549 research outputs found
Preparative and spectroscopic studies of (PtCl3(4-XC6H4NO))-K+ complexes
No full textσN-Coordinated compds. [PtCl3(4-X-C6H4NO)]-K+ were prepd. and studied by 13C NMR spectroscopy and by variable temp. 1H NMR spectroscopy. The anomalous behavior of the NO group on the 13C chem. shifts is modified by coordination but where X = NMe2 or OCH3 the free energy barriers to rotation of the NO group detd. by 1H NMR studies are closely similar to those of the free ligands. Restricted rotation of the NMe2 group was also studied in [PtCl3(2-CH3-4-NMe2-C6H3NO)]-K+
Dynamic NMR investigations of fluxionality of 2-(dimethoxymethyl)pyridine and 2,6-bis(dimethoxymethyl)pyridine in rhenium(I) and platinum(IV) complexes
No full textThe ligands 2-(dimethoxymethyl)pyridine (L-1) and 2,6-bis(dimethoxymethyl)pyridine (L-2) formed bidentate chelate complexes with the isoelectronic transition metal moieties (ReX)-X-I(CO)(3) and (PtXMe3)-X-IV (X=halide). The complexes [ReX(CO)(3)L-1] (X=Cl or Br), [PtXMe3L1] (X=Br or I) and [ReBr(CO)(3)L-2] in organic solvents were shown by NMR to undergo fluxional processes which interconvert co-ordinated and pendant OMe groups. Rates and activation energies of these fluxions were measured by NMR methods (1-dimensional bandshape analysis or 2-dimensional exchange spectroscopy). Magnitudes of DeltaG double dagger (;) (298.15 K) for the fluxions were in the range 59-85 kJ mol(-1) with the order being Re-I-L-1> Re-I-L-2> Pt-IV-L-1. A carbon-carbon bond rotation mechanism is proposed for the fluxions in the L-1 complexes and concerted C-C bond rotation/metallotropic shift processes for the L-2 complexes. Crystal structures of [ReCl(CO)(3)L-1] and [PtIMe3L1] revealed distorted octahedral metal centres with N-M-O 'bite' angles of 73-75 degrees and a trans relationship of the axial halide and pendant OMe group
Coordination properties of unsymmetrical Schiff base ligands containing N3 donor sets when restricted to bidentate chelate bonding modes. Crystal structures of fac-[PtIMe3(PMAMP)] (PMAMP=2-{(2?-pyridylmethylene)aminomethyl}pyridine) and fac-[PtIMe3(PMAQ)] (PMAQ=8-{(2?-pyridylmethylene)amino}quinoline)
No full textThe N3 ligands 2-{(2?-pyridylmethylene)aminomethyl}pyridine, (PMAMP), 8-{(2?-pyridylmethylene)amino}quinoline, (PMAQ) and 2-[{(6?-methyl-2?-pyridyl)methylene}aminomethyl]pyridine (MPMAMP) are analogous to 2,2?:6?,2?-terpyridine in respect of their spatial arrangement of N donor atoms. When acting as bidentate chelates PMAMP and PMAQ bind exclusively to the PtIV moiety PtIMe3 such that the five-membered chelate rings incorporate the imine bond. This was deduced by detailed solution NMR studies and X-ray crystal structures. In contrast, the ligand MPMAMP, with 6-methyl substitution of the pyridyl ring attached to the carbon of the imine bond, preferentially, but not exclusively, coordinates to the nitrogen of the other pyridyl ring. The population ratio of the two complexes formed was 6:1 (303 K, CDCl3 solution), but there was no NMR evidence of exchange between these species, in the temperature range 303–413 K, resulting from 1,4-metallotropic shifts, as occurs in analogous complexes such as fac-[PtIMe3(2,2?:6?,2?-terpyridine)]
The solid- and solution-state structures of 2-nitrosopyridine and its 3-and 4-methyl derivatives
No full text2-Nitrosopyridine, 1, 3-methyl-2-nitrosopyridine, 2, and 4-methyl-2-nitrosopyridine, 3, exist in organic solvents as monomer-azodioxy dimer equilibria with the dimers predominating at ambient temperatures. In the case of compounds 1 and 3 only the Z-dimers co-exist with the monomers, whereas for compound 2 both Z- (major) and E- (minor) dimers are present with the monomer. Variable temperature H-1 NMR bandshape analysis and 2D-EXSY spectra of 1-3 provided thermodynamic and kinetic data for the dissociation equilibria Z- (or E-) dimer reversible arrow 2 monomer, DeltaH(empty set) values being in the range 53-58 kJ mol(-1) and DeltaG double dagger (298.15 K) values in the range 70-82 kJ mol(-1). An X-ray crystal structure of 1 identified the compound as a Z-dimeric species with the two pyridine rings twisted by 62.7 degrees and their heterocyclic N atoms pointing towards each other
Solution fluxionality of some pyridine-2,6-dialdehydes, -diketones and -diesters when acting as bidentate ligands in rhenium(I) and platinum(IV) complexes. Crystal structure of ReBr(CO)(3)L (L = methylethyldipicolinate)
No full text2,6-Disubstituted pyridines, where the substituents are aldehyde, ketone or ester functions, form bidentate chelate complexes with the transition metal moieties fac-(ReX)-X-I(CO)(3) (X = halogen). 2-Substituted pyridines, where the substituents are aldehyde or ester functions, form similar types of complexes with the isoelectronic transition metal moieties fac-(ReX)-X-I(CO), and (PtXMe3)-X-IV. The fac-(ReX)-X-I(CO)(3) complexes of the 2,6-disubstituted pyridine ligands were shown by H-1 NMR spectra to undergo metallotropic shifts whereby the Re coordination switches between adjacent ON pairs of the ONO ligand donor set. Rates and activation energies of these fluxional shifts were measured by dynamic NMR bandshape analysis. Magnitudes of DeltaG(double dagger) (298.15 K) were in the range 59-64 kJ mol(-1) for the diketone and diester ligands. The dialdehyde ligand, 2,6-pyridinedicarboxaldehyde, formed an appreciably less-stable Re-I complex that was highly fluxional and showed a tendency to dissociation at ambient solution temperatures. The unsymmetrical diester ligand, methylethyldipicolinate, formed two distinct Re-I complex species in solution, in the approximate abundance ratio of 2:1, the more abundant structure involving coordination to the carbonyl of the ethyl ester function. This particular complex forms exclusively in the solid state and an X-ray crystal structure of [ReBr(CO)(3)L] (L = methylethyldipicolinate) is reported
Stereochemically non-rigid transition metal complexes of 2,6-bis(phenyliminomethyl)pyridine and derivatives. Crystal structure of fac- ReBr(CO)(3)(PMTFA) (PMTFA=2,6-pyridylene-bis-(methylene-2-trifluoromethylaniline)
No full textThe Schiff bases 2,6-bis(phenyliminomethyl)pyridine and its derivatives (L) form bidentate chelate complexes with transition metals Re-I, Pt-IV and Pd-II of general formulation fac-[ReBr(Co)(3)L], fac-[PtXMe3L] (X = Cl, Br or I), and cis-[Pd(p-CF3C6F4)(2)L]. In solution these complexes are stereochemically non-rigid, undergoing 1,4-metallotropic shifts and restricted rotations of the substituted aromatic rings attached to the metal-coordinated imino nitrogen. Rates and activation energies of these internal motions were measured by one-dimensional NMR bandshape analysis and two-dimensional EXSY NMR experiments over a range of solution temperatures. Free energy values, DeltaG(double dagger) (298.15 K), for the fluxional shifts were in the range 76-97 kJ mol(-1) with the Pd-II complexes having the lowest energies. An X-ray crystal structure of fac-[ReBr(CO)(3)PMTFA] (PMTFA = 2,6-pyridylene-bis(methylene-2-trifluoroaniline)) showed the pendant imine function to be in an E-conformation with its nitrogen trans to the pyridyl nitrogen
Synthesis of Novel Nitroso-Fulleropyrrolidines
No full textNovel fulleropyrrolidines I [R1 = Me, Ph; R2 = O2N, H2N, ON, 4-O2NC6H4O(CH2)12O, 4-H2NC6H4O(CH2)12O, 4-ONC6H4O(CH2)12O], contg. nitro, amino, or nitroso groups directly on the Ph ring or spaced by a long chain from the fulleropyrrolidine moiety, were synthesized and characterized
Nitrosoalkenes and their coordination compounds with palladium chloride
No full textTwo nitrosodithiofulvenes and a nitrosodiselenafulvene formed insol. coordination compds. with Pd chloride, these being the 1st reported coordination compds. of nitrosoalkenes. PdCl2.RNO and PdCl2.(RNO)2 were formed. Variable temp. NMR studies of the nitrosoalkenes demonstrate that the free energy barrier to rotation about the bond is low, values being in the range 58-93 kJ mol-1
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