G. van Koten

1,4-Diaza-1,3-butadiene (a-diimine) ligands: their coordination modes and the reactivity of their metal complexes

Publisher Summary Molecules containing the 1,4-diaza-1,3-butadiene skeleton have attracted much interest because of both their versatile coordination behavior and the interesting properties of their metal complexes. 1,4-diaza-1,3-butadienes (R-DAB) may be prepared by condensation reactions involving glyoxals, α-ketoaldehydes or α, β-–diketones with primary amines RNH2. It was concluded from nuclear magnetic resonance (NMR) spectra, dipole moments, and infrared (IR) spectra that the R-DAB molecule exists in solution in the E configuration at both C=N double bonds while the conformation of the central C–C bond is predominantly s-trans. So far stable complexes containing monodentate R–DAB have only been reported for the square planar d8–metals Pd11, Pt11, and Rh1. The reports of metal complexes with R–DAB ligands date back to 1953 when Krumholz described the synthesis of some ferrous complexes. The unusual stability and characteristic color being ascribed to the presence of π bonding between the metal and the nitrogen atoms. Factors, such as the substituents R and R, the metal atom, and the other ligands bonded to the metal atom, will influence the type of coordination of the R–DAB( R’,R) ligands. Just as 2, 2’-bipyridine, the R–DAB ligands can be readily converted to stable paramagnetic radical anions by potassium in 1,2-dirnethoxyethane or tetrahydrofuran (THF).

Intramolecular Coordination in Organotin Chemistry

Publisher Summary This chapter overviews organotin compounds containing C,Y-chelating ligands particularly, (1) structures in the solid state, (2) fluxional behavior in solution, and (3) stereochemical aspects. Attention is also given to the enhanced reactivity of tin–carbon bonds in tetraorganotin compounds as a result of intramolecular coordination. The first example of an organotin compound having C,Y-chelating ligands, i.e., bis [1, 2-bis(ethoxycarbonyl)ethyl]tin dibromide, for which the structure in the solid state was unambiguously established by an X-ray crystal structure determination. By using the steric and electronic properties of C,Y-chelating ligands, organometallic compounds that have interesting properties and special reactivities can be isolated. Special features of some of these compounds are (1) stabilization of organometallic compounds in which the metal has an unusual oxidation number, e.g., Fe(II1) , Co(I1) , and Ni(II1); (2) the trapping of organometallic species that are supposed to be intermediates in reactions, e.g., organoplatinum compounds in which a di-iodine molecule is coordinated end-on to platinum as a first step in oxidative-addition reactions; (3) the use of a novel organonickel compound as a catalyst in the selective Karasch addition of polyhaloalkanes to olefines ; and (4) the unexpected reactivity of organocopper compounds toward acetylenes.

Metal Heterodiene Complexes

In this article a survey is given of novel results in the field of the chemistry of a-diimine complexes of some metal atoms of the main group, transition metal and post transition metal area. It is shown that a-diimines of the type RN=C(R’)(R”)C=NR (= R-DAB) and 2C&NC(R’)=NR (= R-Pyca) are very versatile with regards to both their coordination chemistry and chemical reactivity when coordinated to a metal or metal cluster. The type of reaction occurring depends critically on the type of metal(s), the other ligands present on the metal(s), the type of coordination of the a-diimines, and particularly on the steric and electronic properties of R,R’ and R” situated on the R-DAB and R-Pyca ligands.

Comparison of free and metal coordinated 1,4-disubstituted-1,4-diaza-1,3-butadienes : Crystal and molecular structures of 1,4-dicyclohexyl-1,4-diaza-1,3-butadiene and trans-[dichloro(triphenylphosphine)(1,4-di-tert-butyl- 1,4-diaza-1,3-butadiene)palladium(II)]

Abstract The crystal and molecular structures of c-Hex-DAB (c-hexyl-NC(H)C(H)N-c-hexyl; DAB = 1,4-diaza-1,3-butadiene) and of trans-[PdCl2(PPh3)(t-Bu-DAB)] are reported. Crystals of c-Hex-DAB are monoclinic with space group C2/c and cell constants: a = 24.70(1), b = 4.660(2), c = 12.268(3)A, β = 107.66(4)°, Z = 4. The molecule has a flat E-s-trans-E structure with bond lengths of 1.258(3)A for the CN double bond and 1.457(3)A for the central CC′ bond. These bond lengths and the NC-C′ angle of 120.8(2)° indicate that the C- and N-atoms are purely sp2-hybridized and that there is little or no conjugation within the central DAB skeleton. Crystals of trans-[PdCl2(PPh3)(t-Bu-DAB)] are triclinic with space group P-1 and cell constants: a = 17.122(3), b = 18.279(3), c = 10.008(5)A, α = 96.77(2), β = 95.29(3), γ = 109.79(2). Z = 4. The t-Bu-DAB ligand is coordinated to the metal via one lone pair only. In this 2e; σ-N coordination mode the E-s-trans-E conformation of the free DAB-ligand is still present and the bonding distances within the DAB-ligand are hardly affected. [CN: 1.261(10)A; CC′: 1.479(10)A (mean).] The PdN-, NC- and central CC′-bond lengths are compared with those found in other metal -R-DAB complexes.

Synthesis andmolecular geometry of [trans-PtCl2PBu3]2 (di-t-Bu-diimine) containing a s,s-N,N' bridging diimine with a planar anti-(trans-P-Pt-NCCN-Pt-P-trans)-skeleton

Abstract Complexes of the type [MCl 2 XR′ 3 ] 2 R-dim (M = Pd or Pt; XR′ 3 = arsine or phosphine) are formed in almost quantitative yield in the reactions of [MCl 2 XR′ 3 ] 2 with α-diimine ( 1 1 molar ratio Pt-dimer/R-dim). An X-ray study of [PtCl 2 PBu 3 ] 2 t-Bu-dim [Z = 2, a = 11.4540(11), b = 16.1169(7), c = 12.9202(12) A and β = 99.82(1); R = 5.9%] reveals a structure consisting of two planar trans-PtCl 2 P-units bridged by a planar NCCN skeleton in anti-configuration [CC 1.48(2), CN 1.27(3), NPt 2.214(10) A]. As a consequence of the orthogonal position of the platinum coordination plane and the NCCN plane the β-imine proton resides a short distance from the platinum atom (about 2.6 A). The structure in solution has been determined by 1 H, 13 C, 31 P and 195 Pt NMR spectroscopy. The observed spectra point to retention of the structural features in solution as evidenced by a large down field shift of the imine protons, e.g. 9.58 ppm and an AA′MM′ pattern in [PdCl 2 PEt 3 ] 2 t-Bu-dim. The present compounds are the first examples of complexes which contain a σ,σ′-N,N′ planar bridging diimine ligand as a general structural feature.

Binuclear metal carbonyl DAB complexes. II. The syntheses and coordination properties of Mn(CO)5M'(CO)3DAB (M' = Mn, Re; DAB = 1,4-diazabutadiene)

Abstract Mn(CO) 5 M′(CO) 3 DAB complexes (M′ = Mn, Re; DAB = R 1 N=C(R 2 )-C(R′ 2 )=NR 1 ) can be easily obtained from the reaction between Mn(CO) 5 − and M′(CO) 3 X(DAB) (M′ = Mn, Re; X = Cl, Br, I). The complexes are formed by a nucleophilic mechanism, while a redistribution is responsible for the formation of a small amount of Mn 2 (CO) 10 . A diastereotopic effect can be observed in the 1 H and 13 C NMR spectra of complexes having isopropyl groups attached to the DAB ligand skeleton. A comparison is made with mononuclear complexes of the same symmetry, and the chemical shift differences for the methyl groups strongly depend on the substituent on the central metal responsible for the asymmetry. The low temperature enhancement of the σ → σ ★ transition localised on the metal—metal bond, which is normally observed for this type of compounds, was not observed for the Mn(CO) 5 M′(CO) 3 (DAB) complexes. The metal—metal bond can be activated by irradiating at the wave lengths associated with the CT transitions between the metal and the DAB ligand. Metal—metal bond cleavage occurs and Mn 2 (CO) 10 is formed.

Group IB organometallic chemistry : XXXII. Arylcopper compounds ArnCun as intermediates in organometallic synthesis. Single-step synthesis and dynamic NMR spectroscopy of diorganotin dihalides Ar2-nRnSnX2 (Ar 2-Me2NCH2C6H4 or (S)-2-Me2NCHMeC6H4; n 0 or 1)

Abstract The selective, single-step synthesis of (2-Me2NCHZC6H4)RSnX2, in which Z  H or Me, R  Me or Ph and X  Cl or Br, starting from the tetranuclear copper cluster compound (2-Me2NCHZC6H4)4Cu4 and RSnX3 is described. Reaction of (2-Me2NCH2C6H4)4Cu4 with SnBr4 in a 1/2 molar ratio afforded (2-Me2NCH2C6H4)2SnBr2 in almost quantitative yield. 1H NMR spectroscopic data of these novel compounds, which are monomeric in solution, indicate that: (i) intramolecular SnN coordination renders the Sn atom in (2-Me2NCHZC6H4)RSnX2 pentacoordinate, with the organo ligands residing in the equatorial plane of a trigonal bipyramidal structure, and the Sn atom in (2-Me2NCH2C6H4)2SnBr2 hexacoordinate, with trans organo groups and a cis arrangement for the Br and the N atoms; (ii) in pyridine the Sn atom in (2-Me2NCHZC6H4)RSnX2 becomes hexacoordinate by complex formation with the solvent but that intramolecular SnN coordination has been retained. The stereochemical lability of the pentacoordinate Sn center in the diorganotin dihalides (2-Me2NCHZC6H4)RSnX2, which contain a dissymmetrical equatorial plane, has been established on the basis of the dynamic NMR spectra of

Dinuclear silver(I) and copper(I) complexes with neutral N2S2 donor ligands and their reactivities towards CO. Structure in solution (1H and INEPT 109Ag NMR) and in the solid (X-ray) of [Ag{m-(R),(S)-1,2-(thiophene-2-CH=N)2-cyclohexane}2] (O3SCF3)2

Abstract The 1/1 reactions of the neutral N2S2 donor system (R)(S)-1,2-(5-R–thiophene-2-CHN)2–cyclohexane (R = H, 1a or Me, 1b) with [M(O3SCF3)] [M = Ag(I) or Cu(I)] yielded ionic complexes, consisting of a dinuclear [M2(1)2]2+ dication and O3SCF3− monoanions. An X-ray crystallographic study characterized the molecular structure of [Ag2–(1a)2](O3SCF3)2, in the monoclinic unit cell, space group P21/n, with Z = 4; a = 17.26(1), b = 15.08(2), c = 19.960(17) A, β = 106.15(4)°, V = 4991 A3. The structure was refined to R is 0.0704. The two N2S2 ligands coor- dinate to the silver(I) centres in a bridging di- bidentate manner with short AgN(imine) [e.g. Ag(1)N(2), 2.152(10); Ag(1)N(7), 2.162(9); Ag(2)N(3), 2.153(10); Ag(2)N(6), 2.158(10) A] and long AgS(thiophene) distances [Ag(1)S(1), 2.961(4); Ag(1)S(8), 2.938(4); Ag(2)S(4), 2.928(4); Ag(2)S(5), 2.995(5) A]. The Ag(1) Ag(I) separation is 2.909(1) A. In solution the coordination properties of the N2S2 ligands to silver(I) and copper(I) have been studied by 1H and INEPT 109Ag NMR spectroscopy. The 1H NMR data revealed, by the presence of two thiophene–imine 1H patterns at 190 K, that at this temperature i) the structural features found for [Ag2(1a)2]2+ in the solid are retained in solution and ii) the silver(I) and copper(I) complexes have similar structures in solution. Furthermore, the presence of 3J(1H107,109Ag) on the imine-H resonances of the silver(I) complexes indicates that at 190 K intermolecular exchange processes are slow on the NMR time scale. From the difference in δ109Ag of the [Ag2(1)2](O3SCF3)2 complexes, R = H (δ + 678) or Me (δ + 659), it was concluded that weak thiopheneSAg(I) interactions are present, and stabilize the formation of the [M2(1)2]2+ dications. However, in the reversible reactions of [Cu2(1)2](O3SCF3)2 with carbon monoxide the thiopheneSCu(I) bonds dissociate and neutral complexes are formed having a [{CuCO(O3SCF3)}2{μ−1}2] type of structure. In these complexes both the carbon monoxide and OSO2CF3 groups are terminally coordinated to Cu(I) (R = H, ν(CO), 2089 cm−1; R = Me, ν(CO) = 2087 cm−1 in CH2Cl2).

Synthesis of 8-(dimethylamino)-1-naphthyllithium etherate. Its structure in the solid (X-ray) and in Solution (7Li and 1H NMR)

The reaction of Bu{4}Li{4} with 4 molar equivalents of 1-(dimethylamino)naphthalene in diethyl ether affords novel 8-(dimethylamino)-1-naphthyllithium. Its molecular structure (X-ray) consists of two 8-(dimethylamino)-1-naphthyl groups each 3 center-2 electron bonded via C(1) to two lithium atoms and via the nitrogen lone pair to one of these lithium atoms. Diethyl ether coordination completes the pseudo tetrahedral lithium coordination sphere. Variable temperature }7{Li and }1{H NMR spectroscopy reveals an equilibrium between the [8-Me{2}NC{1}{0}H{6}Li.OEt{2}]{2} species and the ether-free [8-Me{2}NC{1}{0}H{6}Li]{n}. A tetranuclear structure is proposed for the latter species.

Field desorption mass spectrometry of a series of various metal carbonyl 1,4-diazabutadiene compounds

It is shown that field desorption mass spectrometry is a useful method of characterizing the thermally labile and involatile organometallic complexes mentioned in the title. In most cases only molecular ions are generated, but in some cases also (M@?CO)}+{}.{ fragment ions are observed.