Mohamed A. El-Sayed

Coordination chemistry of benzothiazole derivatives. 2-mercaptobenzothiazole and 2-(o-hydroxyphenyl)benzothiazole complexes with Cu(II), Ni(II) and Co(II)

Abstract The reaction of 2-mercaptobenzothiazole (MBTH) with Cu(II) ions resulted in a yellow diamagnetic Cu(II) complex, while the reaction with Co(II) produced a dimeric tetrahedral complex. The reaction of Ni(II) with MBTH gave a diamagnetic square planar complex. The yellow copper complex formed a blue five coordinate dimeric complex with pyridine. The isolated blue crystals were investigated by electron spin resonances. The reaction of the diamagnetic nickel complex with different bases yielded distorted octahedral dibase adducts. 2-( o -hydroxyphenyl)benzothiazole gave a brown pseudo tetrahedral complex with Cu(II) and a distorted tetrahedral complex wiht Ni(II). The reaction with Co(II) produced a high spin five coordinate polymeric type compound. The solid spectra of the complexes as well as their base adducts were investigated.

Transmetalation: A New Route to Heteropolymetallic Molecules and Materials

Abstract The newly discovered transmetalation of polymetallic molecules by mononuclear transmetalators is an excellent source of a wide variety of related heteropolyatomic molecules and materials that cannot be obtained by other means. The systems discussed involve easily obtained reactants, stoichiometric reactions and easily separated products. Among the factors that affect specific transmetalation patterns are target structure, transmetalator identity and relative stability, redox phenomena, intramolecular ligand transfer and specific types of primary product fragmentation. A feature of reported transmetalation systems that make them excellent candidates for the production of new materials is that they are stoichiometric and flexible. Prospects for extending known systems to new targets and elements are discussed.

Properties and reactions of tetranuclear copper(I) complexes [LCuX]4 (L=N,N-dimethylaminomethylferrocene; X=Cl and Br). Crystal and molecular structure of (μ4-O)L4Cu4Cl6

Abstract Copper(I) chloride and bromide react with equimolar L=N,N-dimethylaminomethylferrocene in methylene chloride or nitrobenzene at room temperature under N2 to give soluble tetranuclear copper(I) complexes [LCuX]4 (VII). The room temperature electronic spectra of L and VII are very similar, indicating little, if any, electronic coupling of copper(I) with the ferrocene moiety. Products [CuX]4 completely reduce O2 to coordinated oxide in the tetranuclear oxocopper(II) products [LCuX]4O2 (VIII) that are converted by excess CO2 to tetranuclear dicarbonatocopper (II) complexes [LCuX]4(CO3)2 (IX). VII are oxidized by O2 to VIII in a second-order reaction whose rate-determining step is insertion of O2 through the halo core of VII. The properties of VIII are consistent with a (μ-O)2[LCuX]4 molecular core structure. The electrochemistry of L is not much affected by coordination to copper(I) or copper(II). Attempted crystallization of VIII and IX (XCl) gives (μ4-O)L4Cu4Cl6 (Xa), which crystallizes in the tetragonal space group P 4 21c, with a=16.930(6), c=13.084(7) A, V=3750 A3 and Z=2. The crystallographic data from 1744 reflections at 233 K were refined to give R=0.047 and Rw=0.052. The core molecular structure of Xa consists of a central oxo group that is tetrahedrally coordinated to four copper(II) centers. Each copper(II) carries a monodentate ligand L and is bridged to three other copper(II) centers by chlorine ligands. This core structure is very similar to those of the N,N-diethylnicotinamide and pyridine analogues. Complexes VIII-X are not transmetalated at practical rates by Co(NS)2 and Ni(NS)2 (NS is monoanionic S- methyl isopropylidenecarbodithioate). Likely reasons are that steric effects interfere with reaction precursor formation and that VIII-X contain very strong copper-L bonds.

The kinetics of primary events in the reactions of L2Cu2X2 complexes (L is an N,N,N′N′-tetraalkyldiamine; X is Cl or Br) with M(NS)2 reagents

Abstract The rate laws for the earliest events in the transmetalation of dimeric copper(I) complexes L 2 Cu 2 X 2 (L = N,N,N′N′ -tetraalkyldiamine; X = Cl or Br) by M(NS) 2 reagents (M = Co, Ni, Cu, Zn; NS is a monoanionic S -methylhydrazinecarbodithioate Schiff base ligand) depend on L, X, M and NS and the aprotic solvent. The kinetic data are compared with those for monotransmetalation of copper(II) complexes (μ 4 -O)N 4 Cu 4 X 6 by M(NS) 2 . Different kinetic behavior is particularly marked for cobalt(II) reactants. Unexpectedly high rates of reactions with Cu(NS) 2 are attributed to electron transfer. The results provide a basis for discussion of transmetalation specificity.

Some Aspects of Aprotic Copper(I)-Dioxygen Systems

Abstract There has been considerable progress in understanding the stoichiometry, products and kinetics of aprotic copper(I)-dioxygen reactions, which are an integral part of all copper-catalyzed dioxygen systems. Attention is focused on the effects of ligands on the reaction stoichiometry and on the stability of the products. The great tendency for complete aprotic dioxygen reduction appears to have both kinetic and thermodynamic origins. It is suggested that immobilization of copper(I) sites is necessary to prevent complete aprotic reduction of dioxygen.

Stoichiometry and products of transmetalation of dimeric copper(I) complexes L2Cu2X2 (L is an N,N,N′,N′-tetraalkylethylenediamine; X = Cl or Br) by M(NS)2 reagents in aprotic solvents

Abstract Dimeric copper(I) complexes L 2 Cu 2 X 2 react with 1 and 2 mol of M(NS) 2 reagents in aprotic solvents to give quantitative yields of products LMX 2 and (NS)M(X,X)M(NS), respectively. Here, L = N,N,N′N′ -tetraethylethylenediamine, X = Cl or Br, M = Co, Ni, Cu and Ns = S -methylisopropylidenehydrazinecarbodithioate. Dimers (NS)Cu(X,X)Cu(NS) are oxidatively unstable. LCoCl 2 crystallizes in the monoclinic space group P 2 1 / c (C 2h 5 ): a = 7.345(1), b = 11.801(1), c = 17.478(2) A, β = 104.98(1)°, Z = 4. The electronic spectra of LMX 2 and (NS)M(X,X)M(NS) complexes are discussed.

Crystal and molecular structure of racemic fac-tris-(S-methylisopropylidene-hydrazinecarbodithioato)cobalt(III), Co(NS)3, and the kinetics of its isomerization in aprotic solvents

Abstract The crystal and molecular structure of fac-tris- (S-methylisopropylidenehydrazinecarbodithioato)cobalt (III) is reported. The dark olive-green Co(NS)3 crystallizes in the monoclinic space group P21/c with Z = 4 in a cell of dimensions a = 17.876(2), b = 9.792(2), c = 14.816(2) A and β = 108.63(1)°. The coordination sphere is relatively undistorted but the cobalt atom does not lie in the center of this sphere. Kinetic studies have shown the fac to mer isomerization to have a very large (⩾100) equilibrium constant and to proceed by a trigonal twist mechanism.

Unusually stable peroxocopper complexes. Stoichiometry, products and kinetics of oxidation of the dimeric copper(I) complex [LCuBr]2 (L=N,N'-diethylethylenediamine) by dioxygen in methylene chloride from -51 to 30°C

Abstract Copper(I) bromide dissolves in deoxygenated methylene chloride and nitrobenzene solutions of equimolar N , N ′- diethylethylenediamine (DEED) to give the colorless copper(I) dimer [(DEED)CuBr] 2 ( D ). Dioxygen uptake, analytical, cryoscopic, spectral and kinetic data show that D is oxidized to the blue tetranuclear mixed valence peroxocomplex [(DEED)CuBr] 4 O 2 ( A ) at temperatures from -51 to 30 °C. The rate law is d[ A ]/d t =koL[O 2 ][ D ] 2 with activation parameters δ H ≠ DL =-1.8±0.4 kcal mol −1 and δSYL=-38±5 cal deg −1 mol −1 at 25 °C. These parameters resemble those for third-order oxidation of the copper(I) dimer [(TEED)CuCI] 2 (TEED is N , N , N ′, N ′- tetraethylethylenediamine) to the peroxocopper product [(TEED)CuCI] 4 O 2 at low temperatures. They are completely different from those for direct, third-order oxidation of [LCuX] 2 dimers to the oxocopper(II) products [LCuX] 2 O at ambient temperatures because of slow transfer of the third electron from copper(I) to O 2 in ambient [(DEED)CuBr] 2 /O 2 and low temperature [(TEED)CuCI] 2 /O2 reactions. As observed in the [(TEED)CuCI] 2 /O 2 system, primary product A relaxes to a different tetranuclear copper complex B , with A thermodynamically favored at higher temperatures up to - 17 °C. First-order decomposition of A to give 2 mol of the oxocopper(II) product [(DEED)CuBr] 2 O ( C ) has an exceptionally long half-life of 3.2 ± 0.1 h at 25 °C. The resistance of A to intramolecular copper(I)→ peroxide electron transfer with L=DEED and X=Br is attributed to (i) hydrogen bonding between the NH groups of DEED and bound peroxide and (ii) stabilization of copper(I) by Br.

Transmetalation of μ-carbonatodicopper(II) complexes with M(NS)2 reagents

Abstract Well characterized binuclear μ-carbonatodicopper( II ) complexes III can be partially and completely transmetalated with Ni(NS) 2 reagents I or II (NS are mononegative anions of S-methyl hydrazinecarbodithioate Schiff bases) to give hetero- and homobinuclear species and Cu(NS) 2 coproducts. The neutral ligand HNS stoichiometrically demetalates III , showing that a major driving force for transmetalation is the formation of stable Cu(NS) 2 coproducts. All nickel-containing products were found to have a strong affinity for water and a tendency to lose their bidentate amine ligands. Products (H 2 O) 6 Ni 2 Cl 2 (CO 3 ) and (Py) 6 Ni 2 (OH)Cl(CO 3 )·6H 2 O have been obtained by direct transmetalation of III using different experimental conditions. Nickel( II ) complexes, Ni(NS) 2 , effectively inhibit the oxidation of 2,6-dimethylphenol by dioxygen initiated by complexes III .

Stoichiometry, products and kinetics of transmetalation of dimeric copper(II) complexes L2Cu2X2Y (L is an N,N,N′,N′-tetraalkyldiamine; X is Cl or Br; Y is O or CO3) by M(NS)2 reagents

Abstract This paper reports the stoichiometry and kinetics of seventeen monotransmetalations of dimeric copper(II) targets L 2 Cu 2 X 2 O ( E ) and L 2 Cu 2 X 2 CO 3 ( F ) by neutral M(NS) 2 transmetalators in nitrobenzene. Here, L is an N,N,N′,N′ -tetraalkyldiamine, X is Cl or Br, M is Co, Ni, or Zn and NS is monoanionic S -methylisopropylidenehydrazinecarbodithioate or S -methylbenzylidenehydrazinecarbodithioate in M(NS) 2 transmetalators C and D , respectively. All these monotransmetalations proceed with rate = k [transmetalator][target] n , where n is 0, 1 or 2. Reaction order n is generally smaller than for monotransmetalations of (μ 4 -O)N 4 Cu 4 X 6 targets by C because terminal X in E and F lead to more stable transmetalation precursors even with X =Cl. Based on derived activation entropies, the formation of discrete transmetalation products is the rate-determining step when n is 1 or 2, but metal exchange is rate-determining in systems involving especially stable precursors when n is zero. The results demonstrate the effects of L, X, NS and M on transmetalation rates and rate laws and suggest selective transmetalation of five-coordinate copper(II) in asymmetrical targets F II .