Amidinato Ligands Research Articles

Synthesis and Reactivity of Amino(Ylide)Stannylenes

AbstractThe synthesis of two stable monoylide‐substituted stannylenes of type YCNSnR [R=Cl (1) or N(SiMe3)2 (2), and YCN=Ph3P(CN)C] starting from the cyanido‐substituted α‐metallated ylide YCN–K and SnCl2 or (SiMe3)2NSnCl is reported. Coordination of the cyano group to the tin center results in the dimerization of both stannylenes 1 and 2 in the solid state as well as in solution, where syn‐ and anti‐isomers are present. X‐ray diffraction analyses in combination with DFT calculations revealed that the π‐electron density of the ylide ligand is predominantly shifted into the cyano moiety rather than towards the tin center. This results in a strong preference of the dimers over the monomers, which is further emphasized by the reaction with 2,5‐di‐tert‐butylhydroquinone, which undergoes a [1+4] addition to the tin center to yield a spiro compound while preserving the cyclic core of the dimer. In contrast, phenyl isocyanate and dicyclohexylcarbodiimide insert into the Sn−Cylide bond, ultimately leading to the cleavage of the dimer and the formation of monomeric stannylenes with an ylide‐substituted thioamidato and amidinato ligand, respectively.

Compounds with Alternating Single and Double Bonds of Antimony and Silicon; Isoelectronic to Ethane-1,2-diimine.

We present an approach for preparing chain-type unsaturated molecules with low oxidation state Si(I) and Sb(I) supported by amidinato ligands that exploit to generate heavy analogues of ethane 1,2-diimine. The reduction of antimony dihalide (R-SbCl2) with KC8 in the presence of silylene chloride afforded L─(Cl)Si═Sb─Tip (1) and L(Cl)Si═Sb─TerPh (2), respectively. Compounds 1 and 2 further undergo reduction with KC8 to produce Tip─Sb═LSi─LSi═Sb─Tip (3) and TerPh─Sb═LSi─LSi═Sb─TerPh (4). The solid-state structures and DFT studies show that all compounds have σ-type lone pairs at each Sb atom. It forms a strong pseudo-π-bond with Si. The pseudo-π-bond is formed by the hyperconjugative donation of the π-type lone pair at Sb to the Si-N σ* MO. The quantum mechanical studies indicate that compounds 3 and 4 has delocalized pseudo-π-MOs arising from hyperconjugative interactions. Hence, 1 and 2 can be considered as isoelectronic to imine, while 3 and 4 are isoelectronic to ethane-1,2-diimine. The proton affinity studies indicate that the pseudo-π-bond resulting from the hyperconjugative interaction is more reactive than the σ-type lone pair.

Structural and Oxidation State Alternatives in Platinum and Palladium Complexes of a Redox-Active Amidinato Ligand.

Reaction of [Pt(DMSO)2Cl2] or [Pd(MeCN)2Cl2] with the electron‐rich LH=N,N’‐bis(4‐dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL2] (1) but dinuclear [Pd2L4] (2), a paddle‐wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV‐vis‐NIR spectroscopy, magnetic resonance) and TD‐DFT calculations as metal(II) species with noninnocent ligands L−. The reversibly accessible cations [PtL2]+ and [Pd2L4]+ were also studied, the latter as [Pd2L4][B{3,5‐(CF3)2C6H3}4] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [PtII(L−)2] or [Pt.(L )2], [PtII(L0.5−)2]+ or [PtIII(L−)2]+, [(PdII)2(μ‐L−)4] or [(Pd1.5)2(μ‐L0.75−)4], and [(Pd2.5)2(μ‐L−)4]+ or [(PdII)2(μ‐L0.75−)4]+. In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL2] with an N‐Pt‐N bite angle of 62.8(2)° in contrast to [Pd2L4], and the dimetal (Pd2 4+→Pd2 5+) instead of ligand (L−→L ) oxidation of the dinuclear palladium compound.

Control of dominant conduction orbitals by peripheral substituents in paddle-wheel diruthenium alkynyl molecular junctions.

Control of charge carriers that transport through the molecular junctions is essential for thermoelectric materials. In general, the charge carrier depends on the dominant conduction orbitals and is dominantly determined by the terminal anchor groups. The present study discloses the synthesis, physical properties in solution, and single-molecule conductance of paddle-wheel diruthenium complexes 1R having diarylformamidinato supporting ligands (DArF: p-R-C6H4-NCHN-C6H4-R-p) and two axial thioanisylethynyl conducting anchor groups, revealing unique substituent effects with respect to the conduction orbitals. The complexes 1R with a few different aryl substituents (R = OMe, H, Cl, and CF3) were fully characterized by spectroscopic and crystallographic analyses. The single-molecule conductance determined by the scanning tunneling microscope break junction (STM-BJ) technique was in the 10−5 to 10−4G0 region, and the order of conductance was 1OMe > 1CF3 ≫ 1H ∼ 1Cl, which was not consistent with the Hammett substituent constants σ of R. Cyclic voltammetry revealed the narrow HOMO–LUMO gaps of 1R originating from the diruthenium motif, as further supported by the DFT study. The DFT-NEGF analysis of this unique result revealed that the dominant conductance routes changed from HOMO conductance (for 1OMe) to LUMO conductance (for 1CF3). The drastic change in the conductance properties originates from the intrinsic narrow HOMO–LUMO gaps.

Synthesis and Reactivity of Functionalized Silicon(II) Compounds: Iminosilylene, Phosphinosilylene, Hydrosilylene, and Related Compounds

Abstract Recent decades have witnessed the isolation of a large number of stable silicon(II) compounds along with their applications toward small molecule activation and as versatile ligand systems for transition-metal complexes. The employment of donor stabilization techniques has proven to be an effective mean for stabilization of such silicon(II) systems that is consequently helpful in further reactivity investigations. In this context, an overview of the study of donor-stabilized silicon(II) compounds bearing unique functionalities that have recently been investigated in our research group is presented. By the use of amidinato ligand or N-heterocyclic carbene (NHC), the access to heteroatom-functionalized silicon(II) compounds has been achieved and exploration of further reactivity has led to the isolation of additional novel silicon(II) species. Applications of these silicon(II) compounds as ligands towards transition-metal complexes and in activation of organic and inorganic small molecules are also described.

Calcium Complexes Having Different Amidinate Ligands ‐ Synthesis and Structural Diversity

AbstractA one‐pot reaction of α‐diimine ligand 1,4‐disubstituted diazabutadienes (DAD) with potassium benzyl and anhydrous calcium iodide in 1:1:1 molar ratio afforded unprecedented 3‐phenylprop‐2‐ene‐di‐amido calcium compound [κ2‐(THF)4Ca{DippNC(=CHPh)CH2NDipp}] (1) (Dipp = 2,6‐diisopropylphenyl) in good yield. The solid‐state structure of the compound 1 revealed the formation of dianionic 3‐phenylprop‐2‐ene‐di‐amido ligand having an exocyclic olefinic bond derived from neutral α‐diimine fragment. However, analogous reactions with three different carbodiimides (RN=C=NR; R=Cy, iPr and tBu) with alkyl potassium and anhydrous calcium diiodide yielded corresponding homoleptic calcium compounds with amidinato ligand [κ2‐(THF)2Ca{RN=C(CH2Ph)NR}2] [R=Cy (2), iPr (3) and tBu (4)]. A separate reaction of DAD ligand, LiCH2SiMe3 and anhydrous ZnCl2 in diethylether solvent produced tri‐coordinated zinc compound [κ2‐ {DippN=C(CH2SiMe3)CH2NDipp}Zn[κ1‐{DippN=C(CH2SiMe3)CH2N‐Dipp}] (5) having amidinato moieties in the zinc coordination sphere in high yield. Molecular structures of compounds 2–5 in their solid states were also established.

Addition of dimethylaluminium chloride to N,N′-Disubstituted carbodiimides

Reactivity of trimethylaluminium, dimethylaluminium chloride and methylaluminium dichloride with N,N′-diisopropyl-, N,N′-dicyclohexyl- or N,N′-bis(diisopropylphenyl) carbodiimide (Dipp-NCN-Dipp) via the nucleophilic addition mechanism was studied. Six aluminium(III) complexes containing amidinato ligands were prepared and isolated. All reactions as well as the purity and structural confirmation of products were monitored using 1H and 13C NMR techniques. Reactions of prepared [Dipp-N-C(Me)–N-Dipp]AlMeCl with potassium mirror or pivalonitrile were also investigated. Molecular structures of five aluminium(III) mono- or bisamidinates and two dinuclear oxo-aluminium(III) amidinato by-products displaying four- or five-coordinated aluminium atom were determined by X-ray diffraction techniques.

Synthesis, structure and reactivity of a donor-stabilised silylene with a bulky bidentate benzamidinato ligand.

The novel donor-stabilised silylene was prepared in a four-step synthesis, starting from bis(2,6-diisopropylphenyl)carbodiimide (Dipp-N[double bond, length as m-dash]C[double bond, length as m-dash]N-Dipp), and its reactivity was studied in a series of oxidative addition reactions and a nucleophilic substitution reaction. The three-coordinate silicon(ii) complex contains the bulky bidentate amidinato ligand Dipp-NC(Ph)N-Dipp(-) and a dimethylamido ligand. Treatment of with N2O afforded the dinuclear five-coordinate silicon(iv) complex (SiO2N3 skeletons), and the reaction with S8 yielded the dinuclear four-coordinate silicon(iv) complex (SiS2N2 skeletons). Treatment of with Se and Te afforded the respective four-coordinate silicon(iv) complexes (SiSeN3 skeleton) and (SiTeN3 skeleton), which contain an Si[double bond, length as m-dash]Se and Si[double bond, length as m-dash]Te double bond, respectively. The reaction of with the silyl azide Me3SiN3 yielded the four-coordinate silicon(iv) complex (SiN4 skeleton) with an Si[double bond, length as m-dash]N double bond, whereas the reaction with the alkyl azide PhSCH2N3 gave the four-coordinate silicon(iv) complex (SiSN3 skeleton), the first silicon(iv) complex with an unsubstituted methyleneamido ligand. The reaction of with [Fe(CO)5] afforded the four-coordinate silicon(ii) complex (SiFeN3 skeleton) with an Si-Fe bond. Compounds (and the precursors and (five-coordinate silicon(iv) complexes with an SiCl3N2 and SiCl2N3 skeleton, respectively) in the synthesis of ) were characterised by elemental analyses, crystal structure analyses and multinuclear NMR spectroscopic studies in the solid state and in solution.

Synthesis, structure and reactivity study of magnesium amidinato complexes derived from carbodiimides and N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-butadiene ligands.

We report an amidinato ligand-supported series of magnesium complexes obtained from the insertion of a magnesium-carbon bond into a carbon-nitrogen double bond of different carbodiimides and α-diimine ligands. The magnesium complexes [Mg(CH2Ph){CyN[double bond, length as m-dash]C(CH2Ph)NCy}]2 (), [Mg(CH2Ph){(i)PrN[double bond, length as m-dash]C(CH2Ph)N(i)Pr}]2 () and the homoleptic [Mg{(t)BuN[double bond, length as m-dash]C(CH2Ph)N(t)Bu}2] () (Cy = cyclohexyl, (i)Pr = isopropyl, (t)Bu = tert-butyl) were prepared by the reaction of dibenzyl magnesium [Mg(CH2Ph)2(Et2O)2] with the respective carbodiimides either in 1 : 1 or 1 : 2 molar ratio in toluene. The analogous reaction of [Mg(CH2Ph)2(Et2O)2] with the N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (Dipp2DAD) ligand afforded the corresponding homoleptic magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}2] () (Dipp = 2,6 diisopropylphenyl) in good yield. The solid-state structures of magnesium complexes were confirmed by single-crystal X-ray diffraction analysis. It was observed that in each case, a magnesium-carbon bond was inserted into the carbon-nitrogen double bond of either carbodiimides or Dipp2DAD resulting in a monoanionic amido-imino ligand. In a further reaction between and N-aryliminopyrrolyl ligand 2-(2,6-(i)Pr2C6H3N[double bond, length as m-dash]CH)C4H3NH (ImpDipp-H) in 1 : 2 molar ratio, a new magnesium complex [Mg(ImpDipp)2{CyN[double bond, length as m-dash]C(CH2Ph)NHCy}] (), with one amidinato and two aryliminopyrrolyl ligands in the coordination sphere, was obtained in good yield. In contrast, the homoleptic magnesium complex reacted with one equivalent of N-aryliminopyrrolyl ligand (ImpDipp-H) to produce another mixed ligated magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}(ImpDipp)] (), with a benzylated DAD ligand and aryliminopyrrolyl ligands in the coordination sphere. Further reaction of complex with benzyl alcohol (PhCH2OH) afforded the third mixed ligated magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}(OCH2Ph)2] () in very good yield. The magnesium complexes were characterised using standard analytical/spectroscopic techniques and their solid-state structures were established by single-crystal X-ray diffraction analysis.

Bis[N,N′-diisopropylbenzamidinato(−)]silicon(II): Cycloaddition Reactions with Organic 1,3-Dienes and 1,2-Diketones

Reaction of the donor-stabilized silylene 1 (which is three-coordinate in the solid state and four-coordinate in solution) with organic 1,3-dienes (2,3-dimethyl-1,3-butadiene, 1,3-butadiene, (E,E)-1,4-diphenyl-1,3-butadiene, 2,3-dibenzyl-1,3-butadiene, 1,3-cyclohexadiene, or cyclooctatetraene) and 1,2-diketones (3,5-di-tert-butyl-1,2-benzoquinone or 1,2-diphenylethane-1,2-dione) leads to the formation of the respective cycloaddition products 2–9. Compounds 2–9 were characterized by crystal structure analyses (7 was studied as the hemi solvate 7·0.5n-C6H14) and NMR spectroscopic studies in the solid state and in solution. As the amidinato ligands can switch between a monodentate and bidentate coordination mode, for some of the cycloaddition products studied, the silicon coordination number in the solid state and in solution is different. For example, compound 4 is four- (4a) and six-coordinate (4b) in the solid state (isolated as a 1:1 cocrystallizate of 4a and 4b) and five-coordinate in solution. As demon...

Formation and reactivity of an (alkene)peroxoiridium(iii) intermediate supported by an amidinato ligand

An Ir(I) complex of an acetamidinato ligand was synthesized by reaction of N,N'-diphenylacetamidine, PhN[double bond, length as m-dash]C(Me)NHPh, with either MeLi and [{Ir(cod)}2(μ-Cl)2] or [{Ir(cod)}2(μ-OMe)2] and was characterized by X-ray crystallography as a mononuclear complex, [Ir{PhNC(Me)NPh}(cod)] (1; where cod = 1,5-cyclooctadiene). Reaction of 1 with CO afforded a dinuclear carbonyl complex, [{Ir(CO)2}2{μ-PhNC(Me)NPh-κN:κN'}2] (2), as indicated by EI mass spectrometry and solution- and solid-state IR spectroscopy [νCO (n-pentane) = 2067, 2034 and 1992 cm(-1)]. Activation of O2 by 1 in solution at 20 °C was irreversible and produced an (alkene)peroxoiridium(iii) intermediate, [Ir{PhNC(Me)NPh}(cod)(O2)] (3), which was characterized by one- and two-dimensional NMR techniques and IR spectroscopy (for 3, νOO = 860 cm(-1); for 3-(18)O2, νOO = 807 cm(-1)). Complex 3 oxidized PPh3 to OPPh3, and its decay in the absence of added substrates followed by reaction with cod yielded 4-cycloocten-1-one and a minor amount of 1. In comparison with the results for the previously reported guanidinato complex [Ir{PhNC(NMe2)NPh}(cod)(O2)] (4), the formation of 3 and its reaction with PPh3 are significantly faster, indicating considerable ligand effects in these reactions.

Bis(amidinato)germylenerhodium Complexes: Synthesis, Structure, and Density Functional Theory Calculations

The first monogermylenerhodium complexes stabilized by bulky amidinato ligands on the divalent germanium center have been synthesized and characterized by NMR spectroscopy and X-ray crystallography. Their stability strongly depends on the steric hindrance of the amidinato ligand. With trimethysilyl groups on the nitrogen atoms of the amidinato ligand, only the germylene oxide rhodium complex could be obtained; by contrast, with t-Bu groups, the germylenerhodium complex was isolated. In both cases, the formation of amidinatorhodium complexes was observed. The donating ability of the germylene ligand has been assessed from the CO stretching frequency of the corresponding dicarbonylrhodium complex and was confirmed by density functional theory calculations.

Reactivity of lithium n-butyl amidinates towards group 14 metal(ii) chlorides providing series of hetero- and homoleptic tetrylenes

The new class of homo- and heteroleptic n-butyl-N,N'-disubstituted amidinato group 14 metal(II) complexes were prepared by salt elimination from starting lithium amidinates and metal(II) chlorides both in stoichiometric ratio 2:1 and 1:1, respectively. The target amidinates contain less bulky isopropyl or cyclohexyl as well as a sterically demanding aromatic substituent. Desired 1:1 Pb(II) complexes are not accessible by the described procedure. Ligand transfer from Pb to Sn is taking place if homoleptic Pb(II) compounds are reacted with SnCl(2). Prepared tetrylenes were characterized by (1)H, (13)C, (119)Sn and (207)Pb NMR spectroscopy in C(6)D(6) or THF-d(8). X-Ray diffraction studies of one heteroleptic Ge(II) monomeric where the coordination polyhedron of the three coordinated germanium atoms is a trigonal pyramid, two different dimeric structures of heteroleptic Sn(II) complexes, one amidine hydroiodide byproduct and the oxidation product of the heteroleptic chloro Sn(II) amidinate as a tetranuclear species with two Sn(IV) and two Sn(II) atoms in central Sn(2)O(2) planar ring were performed on appropriate single crystals. The dimer of one of the heteroleptic stannylenes reveals a new type of monomeric units connection, weak Sn-Cl contact and an interaction of the tin atom with delocalized N-C(C)-N system of the amidinato ligand of the second molecule.

A P4 Chain and Cage from Silylene‐Activated White Phosphorus

An acyclic P4 chain supported by a silicon-substituted amidinato ligand was formed from the reaction of PhC(NtBu)2SiN(TMS)2 with P4 (TMS=Me3Si). This is the first example of an acyclic SiP chain that contains 6π electrons. When the benzamidinato moiety was replaced with Cp* (Cp*=Me5C5), an unusual silicon–phosphorus cage surprisingly formed (see scheme).

Novel Stable Silyl, Germyl, and Stannyl Germanium(II) Compounds Containing an Amidinato Ligand

Reactions of the N,N′-chelated chlorogermanium(II) compound [Me3SiNC(Ph)NSiMe3]GeCl with the magnesium reagents Mg[E(SiMe3)3]2 (E = Si, Ge, Sn) gave the new metallyl germylenes [Me3SiNC(Ph)NSiMe3]GeE(SiMe3)3, representing the first isolated silyl- and stannylgermylenes. These compounds have been fully characterized by multinuclear NMR spectroscopy and their structures determined by X-ray diffraction analysis.

Synthesis of Stable Silicon Heterocycles by Reaction of Organic Substrates with a Chlorosilylene [PhC(NtBu)2SiCl

Heteroleptic chlorosilylene (PhC(NtBu)(2)SiCl) (1) reacts with unsaturated organic compounds under oxidative addition. Reactions of 1 with cyclooctatetraene (COT) and a diimine afford [1+4]-cycloaddition products 3 and 6, respectively. In the case of COT, one Si-N bond of the amidinato ligand is cleaved, resulting in tetracoordinate silicon, whereas with a diimine a pentacoordinate silicon is formed. Treatment of 1 with ArN=C=NAr (Ar=2,6-iPr(2)C(6)H(3)) yields silaimine complex 4 with cleavage of one of the C=N bonds. The facile isolation of silaimine complexes is probably due to the kinetic protection afforded by the bulky Ar moiety. When 1 is treated with tert-butyl isocyanate, cleavage of the C=O bond is observed, which leads to formation of the four-membered Si(2)O(2) cycle 5. The same product is formed when 1 is allowed to react with trimethylamine N-oxide. When 1 is treated with diphenyl disulfide, cleavage of the S-S bond occurs to form 7. All products have been characterized by multinuclear NMR spectroscopy, EI mass spectrometry, and elemental analysis. In addition, the molecular structures of 3-6 have been determined by single-crystal X-ray diffraction studies. Collectively, these results suggest that owing to the presence of the lone pair of electrons, the propensity of 1 to undergo oxidative addition is very high.

Synthesis of a Stable Four-Membered Si2O2 Ring and a Dimer with Two Four-Membered Si2O2 Rings Bridged by Two Oxygen Atoms, with Five-Coordinate Silicon Atoms in Both Ring Systems

The base-stabilized bis-silylene (LSi−SiL, L = PhC(NtBu)2) was reacted with benzophenone in a 1:2 ratio in THF, which afforded a Si2O2 four-membered ring, stabilized by bulky amidinato ligands. The most striking phenomenon is the abstraction of oxygen from benzophenone and the simultaneous formation of a silicon carbon bond. The four-membered Si2O2 ring is planar, and both the silicon atoms are five-coordinate. The two silicon atoms are arranged opposite each other in the four-membered Si2O2 ring. Moreover LSi−SiL was treated with N2O to afford two four-membered Si2O2 rings connected with two oxygen atoms. In this structure also the silicon atoms are five-coordinate.

Low coordinate lanthanide(ii) complexes supported by bulky guanidinato and amidinato ligands

The preparation of a series of homoleptic, four-coordinate lanthanide(ii) complexes, [Ln(Priso)(2)] (Ln = Sm, Eu or Yb) incorporating the bulky guanidinate ligand Priso(-) ([(ArN)(2)CNPr(i)(2)](-), Ar = 2,6-diisopropylphenyl) is described. X-ray crystallography shows the complexes to be isostructural and to exhibit coordination geometries midway between tetrahedral and planar. Comparisons between the geometries of the complexes and those of the bulkier systems, [Ln(Giso)(2)] (Giso(-) = [(ArN)(2)CNCy(2)](-), Cy = cyclohexyl) are discussed. Attempts to prepare the less hindered amidinate complexes, [Ln(Piso)(2)] (Piso(-) = [(ArN)(2)CBu(t)](-)), were not successful, but did give rise to the heteroleptic complex, [(kappa(1)-N,eta(6)-Piso)Sm(THF)(mu-I)(2)Sm(kappa(1)-N,eta(6)-Piso)]. Whereas the amidinate ligands in this complex chelate the samarium centre in an kappa(1)-N,eta(6)-Ar-fashion, in the closely related complex, [{(kappa(2)-N,N'-Priso)Yb(THF)(mu-I)}(2)], the ytterbium atoms are kappa(2)-N,N'-chelated by the guanidinate ligand. The facility of the planar four-coordinate complex, [Sm(Giso)(2)], to act as a one-electron reducing agent towards a variety of unsaturated substrates has also been explored. The complex has been shown to selectively reductively couple CS(2), via a C-S bond formation, to give the samarium(iii) dimer, [(Giso)(2)Sm(mu-eta(2)-:eta(2)-S(2)CSCS)Sm(Giso)(2)].

Solution Behavior of Amidine Complexes: An Unexpected cis/trans Isomerization and Formation of Di- and Trinuclear Platinum(III) and Platinum(II) Species

Platinum bis-amidine complexes (both the cis and trans isomers) are stable in acetone and chlorinated solvents but are unstable in protic solvents such as methanol or water. In the latter solvents an initial cis/trans isomerization leads to formation of an equilibrium mixture with a cis/trans ratio of about 1:4; subsequently a dinuclear platinum(III) complex (1) is formed under aerobic conditions while, under anaerobic conditions, a trinuclear platinum(II) compound (2) is obtained. We hypothesize that the process of isomerization and formation of polynuclear compounds (1 and 2) have a common precursor: a dinuclear platinum(II) species supported by two bridging amidinato ligands (3), formed in small yield, which can either dissociate back to monomers of cis/trans configuration or evolve in two different polynuclear species depending upon the aerobic/anaerobic conditions. In aerobic conditions, oxidation of platinum(II) to platinum(III) together with formation of two additional amidinato bridges across the two platinum centers takes place leading to compound 1. In contrast, in anaerobic conditions, oxidation of platinum is prevented and the dinuclear platinum(II) precursor remains in solution until it reacts with an extra molecule of the starting mononuclear complex which loses its two amidine ligands and cross-links the two bridging amidinato ligands of 3 to yield compound 2. This latter features two triply bridging amidinato ligands linking the three platinum units to form a pocket. Complexes 1 and 2 have been characterized by means of IR and NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray crystallography.

The Template Effect of Palladium(II): Synthesis, Characterization, and Crystal Structures of 2,4‐Substituted 1,3,5‐Triazapentadienatopalladium(II) Complexes

AbstractThe reaction of LiN(SiMe3)2 with two equivalents of 2‐, 3‐, or 4‐cyanopyridine followed by the addition of half an equivalent of [PdCl2(PhCN)2] gives neutral 1,3,5‐triazapentadienato complexes of the general formula [Pd{HNC(Py)NC(Py)NH}2] (Py = 2‐pyridyl 1, 3‐pyridyl 2, 4‐pyridyl 3). When the above reaction was carried out with benzonitrile and then 3‐ or 4‐cyanopyridine was added followed by half an equivalent of [PdCl2(PhCN)2] neutral unsymmetrical 1,3,5‐triazapentadienato complexes of the general formula [Pd{HNC(Ph)NC(Py)NH}2] (Py = 3‐pyridyl 4, 4‐pyridyl 5) were obtained. When LiN(SiMe3)2 was treated with one equivalent of benzonitrile in THF, followed by the addition of a quarter of an equivalent of anhydrous palladium chloride and workup in air, the trinuclear complex tetrakis(benzamidinato)bis(2,4‐diphenyl‐1,3,5‐triazapentadienato)tripalladium(II) (6) was obtained as yellow crystals in 19 % yield. All complexes were fully characterized by elemental analysis, 1H NMR spectroscopy, and mass spectrometry. The solid‐state structures of compounds 2, 3, and 6 were determined by X‐ray crystallography. Structural analyses revealed that the 2,4‐bis(pyridyl)‐1,3,5‐triazapentadienyl ligands in 2 and 3 behave as didentate ligands to form six‐membered rings with the metal ion. For 6, the 2,4‐diphenyl‐1,3,5‐triazapentadienyl ligands also behave as didentate ligands to form six‐membered rings with the metal ion, whereas the amidinato ligands behave as bridging didentate ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)