Antonio Mantovani

Binuclear complexes of 1,4-diaza-3-methylbutadien-2-Yl-palladium(II) derivatives with palladium(II) and platinum(II) chlorides

The organometallic 1,4-diazabutadienes, RN=C(R′)C(Me)=NR [R = p-C6H4OMe, R′ = trans-PdCl(PPh3)2 (DAB); PdCl(LL), LL = 1,2-bis(diphenylphosphino)-ethane (DABI), LL = cis-1,2-bis(diphenylphosphino)ethylene (DABII); Pd(dmtc)-(PPh3), dmtc = dimethyldithiocarbamate (DABIII)] react with ethylene or nitrile derivatives of palladium(II) and platinum(II), [PdCl2(CH2 = CH2)]2, K[PtCl3-(CH2=CH2)], [PdCl2(NCMe)2], [PtCl2(NCPh)2] usually to give binuclear complexes of the type [MCl2{RN = C(R′)C(Me)=NR}] (M = Pd, Pt), in which the 1,4-diazabutadiene group acts as a chelating bidentate ligand. The stability of these compounds in hot 1,2-dichloroethane or acetonitrile markedly depends on the nature of the ancillary ligands on the palladium atom of the group R′. When a chelating diphosphine is present, as in the case of DABI and DABII, the corresponding binuclear complexes are recovered unchanged even after long refluxing times. In the case of DAB and DABIII adducts, a transfer of PPh3 and dmtc ligands from the Pd atom of R′ to the metal atom M of the coordinated MCl2 unit occurs with the formation of trans-MCl2(PPh3)2] and of the new bimetallic complexes, [M(dmtc) {RN=C(R″)C(Me)=NR}] (R″ = cis-PdCl2(PPh3) (DABIV)), respectively. The rates of ligand transfer for the PdCl2 adducts are much higher than for the PtCl2 analogues.

Carbonmetal bonded heterocycles. Synthesis and characterisation of [MCl{C5H3N(6-Cl)-C2}(PR3)2] (M = Pd, Pt; PR3 = PPh3, PMePh2; OR (PR3)2 = dppe)

Abstract The complexes [Pd(PPh 3 ) 4 ] and [Pt(PPh 3 ) 4 ] react with 2,6-dichloropyridine at high temperature to give trans -[MCl{C 5 H 3 N(6-Cl)- C 2 }(PPh 3 ) 2 ] (M = Pd, Ia; M = Pt, Ib). Ligand substitution reactions of these complexes with 1,2-bis(diphenylphosphino)ethane, dimethyldithiocarbamate, and LiBr have been carried out, and also insertion of CO into the PdC bond of Ia. Oxidation of Ia with H 2 O 2 , giving the dimeric complex [PdCl{C 5 H 3 (6-Cl)- C 2 }(PPh 3 )] 2 is also reported. The complex analogous to Ia but containing PMePh 2 in place of PPh 3 has been obtained by oxidative addition to the Pd(dba) 2 /PMePH 2 system (dba = dibenzylideneacetone).

Preparation and reactivity of 1,2-bis(imino)ethylpalladium(II) complexes

Abstract The 1,2-bis(imino)ethylpalladium complex, t r a n s − [ P d C I { C ( = N R ) ︹ C H = N R } ( P P h 3 ) 2 ] (R =p-C6H4OMe, DABI) can be prepared by treatment of [Pd(PPh3)4] with two equivalents of CNC6H4OMe-p followed by slow addition of HCl at −70° C. The σ-bonded 1,2-bis(imino) group can be easily monoprotonated and undergoes acid hydrolysis to give the α-aldehydoimidoyl derivative t r a n s − [ P d C I { C ( = N R ) ︹ C H = O } ( P P h 3 ) 2 ] . Condensation of the aldehydic carbonyl group with methylamine yields the product t r a n s − [ P d C I { C ( = N C 6 H 4 O M e − p ) ︹ C H = N M e } ( P P h 3 ) 2 ] , DABII, with different substituents on the N-imino atoms. Substitution of ancillary ligands at the palladium center of DABI by dimethyldithiocarbamate anion (dmtc) affords the complex [ P d ( dmtc ) { C ( = N R ) ︹ C H = N R } ( P P h 3 ) ] , DABIII. The DABI, DABII and DABIII derivatives react with anhydrous metal chlorides, MCl2 (M = Co, Ni, Cu, Zn) to give1/1 adducts in which the 1,2-bis(imino)ethyl group acts as a chelating bidentate ligand. Magnetic moment measurements and the far-infrared and electronic spectra of these binuclear compounds indicate an essentially pseudo-tetrahedral configuration at M. The reaction of DABI with [PdCl(η3-2-MeC3H4)]2, or [PtCl(C3H5)]4, (DABI/Pd or Pt ratio,1/2) involves the exchange of Cl− and PPh2 ligands, which leads to the formation of the zwitterionic binuclear derivatives [Pd(η3-2-MeC3H4)(DABIV)], or [ P t ( η 3 − C 3 H s ) ( D A B I V ) ] ( D A B I V = c i s − P d C I 2 { C ( = N R ) ︹ C H = N R } ( P P h 3 ) ) , and [PdCl(η3-2-MeC3H4)(PPh3)], or [PtCl(η3-C3H5)(PPh3)].

Adducts of 1,4-diazabutadienes with group IIB metal halides

Abstract The reactions of 1,4-diazabutadienes (or α-diimines) RNC(R′)C(R″)NR, DAB, (R = p -C 6 H 4 OMe, R′ = R″ = H, DAB I ; R = p -C 6 H 4 OMe,R′ = H, R″ = Me, DAB II ; R = p -C 6 H 4 OMe, R′= R″ = Me; DAB III ; R = CMe 3 , R′ = R″ = H, DAB IV ) with MX 2 M = Zn, Cd, Hg; X = CI, Br) yield in general 1/1 adducts. These species are assigned a monomeric configuration with a σ,σ′-N,N′, chelating DAB ligand for M = Zn, Hg, whereas the CdCl 2 adducts have polymeric structures with terminal and/or bridging chlorides. In the reactions of CdCl 2 with DAB I or DAB IV polymeric species [(CdCl 2 ) 2 (DAB)] x are obtained in which all chlorides are bridging. Spectrophotometric dissociation equilibrium constants have been determined by titration methods in 1,2-dichloroethane for some Zn and Hg 1/1 adducts. The stability constants depend markedly on the substituents on the imine C and N atoms. When R = CMe 3 (DAB) IV no dissociation is detected, whereas with R = p -C 6 H 4 OMe the stability constants increase in the order: DAB I II ⩽ DAB III which is apparently the order of increasing σ-donor ability of the α-diimine ligands. The [ZnCl 2 (DAB I )] complex is ca. 30 times more stable than its Hg analogue. Computational details of the equilibrium measurements are also discussed.

Elucidation of the degradation mechanism of 2-chloroethanol by hydrogen peroxide under ultraviolet irradiation

Abstract Oxidation of 2-chloroethanol by H 2 O 2 under UV irradiation has been studied. Analysis of reactants and products was performed by gas and ion chromatography. In this study we have compared the disappearance of 2-chloroethanol with the contemporaneous appearance of Cl − ions and conductivity changes of the solution. It was found that the oxidation of 2-chloroethanol yields quantitative amounts of Cl − ions. Moreover, the rate of change of the solution conductivity is comparable with the rate of formation of Cl − . Acetic, glycolic and formic acids and acetaldehyde were formed in the reaction although at low concentrations.

Insertion of isocyanides into the palladium-(2-pyridyl) bond

The reaction of the pyridyl-bridged binuclear complex [PdBr(μ-2-C5H4N)(PPh3)]2 with isocyynides CNR (R  p-C6H4OMe, Me, C6H11) yields the complex PdBr{(&2.dbnd;NR)C(&2.dbnd;NR) (2-C5H4N)}(PPh3)] containing a C,N-chelated 1,2-bis(imino)-2-(2-pyridyl)ethyl group, which results from successive insertions of two isocyanides molecules into the palladium2-pyridyl bond. The mononuclear compound trans-[PdBr(2-C5H4N)(PMePh2)2] readily reacts with various CNR ligands (R  p-C6H4OMe, Me, C6H11, CMe3) to give the imino(2-pyridyl)methylpalladium(II) derivatives, trans-[Pdbr{C(=NR)(2-C5H4N)} (PMePh2)2].

Migration of bidentate anionic ligands in binuclear compounds derived from 1,2-bis(imino)propyl-palladium(II) complexes

Abstract The complexes [Pd(AB){C(NR)CMeNR}(PPh3)] (I; AB = 2,4-pentanedionate, N-methylsalicylaldiminate, pyrrole-2-N-methylaldiminate; R = p-C6H4OMe) react with ‘MCl2’ (‘MCl2’ = CoCl2, NiCl2, CuCl2, ZnCl2, [PdCl2(NCMe)2], K[PtCl3(CH2CH2)]) to give either the binuclear adducts [(PPh3)(AB)Pd{C(NR)CMeNR}MCl2] (II) or the zwitterionic isomers [(PPh3)Cl2Pd{C( NR)CMeNR}M (AB)] (III) depending on the nature of the metal M and of the anionic ligand AB. The formation of products III is accounted for in terms of an intramolecular migration of ligands between the two metal centers Pd and M of the initially formed MCl2 adducts II.

Organometallic complexes as ligands. Synthesis oftrans-\([||P\overline {dClC( = NR) \{ C_5 H_3 N(6 - Cl)---| } C^2 \} (PPh_3 )_2 ]\) (R=p—OMeC6H4,CH3,c-C6H11,Bu t ) and new information on the isocyanide insertion into the Pd-C σ bond

The pyridyl complextrans-[PdCl{C5H3N(6-Cl)-C2}(PPh3)2] easily undergoes insertion of isocyanides into the palladium—carbon bond via an ionic intermediate to give the title compounds. Details on the insertion pathway were obtained through IR,31P-NMR and conductivity measurements. The presence of the NCCN moiety in the resulting imino(2-pyridyl)methyl palladium(II) complexes is supported by formation of an 1:1 adduct with CuCl2.ZusammenfassungDer Pyridyl-Komplextrans-[PdCl{C5H3N(6-Cl)-C2} (PPh3)2] geht leicht — über eine ionische Zwischenverbindung — eine Isocyanid-Insertionsreaktion in die Pd-C-Bindung ein und ergibt dabei die Titelverbindungen. Details über den Ablauf dieser Insertion wurden durch IR,31P-NMR und Leitfähigkeitsmessungen erhalten. Die Gegenwart von NCCN in den resultierenden Imino(2-pyridyl)methyl-palladium(II)-Komplexen wird durch die Bildung eines 1:1-Addukts mit CuCl2 unterstützt.

Oxidative addition of α-ketoimidoyl chlorides to palladium(O) and platinum(O) complexes

The reaction of α-ketoimidoyl chlorides with palladium(O) and platinum(O) derivatives yields trans-[MCl{C(NR)COMe}(PMennPh3−n)2] (M = Pd; R = p-C6H4OMe, c-C6H11, t-Bu; n = 0, 1; M = Pt; R = p-C6H4OMe; n = 1) and cis-[PtCl{C(N-p-C6H4OMe)COMe)}(PPh3)2], which have been characterized by IR, 1H and 31P NMR spectra and by condensation with MeNH2.

Preparation and co-ordination properties of trans-chloro-[1-(p-methoxyphenylimino)-2-(methylimino)propyl]bis(triphenylphosphine)-platinum. Crystal and molecular structure of the ionic compound [PtCl{C(NR)CMeNMe[Rh(CO)2]}(PPh3)2][RhCl2(CO)2](R = C6H4OMe-p)

The 1,2-bis(imino)propyl complex trans-[PtCl{[graphic omitted]MeNR′}(PPh3)2](2)(R = C6H4OMe-p, R′= Me) can be prepared by the condensation reaction of monomethylamine with the carbonyl group of [PtCl{[graphic omitted]MeO}(PPh3)2](1). Complex (2) reacts with MCl2 and K[PtCl3(CH2CH2)] to give the adducts [PtCl{C([graphic omitted]Cl2)}(PPh3)2][ClO4](3)(M = Cu, Zn, or Pt), and with chloro-bridged dimers [{M′CIL2}2] in the presence of NaClO4(molar ratio Pt : M′= 1 : 1) to give the cationic complexes [PtCl{C([graphic omitted]L2)}(PPh3)2][ClO4](4)[M′L2= Pd(η3-2-MeC3H4) or Rh(cod)(cod =η4-Cyclo-octa-1,5-diene)]. In the binuclear complexes (3) and (4) the 1,2-bis(imino)propyl group of (2) is σ : σ′-N,N′-chelated to the metal centres M and M′ respectively. The reaction of (2) with [{M′CIL2}2](molar ratio Pt : M′= 1 : 2) yields the [PtCl{C([graphic omitted]L2)}(PPh3)2]-[M′Cl2L2](5), which are characterized in solution by conductivity measurements and 1H and 31P n.m.r. spectroscopy. The 1H n.m.r. data indicate an interaction between the cationic and the anionic species of (5) which involves breaking of one of the M′-Nimino bonds in the binuclear cation, without exchange of PPh3 and chloride ligands between the Pt and M′ metal centres. When M′L2= Rh(CO)2, the reaction affords the complex [PtCl{C([graphic omitted]h(CO)2]}(PPh3)2][RhCl2(CO)2](5c) as a red-brown microcrystalline product, which is partially associated in solution. The crystal and molecular structure of (5c) has been determined by X-ray diffraction analysis. Crystals are monoclinic, space group P21/a, with a= 19.521 (3), b= 17.212(7), c= 15.910(3)A, β= 104.11 (2)°, and Z= 4. The structure has been determined by the heavy-atom method and refined to the conventional R of 0.055 for 3 892 counter reflections (up to 2θ= 43°, Mo-Kα radiation). The structure consists of discrete, well separated cationic binuclear species and distorted square-planar cis-[RhCl2(CO)2]– anions. In the cation the rhodium co-ordination plane forms a dihedral angle of 81° with the platinum co-ordination plane, with bond distances in the normal range (mean values : Rh–Cl 2.342, Pt–P 2.330, Rh–N 2.07, Rh–CO 1.81, Pt–Cl 2.375, Pt–C(sp2) 1.97 A). In the solid state there are no unusually short intermolecular contacts.