Synthesis and characterization of novel dinuclear copper(I) complexes. Dimerization of [CuL(PPh3)2] (L = methyl 3-hydroxy-3-(p-R-phenyl)-2-propenedithioate)

We report the synthesis of new copper(I) complexes 6a-e from methyl 3-hydroxy-3-(p-R-phenyl)-2-propenedithioate ligands. These complexes were characterized by IR and 1H, 13C, and 31P NMR spectroscopy. The expected O,S-coordination mode was confirmed by the X-ray diffraction studies of 6b and 6e. The unexpected dimerization of 6b-e leads to the formation of four novel dinuclear copper(I) compounds (7b-e). The dinuclear complex structure was fully established by the X-ray diffraction analysis of 7a, in which the presence of a Cu-Cu interaction was observed.     

Synthesis and Metal Complexes of Thiourea Ligands Containing Carbohydrate‐Derived Substituents

Two glucose‐derived thiourea derivatives, 2a and 2b , were prepared by addition of the corresponding amino sugars to a solution of 4‐nitrobenzoyl isothiocyanate (Scheme 1). The thioureas were isolated as colorless solids in good yields and were fully characterized by NMR spectroscopy, optical rotation, elemental analysis, and also by single‐crystal X‐ray diffraction. Attempts to obtain Cu^II and Ni^II bis(chelate) complexes with these thioureas failed. However, the C(1)‐protected thiourea derivative 2a reacted with orthopalladated acetato‐bridged dimers to afford the corresponding monomeric Pd^II complexes 3 and 4 (Scheme 2). In these compounds, the thiourea coordinates to the metal as monoanionic O,S chelate ligand, which was confirmed by X‐ray crystallography.     

3,5-Dimethyl and 3,5-di-tert-butylpyrazolato complexes with alkali metals: monomeric, dimeric, cluster, and 1D chain structures

The pyrazolato complexes [(Me(2)pz)(THF)Li] (1), [((t)Bu(2)pz)Li](4) (2), [((t)Bu(2)pzH)((t)()Bu(2)pz)Li](2) (2a), [(Me(2)pz)Na] (3), [((t)Bu(2)pz)Na](4), [((t)Bu(2)pz)(6)(OH)Na(7)] (4a), [((t)Bu(2)pz)(18-crown-6)Na] (4b), and [((t)Bu(2)pz)K] (5) were synthesized by metalation reactions between R(2)pzH (R = Me, (t)()Bu) and alkyllithium, elemental sodium, or potassium. All the complexes were characterized by spectroscopic methods and microanalysis, and in addition, the crystal structures of 2, 2a, 3, 4a, 4b, and 5 were obtained by single-crystal X-ray diffraction. They show monomeric, dimeric, cluster, and 1D chain structures in the solid state. Ab initio calculations on the structure and stabilities of the monomeric pzM complexes were performed at the MP2 level of theory showing good agreement with the coordination preferences of the pyrazolato ligand to a particular alkali ion.     

Syntheses, reactions, and ethylene polymerization of half-sandwich titanium complexes containing salicylbenzoxazole and salicylbenzothiazole ligands

Half-sandwich titanium salicylbenzoxazole complexes CpTiLCl(2) 2a-2c [L = R-2-(benzo[d]xazol-2-yl)phenol (R = H (2a), R = 6-CH(3) (2b), R = 4-CH(3)-6-(t)Bu (2c)] and salicylbenzothiazole complexes CpTiLCl(2) 2d-2g [L = R-2-(benzo[d]thiazol-2-yl)phenol (R = H (2d), R = 6-CH(3) (2e), R = 6-(t)Bu (2f), R = 4-Cl (2g)] were synthesized by the reaction of CpTiCl(3) with the sodium salts of their corresponding precursors. Complexes 2a-2g were fully characterized by (1)H and (13)C NMR spectra and elemental analyses. The molecular structures of 2a and 2b were determined by single crystal X-ray diffraction methods. When activated by excess methylaluminoxane (MAO) these half-sandwich titanium complexes showed moderate to high activities for ethylene polymerization and produced high molecular weight polyethylenes. The half-sandwich titanium salicylbenzoxazole complexes (2a-2c) exhibited higher activities, of up to 1.23 × 10(6) g PE mol Ti(-1) h(-1) for the 2b/MAO system, than those of their analogues, half-sandwich titanium salicylbenzothiazole complexes (2d-2g).     

Chemistry of bridging phosphanes: PdI dimers bearing 2,5-dipyridylphosphole ligands

Two synthetic routes to Pd(I) dimers that feature a bridging 1-phenyl- and 1-cyclohexyl-2,5-di(2-pyridyl)phosphole ligand, 3 a and 3 b, respectively, are described. The first involves a conproportionation process between Pd(II) and Pd(0) complexes, while the second involves ligand displacement from a preformed Pd(I) dimer. Both routes are operable for 1-phenylphosphole 1 a, whereas the former failed with 1-cyclohexylphosphole 1 b. A mechanistic study revealed that the conproportionation pathway implies a reversible oxidative addition of the P-C(phenyl) bond of Pd(II)-coordinated 1 a to Pd(0) leading to a bimetallic Pd(II) complex 5. The structures of complexes 3 a and 3 b were studied by means of X-ray diffraction. The similarity of these solid-state structures suggests that the bridging mode of the P atom is due to mu-1kappaN:1,2kappaP:2kappaN coordination of ligands 1 a, b. The electrochemical behaviour and UV/Vis absorption properties of complexes 3 a, b are reported. Complex 3 a is inert towards CO, PPh(3) and 1,3-dipoles. It reacted with dimethylacetylene dicarboxylate to give complex 6 as a result of insertion of the alkyne into the Pd-Pd bond. X-ray diffraction studies of complexes 5 and 6 are also presented.     

Synthetic,Structural and Biological Studies on Divalent Tin Complexes of Sixteen to Twenty-Four Membered Tetraaza Macrocycles

A new series of 16- to 24-membered macrocycles of tin(II) containing tetraaza groups has been prepared by the template condensation reaction of glutaric acid and phthalic acid with 1,2-phenylenediamine, 2,6-diaminopyridine, and diethylenetriamine in 1:2:2 molar ratios. The reaction products were characterized by elemental analyses, molecular weight determinations, infrared, 1 H NMR, 119 Sn NMR, and mass spectral studies. X-ray powder diffraction spectrum of one representative compound also has been reported. The hexacoordinated state for tin has been confirmed by spectral studies. An octahedral geometry for these complexes has been proposed as the binding sites are the nitrogen atoms of the macrocycle. The formulation of the complexes as [Sn(N 4 MaC n )Cl 2 ] (where N 4 MaCn represent the ligand molecule and n = 1 to 6 has been established on the basis of the chemical composition. All of the complexes are monomeric. The ligands and their complexes also have been screened for their antimicrobial activities and the results are discussed.     

二(四氢糠基茚)稀土氯化物的合成及晶体结构

将四氢糠基茚锂分别与无水三氯化钇和无水三氯化钆以摩尔比2;1反应,除去不溶物和溶剂后,将产物在甲苯/THF中冷冻得到晶体(C₄H₇OCH₂C₉H₆)₂LnCl[Ln=Y(1);Ln=Gd(2)].这两种配合物都是单分子无溶剂化合物,在空气中稳定.配合物1和2的晶体结构都属于正交晶系,P2₁2₁2₁空间群,晶胞参数分别为a=1.04252(9)nm,b=1.47455(12)nm,c=1.49799(13)nm,Z=4,Dc=1.508g/cm³;a=1.03701(10)nm,b=1.47233(12)nm,c=1.51354(14)nm,Z=4,Dc=1.699g/cm³.它们的结构相似,但空间构象不同.稀土中心离子分别与两个茚中的五元环和两个氧原子及氯原子成键,形成九配位结构.     

Lutetium alkyl and hydride complexes in a non-cyclopentadienyl coordination environment

Lutetium alkyl complexes [Lu(L)(CH(2)SiMe(3))(THF)(n)], which contain a sulfur-linked bis(phenolato) ligand such as 2,2'-thiobis(6-tert-butyl-4-methylphenolate) (L=tbmp, 1) or 1,4-dithiabutanediyl-bis(6-tert-butyl-4-methylphenolate) (L=etbmp, 2), were isolated from the reaction of the lutetium tris(alkyl) complex [Lu(CH(2)SiMe(3))(3)(THF)(2)] with H(2)L. The monomeric structures of these complexes were confirmed by X-ray diffraction studies, showing distorted octahedral geometry around the metal centre. The reaction of [Lu(tbmp)(CH(2)SiMe(3))(THF)(2)] (1) with alcohols ROH (R=iPr, CHPh(2), CPh(3)) results in the formation of the corresponding alkoxide complexes [Lu(tbmp)(OR)(THF)(n)] (4-6). With PhSiH(3) hydride complexes [Lu(L)(mu-H)(THF)(n)](2) (L=tbmp, 7; etbmp, 8) have been prepared in moderate to good yields. They adopt a dimeric form in the solid state as revealed by the X-ray crystal structure of 7. The reactivity of the hydride complexes and their catalytic activity in the ring-opening polymerisation of L-lactide and the hydrosilylation of alkenes are also discussed.     

Rare-earth metal complexes supported by 1,omega-dithiaalkanediyl-bridged bis(phenolato) ligands: synthesis, structure, and heteroselective ring-opening polymerization of rac-lactide

Monomeric yttrium and lutetium bis(phenolato) complexes [Ln(OSSO){N(SiHMe 2) 2}(THF)] (Ln = Y, Lu) were prepared from the reaction of silylamido complexes [Ln{N(SiHMe 2) 2} 3(THF) 2] with 1 equiv of tetradentate 1,omega-dithiaalkanediyl-bridged bis(phenol) (OSSO)H 2 1- 9 in moderate to high yields. In contrast to the rigid configuration of scandium analogues, the yttrium complexes 2b and 3b and the lutetium complex 3c that contain a C 2 bridge between the two sulfur donors of the ligand are symmetric in solution. The monomeric nature of these complexes was indicated by an X-ray diffraction study of the yttrium complex 6b. The yttrium center in 6b is coordinated to the tetradentate [OSSO]-type ligand, one silylamido group and one THF ligand with the two oxygen donors of the [OSSO]-type ligand located trans. Corresponding bis(phenolato) silylamido complexes of larger rare-earth metals could not be obtained from similar reactions: Reaction of [La{N(SiHMe 2) 2} 3(THF) 2] with 1,2-xylylene-linked bis(phenol) gave a dinuclear lanthanum complex 6d of the formula [La 2(OSSO) 3] with two inequivalent eight-coordinate metal centers. The yttrium and lutetium complexes efficiently initiated the ring-opening polymerization (ROP) of lactides in THF. The heteroselectivity during the ROP of rac-lactide was enhanced when the steric demand of the bis(phenolato) ligand was increased, either by extending the bridge length or by introducing bulky ortho-substituents in the phenoxy units. A C 3 bridge within the ligand backbone is essential to allow configurational interconversion of the active site between Lambda and Delta configuration during polymerization, allowing accommodation of both enantiomers of the monomer in an alternating fashion.     

Aluminium alkyl complexes supported by [OSSO] type bisphenolato ligands: synthesis, characterization and living polymerization of rac-lactide

Aluminium alkyl complexes [(OSSO)AlR](1-3: R = Me, Et) were isolated in good yields from the protonolysis reaction of AlR3 with the corresponding tetradentate 1,omega-dithiaalkanediyl-bridged bisphenols (1,4-dithiabutanediyl-bis(6-tert-butyl-4-methylphenol), etbmpH2; ortho-xylylenedithio-bis(6-tert-butyl-4-methylphenol), xytbmpH2). The monomeric structures of all three complexes were confirmed by X-ray diffraction studies. Complexes 1 and 2 have an isotypic packing arrangement. The aluminium center is coordinated by the etbmp ligand and one alkyl group with distorted trigonal bipyramidal geometry. Complex 3 shows Cs symmetry with square pyramidal geometry around the metal center. Substitution reaction of complex 1 with trityl alcohol gave the monomeric alkoxide complex [(etbmp)Al(OCPh3)] 4, which has a similar trigonal bipyramidal geometry around the aluminium atom as complex 1. In the presence of isopropanol, complexes 1-3 initiated the living ring-opening polymerization of rac-lactide (PDI = 1.03-1.06, Mw/Mn). The ligand structure influenced the tacticity of the obtained polymer, with complex 3 giving heterotactic-enriched polylactides.     

Addition of S-H bonds across electron-deficient olefins catalyzed by well-defined copper(I) thiolate complexes

A series of monomeric (NHC)Cu(SR) (R = Ph or CH2Ph; NHC = N-heterocyclic carbene) complexes have been synthesized and fully characterized including single-crystal X-ray diffraction studies. These complexes catalyze the addition of S-H bonds across electron-deficient olefins to regioselectively produce "anti-Markovnikov" products.     

Malonate complexes of dysprosium: synthesis, characterization and application for LI-MOCVD of dysprosium containing thin films

A series of malonate complexes of dysprosium were synthesized as potential metalorganic precursors for Dy containing oxide thin films using chemical vapor deposition (CVD) related techniques. The steric bulkiness of the dialkylmalonato ligand employed was systematically varied and its influence on the resulting structural and physico-chemical properties that is relevant for MOCVD was studied. Single crystal X-ray diffraction analysis revealed that the five homoleptic tris-malonato Dy complexes (1-5) are dimers with distorted square-face bicapped trigonal-prismatic geometry and a coordination number of eight. In an attempt to decrease the nuclearity and increase the solubility of the complexes in various solvents, the focus was to react these dimeric complexes with Lewis bases such as 2,2'-biypridyl and pyridine (6-9). This resulted in monomeric tris-malonato mono Lewis base adduct complexes with improved thermal properties. Finally considering the ease of synthesis, the monomeric nature and promising thermal characteristics, the silymalonate adduct complex [Dy(dsml)(3)bipy] (8) was selected as single source precursor for growing DySi(x)O(y) thin films by liquid injection metalorganic chemical vapor deposition (LI-MOCVD) process. The as-deposited films were analyzed for their morphology and composition by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Rutherford backscattering (RBS) analysis and X-ray photoelectron spectroscopy.     

Synthesis, characterization, and reactivity of rhodium(I) acetylacetonato complexes containing pyridinecarboxaldimine ligands

Addition of o-C 6H 4NCHNAr to Rh(coe) 2(acac) (coe = cis-cyclooctene, acac = acetylacetonato) gave several new iminopyridine rhodium(I) complexes of the type Rh(acac)(kappa (2)- o-C 6H 4 NCH NAr) ( 1a Ar = 4-C 6H 4-OMe; 1b Ar = 2,6-C 6H 3-Me 2; 1c Ar = 2,6-C 6H 3-Et 2; 1d Ar = 2,6-C 6H 3- i-Pr 2). All new rhodium complexes have been characterized by a number of physical methods, including multinuclear NMR spectroscopy and X-ray diffraction studies for 1b and 1c. Addition of CHCl 3 to 1a afforded the corresponding rhodium(III) complex trans-Rh(kappa (2)- o-C 6H 4 NCH NAr)(CHCl 2)(Cl)(acac) ( 2). Addition of B 2cat 3 (cat = 1,2-O 2C 6H 4) to 1 gave zwitterionic Rh(eta (6)-catBcat)(kappa (2)- o-C 6H 4 NCH NAr) ( 3). The molecular structure of 3b has been confirmed by a single crystal X-ray diffraction study and shows that the N 2Rh fragment is bound to the catBcat anion via one of the catecholato groups in a eta (6)-fashion. These complexes have also been examined for their ability to catalyze the hydroboration of a series of vinylarenes. Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation mechanism to give a number of boronated products.     

Salalen aluminium complexes and their exploitation for the ring opening polymerisation of rac-lactide

In this paper we report the first use of Al(III) salalen complexes for the ring opening polymerisation of rac-lactide. Polylactides with narrow polydispersities (PDIs range from 1.04-1.65) and moderate degrees of stereoselectivity were formed. Eight salalen Al(III) complexes have been prepared and fully characterised by solution-state NMR spectroscopy and, where appropriate, single crystal X-ray diffraction. With ligand 3H(2) either a monomeric or dimeric Al(III) species was formed, the dimeric species was favoured at low concentrations. The complexes were tested for the ring opening polymerisation of rac-lactide in toluene at 80 or 100 °C. Interestingly, various tacticities of polymer were formed, which were dependent upon the nature of the group bound to the amine nitrogen centre.     

Synthesis, structure, and acid-base and redox properties of a family of new Ru(II) isomeric complexes containing the trpy and the dinucleating Hbpp ligands

Three pairs of mononuclear geometrical isomers containing the ligand 3,5-bis(2-pyridyl)pyrazole (Hbpp) of general formula in- and out-[RuII(Hbpp)(trpy)X](n+) (trpy=2,2':6',2' '-terpyridine; X=Cl, n=1, 2a,b; X=H2O, n=2, 3a,b; X=py (pyridine), n=2, 4a,b) have been prepared through two different synthetic routes, isolated, and structurally characterized. The solid state structural characterization was performed by X-ray diffraction analysis of four complexes: 2a-4a and 4b. The structural characterization in solution was performed by means of 1D and 2D NMR spectroscopy for complexes 2a,b and 4a,b and coincides with the structures found in the solid state. All complexes were also spectroscopically characterized by UV-vis which also allowed us to carry out spectrophotometric acid-base titrations. Thus, a number of species were spectroscopically characterized with the same oxidation state but with a different degree of protonation. As an example, for 3a three pKa values were obtained: pKa1(RuII)=2.13, pKa2(RuII)=6.88, and pKa3(RuII)=11.09. The redox properties were also studied, giving in all cases a number of electron transfers coupled to proton transfers. The pH dependency of the redox potentials allowed us to calculate the pKa of the complexes in the Ru(III) oxidation state. For complex 3a, these were found to be pKa1(RuIII)=0.01, pKa2(RuIII)=2.78, and pKa3(RuIII)=5.43. The oxidation state Ru(IV) was only reached from the Ru-OH2 type of complexes 3a or 3b. It has also been shown that the RuIV=O species derived from 3a is capable of electrocatalytically oxidizing benzyl alcohol with a second-order rate constant of kcat=17.1 M(-1) s(-1).     

Uranium (III) scorpionates: synthesis and structure of [(TpMe2)2U[N(C6H5)2]] and [(TpMe2)2U[N(SiMe3)2]

Reaction of [(Tp(Me)2)(2)UI] with KNR(2) (R = C(6)H(5), SiMe(3)) in tetrahydrofuran (THF) afforded the monomeric trivalent actinide amide complexes [(Tp(Me)2)(2)U[N(C(6)H(5))(2)]], 1, and [(Tp(Me)2)(2)U[N(SiMe(3))(2)]], 2. The complexes have been fully characterized by spectroscopic methods and their structures were confirmed by X-ray crystallographic studies. In the solid state 1 and 2 exhibit distorted pentagonal bipyramidal geometries. The U-NR(2) bond lengths in both complexes are the same but in complex 2 the greater steric demands of the N(SiMe(3))(2) ligand led to elongated U-N(pz) bonds, especially those opposite the amido ligand.     

The influence of phosphane coligands on the nuclearity of rhodium(I) 4-thiolatobenzoic acid complexes

[RhCl(PR3)3] (R = Ph, Et) reacts with the potassium salt of 4-mercaptobenzoic acid to give a mixture of the monomeric and dimeric complexes, [Rh(SC6H4COOH)(PR3)3] and [{Rh(-SC6H4COOH)(PR3)2}2], respectively. With the labile PPh3 coligand, the dimer is the major product, while for the electron-richer coligand PEt3, the equilibrium is easily shifted to the monomer by the addition of excess PEt3. Phosphane dissociation and dimerization could be prevented by using the chelating coligand PPh(C2H4PPh2)2. [{Rh(-SC6H4COOH)(PPh3)2}2] (2b), [Rh(SC6H4COOH)(PEt3)3] (3a), and [Rh(SC6H4COOH){PPh(C2H4PPh2)2}] (4) were fully characterized by nuclear magnetic resonance and infrared spectroscopy, mass spectrometry, and elemental analysis. The molecular structures of 2b and 4 were determined by X-ray structure analysis. In solution, the lability of the phosphane ligands leads to the decomposition of 2b. One of the decomposition products, namely, the mixed-valent complex [{RhIRhIII(-SC6H4COO)(-SC6H4COOH)(SC6H4COOH)(PPh3)3}2] (5), was characterized by X-ray structural analysis. The dinuclear rhodium(III) complex [{Rh(-SC6H4COO)(SC6H4COOH)(PEt3)2}2] (6) was shown to be a byproduct in the synthesis of 3a, and this demonstrates the reactivity of the rhodium(I) complexes toward oxidative addition. The structurally characterized complexes 2b, 4, 5, and 6 show hydrogen bonding of the free carboxyl groups.     

Synthesis and X-ray crystallography of diverse metal complexes derived from xanthone-crown ether

A series of sandwich, monomeric, dimeric and polymeric complexes supported with 1,8-xanthone-18-crown-5 (L) were synthesised. Mass spectrum experiments suggested the existence of sandwich and monomeric complexes in solution. And the structure characterisations of six new complexes by single-crystal X-ray diffraction show the strong coordination of xanthone-18-crown-5 carbonyl oxygen with alkaline earth metal cation, which results high fluorescent increase in alkaline earth metal complexes.     

Synthesis and study of hexanuclear molybdenum clusters containing thiolate ligands

Four hexanuclear molybdenum chloride cluster complexes containing terminal thiolate ligands have been synthesized and fully characterized. (Bu 4N) 2[Mo 6Cl 8(SEt) 6] was prepared by reacting Na 2[Mo 6Cl 8(OMe) 6] with an excess of ethanethiol in refluxing tetrahydrofuran. (PPN) 2[Mo 6Cl 8(SBu) 6], (Bu 4N) 2[Mo 6Cl 8(SBn) 6], and (Bu 4N) 2[Mo 6Cl 8(SNC 8H 6) 6] (C 8H 6NS (-) = 3-indolylthiolate) were subsequently prepared in the reaction of [Mo 6Cl 8(SEt) 6] (2-) with an excess of HSR (R = Bu, Bn or 3-indolyl). Single crystal X-ray diffraction analyses were performed on two of these complexes: (PPN) 2[Mo 6Cl 8(SEt) 6].Et 2O, crystallizes in the triclinic space group P1 with a = 12.3894(11), b = 13.7651(12), c = 15.0974(13), alpha = 103.975(2), beta = 99.690(2), gamma = 98.062(2), and Z = 1; (PPh 3Me) 2[Mo 6Cl 8(SBn) 6].2NO 2CH 3, also crystallizes in the P1 space group with a = 12.1574(16), b = 13.4441(17), c = 14.2132(18), alpha = 89.654(2), beta = 88.365(2), gamma = 71.179(2), and Z = 1. Our studies demonstrate that [Mo 6Cl 8(SEt) 6] (2-) displays luminescent properties and that the same complex undergoes substitution reactions with different thiols, as well as reaction with electrophilic reagents such as MeI.     

Synthesis and characterization of novel Pd(II) complexes with chelating and non-chelating heterocyclic iminocarbene ligands

The imidazolium salts [3-R1-1-{2-Ar-imino)-2-R2-ethyl}imidazolium] chloride (C-N; Ar = 2,6-iPr2C6H3; R1/R2 = Me/Me (a), Me/Ph (b), Ph/Me (c), 2,4,6-Me3C6H2 (d), 2,6-iPr2C6H3 (e)) react with Ag(2)O to give Ag(I) iminocarbene complexes (C-N)AgCl (4a-e) in which the iminocarbene ligand is bonded to Ag via the imidazoline-2-ylidene carbon atom. The solid-state structures of 4b and 4d were determined by X-ray crystallography and revealed the presence of monomeric (carbene)AgCl units with Z and E configurations at the imine C=N bonds, respectively. Carbene transfer to Pd occurs when compounds 4b-e are treated with (COD)PdCl2 to yield bis(carbene) complexes (C-N)2PdCl2 (6b-e) containing two kappa1-C bonded iminocarbene moieties. NMR spectroscopic data indicated a trans coordination geometry at Pd. This conclusion was supported by an X-ray structure determination of 6b which clearly demonstrated the non-chelating nature of the iminocarbene ligand system. EXSY 1H NMR spectroscopy suggests that the non-chelating structures undergo E/Z isomerization at the imine C[double bond, length as m-dash]N double bonds in solution. The preparative results contrast our earlier report that the reaction between 4a and (COD)PdCl2 results in a chelating kappa2-C,N bonded iminocarbene complex (C-N)PdCl2. The coordination mode and dynamic behavior of the iminocarbene ligand systems have been found to be dramatically affected by changes in the substitution pattern of the ligand system. Sterically unencumbered systems (a) favor the formation of kappa2-C,N chelate structures containing one iminocarbene moiety per metal upon coordination at Pd(II); these complexes were demonstrated to engage in reversible, solvent-mediated chelate ring-opening reactions. Sterically encumbered systems (b-e) form non-chelating kappa1-C iminocarbene Pd(II) complexes containing two iminocarbene ligands per metal. Transannular repulsions across the chelate ring are believed to be the origin of these structural differences.