Azido Complexes Research Articles

End-on double azido bridged copper (II) complex with (N, N, O) schiff base: synthesis, structure and magnetic study

A rare asymmetric end-on double-bridged copper (II) azido complex with ∠Cu–N(azide)–Cu=89.1°, has been synthesized and characterized structurally and magnetically. The Cu–N(azide)–Cu angle is unusually low in the complex reported here in comparison to the same in other similar complexes. The magnetic study reveals that the interaction between metal centers in this complex is antiferromagnetic in nature. Though a ferromagnetic interaction between the metal centers is expected in the complex the coupling has actually been found to be antiferromagnetic, instead.

Cyclometallated Pd(ii) azido complexes containing 6-phenyl-2,2′-bipyridyl or 2-phenylpyridyl derivatives: synthesis and reactivity toward organic isocyanides and isothiocyanates

Cyclometallated palladium(II) azido complexes containing C,N,N- or C,N-donor ligands, [Pd(N(3))L](HL = 6-phenyl-2,2'-bipyridine or 2-phenylpyridyl derivatives), showed different reactivities toward organic isocyanides and isothiocyanates. In particular, aryl isocyanides (CN-Ar) underwent insertion into the orthometallated Pd-C bond on the phenyl moiety of the supporting ligand (L) in [Pd(N(3))L] or [Pd(N(3))(PR(3))L] to selectively give carbodiimido [[Pd(N=C=N-Ar)L]], imidoyl [[Pd(N(3))(-C=N-Ar)(PR(3))L]], or imidoyl carbodiimido complexes [[Pd(N=C=N-Ar)(-C=N-Ar)L] or [Pd(N=C=N-Ar)(-C=N-Ar)(PR(3))L]], depending on reaction conditions. Interestingly, reactions of [Pd(N(3))(PR(3))L] with organic isothiocyanates gave unusual dinuclear complexes [(micro-SCN(4)-R)PdL](2), exhibiting the concurrent S- and N-coordinating thio-tetrazole bridge.

Photoredox Reactions Occurring in Methanolic Solutions of Iron(III) Azido Complexes with N,N′-Ethylenebis (salicylaldiminato) Schiff Base Derivatives

Photoredox reactions occurring in irradiated methanolic solutions of trans-[Fe(N 2 O 2 ) (CH3OH)N3], where N 2 O 2 2− are tetradentate open-chain N 2 O 2 -Schiff base N,N′-ethylenebis(R-salicylaldiminato) or N,N′-1-methylethylenebis(R-salicylaldiminato) ligands denoted as R-salen and R-sal(Me)en, respectively (R=H, 5-Cl, 5-Br, 4-OCH3), have been investigated and their mechanism has been proposed. The complexes are redox stable in the dark. Ultraviolet and/or visible irradiation of methanolic solutions of the complexes induces photoreduction of Fe(III) to Fe(II). As an intermediate, •CH2OH radicals were identified by EPR spin trapping technique. The final product of the photooxidation coupled with the photoreduction of Fe(III) is formaldehyde. The efficiency of the photoredox processes is strongly wavelength dependent and influenced by the peripheral groups R of the tetradentate ligands. Differences between the course of photochemical changes induced by 254 nm radiation and the other wavelengths of incident radiation is rationalized by involving azide anions photoreactivity in observed redox changes.

Synthesis of Ruthenium Triazolato and Tetrazolato Complexes by 1,3-Dipolar Cycloadditions of Ruthenium Azido Complex with Alkynes and Alkenes and Regiospecific Alkylation of Triazolates

The [3+2] cycloaddition reactions of alkynes and alkenes with ruthenium azido complex [Ru]-N3 (1, [Ru] = (η5-C5H5)(dppe)Ru, dppe = Ph2PCH2CH2PPh2) have been investigated. The metal-bound heterocyclic complexes produced are triazolates [Ru]N3C2(CO2Me)2 (2) and [Ru]N3C2HCO2Me (3) from dimethyl acetylene dicarboxylate and methyl propiolate, respectively. Reaction of 1 with fumaronitrile in CH2Cl2 at room temperature results in removal of a HCN molecule and produces the triazolato complex [Ru]N3C2HCN (4). In contrast, reaction of tetracyanoethene with 1 affords the tetrazolato complex [Ru]N4C[C(CN)C(CN)2] (5). The structures of these complexes are all clearly established as N(2)-bound. Alkylation of 2 with organic bromides causes cleavage of the Ru−N bond and affords [Ru]-Br and N(1)-alkylated five-membered-ring organic triazoles N3(R)C2(CO2Me)2 (6a, R = CH2C6F5; 6b, R = CH2Ph; 6c, R = CH2CO2Me). Reaction of 3 with excess methyl propiolate gives a mixture of Z- and E-form zwitterionic N(1)-bound N(3)-alkylated-4-substituted triazolato complexes [Ru]N3(CHCHCO2Me)C2H(CO2) (7) in a ratio of ca. 4:1. Reaction of (Z)-7 with ICH3 affords {[Ru]N3(CHCHCO2Me)C2H(CO2Me)}[I] (8a) and the following cleavage of the Ru−N bond gives [Ru]-I and an organic triazole, N3(CHCHCO2Me)C2H(CO2Me) (9a). A regiospecific alkylation happens by treatment of 3 with organic halides and gives a series of cationic N(1)-bound N(3)-alkylated-4-substituted triazolato complexes exclusively with high yields. The structures of 2, 3, 4, 5, (Z)-7, and 10a have been determined by single-crystal X-ray diffraction analysis.

Copper(II) azido complexes containing trinitrogen ligands: [Cu(η 3-L)(N 3)] 2[Cu 2Cl 2(N 3) 4] [L=2,6-bis(3,4-dihydro-2 H-pyrrol-5-yl)pyridine], a tridimensional network of cationic and anionic copper complexes

A series of copper(II) azido complexes containing a tridentate trinitrogen ligand, [Cu(η 3-L)(N 3)] + [L=2,6-bis(3,4-dihydro-2 H-pyrrol-5-yl)pyridine] as well as [Cu(η 3- R, S-LH 4)(N 3)] +, [Cu(η 3- S, S-LH 4)(N 3)] + and [Cu(η 3- R, R-LH 4)(N 3)] + [LH 4=2,6-bis(pyrrolidin-2-yl)pyridine] have been synthesised from Cu(ClO 4) 2·6 H 2O, NaN 3 and the corresponding tridentate ligand and crystallised from methanol as the perchlorate salts. The single crystal X-ray structure analyse show these complexes to form one-dimensional networks by Cu⋯N(azide) intermolecular interactions, depending on the conformation of the tridentate ligand. In the case of L, an excess of sodium azide leads to the formation of the salt [Cu(η 3-L)(N 3)] 2[Cu 2Cl 2(N 3) 4], the crystal structure analysis of which reveals a surprising tridimensional network of cationic and anionic copper(II) complexes linked by Cu⋯N(azide) and Cu⋯N(L) interactions.

Uranium tris-aryloxide derivatives supported by triazacyclononane: engendering a reactive uranium(III) center with a single pocket for reactivity.

The synthesis and spectroscopic characterization of the mononuclear uranium complex [((ArO)(3)tacn)U(III)(NCCH(3))] is reported. The uranium(III) complex reacts with organic azides to yield uranium(IV) azido as well as uranium(V) imido complexes, [((ArO)(3)tacn)U(IV)(N(3))] and [((ArO)(3)tacn)U(V)(NSi(CH(3))(3))]. Single-crystal X-ray diffraction, spectroscopic, and computational studies of this analogous series of uranium tris-aryloxide complexes supported by triazacyclononane are described. The hexadentate, tris-anionic ligand coordinates to the large uranium ion in unprecedented fashion, engendering coordinatively unsaturated and highly reactive uranium centers. The macrocyclic triazacyclononane tris-aryloxide derivative occupies six coordination sites, with the three aryloxide pendant arms forming a trigonal plane at the metal center. DFT quantum mechanic methods were applied to rationalize the reactivity and to elucidate the electronic structure of the newly synthesized compounds. It is shown that the deeply colored uranium(III) and uranium(V) species are stabilized via pi-bonding interaction, involving uranium f-orbitals and the axial acetonitrile and imido ligand, respectively. In contrast, the bonding in the colorless uranium(IV) azido complex is purely ionic in nature. The magnetism of the series of complexes with an [N3O3-N(ax)] core structure and oxidation states +III, +IV, and +V is discussed in context of the electronic structures.

Highly Soluble Sulfur-Rich [Ni(L)(siS3)] Complexes Containing the New Ligand Bis(2-mercapto-3-trimethylsilylphenyl) Sulfide(2−) (siS32−)

The new organosulfur ligands siS3-H2 [siS32− = bis(2-mercapto-3-trimethylsilylphenyl) sulfide(2−)] and caS3-H2 [caS32− = bis(2-mercapto-3-carboxyphenyl) sulfide(2−)] were synthesized from HS3-H2 [HS32− = bis(2-mercaptophenyl) sulfide(2−)], n-butyllithium, and Me3SiCl or CO2/H+. Reaction of siS3-H2 with Ni(ac)2·4H2O gave the air-stable and well-soluble trinuclear complex [Ni(siS3)]3 (1) whose structure was determined by X-ray crystallography. Reactions of complex 1 with nucleophiles L [L = PR3 (R = nPr, Ph, Cy), N2H4, StBu−, and Cl−] yielded the corresponding neutral or anionic complexes, which were isolated as [Ni(PR3)(siS3)] [R = nPr (2), Ph (3), Cy (4)], Bu4N[Ni(Cl)(siS3)] (5), Bu4N[Ni(StBu)(siS3)] (6), and [Ni(N2H4)(siS3)] (8). The azido complex Et4N[Ni(N3)(siS3)] (7) was prepared from Me3SiN3 and the precursor chloro complex Et4N[Ni(Cl)(siS3)]. Reaction of 1 with NH3 yielded labile [Ni(NH3)(siS3)] (9), which was characterized in solution by 1H and 13C NMR spectroscopy. Analogously, 1 reacts with nicotinamide (NA) or diethylnicotinamide (NAEt2) to give, from equilibrium reactions, the corresponding mononuclear [Ni(L)(siS3)] complexes with L = NA, NAEt2. X-ray structure determinations showed that 1, 3, 4, 5, and 7 all exhibit tetrahedrally distorted planar [Ni(L)(siS3)] fragments. Complex 7 is the first structurally characterized azidonickel complex with a coligand having exclusively sulfur donors. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

A comparative study on structures and theoretical models of Rh azido complexes

The syntheses of PF 6 − salt of six-coordinate Rh(III) azido complexes containing polypyridyl ligands have been accomplished by treatment of the corresponding Rh(III) chloride with NaN 3 in EtOH–H 2 O followed by the addition of NH 4 PF 6 . The complexes have been characterized by UV–vis, FTIR, 1 H and 14 N-NMR spectroscopy along with elemental analysis. The X-ray crystal structures of compounds [Rh(tpy)(phen)(N 3 )](PF 6 ) 2 ( 1 ·(PF 6 ) 2 , tpy: 2,2′:6′,2″-terpyridine, phen: 1,10-phenanthroline) and [Rh(tpy)(bpy)(N 3 )](PF 6 ) 2 ( 2 ·(PF 6 ) 2 , bpy: 2,2′-bipyridine) confirm that a rhodium atom is six-coordinate and the tpy and bpy or phen ligands are orthogonal and the RhN 3 distances are 2.038(7) and 2.048(6) A, respectively. The two NN distances for the coordinated azide in complex 1 ·(PF 6 ) 2 are identical with distances of 1.17 (1) and 1.17 (1) A. However, the two NN distances for the azido group in the complex 2 may or may not be inequivalent with 1.170(8) and 1.15(1) A. The bond angles formed by the azide group, Rh, and the axially-positioned nitrogen atom are 172.1(3) and 173.5(8)°. In order to answer the question as to whether the two NN distances in 2 would be expected to be different, calculations were carried out at HF/LANL2DZ and HF/SDD levels of theory. The results indeed predict the NN distances in 2 to be different.

Comment on mu(1,3)-azido-diazidotetrakis(1,10-phenanthroline)dicopper(II) azide tetrahydrate.

The supramolecular structure of the title dimeric azido complex of copper(II), [Cu(2)(mu(1,3)-N(3))(N(3))(2)(phen)(4)](N(3)) x 4H(2)O (phen is 1,10-phenanthroline, C(12)H(8)N(2)) [Cheng, Hu, Wang & Ye (2002). Acta Cryst. C58, m12-m13], which was originally described in terms of hydrogen-bonded chains, has been re-interpreted as two-dimensional hydrogen-bonded sheets built from R(6)4(12) and R(10)10(28) rings, taking into account the complete hydogen-bonding pattern.

Synthesis and Crystal Structures of Polymeric Nitridomanganese(V) and Nitridochromium(V) Complexes with a Tetradentate Schiff Base Ligand

Novel polymeric nitridomanganese(V) and nitridochromium(V) complexes with a Schiff base ligand, [MnN(salpn)] and [CrN(salpn)] (H 2 (salpn): N , N '-disalicylidene-1,3-propanediamine) were prepared by photolysis of azido complexes. X-ray crystal structure analyses show that the complexes have an isostructural polymeric structure (···M≡N···M≡N···) with the N···M distances being 2.528(3) Å for M=Mn, and 2.508(2) Å for M=Cr.

Synthesis, spectral, magnetic and crystal structural characterization of two new copper(II) azido complexes: catena-[μ(N 3)Cu(pyridine) 3] n(PF 6) n and dimeric [Cu(4-ethylpyridine)(N 3) 2] 2

Two new copper(II) azide complexes, namely [Cu(pyridine) 3(N 3)](PF 6) ( 1) and Cu(4-ethylpyridine)(N 3) 2 have been synthesized and characterized by spectroscopic and crystallographic methods. The structure of 1 contains a polymeric cation [Cu(pyridine) 3(N 3)] + and PF 6 − anion. Each copper atom, in the cation, is five coordinated by three nitrogen atoms from the pyridine ligands and two nitrogens from two μ(1,3) azide bridges forming a 1D structure. The geometry around each copper atom is best described as a square pyramid, and the azide group is asymmetric. The structure of complex 2 features dimeric molecules, copper atoms coordinated by three nitrogen atoms from two μ(1,1) azide bridges forming a Cu 2N 2 unit and a third azide group, the fourth site is occupied by the pyridine nitrogen. The third azide group links another two different copper atoms from an adjacent dimer at CuN distances of 2.729(12) and 3.206(12) Å. Thus this azide group functions as a μ(1,1,3) tridentate bridging ligand. The IR and electronic spectra are reported. Strong absorption bands due to N 3→Cu II CT transitions are observed in spectra of solids and solutions of both complexes. Magnetic susceptibilities at different temperatures of both complexes are presented and discussed.

Bis-(tetraethylammonium)[tetraazidocuprate(II)] and catena-di-μ-1,1-azido-[di-μ-1,1-azido-bis-(2,4-dimethylpyridine)dicopper(II)

Two new copper(II) azido complexes, namely bis-(tetraethylammonium)[tetraazidocuprate(II)] (1) and catena-di-μ-1,1-azido-[di-μ-1,1-azido-bis-(2,4-dimethylpyridine)dicopper(II)] (2), have been prepared and characterized by spectroscopic and crystallographic methods. Complex (1) consists of isolated NEt+4 cations and [Cu(N3)4]2− anions. The site symmetry around the copper atom in the anion is 4/m. Complex (2) features a 1 D chain structure, five coordinated square pyramidal copper(II) atoms with both azides functioning as μ-1,1-bridges. The i.r. spectra reveal that both complexes contain asymmetric azido ligands. The solid and solution electronic spectra of (1) and (2) show very strong absorption bands in the visible region associated with N−3 → CuII charge-transfer transitions. The e.p.r. spectra of powder samples and solutions at room temperature were recorded and discussed.

New C-tetrazolato complexes of rhodium(III), palladium(II) and gold(III)

The azido complexes [RhCp*(μ-N 3)(N 3)] 2 (Cp*=η-C 5Me 5), trans-Rh(N 3)(CO)(PPh 3) 2, Na 2[Pd(N 3) 4], Na 2[Pd 2(μ-N 3) 2(N 3) 4] and Na[Au(N 3) 4], prepared in situ from metal halide precursors and a three- to ten-fold excess of NaN 3 in water, react with aliphatic isocyanides to give a series of new metal–carbon bonded tetrazolato complexes. All azide ligands in the coordination sphere undergo this cycloaddition with isocyanides except on palladium(II) where only two tetrazol-5-ato groups are formed. In the neutral species HAu(CN 4R) 4 (R= t Bu ( 2c), Cy ( 2d)) presumably one of the four tetrazol-5-ato groups has been protonated to afford a tetrazol-5-ylidene (carbene) ligand. The reactivities of the isocyanides decrease in the order CN t Bu>CNCy>CN(CH 2) 4Cl>CN-allyl>CNCH 2CO 2Na; surprisingly, no reaction occurs with methylisocyanide. With tert-butyl isocyanide in the cold, [Ru(μ-N 3)(N 3)(η-C 10H 14)] 2 (C 10H 14:4-isopropyltoluene) only reacts with cleavage of the azido bridges giving rise to [Ru(N 3) 2(η-C 10H 14)CN t Bu] ( 5a), while heating of the same mixture affords a second azido-isocyanide complex, trans-[Ru(N 3) 2(CN t Bu) 4] ( 5b), of which an X-ray structure analysis has been carried out. In some cases the reactions proceed with N 2 evolution, and rhodium complexes 6a– c are also formed probably containing cyanamido (N{R}CN) or carbodiimido (NCNR) ligands, respectively.

Synthesis and properties of arylpalladium(II) azido complexes PdAr(N 3)(PR 3) 2. Nucleophilic reactions of the azido ligand with CO and with isocyanides to afford Pd(II) isocyanate, C-tetrazolate and carbodiimide complexes

The tmeda ligand in the complexes, PdAr(N 3)(tmeda) is easily replaced by addition of tertiary phosphine or chelated phosphine to give the corresponding palladium(II) azido complexes with the phosphines ligand, PdAr(N 3)L 2 ( 1: Ar=Ph, L=PMe 3; 2: Ar=Ph, L=PEt 3; 3: Ar=tolyl, L=PMe 3; 4: Ar=naphthyl, L=PMe 3; 5: L 2=dppe). Complex 3 was characterized by X-ray crystallography. Complexes 1– 2 react with CO (1 atm) to afford Pd(II) isocyanates, PdPh(NCO)L 2 ( 6, L=PMe 3; 7: L=PEt 3), in 98 and 76% yields, respectively. In contrast, the reaction of trans-PdMe(N 3)(PMe 3) 2 with CO gives acetylpalladium isocyanate, trans-Pd(COMe)(NCO)(PMe 3) 2 ( 8) in 96% yield, which is characterized by X-ray crystallography. Reactions of 1 with an equal amount of tert-butyl and cyclohexyl isocyanides cause 1,3-dipolar addition of the isocyanides to the azido ligand, to give the complexes, trans-PdPh[CN 4(R)](PMe 3) 2 (R=C(CH 3) 3, 9; C 6H 11, 10) with a five-membered heterocyclic ring ( C-coordinated tetrazolato group). However, similar reactions of 1 and 3 with 2,6-dimethylphenyl isocyanide result in the unusual formation of Pd(II) complexes containing carbodiimido ligand, trans-( p-Y-C 6H 4)Pd(NCN-2,6-Me 2C 6H 3)(PMe 3) 2 (Y=H, 11; Y=Me, 12) in 51 and 94% yields, respectively. Reactions of 1 with protonating agents such as benzenthiol and phenylacetylene are also described.

Nickelatetrazoles as Intermediates in the Course of the Photolysis of Nickel(II) Azido Complexes? - A Theoretical Study

The primary photoreactions due to charge transfer excitation of d8 transition metal complexes of [MP2(N3)2] constitution (P2: mono- or diphosphane ligands) are strongly influenced by the central ion. While [MP2(N3)2] complexes of both palladium(II) and platinum(II) yield primarily the corresponding metal(I) species and azidyl radicals, nickel(II) complexes of the same constitution lead to intermediate generation of nitrenes as has been indirectly shown by various scavenging reactions. During the course of the succeeding reactions, the intermediate generation of nickelatetrazoles is assumed. Both nitrene and metallatetrazole intermediates could not be identified directly so far. Therefore, the proposed reaction pathway has been modeled theoretically to get indications regarding the probability of the formation of such intermediates. Based on density functional theory (DFT) calculations, the energetics of the proposed pathway is compared with those of possible other pathways. The calculations support the proposed reaction pathway and point to possible reasons for the different behaviour of nickel(II) compared to palladium(II) and platinum(II). Nickelatetrazole als Intermediate im Verlauf der Photolyse von Nickel(II)-Azidokomplexen? – Eine theoretische Studie Die primären Photoreaktionen infolge Charge-Transfer-Anregung von d8-Übergangsmetallkomplexen der Zusammensetzung [MP2(N3)2] (P2: Mono- oder Diphosphanligand) sind stark beeinflußt durch das Zentralion. Während [MP2(N3)2]-Komplexe von Palladium(II) und Platin(II) primär die entsprechenden Metall(I)-Species und Azidylradikale liefern, führen Nickel(II)-Komplexe der gleichen Zusammensetzung zu intermediärer Bildung von Nitrenen, wie indirekt durch verschiedene Abfangreaktionen gezeigt wurde. Während des Verlaufs der Folgereaktionen wird die intermediäre Bildung von Nickelatetrazol angenommen. Sowohl Nitren- als auch Metallatetrazol-Intermediate konnten bisher nicht direkt nachgewiesen werden. Deshalb wurde der vorgeschlagene Reaktionsweg theoretisch modelliert, um Hinweise über die Wahrscheinlichkeit der Bildung solcher Intermediate zu erhalten. Basierend auf Dichtefunktionaltheorie(DFT)-Rechnungen wird die Energetik des vorgeschlagenen Reaktionsweges mit der möglicher anderer Wege verglichen. Die Berechnungen unterstützen den vorgeschlagenen Reaktionsweg und weisen auf mögliche Ursachen für das unterschiedliche Verhalten von Nickel(II) verglichen mit Palladium(II) und Platin(II) hin.

Thermal analysis of some cobalt(II) azido complexes of the type CoL 4(N 3) 2 for L = pyridine derivative ligands

The thermal dissociation of three cobalt(II) azido complexes of the type CoL 4(N 3) 2 where L = 4-benzoyl-, 4-ethyl-, and 3-hydroxypyridine, have been studied by thermogravimetry (TGA and DTA) and IR spectroscopy. The three complexes form an intermediate 1 : 2 complex which explodes in the case of the 4-benzoylpyridine complex. Hydrogen bonding plays a significant role in the stability and decomposition of the 1 : 4 and 1 : 2 complexes in the case of 3-hydroxypyridine ligand.

Synthesis and characterization of a new series of 1D cobalt(II) complexes of pyridine derivative ligands with a single azido bridge and X-ray crystal structure of catena-(μ-N 3)[Co(4-methylpyridine) 4](PF 6)

A new series of polymeric cobalt(II) azido complex cations of the formula [CoL 4(N 3)]PF 6– nH 2O ( n=0 or 1), for L=some pyridine derivative ligands, have been prepared and characterized. Solid state electronic spectra suggest six-coordinated cobalt(II) in all complexes. IR spectral results reveal the existence of symmetrical azido ligand, except for complexes of L=3-Etpy and 4-Etpy(red) which contain asymmetrical azides, as well as PF 6 − counter ions in all complexes. X-ray crystal structure determination has shown the complex for L=4-methylpyridine to contain polymeric [CoL 4(N 3)] + cation and PF 6 − anions. In the cation, each cobalt(II) atom is coordinated by four nitrogen atoms from the pyridine ligands and two nitrogen atoms each from a μ-(1,3)-bridging azide giving rise to polymeric chains (1D) of six-coordinate Co(II) polyhedra. The azide ligand is symmetrical [N 1–N 2=N 2–N 3=1.170(3) Å] and linear within experimental error.

Fe(III)–azido complex with tetragonally compressed octahedral FeN 6 geometry: synthesis, spectroscopic and X-ray single crystal analysis of [Fe(cyclam)(N 3) 2](ClO 4)

An Fe(III)–azido complex with the formula [Fe(cyclam)(N 3) 2]ClO 4 (cyclam=1,4,8,11-tetraazacyclotetradecane) has been synthesized from the reaction of cis-[Fe(cyclam)Cl 2]Cl with sodium azide in methanol. The X-ray structural analysis reveals that the Fe(III) atom possesses a tetragonally compressed octahedral geometry with a trans configuration of two azido ions. Variable-temperature (4.5–295 K) magnetic susceptibility measurements show that the complex is low spin over the whole temperature range. 57Fe Mössbauer spectral measurements also suggest the same spin state of the Fe(III) ion.

Carbon–oxygen bond cleavage: a new reaction mode for amides bonded through oxygen to cobalt(III)

Azide ion competition experiments and oxygen-17 and -18 studies have been used to determine the extent of cleavage of the coordinated oxygen–carbon bond when (amide- O)pentaamminecobalt(III) complexes were reacted in aqueous base. Base hydrolysis in the presence of azide ion at 22°C (0.10 M NaOH, 1.0 M NaN 3) of [(NH 3) 5CoOC(CH 3)NH 2] 2(S 2O 6) 3·3H 2O and [(NH 3) 5CoOC(CH 3)N(CH 3) 2](CF 3SO 3) 3·H 2O produced 12.5 and 13.0% azido complex respectively, as expected for tripositive complexes reacting solely by cobalt–ligand bond cleavage. However reaction of [(NH 3) 5CoOC(C 6H 5)NH 2] 2(S 2O 6) 3·3H 2O produced only 10.5% azido complex and this implied that 17% of the complex was reacting by carbon–oxygen bond cleavage. 17O NMR spectroscopy of the products of base hydrolysis of [(NH 3) 5CoOC(CH 3)N(CH 3) 2](CF 3SO 3) 3·H 2O in 22 atom% H 2 17O confirmed that it reacted largely by ligand substitution but the same experiment using [(NH 3) 5CoOC(CH 2F)NH 2] 2(S 2O 6) 3·3H 2O was inconclusive because of secondary hydrolysis of the liberated amide. Oxygen-18 analysis of coordinated water has demonstrated conclusively that for complexes of primary or secondary amides with electron-withdrawing substituents carbon–oxygen bond cleavage in aqueous base is a significant reaction: [(NH 3) 5CoOC(C 6H 5)NH 2] 2(S 2O 6) 3·3H 2O, 19%; [(NH 3) 5CoOC(CH 2F)NH 2] 2(S 2O 6) 3·3H 2O, 10%; and [(NH 3) 5Co(succinimido- O)](CF 3SO 3) 2·H 2O, 9%. The reaction was not detected when [(NH 3) 5CoOC(CH 3)NH 2] 2(S 2O 6) 3·3H 2O and [(NH 3) 5CoOC(CH 3)N(CH 3) 2](CF 3SO 3) 3·H 2O were dissolved in aqueous base as these amides are not electronically activated, nor was it detected for reaction of [(NH 3) 5CoOC(H)N(CH 3) 2](CF 3SO 3) 3·H 2O; this complex is activated towards addition by hydroxide ion (84% C–N cleavage) but lacks an ionisable proton on the amide nitrogen to facilitate proton transfer in the intermediate in the C–O bond rupture process.

Base hydrolysis of [Co(triamine)(diamine)Cl] 2+ and epimerization of [Co(triamine)(diamine)OH] 2+: studies on resolved cobalt(III) complexes of 3-aza-hexane-1,6-diamine (2,3-tri)

The kinetics and stereochemistry of base hydrolysis have been investigated for the 12 systems endo- and exo- mer-[Co(triamine)(diamine)Cl] 2+ where the triamine is 2,2, 2,3 or 3,3-tri (2,3-tri = NH 2(CH 2) 2NH(CH 2) 3NH 2) and the diamine is en or tn. Some of these complexes are the `missing mer isomers' in the series of complexes known for some years. The complete series of mer-aqua and azido complexes have been isolated as well; these are all new. The 2,3-tri complexes are chiral on the sec-NH centre and all four have been optically resolved for the first time. These mer-chloro complexes base-hydrolyse with complete retention of the mer configuration, but with some inversion at the sec-NH site. For the dien systems (2,2-tri), the steric course of base hydrolysis has been determined for all four isomers ( fac and mer) for both tn and en systems, and the results substantiate the edge displacement principle. Endo-/ exo-epimerization rates have been measured for the [Co(triamine)(diamine)OH] 2+ ions. For the resolved 2,3-tri complexes, azide competition is observed, and the common racemic exo- and endo-product distribution indicates a common trigonal bipyramidal intermediate with a `flat' deprotonated sec-amine. The endo- and exo- mer-[Co(2,3-tri)(diamine)OH] 2+ complexes are rapidly anated by the azide ion to give the same (kinetic) endo-/ exo- mer-[Co(2,3-tri)(diamine)N 3] 2+ distribution, at pH-independent rates, and it is shown that these complexes react via an internal conjugate base complex where the sec-NH is deprotonated and water is the leaving group. The epimerization rates for [Co(triamine)(diamine)OH] 2+ and base hydrolysis rates for [Co(triamine)(diamine)Cl] 2+ are discussed in terms of topology, N-configuration and ring size. The exo- mer-[Co(3,3-tri)(tn)Cl] 2+ ion is established to be the fastest-reported hydrolysing pentaaminecobalt(III) complex, and it is shown to aquate in acid without exchange at any of the NH sites, nor inversion at the sec-NH, thereby excluding a conjugate base pathway where the base is water (rather than OH −).