Gerard Van Koten

Stable 1,4-diaza-1,3-butadiene(α-diimine)-zinc and -aluminium radicals formed in single electron transfer reactions: their consequences for organic syntheses

Abstract A discussion is given of the formation of complexes of the reaction of 1,4-di-t-butyl-1,4-diaza-1,3-butadiene t-Bu-NCHCHN-t-Bu (t-Bu-DAB) or of t-Bu-NCH-2-C 5 H 4 N (t-Bu-Pyca) with Et 2 Zn or Et 3 Al. It is shown that after the initial formation of four-coordinate complexes Et 2 Zn(t-Bu-DAB)_and Et 2 Zn(t-Bu-Pyca) with chelated diimine groups and of Et 3 Al(t-Bu-DAB) and Et 3 Al(t-Bu-Pyca) with monodentate bonded diimine groups a variety of reactions may occur. These reactions involve ethyl transfer to either the C- or the N-atoms of the ligand NCCN skeleton, and the formation of persistent organo-zinc and -aluminium radical complexes was also observed. The latter radical complexes have been studied by ESR spectroscopy. In the case of zinc the radical complex [EtZn(t-Bu-DAB) . ] is in equilibrium with a dinuclear complex in which the two t-Bu-DAB ligands are coupled via a CC bond. The mechanistic aspects of the reaction are briefly discussed.

Aspects of transmetallation reactions of 2-Me2NCH2C6H4- and 2,6-(Me2NCH2)-C6H3-metal (Pd,Pt,Hg,Tl) complexes with metal carboxylates and low-valent metal (Pd,Pt) complexes

Abstract A study has been made of reactions involving organometallic compounds containing ortho -Me 2 NCH 2 substituted aryl ligands. The single step syntheses of the new compounds [(2-Me 2 NCH 2 C 6 H 4 ) 2 TlCl], [ [{( S )-2-Me 2 NCH(Me)C 6 H 4 } 2 TlCl], [{( S )-2-Me 2 NCH(Me)C 6 H 4 }TlCl 2 ], [{2,6-(Me 2 NCH 2 ) 2 C 6 H 3 }TlClBr] and [{2,6-(Me 2 NCH 2 ) 2 C 6 H 3 }HgCl] are described. Stable internal NTl coordination at low temperatures has been established for the C-chiral thallium compounds. Reactions of the other Tl and Hg compounds and of [(2-Me 2 NCH 2 C 6 H 4 ) 2 Hg] with Pd(O 2 CMe) 2 , and also of the reverse reaction of cis -[(2-Me 2 NCH 2 C 6 H 4 ) 2 Pd] with Hg(O 2 CR) 2 or Tl(O 2 CR) 3 , gave transmetallation of one organo ligand and led to a single mono-organopalladium compound and corresponding by-products. Reaction of cis -[( 2 -Me 2 NCH 2 C 6 H 4 ) 2 Pd] with Pd(O 2 CR) 2 gave the dimeric compound [{(2-Me 2 NCH 2 C 6 H 4 )Pd(O 2 CR)} 2 ]. cis -[(2-Me 2 NCH 2 C 6 H 4 ) 2 Pt] did not react with Pd(O 2 CMe) 2 , while reaction of trans -[(2-Me 2 NCH 2 C 6 H 4 ) 2 Pt] or cis -[(2-Me 2 NC 6 H 4 CH 2 ) 2 Pt] with Pd(O 2 CMe) 2 resulted in decomposition. Upon heating, trans -[(2-Me 2 NCH 2 C 6 H 4 ) 2 Pt] was isomerized to cis -isomer. A redox reaction between [(2-Me 2 NCH 2 C 6 H 4 ) 2 Hg] and [Pt(COD) 2 ] (COD  1,5-cyclo-octadiene) and [Pd 2 (DBA) 3 ] (DBA  dibenzylideneacetone) gave the cis -isomers of [(2-Me 2 NCH 2 C 6 H 4 ) 2 M] (M  Pd, Pt). The results are discussed in terms of influence of internal coordination of the CH 2 NMe 2 group. It is concluded that although internal coordination of the CH 2 NMe 2 ligand can stabilize metal—carbon bonds it cannot prevent cleavage of such bonds by electrophiles. In this respect, there is no difference in the behaviour of Hg(O 2 CR) 2 and Tl(O 2 CR) 3 . The reactions are influenced by the metal—nitrogen bond strength, which follows the order PtN > PdN > HgN, TlN. The reactivity of Pt compounds is greatly influenced by their structure and type of ligand. It is proposed that cleavege of PdC bonds occurs mainly by a mechanism involving direct electrophilic attack at the carbon centre.

Synthesis and reactivity towards diiodine of palladium(II) and platinum(II) complexes with non-cyclic and cyclic ligands (C6H3{CH2NR1R2}2-2,6)−. End-on diiodine-platinum(II) bonding in macrocyclic [PtI(C6H3{CH2NMe(CH2)7MeNCH2}-2,6)(η1-I2)]

Several new organo-platinum(II) and -palladium(II) complexes [MX(C{6}H{3}{CH{2}NR}1{R}2{}{2}-2, 6)] (X = halide, M = Pt, Pd; R}1{ = R}2{ = Et; R}2{ = Me, R}1{ = }t{Bu, M = Pt: R}2{ = Me, R}1{ = Ph) have been synthesized from [PtCl{2}(SEt{2}){2}] or [PdCl{2}(COD)] (COD = 1, 5-cyclooctadiene) by reaction with [Li(C{6}H{3}{CH{2}NR}1{R}2{}{2}-2,6]{n}. Two of the intermediate Li complexes, i.e. [Li((tBu)MeNCN)]{2} and [Li((Ph)MeNCN)]{2} were isolated. In the platinum and palladium complexes the NCN ligands are terdentate bonded through C{i}{p}{s}{o} and two trans-positioned amine donor atoms. The complexes [PtI(C{6}H{3}{CH{2}NMe(CH{2}){7}MeNCH{2}}-2,6)] (4), in which the N(Me) atoms of the terdentate ligand are connected by a short (CH{2}){7} chain, and [PtCl(C{6}H{3}{CH{2}NPh{2}}{2}-2,6)(SEt{2}){2}], in which the Ph{2}NCN ligand is chain, and [PtCl(C{6}H{3}{CH{2}NPh{2}}{2}-2,6)(SEt{2}){2}], in which the Ph{2}NCN ligand is only monodentate bonded via C{i}{p}{s}{o}, were also made. The coordination ability of the NR}1{R}2{ donor atoms in these compounds was found to decrease in the order Me{2}N ~ (}t{Bu)MeN > Et{2}N > (Ph)MeN > Ph{2}N.

Syntheses and structural aspects of rigid aryl- palladium(II) and -platinum(II) complexes. X-ray crystal structure of o,o′-bis[(dimethylamino)methyl]phenyl- platinum(II) bromide

Abstract The tridentate monoanionic ligand o,o ′-(Me 2 NCH 2 ) 2 C 6 H 3 (NCN′) has been used to synthesize novel aryl-palladium(II) and -platinum(II) complexes [PtR(NCN′)] and [MX(NCN′)] (M = Pt, Pd). Three synthetic procedures are described, namely: (i) reaction of the cationic complex [M(NCN′)(H 2 O)] + with KX or NaX to give [MX(NCN′)] (X = Cl, I, O 2 CH, NCS, NO 2 , NO 3 ); (ii) displacement reactions using AgX with [MBr(NCN′)] to give [MX(NCN′)] (X = CN, O 3 SCF 3 . O 2 CMe, O 2 CCF 3 ) and (iii) transmetallation reactions of [PtBr{C 6 H 3 (CH 2 NMe 2 ) 2 - o,o ′}] with organolithium to give [PtR{C 6 H 3 (CH 2 NMe 2 ) 2 - o,o ′}] (R = Ph, o -, m -, p -tolyl, CCPh, CC- p -tolyl). All complexes have been characterized by elemental analysis, and IR, 1 H and 13 C NMR spectroscopy. An X-ray diffraction study has shown that [PtBr{C 6 H 3 (CH 2 NMe 2 ) 2 - o,o ′}] ( 2 ) has a square-planar structure, in which the tridentate ligand is bonded via C( ipso ) (PtC 1.90(1) A), and two mutually trans -N donor atoms (PtN(1) 2.07(1), PtN(2) 2.09(1) A). The fourth site trans to C( ipso ) is occupied by bromine (PtBr 2.526(2) A). The two chelate rings (NPtC( ipso ) 82.9(5) and 81.5(5)°) are distinctly puckered, with the two NMe 2 groups on opposite sides of the aryl plane. The PtC bond in 2 is shorter than analogous bonds in other arylplatinum(II) complexes, as a result of (i) the rigid structure of the tridentate ligand and (ii) the presence of two hard N donor atoms trans to one another across the platinum centre.

Structural investigation of aryllithium clusters in solution I. A 13C and 7Li NMR study of phenyllithium and some methyl-substituted phenyllithium derivatives

Abstract 13C and 7Li NMR spectra of phenyllithium and several methyl subsituted phenyllithium derivatives have been recorded in the presence of known amounts of coordinating solvents such as monodentate diethyl ether and THF and the potentially bidentate TMEDA (tetramethylethylenediamine). The relative amounts of the tetrameric and dimeric aggregates identified in these spectra depend on the donor strength, on the amount and denticity of added donor, and the presence or absence of ortho substituents in the phenyl group. Discrete solvated tetrameric aggregates were formed upon addition of exactly one equivalent of the monodentate donor solvent to an aryllithium compound having no ortho substituents; the addition of either two equivalents or excess of monodentate donor solvent or one equivalent of bidentate donor ligand afforded dimeric species. When one or two methyl substituents were present ortho to the lithium-carbon bond, either a mixture of dimeric and tetrameric species was formed (one methyl group) or the dimeric species was exclusively formed (two methyl groups).

Structural investigations of aryllithium clusters in solution II. A. 13C and 7Li NMR study of substituted phenyllithium compounds containing ortho-directing NME2 and CH2NMe2 groups

Abstract 7Li and 13C NMR spectroscopic studies have been made on the behaviour of several aryllithium compounds containing a N,N-dimethylamino substituent suitably positioned for intramolecular coordination to lithium in the presence of accurately known quantities of coordinating solvents (diethyl ether, THF) and ligand (TMEDA). The solvent molecules compete with the internal nitrogen coordination, and if their donor strength is sufficient and the steric situation is favourable they can fully replace intramolecular N-coordination. In the presence of more than one equivalent of the solvent, the aryllithium cluster can be broken down to afford solvent coordinated dimeric species. This change is reflected in an upfield shift of ca. 10 ppm for the 13C NMR C-ipso signal, with a concomitant change of 1J(7Li,13C) from ca. 11 to 20 Hz, and by an upfield shift of the 7Li NMR signal by ca. 1 ppm.

Syntheses and characterization of neutral complexes of Zn(II) with mono- and dianionic pyrrole-2-imine ligands [(pyrrole-2-CH=N)n-R]n- (n = 1, 2)

The reactions of the dianionic [(pyrrole-2-CHN)2R]2− ligands [(N′2N2)2−] (R = (R)(S)-1,2-cyclohexane or 1,2-ethane) with Zn(II) yield neutral dimeric [Zn2(N′2N2)2] complexes. The dimeric nature of the complexes was established by field-desorption mass spectrometry. 1H NMR studies show that these complexes have dimeric structures in solution in which the (N′2N2)2− ligands act as di-bidentates. The metal centres have tetrahedral geometries and bot have Δ or Λ configurations. The complex with the (R)(S)-1,2-cyclohexanediyl bridges has a rigid structure in solution. Neither intermolecular nor intramolecular exchange processes are observed The 1H NMR spectrum of the complex with the 1,2-ethanediyl bridging groups shows that at 213 K in CDCl3 a fast conformational movement is already taking place between two identical structures of the complex. It is not possible to determine whether in this complex intermolecular exchange processes are also taking place. The reactions of the anionic [pyrrole-2-CHNR′]− ligands [(N′N)−] (R′ = t-Bu, i-Pr, (S)-CHMePh or 2,6-xylyl) with Zn(II) yield the neutral Zn(N′N)2 complexes. These complexes were synthesized to study the coordination properties of the [pyrrole-2-CHNR′]− moieties with Zn(II). A 1H NMR study established that the zinc centres in the complexes containing the prochiral i-Pr or chiral (S)-CHMePh substituents have tetrahedral geometries with Δ or Λ configurations in CDCl3 at 213 K. These complexes undergo an intramolecular exchange process at higher temperatures (above 260 K when R′ = i-Pr) which involves inversion of the configuration of the zinc centre. A mechanism for this exchange process is proposed.

Iron and ruthenium complexes [M2(CO)6(pyridine-2-carbaldehyde-imine)] having a σ-N,μ2-N′, η2-CN′ bonded 6-R1-py-2-C(R2)NR ligand; x-ray structure of [Ru2(CO)5 &{1,2-bis(μ-isopropylamido)-1,2-bis(2-pyridyl)ethane}] containing two C|C linked pyridine-2-carbaldehyde-imine ligands

Abstract The pyridine-2-carbaldehyde-imines R 1 -py-2-C(R 2 )NR (R-Pyca) react with Fe 2 (CO) 9 to give Fe 2 (CO) 6 (R-Pyca) and Fe(CO) 3 (R-Pyca) and with Ru 3 (CO) 12 to Ru 2 (CO) 6 (R-Pyca). Further reaction of Ru 2 (CO) 6 (R-Pyca) with R-Pyca gives Ru 2 (CO) 5 (R-APE)(R-APe = 1,2-bis(μ-alkylamido)-1,2-bis(2-pyridyl)ethane), in which R-APE consists of two CC linked R-Pyca ligands. One representative Ru 2 (CO) 5 (R-APE) compound, viz. that with R = i-Pr, has been studied by X-ray diffraction. The compound Ru 2 (CO) 5 (i-Pr-APE) is monoclinic, space group P 2/ n with two molecules in a unit cell of dimensions a 14.499(5), b 9.051(3), c 9.772(4) A and β 103.54(4)°; Z = 2, R = 0.057 for 1743 observed reflections. Although the crystals were not of sufficient quality to warrant detailed discussion of the structure, it is clear that the 10e donor APM ligand bridges the Ru 2 (CO) 5 unit in which there is no RuRu bond. 1 H and 13 C NMR data for the free ligands and their Fe and Ru complexes are discussed, with emphasis on π-backbonding from the Group VIII metal to the imine CN′ bond.

Arylmercury(II) compounds involving intramolecular coordination via 2-Me2NCH2- and chiral (S)-2-Me2NCHMe-ring substituents

Abstract Arylmercury compounds of the type Ar 2 Hg and ArHgX (X = Cl, OAc) have been synthesized and characterized by 1 H and 13 C NMR spectroscopy; the Ar group was either 2-Me 2 NCH 2 C 6 H 4 or ( S )-2-Me 2 NCH(Me)C 6 H 4 , both of which contain N-donor ligands. The observation of anisochronous NMe resonances in ( S )-2-Me 2 NCH(Me)C 6 H 4 HgX (X = Cl, OAc) at low temperature indicates that in solution the mercury centre is three-coordinate as a result of stable intramolecular HgN coordination

8-(DIMETHYLAMINO)NAPHTHYLCOPPER(I), A NOVEL STABLE ORGANOCOPPER COMPOUND WITH UNUSUAL STRUCTURAL FEATURES. ITS SYNTHESIS, CRYSTAL STRUCTURE (X-RAY), AND REACTIVITY *

Summary The synthesis and isolation of a hydrocarbon- and ether-insoluble organocopper compound containing the rigid 8-(dimethylamino)naphthyl group is described. An X-ray determination of its structure revealed a tetranuclear copper aggregate, in which the Cu atoms are arranged in a parallelogram (Cu.. . Cu 2.407(2) and 2.430(2) A) and are three-center, two-electron bridged by C(@so) (Cu-C 2.025(6) A mean) of the naphthyl group. The amine ligands coordinate pairwise to opposite copper atoms. The copper aggregate thus contains two distinct types of Cu atoms, involving two nucleophilic two-coordinate and two electrophilic four-coordinate sites, pointing to a strong cuprate character. Reaction of the organocopper compound with several copper(I) salts resulted either in the formation of binaphthyl and dimethylaminonaphthalene or a stable mixed copper cluster, depending on the anion in the copper salt. With dimethyl acetylenedicarboxylate the copper compound, without added lithium or magnesium salts, gave the (syn) addition product 8Me,NnaphthylC(CO,Me)=C(CO,Me)Cu. These reactions are discussed in relation to the structural features of the tetranuclear organocopper compound.