) is proposed to be due to steric factors. Yields of ammonia and hydrazine formed from all the nitrogen hydride complexes are summarized.

Reactions of dinitrogen and hydrazido(2-) complexes of molybdenum containing a tridentate ligand : the effect of adding reducing agents upon ammonia formation

Abstract The reaction of HBr with trans-[Mo(N2)2(dppee)(PR3)] (1), where dppee = O(CH2CH2PPh2)2 and PR3 = PPh3, PPh2Me, in CH2Cl2 yields a hydrazido(2-) complex which reacts further to form ammonia and hydrazine. During this reaction an intermediate can be isolated which upon hydrolysis produces hydrazine in almost quantitative yield. Addition of SnCl2 (4 mol), a two-electron reducing agent, to the reaction mixture causes a doubling of the ammonia yield and concomitant decrease in the yield of N2. The relationship to the electrochemical two-electron reduction of two different hydrazido(2-) complexes will be discussed.

Synthesis and characterization of arene, mono- and dihydrido-arene, monohydrido-cyclopentadienyl, and phosphite complexes of molybdenum containing the tridentate ligand PhP(CH2CH2PPh2)2

Abstract The reduction of [MoCl3(TRI)], where TRI=PhP(CH2CH2PPh2)2, with sodium amalgam in benzene, toluene or anisole resulted in the formation of the corresponding [Mo(ν6-arene)(TRI)] complex. Each complex displayed a reversible one-electron oxidation in the cyclic voltammogram at ∼−1.0 V versus the ferrocenium/ferrocene couple at 0.0 V. corresponding to the oxidation of Mo(0) to Mo(1+). A second pseudo-reversible oxidation occurred at ∼0.7 V more positive. Monoprotonation of the arene complexes with CF3COOH in THF resulted in the isolation of [Mo(H)(ν6-arene)[TRI)] [CF3COO] (δ(MoH) ∼ −6 ppm). In neat CF3COOH or HBF4, evidence of diprotonation of the arene complexes was observed in the 1H NMR spectra. Upon work-up, only the monoprotonated product was isolated. [Mo(TRI)(P(OMe)3)] was formed by the reduction of [MoCl3(TRI)] in the presence of a small excess of P(OMe)3. Attempts to prepare [Mo(TRI)(PMe)3)3] by a similar method resulted in a product that readily absorbed N2 to form fac-[Mo(N2)(TRI)(PMe3)2]. Yellow [Mo(H) (ν5-C5H5) (TRI)] was formed by (i) the reduction of [MoCl3(TRI)] with sodium amalgam in the presence of cyclopentadiene, or (ii) heating fac-[Mo(N2)(TRI)(PMe3)2] with cyclopentadiene in heptane, or (iii) heating trans-[Mo(N2)2(TRI)(PPh3)] with cyclopentadiene in THF.

Synthesis of phenyldiazenido, phenylhydrazido and diorganohydrazido complexes of molybdenum and tungsten and their reactions with acids: A comparison with analogous unsubstituted hydrazido (NNH2) complexes. The crystal structure of [WCl2(NN(H)Ph)(PMe2Ph)3]

Abstract The phenyldiazenido complexes [MCl(NNPh)(PMe 2 Ph) 4 ] (M = Mo,W) and phenyl- and diorganohydrazido(2-) complexes [WCl 2 (NN(H)Ph)(PMe 2 Ph) 3 ], [MCl 2 (NNRR′)(PMe 2 Ph) 3 ]] (M = Mo, W ; R = R′ = Me, R = R′ = Ph ; M = W, R = Me, R′ = Ph), [MCl 2 (NNPh 2 )(dppe)(PMe 2 Ph)] (M = Mo,W; dppe = Ph 2 PCH 2 CH 2 PPh 2 ), [MCl(NNPh 2 )(dppe) 2 ]Cl (M = Mo,W), and [WCl(NN(Me)Ph)(dppe) 2 ]Cl were synthesized, characterized and their reactions with acids studied. These complexes were prepared in a series of reactions starting with WCl 6 or (MoCl 5 ) 2 involving (i) introduction of the organohydrazido(2 -) group (NNRR′) using the corresponding hydrazine (R = R′ = Me) or hydrazine hydrochloride (R = R′ = Ph; R = Ph,R′ = H or Me), and (ii) incorporation of phosphine ligands under reducing conditions. The particular product formed in the last step depended upon the reduction time. In almost all cases reaction of the complexes with acid (1 M HCl in Et 2 O or H 2 SO 4 in MeOH) resulted in the formation of some amine and a correspondingly smaller amount of ammonia. For example, the yields of aniline and ammonia when [MCl(NNPh)(PMe 2 Ph) 4 ]Cl reacted with H 2 SO 4 in MeOH were ca 0.2 mol and ca 0.1 mol per mol of W, and 0.70 mol and 0.65 mol per mol of Mo, respectively. A comparison of acid reactions of organodiazenido and organohydrazido(2- ) is made with those of unsubstituted hydrazido(2 -) complexes prepared from coordinated dinitrogen. The crystal structure of reddish-brown [WCl 2 (NN(H)Ph)(PMe 2 Ph) 3 ] revealed a distorted octahedral complex in which the hydrazido(2 -) moiety is trans to a chlorine atom and the hydrazido(2 -) phenyl group is coplanar with the plane containing W, N, N and C(Ph) atoms. The second chlorine atom, cis to the hydrazido(2 -) ligand, has a close intermolecular contact (2.62 A) with the hydrazido(2 -) hydrogen atom of a neighbouring molecule and close intramolecular contact (2.76 A) with the endo o -phenyl hydrogen atom of the hydrazido(2 -) ligand. Comparison of structural data with those for [WCl 2 (NNR 2 )(PMe 2 Ph) 3 ] (R 2 = Me 2 or Ph 2 ) indicates significant differences in W-N(1) and W-Cl( trans ) distances between the dimethyl-, and the phenyl- and diphenyl-hydrazido(2 -) complexes, respectively.

ELECTROCHEMICAL CLEAVAGE OF THE NITROGEN-NITROGEN BOND IN HYDRAZIDO(2-) COMPLEXES OF MOLYBDENUM : FORMATION OF AMMONIA

Abstract The controlled potential electrolysis of a series of hydrazido(2-) complexes of molybdenum, [MoX(NNH2)(TR1)(PPh3)]Y[TR1 = PhP(CH2CH2PPh2)2; 1, X = Y = Br; 2, X = Y = Cl; 3, X = F, Y = BF4] in tetrahydrofuran (thf) at a mercury-pool electrode with 85% phosphoric acid as the proton source generates ammonia. The yield of ammonia is quantitative for 2. For 1 and 3 the yields are 0.32 and 0.24 mol of ammonia per mole of complex, respectively. These data are compared with yields of ammonia obtained from non-electrolysis methods.

Electrochemical carbon–carbon coupling of diazomethane ligands

Carbon–Carbon bond formation via electrochemical coupling of diazoalkane ligands has been investigated; one-electron reduction of trans-[WF(N2CH2)L2]+ in a MeCN electrolyte at a Hg pool cathode affords [L2FW{N2CH2CH2N2}WFL2] in moderate yield (L = Ph2PCH2CH2PPh2).

New mono-dinitrogen complexes of molybdenum

Abstract The synthesis is reported of a mono-dinitrogen complex of molybdenum, Mo(N2)(triphos)(PMe2Ph)2, where triphos = PhP(CH2CH2PPh2)2, that yields significant yields of ammonia and hydrazine when treated with HCl or HBr in organic solvents. Generally, increasing the temperature increases the combined yield of ammonia and hydrazine.