Azo Complexes of Osmium(II): Preparation and Reactivity of Organic Azide and Hydrazine Derivatives

Iron(II) Mediated Deazotation of Benzyl Azide: Trapping and Subsequent Transformations of the Benzaldimine Fragment

The mono-benzaldimine (HN═CHPh) complex [(^tBupyrpyrr₂)Fe(HN═CHPh)] (1-HN═CHPh) has been prepared by reaction of [(^tBupyrpyrr₂)Fe(OEt₂)] (1-OEt₂) (^tBupyrpyrr₂ = 2,6-bis(3,5-di-tert-butyl-pyrrolyl)pyridine) with one equivalent of benzyl azide. Compound 1-HN═CHPh retains the cis-divacant octahedral coordination geometry akin to 1, as established by single crystal X-ray diffraction study. A bis-HN═CHPh complex [(^tBupyrpyrr₂)Fe(HN═CHPh)₂] (2) was also prepared by the addition of two equivalents of benzyl azide to 1, and its molecular structure exhibits the two HN═CHPh ligands coordinated trans to each other, thereby forming a square pyramidal coordination geometry at the Fe^II center. Reaction of 1 with excess benzyl azide yields [(^tBupyrpyrr₂)Fe(HN═CHPh)₂·PhCHNCH(NH₂)Ph] (2-PhCHNCH(NH₂)Ph), which contains an unstable benzylideneamino phenyl methanamine fragment, effectively hydrogen bonded to 2. Thermolysis of 2 or 2-PhCHNCH(NH₂)Ph releases the HN═CHPh self-coupling products hydrobenzamide (A), N-benzylidine benzylamine (B), and benzonitrile (C). Under catalytic conditions, free HN═CHPh (cis/trans-HN═CHPh mixture) is produced using 2.5 mol % of 1 in 90% spectroscopic yield. These studies provide a clearer understanding for the conversion of the HN═CHPh in 2 or 2-PhCHNCH(NH₂)Ph to the C-C and C-N coupled products. Reduction of 1-HN═CHPh with KC₈ yields the reductively coupled benzylamide complex [K(OEt₂)]₂[(^tBupyrpyrr₂)₂Fe₂(μ₂-NHCHPhCHPhNH)] (3) as the result of a new C-C bond formed between two radical benzylamide fragments.

Facile synthesis of air-stable heterobimetallic osmium-silver hydride complexes

The synthesis and characterization of air-stable heterobimetallic Os-Ag hydrides are described. All of the new heterobimetallic Os-Ag hydrides are neutral, and the in situ generated and presynthesized cis-[Os](H)-CC-R units in these frameworks act as organometallic bidentate chelating ligands coordinating with the AgPPh₃ cation, which makes these complexes more stable. Our results provide a new synthetic route for the construction of stable heterobimetallic complexes.

Pentamethylcyclopentadienyl half-sandwich hydrazine complexes of ruthenium: preparation and reactivity

The preparation and selective oxidation of hydrazine complexes of ruthenium stabilised by a pentamethylcyclopentadienyl fragment are described. The formation of the sandwich complex [Ru(η⁵-C₅Me₅)(η⁶-C₆H₆)]BPh₄ through the oxidation of coordinate phenylhydrazine is also reported.

Preparation and reactivity of half-sandwich organic azide complexes of osmium

Organic azide complexes [Os(η5-C5H5)(κ1-N3R)(PPh3){P(OR1)3}]BPh4 (1, 2) [R = CH2C6H5 (a), CH2C6H4-4-CH3 (b), CH(CH3)C6H5 (c), C6H5 (d); R1 = Me (1), Et (2)] were prepared by allowing bromo-compounds [OsBr(η5-C5H5)(PPh3){P(OR1)3}] to react first with AgOTf and then with an excess of azide in toluene. Benzylazide complexes reacted in solution leading to imine derivatives [Os(η5-C5H5){κ1-NH[double bond, length as m-dash]C(R2)Ar}(PPh3){P(OR1)3}]BPh4 (3, 4) [R2 = H (a, b), CH3 (c); Ar = C6H5, C6H4-4-CH3; R1 = Me (3), Et (4)]. Phenylazide, on the other hand, reacted in solution affording the dinuclear dinitrogen complex [{Os(η5-C5H5)(PPh3)[P(OMe)3]}2(μ-N2)](BPh4)2 (5). Depending on the nature of the R substituent, the reaction of the p-cymene complex [OsCl2(η6-p-cymene)(PPh3){P(OEt)3}] with RN3 yielded imine [OsCl(η6-p-cymene){κ1-NH[double bond, length as m-dash]C(H)Ar}{P(OEt)3}]BPh4 (6) (Ar = C6H4-4-CH3) and amine derivatives [OsCl(η6-p-cymene)(κ1-NH2C6H5){P(OEt)3}]BPh4 (7). The complexes were characterised spectroscopically (IR, 1H, 31P, 15N NMR) and by the X-ray crystal structure determination of [{Os(η5-C5H5)(PPh3)[P(OMe)3]}2(μ-N2)](BPh4)2 (5).

Irida-β-ketoimines Derived from Hydrazines To Afford Metallapyrazoles or N-N Bond Cleavage: A Missing Metallacycle Disclosed by a Theoretical and Experimental Study

Unprecedented metallapyrazoles [IrH₂{Ph₂P(o-C₆H₄)CNNHC(o-C₆H₄)PPh₂}] (3) and [IrHCl{Ph₂P(o-C₆H₄)CNNHC(o-C₆H₄)PPh₂}] (4) were obtained by the reaction of the irida-β-ketoimine [IrHCl{(PPh₂(o-C₆H₄CO))(PPh₂(o-C₆H₄CNNH₂))H}] (2) in MeOH heated at reflux in the presence and absence of KOH, respectively. In solution, iridapyrazole 3 undergoes a dynamic process due to prototropic tautomerism with an experimental barrier for the exchange of ΔG_coal^⧧ = 53.7 kJ mol^-1. DFT calculations agreed with an intrapyrazole proton transfer process assisted by two water molecules (ΔG = 63.1 kJ mol^-1). An X-ray diffraction study on 4 indicated electron delocalization in the iridapyrazole ring. The reaction of the irida-β-diketone [IrHCl{(PPh₂(o-C₆H₄CO))₂H}] (1) with H₂NNRR' in aprotic solvents gave irida-β-ketoimines [IrHCl{(PPh₂(o-C₆H₄CO))(PPh₂(o-C₆H₄CNNRR'))H}] (R = R' = Me (5); R = H, R' = Ph (8)), which can undergo N-N bond cleavage to afford the acyl-amide complex [IrHCl(PPh₂(o-C₆H₄CO))(PPh₂(o-C₆H₄C(O)N(CH₃)₂))-κP,κO] (6) or [IrHCl(PPh₂(o-C₆H₄CO))(PPh₂(o-C₆H₄CN)-κP)(NH₂NHPh-κNH₂)] (9) containing o-(diphenylphosphine)benzonitrile and phenylhydrazine, respectively. From a CH₂Cl₂/CH₃OH solution of 9 kept at -18 °C, single crystals of [IrHCl(PPh₂(o-C₆H₄CO))(PPh₂(o-C₆H₄CN)-κP))(HN═NPh-κNH)] (10) containing o-(diphenylphosphine)benzonitrile and phenyldiazene were formed, as shown by X-ray diffraction. The reaction of 1 with methylhydrazine in methanol gave the hydrazine complex [IrCl(PPh₂(o-C₆H₄CO))₂(NH₂NH(CH₃)-κNH₂)] (7). Single-crystal X-ray diffraction analysis was performed on 6 and 7.

Reactivity of vinylidene complexes of ruthenium with hydrazines and hydroxylamines

Reaction of vinylidene complexes of Ru with hydrazines and hydroxylamines affords nitrile derivatives and amine or water. A reaction path based on ¹⁵N NMR studies and DFT calculations is proposed.

Preparation and reactivity towards hydrazines of bis(cyanamide) and bis(cyanoguanidine) complexes of the iron triad

Bis(diethylcyanamide) [Fe(N≡CNEt2)2L4](BPh4)2 1a and bis(cyanoguanidine) [Fe{N≡CN(H)C(NH2)=NH}2L4](BPh4)2 1b [L = P(OEt)3] complexes were prepared by allowing iron(II) chloride to react first with an excess of P(OEt)3 and then of the appropriate cyanamide, followed by addition of an excess of NaBPh4. Instead, bis(complexes) of ruthenium and osmium [M(N≡CNEt2)2L4](BPh4)2 2a, 3a and [M{N≡CN(H)C(NH2)=NH}2L4](BPh4)2 2b, 3b (M = Ru 2, Os 3) were prepared by reacting hydrides MH2L4 first with either triflic acid HOTf or methyltriflate MeOTf and then with an excess of the appropriate cyanamide. Hydride-diethylcyanamide [MH(N≡CNEt2)L4]BPh4 4a, 5a and hydride-cyanoguanidine complexes [MH{N≡CN(H)C(NH2)=NH}L4](BPh4)2 4b, 5b (M = Ru 4, Os 5) were also obtained by reacting MH2L4 first with one equivalent of HOTf or MeOTf and then with the appropriate cyanamide. Treatment of bis(cyanamide) and bis(cyanoguanidine) complexes 1-3 with hydrazines RNHNH2 afforded hydrazinecarboximidamide derivatives [M{η(2)-N(H)=C(NEt2)N(R)NH2}L4](BPh4)2 6a-12a and [M{η(2)-N(H)=C[N=C(NH2)2]N(R)NH2}L4](BPh4)2 6b-12b (M = Fe 6-8, Ru 9, 10, Os 11, 12; R = H 6, 9, 11, Me 7, 10, 12, Ph 8). A reaction path involving nucleophilic attack by hydrazine on the cyanamide carbon atom is proposed. All the complexes were characterised by spectroscopy and X-ray crystal structure determination of [Os{η(2)-NH=C[N=C(NH2)2]N(CH3)NH2}{P(OEt)3}4](BPh4)2 12b.