Equatorial Coordination Research Articles

Syntheses and crystal structures of oxovanadium(IV) complexes with N,N′-ethylenebis(amino acids)

The oxovanadium(IV) complexes with N,N′-ethylenebis(amino acids) ([VO(XeX)(H 2O)], where X=A (( S)-Ala), V (( S)-Val) and P (( S)-Pro)) are synthesized and characterized by X-ray analyses and IR spectra. The crystal structure analyses reveal that the geometry around the vanadium cation of each complex is distorted octahedral and is coordinated by a water molecule and the tetradentate N,N′-ethylenebis(amino acidate) anion with Δ- cis-α configuration, in which the water oxygen atom occupies equatorial coordination position and one of the two secondary or tertiary nitrogen atoms of each tetradendate ligand is bound trans to the vanadyl oxo moiety. The compilation of bond lengths for present and previous VO complexes containing nitrogen and oxygen donating ligands shows that the tertiary amine groups of PeP ligand elongate VN bonds. Comparison of the sum of the bond angles of three five-membered rings (one ethylenediamine ring and two amino acidate rings) indicates that the ring strain is mostly concentrated in the ethylenediamine ring and the strain of amino acidate ring lying in the equatorial plane of V(IV) ion is more pronounced than that in another amino acidate ring. The IR observations of the present complexes are well consistent with the crystallographic studies of them.

Structures and Magnetic Properties of [o- and p-MePyNN+]2[Cu(ox)2] (MePyNN+ = Nitronyl Nitroxyl Radical Cation)

Abstract Reactions of [o-MePyNN+]PF6 and [p-MePyNN+]PF6 with [n-Bu4N]2[Cu(ox)2] in acetonitrile yielded dark-blue crystals of [o-MePyNN+]2[Cu(ox)2]·2CH3OH (1) and [p-MePyNN+]2[Cu(ox)2]·2H2O (2), respectively, where [o-MePyNN+] or [p-MePyNN+] represents the 2-(2 or 4-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazo-1-oxyl 3-oxide radical cation. X-ray structural analyses showed that the crystals of 1 and 2 are isomorphous. The coordination geometry of the Cu2+ ions in 1 and 2 is an elongated octahedron, and the equatorial and apical coordination sites of the Cu2+ ions are occupied by two oxalato groups and two radial cations, respectively. Magnetic susceptibility measurements for 1 and 2 revealed that the copper and radical centers are ferromagnetically coupled with J = +8.2(1) and +7.8(1) cm-1 (H = -2J∑SCu·Srad), respectively.

EPR study of the dinuclear active copper site of tyrosinase from Streptomyces antibioticus

The [Cu(I)–Cu(II)] half-met form of the dinuclear copper site of tyrosinase has been probed by continuous wave electron paramagnetic resonance (EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopy in the presence and absence of inhibitors. In all cases the EPR spectrum is indicative of a d x 2− y 2 ground state for the unpaired electron. From the cross-peaks observed in the HYSCORE spectra, proton hyperfine coupling constants were obtained that are compatible with a hydroxide ion in an equatorial coordination position of the paramagnetic copper. After changing the water solvent to D 2O or after addition of the inhibitors p-nitrophenol or L-mimosine, the proton signals disappear. The relevance of these findings for understanding the catalytic cycle is discussed.

Structure and Dynamic Behavior of (η3-Allyl)bromodicarbonylmolybdenum(II) Complexes Containing Polydentate 2-Pyridylphosphanes or Their Oxides as Chelating Ligands: Occurrence of Three Fluxional Processes

The pseudo-octahedral complexes [Mo(η3-allyl)Br(CO)2(PPynPh3–n-P,N)] (Py = 2-pyridyl; n = 2, 3) and [Mo(η3-allyl)Br(CO)2(OPPymPh3–m-O,N)] (m = 1, 2, 3) undergo three different dynamic processes in solution, depending on the chelating ligand. The complexes containing PPhPy2 and PPy3 as chelating P,N-donors undergo a novel “pivoted double switch” mechanism which scrambles two equatorial coordination sites with racemization, while maintaining the identity of the phosphorus atom trans to the allyl ligand. The complexes containing 2-pyridylphosphane oxides as chelating O,N-donors undergo a nondissociative intramolecular trigonal-twist (or turnstile) rearrangement which maintains the identity of the phosphane oxide oxygen atom coordinated in an equatorial position. All the complexes containing uncoordinated pyridyls undergo a slow dissociative exchange of pyridyls without coordination site scrambling. The structure of the complex [Mo(η3-allyl)Br(CO)2(OPPy3-O,N)] has been determined by X-ray diffraction.

Structure and Dynamic Behavior of (η3-Allyl)bromodicarbonylmolybdenum(II) Complexes Containing Polydentate 2-Pyridylphosphanes or Their Oxides as Chelating Ligands: Occurrence of Three Fluxional Processes

The pseudo-octahedral complexes [Mo(η3-allyl)Br(CO)2(PPynPh3–n-P,N)] (Py = 2-pyridyl; n = 2, 3) and [Mo(η3-allyl)Br(CO)2(OPPymPh3–m-O,N)] (m = 1, 2, 3) undergo three different dynamic processes in solution, depending on the chelating ligand. The complexes containing PPhPy2 and PPy3 as chelating P,N-donors undergo a novel “pivoted double switch” mechanism which scrambles two equatorial coordination sites with racemization, while maintaining the identity of the phosphorus atom trans to the allyl ligand. The complexes containing 2-pyridylphosphane oxides as chelating O,N-donors undergo a nondissociative intramolecular trigonal-twist (or turnstile) rearrangement which maintains the identity of the phosphane oxide oxygen atom coordinated in an equatorial position. All the complexes containing uncoordinated pyridyls undergo a slow dissociative exchange of pyridyls without coordination site scrambling. The structure of the complex [Mo(η3-allyl)Br(CO)2(OPPy3-O,N)] has been determined by X-ray diffraction.

Cyano bridged dinuclear Cu(II) complexes

The reaction of [CuL(OH2)]2+, where L is one of the tripodal tetradentate ligands, tris(2-pyridylmethyl)amine (tpa) or tris(2-aminoethyl)amine (tren), with cyanide ions, has yielded two cyano-bridged dinuclear copper(II) complexes with composition, [{Cu(tpa)}2(CN)][ClO4]3 (1) and [{Cu(tren)}2(CN)][ClO4]3·H2O (2), and a mononuclear complex, [Cu(tpa)(CN)][ClO4]·3H2O (3). Room temperature single-crystal X-ray studies on 1, the mono(DMF) hemihydrate of 2 and the hemihydrate of 3, have confirmed that the Cu(II) centers in each complex adopt geometries that are close to trigonal bipyramidal (TBP), a feature of Cu(II) complexes of such tripodal tetradentate ligands. The tertiary amine nitrogen is located in an axial position trans to the cyano ligand and the other ligand nitrogens are located within the equatorial plane. In the dinuclear complexes the Cu-CN-Cu bridging moieties deviate slightly from linearity and give the complex a slightly bowed appearance. The Cu⋯Cu distances are ca. 5 Å and the Cu(II) atoms are displaced by ca. 0.3 Å away from the equatorial plane towards the cyano group. Variable temperature magnetic susceptibility studies have confirmed that the cyano bridges mediate antiferromagnetic coupling between the Cu(II) centers with J values of −53.2 and −87.1 cm−1 for 1 and 2, respectively. These values are typical of axially connected TBP cyano Cu(II) complexes and are larger than those found for related complexes connected at equatorial coordination sites.

Uranyl Incorporation into Calcite and Aragonite: XAFS and Luminescence Studies

X-ray absorption, luminescence, and Raman spectroscopic studies of U(VI)-containing calcite and aragonite show that the U ion, the dominant and mobile form of dissolved uranium in near-surface waters, has a disordered and apparently less stable coordination environment when incorporated into calcite in comparison to aragonite, both common polymorphs of CaCO3. Our findings suggest that calcite, a widely distributed authigenic mineral in soils and near-surface sediments and a principal weathering product of concrete-based containment structures, is not likely to be a suitable host for the long-term sequestration of U(VI). The more stable coordination provided by aragonite suggests that its long-term retention should be favored in this phase, until it inverts to calcite. Consequently, future remobilization of U(VI) coprecipitated with calcium carbonate minerals should not be ruled out in assessments of contaminated sites. Our observation of a similar equatorial coordination of U in aragonite and the dominant...

Preparation of trichloro- and tribromocyclopentadienyltungsten(IV)

The thermal decarbonylation of (Ring)WX 3(CO) 2 in refluxing toluene has led to the preparation of the CO-free compounds [(Ring)WX 3] 2 [Ring=η 5-C 5H 5 (Cp) and X=Cl ( 1a) or Br ( 1b); Ring=η 5-C 5H 4Me (Cp′), X=Cl ( 2a) or Br ( 2b); Ring=η 5-C 5Me 5 (Cp*), X=Cl ( 3)]. The NMR properties of these molecules are consistent with diamagnetism and thereby indicate a different structure from that of the paramagnetic molybdenum analogues. Compounds 1a and 2a react with dppe to afford mononuclear 18-electron adducts, (Ring)WCl 3(dppe) (Ring=Cp ( 4) or Cp′ ( 5)). The X-ray structure of 5 shows a pseudo- fac-octahedral geometry with the dppe ligand occupying two equatorial (e.g. cis relative to Cp′) coordination sites. The X-ray structure of two by-products of the synthetic processes are also reported, e.g. Cp′ 3W 3Cl 3(μ 2-Cl) 2(μ 3-O) ( 6) and [Cp*WCl 3] 2(μ-O) ( 7).

Equilibrium and structural studies on copper(II) complexes of tetra-, penta- and hexa-peptides containing histidyl residues at the C-termini

The stoichiometry, stability constants and solution structure of the complexes formed in the reaction of copper(II) with oligopeptides containing histidyl residues at the C-termini (Gly3His, Gly4His and Gly5His) have been determined by potentiometric, UV–VIS and EPR spectroscopic methods. The formation of the species [CuHL]2+, [CuL]+, [CuH−1L], [CuH−2L]– and [CuH−3L]2− was detected in all cases. Binding modes of the species [CuL]+, [CuH−1L] and [CuH−2L]− were characterized by the metal ion co-ordination of the terminal amino group, carbonyl oxygen or one or two deprotonated amide nitrogens in joined five-membered chelates from the N-termini, while the fourth co-ordination site of the metal ion was occupied by nitrogen donors of imidazole in the form of a macrochelate. The stability of the macrochelate was decreased upon increasing the length of the peptide molecule. For the penta- and hexa-peptides the species [CuH−3L]2− was characterized as a 4N-complex with equatorial co-ordination of the terminal amino group and subsequent three deprotonated amide nitrogens, with unco-ordinated imidazolyl residues, while a 5N-species was suggested to form for Gly3His with axial interaction of the imidazole-N donor atom. Copper(II) complexes of Gly2His and pentaglycine were also investigated for reliable comparison.

Structure and properties of di-μ-acetato-dichlorobis(2,2′-bipyridine)dirhodium(II)-trihydrate

Reduction of [Rh2(μ-OAc)2(bpy)2(H2O)2](OAc)2 and [Rh2Cl2(μ-OAc)2(bpy)2] · 3H2O complexes with ethanol and [Cr2(OAc)4(H2O)2] has been investigated using e.p.r. and u.v.–vis. spectra. The results indicate that stable complexes containing the [Rh23+] entity are not formed. The X-ray structure of [Rh2Cl2(μ-OAc)2(bpy)2] · 3H2O has been determined. Coordination around the Rh atom is in the form of a distorted octahedron. The complex shows an almost ideal eclipsed conformation. The equatorial coordination sites are occupied by bridging carboxylato ligands and 2,2′-bipyridine and axial positions by the Cl ligand and the rhodium atom. The Rh–Rh distance is 2.574 A.

Rhenium and technetium complexes with diphenyl(2-pyridyl)phosphine

The potentially bidentate ligand diphenyl(2-pyridyl)phosphine (PPh 2py) reacted with (NEt 4) 2[M IX 3(CO) 3] complexes (M=Re, Tc; X=Cl, Br) to give (NEt 4)[M IX 2(CO) 3(PPh 2py-P)] or [M IX(CO) 3(PPh 2py-P) 2] depending on the amount of the ligand used. The reaction with (NBu 4)[Tc VINCl 4] yielded [Tc VNCl 2(PPh 2py-P) 2] whereas from the reaction with (NBu 4)[ReOCl 4] the complexes [Re VOCl 3(PPh 2py-P,N)], [Re VOCl 3(OPPh 2py-O,N)], [Re IVCl 4(OPPh 2py-O,N) and [Re IVCl 3(OH)(OPPh 2py-O,N)] have been isolated. Reduction of the metal center occurs using an excess of PPh 2py and heating of the reaction mixtures under reflux. The products have been characterised spectroscopically and by X-ray structure analysis. Monodentate co-ordination via phosphorus has been found for the rhenium(I) carbonyl complexes and [Tc VNCl 2(PPh 2py-P) 2]. In the latter compound a trigonal-bipyramidal coordination sphere is formed with the phosphines as axial ligands (bond angle P–Tc–P: 161.69(3)°). The chelated complexes show small N–Re–P and N–Re–O bite angles of 63.6° and 77.7–82.2° due to the four-membered or five-membered chelate rings. The pyridine nitrogen occupies the axial position ( trans to “O 2−”) in [ReOCl 3(PPh 2py-P,N)] whereas equatorial co-ordination is found in [ReOCl 3(OPPh 2py-O,N)].

Solvent stabilized transition metal cations as initiators for cyclopentadiene polymerization

Solvent stabilized transition metal cations are excellent initiators for the polymerization of cyclopentadiene. The product yield is – in first approximation – directly proportional to the reaction time. Partial substitution of the solvent molecules by ligands with different donor strength and charge allows the synthesis of initiators with tailor made activity. The presence of a metal-metal multiple bond seems not to be of significant importance for the catalytic activity of the initiator systems. The crucial point for the activity of the complexes described here is the presence of labile and therefore easily replacable ligands in equatorial coordination sites.

Alkyne Dicobalt Carbonyl Complexes with Sulfide Ligands. Synthesis, Crystal Structure, and Dynamic Behavior

Hexacarbonyl dicobalt complex of bis(tert-butylsulfonylethyne) [Co2(μ-ButSO2C)2(CO)6, 3] experiences a thermally induced ligand exchange process with methyl p-tolyl sulfide, dibenzyl sulfide, and diethyl sulfide to give the corresponding stable sulfide complexes [Co2(μ-ButSO2C)2(CO)5SR2] 4, 5, and 6, respectively, in good yield (59−65%). The reaction with tetrahydrothiophene gives a disubstituted complex 7 in 74% yield. Oxathiane 9, derived from (+)-(2R)-10-mercaptoisoborneol, also reacts with 3 to generate a chiral sulfide complex 8 (58%). The solid-state structures of 5 and 8 have been established by X-ray crystallography and reveal the preference of the incoming sulfur ligand to occupy an equatorial coordination site. Further structural studies on 5 have been performed by low-temperature 1H NMR analysis and by theoretical procedures at the PM3(tm) level of theory. Analysis of the low-temperature 1H NMR spectrum of 5 shows a signal splitting consistent with the freezing of an equilibrium between two equ...

ESR study of the copper(II)–glycylglycine equilibrium system in fluid aqueous solution. Computer analysis of overlapping multispecies spectra

Various predominant and minor complexes of glycylglycine with the copper(II) ion were studied in fluid aqueous solution by ESR spectroscopy. The computer analysis of a series of overlapping spectra was carried out including at most four independent species. The spectra were built as a hyperfine structure of copper isotopes and a variable number of non-equivalent nitrogen atoms. The isotropic ESR parameters and relative concentrations of different species were optimized giving a good spectral fit. The variations of the relative concentrations of the complexes are consistent with those calculated from formation constants obtained by pH-metric and spectrophotometric studies, and the ESR parameters of each species determined from different spectra agree well. For the complex [CuL2H−1]− two kinds of coordination exist. In both isomers one of the glycylglycine ligands is coordinated equatorially through its amino nitrogen, deprotonated peptide nitrogen and carboxylate oxygen atoms. For the major isomer the amino group of the second ligand occupies an axial position, while the fourth equatorial donor atom is the peptide oxygen. For the minor isomer the donor atoms of the second ligand are interchanged. For the 1 : 1 complexes also the above terdentate equatorial coordination of the ligand exists, except for [CuL]+. Some features of the metal–ligand bonds and geometric distortions for the various species are discussed. Copyright © 1999 John Wiley & Sons, Ltd.

Cluster-Mediated Conversion of Diphenylacetylene into α-Phenylcinnamaldehyde. Construction of a Catalytic Hydroformylation Cycle Based on Isolated Intermediates

The present paper deals with a rational attempt to achieve the hydroformylation of diphenylacetylene onto a hydrido triruthenium cluster complex incorporating the 2-(methylamino)pyridyl group (abbreviation: MeNpy) as a hemilabile ancillary ligand [note: in all species discussed below, the bridgehead μ2-N atom is linked to the centers labeled as Ru(1) and Ru(2), whereas the pyridyl nitrogen is bound to Ru(3)]. The complex Ru3(μ-H)(μ-MeNpy)(CO)9 (1) is shown to react cleanly with diphenylacetylene to give the alkenyl complex Ru3(μ-MeNpy)(μ-PhCCHPh)(CO)8 (2), the structure of which is reported. The reaction of 2 with 1 equiv of PPh3 proceeds to completion within less than 3 min at 25 °C, giving two propenoyl complexes, namely, Ru3(μ-MeNpy)(μ-OC−PhCCHPh)(PPh3)(CO)7 (3) (48% yield) and Ru3(μ-MeNpy)(μ-OC−PhCCHPh)(PPh3)2(CO)6 (4) (19% yield), both fully characterized by spectroscopic methods and X-ray analysis. Complex 3 is an adduct of 2 with PPh3. The incorporation of the phosphine has caused a migratory CO insertion of the alkenyl group. The phosphine occupies an equatorial coordination site on Ru(1), in cis position relative to the nitrogen atom of the amido bridge. The newly formed propenoyl group occupies an equatorial bridging position across the Ru(1)−Ru(3) edge, with the acyl oxygen bound to Ru(1), in cis position relative to both the bridgehead nitrogen atom and the phosphine. The molecular structure of the second propenoyl compound, Ru3(μ-MeNpy)(μ-OC−PhCCHPh)(PPh3)2(CO)6 (4), is formally derived from the previous one, 3, by a simple substitution of an equatorial CO of Ru(2) by PPh3. The use of a 2-fold amount of phosphine for the above reaction modifies only slightly the relative abundance of 3 (30%) and 4 (44%). This indicates that 3 is not the kinetic product of the reaction between 2 and a phosphine. Further reaction of 4b with CO induces loss of one PPh3 and incorporation of two CO ligands. This produces the open 50e cluster Ru3(μ-MeNpy)(μ-OC−PhCCHPh)(PPh3)(CO)8 (5), in which the bridging propenoyl group now spans the open edge Ru(1)−Ru(2) (the remaining phosphine occupies an equatorial site cis to the acyl oxygen). Treatment of 2b with CO (1 atm, 25 °C, 20 min) also promotes migratory CO insertion, giving the 50e propenoyl complex Ru3(μ-MeNpy)(μ-OC−PhCCHPh)(CO)9 (6b), whose structure has been determined. The propenoyl group spans the open edge Ru(1)−Ru(2). Although stable in CO-saturated solutions under CO atmosphere, the complex reverts rapidly to 2 within 30 s under inert atmosphere. Treatment of 6 with CO/H2 gas mixtures under ambient conditions produces α-phenylcinnamaldehyde with concomitant recovery of 1, showing that the hydroformylation of diphenylacetylene can be achieved in a stepwise manner through the cyclic reaction sequence 1 → 2 → 6 → 1. Under nonoptimized catalytic conditions, the amount of α-phenylcinnamaldehyde obtained corresponds to about eight cycles. The metal-containing species recovered in the reactor through the catalytic runs is isolated and formulated as the bimetallic carboxamido complex [Ru{−C(O)−MeNpy}(CO)3]2 (7). Thus, it appears that deactivation of the system has taken place via CO insertion into the metal−amide bond.

Metal-Mediated Conversion of Methylcycloarsoxane (CH3AsO)n to Macrocyclic Octa- and Decanuclear Ligands –Trigonal Bipyramidal Coordination of Trivalent Arsenic

Reaction of cyclo-(CH3AsO)n with MCl3 · x H2O in acetonitrile at 100 °C affords [MCl2{cyclo-(CH3AsO)8}] [M = Ru (1), M = Os (2)] in which cyclooctamers (CH3AsO)8 are stabilised in a ĸ4As1,3,5,7 binding mode in the equatorial coordination sphere of the Group 8 metals. In contrast treatment of K2PtCl4 with alternatively AgNO3 or Ag2CO3 and cyclo-(CH3AsO)n at 100 °C in the same solvent leads to the formation of respectively octa- or decanuclear cagelike ligands in [Pt2{[cyclo-(As[CH3]OAs[NC(O)CH3]O)2]2}] (3) and [Pt2{[{CH3C(O)N}2As5(CH3)5O4]2}] (4) by metal-assisted reactions between cyclo-(CH3AsO)n and acetonitrile. λ5-AsIII atoms in these complexes participate in square-planar PtII coordination and themselves exhibit distorted trigonal bipyramidal coordination geometries.

1,4-Dimethylpyridinium (1,3-dithiole-2-thione-4,5-dithiolato)(isothiocyanato)diphenylstannate(1–)

In the title compound, 1,4-dimethylpyridinium [4,5-dimercapto-1,3-dithiole-2-thione-S4,S5)(isothiocyanato)diphenylstannate(1−), (C7H10N)[Sn(NCS)(C6H5)2(C3S5)], the anion has distorted trigonal-bipyramidal coordination at the Sn atom, with the thiocyanato N and a thiolato S atom axial [Sn—N 2.262 (3), Sn—S 2.5917 (10) Å and N—Sn—S 164.58 (8)°]. The remaining thiolato S and two phenyl C atoms complete the equatorial coordination at Sn [Sn—S 2.4399 (10), and Sn—C 2.137 (4) and 2.139 (4) Å].

Synthesis, characterization and kinetics of the metallation of the intermediate compound [formula omitted] to produce compound [formula omitted] · (H 2O) from Rh(II) tetraacetate

Photochemical irradiation of mixtures of [Rh 2(μ-O 2CCH 3) 4]·(HOCH 3) 2 and P(2-(CH 3O)C 6H 4)Ph 2 (POMe) in CH 2Cl 2 solution (1:1 molar ratio) yields quantitatively compound [ Rh 2(μ- O 2 CCH 3) 3( O 2 CCH 3)(η 2- P(2-( CH 3 O) C 6 H 4) Ph 2 ]·( H 2 O) ( 1) containing a POMe acting as a chelating equatorial ( P ) axial ( O ) donor ligand. This compound undergoes intramolecular CH activation reaction at one of the phenyl rings in CHCl 3 or CH 3COOH/toluene solution at room temperature to form the monometallated compound [ Rh 2(μ- O 2 CCH 3) 3(μ-( C C 3 H 4) P(2-( CH 3 OC 6 H 4) Ph)]· ( H 2 O) ( 2 ). The kinetics of the 1 → bd2 reaction have been studied in acid media (CH 3COOH, CH 3COOD, CH 3COOH/CF 3SO 3H, CH 3COOH/toluene) and aprotic solvents (chloroform, toluene) at variable temperatures and pressures: the results are interpreted in view of those published for similar dinuclear Rh(II) compounds. The values found for δH*, ΔS* and ΔV* (84 kJmol 1 −51 J K −1 mol −1, 1.3 cm 3 mol −1 in CH 3COOH; and 68 kJ mol −1, −121 J K −1 mol −1, −15 cm 3 mol −1 in aprotic solvents) agree with those found for similar monometallation reactions studied on Rh(II) 2 core compounds. The more positive values found in this study for ΔS* and ΔV* could be attributed both to a bond-breaking expansion of the axial RhO(phosphine) bond and to the transfer of the monodentated acetato ligand from a tight inert equatorial coordination position to a labile axial position. Compound 1 has to undergo these processes in order to reach the highly ordered transition state needed for the CH bond activation to take place if the steric demands of the phosphine ligand are taken into account.

Zigzag-Chain and Cyclic-Tetrameric Compounds Derived by Deprotonation of Mononuclear Copper(II) Complexes with N,N'-Bis(2-substituted-imidazol-4-ylmethyl- idene)-1,4-diaminobutane (2-Substituent = H, Me): Synthesis, Characterization, Structure, Substituent Effect, and Interconvertibility.

Two copper(II) complexes with N,N'-bis(2-substituted-imidazol-4-ylmethylidene)-1,4-diaminobutane (2-substituent = H, 1; Me, 2) were synthesized, and their deprotonation assembly behavior was studied. X-ray analyses of 1 and 2 revealed that the molecules assume a butterfly shape bent by a line of N(2)-Cu-N(4) where the angle of N(3)-Cu-N(5) representing the extent of the molecular bend is 150.9(2) degrees and 105.66(8) degrees for 1 and 2, respectively. Due to the molecular bend, two imidazole moieties (sites A and B) are recognized as two inequivalent groups for the deprotonation process in which the imidazole group of site A is in an equatorial CuN(3) plane, while that of site B is in a CuN(2) plane bent from the equatorial coordination plane. 1 dissociates a proton of site B first to give an infinite zigzag-chain compound 1', while 2 dissociates a proton of site A first to give a cyclic-tetranuclear compound 2'. 2' undergoes a further deprotonation to give an electrically neutral di-deprotonated complex 2". The interconversion between the protonated monomer and the deprotonated oligomer/polymer was investigated by pH-dependent potentiometric and absorption spectrometric titrations.

Electron Withdrawing Substituents on Equatorial and Apical Phosphines Have Opposite Effects on the Regioselectivity of Rhodium Catalyzed Hydroformylation

The electronic effects of electron withdrawing aryl substituents on equatorial and apical diphosphines were investigated. Chelating diphosphines designed to coordinate in diequatorial or in apical−equatorial positions were synthesized, and their effects on the regioselectivity of rhodium catalyzed 1-hexene hydroformylation were observed. Only diequatorial coordination was observed for 2,2‘-bis[(diphenylphosphino)methyl]-1,1‘-biphenyl (BISBI) complexes (BISBI)Ir(CO)2H (8) and [BISBI-(3,5-CF3)]Ir(CO)2H (10), and only apical−equatorial coordination was seen for 1,2-bis(diphenylphosphino)ethane (DIPHOS) complexes (DIPHOS)Ir(CO)2H (14) and [DIPHOS-(3,5-CF3)]Ir(CO)2H (15). For the trans-1,2-bis[(diphenylphosphino)methyl]cyclopropane (T-BDCP) complexes, a mixture of diequatorial and apical−equatorial complexes was seen. For (T-BDCP)Ir(CO)2H (12), 12-ae was favored over 12-ee by 63:37, but for [T-BDCP-(3,5-CF3)]Ir(CO)2H (13) the conformational preference was reversed and a 10:90 ratio of 13-ae:13-ee was seen. The electron withdrawing groups in the equatorial positions of BISBI-(3,5-CF3) (1) and T-BDCP-(3,5-CF3) (2) led to an increase in n-aldehyde regioselectivity in rhodium catalyzed hydroformylation. However, electron withdrawing aryl substituents in the apical positions of DIPHOS-(3,5-CF3) (3) led to a decrease in n-aldehyde regioselectivity in rhodium catalyzed hydroformylation.