Peter J. Heard

1,2-Metallotropic shifts in trimethylplatinum(IV) and tricarbonylrhenium(I) halide complexes of pyridazine and 4-methylpyridazine

Pyridazine (pydz) and 4-methylpyridazine (4Me-pydz) form stable bis(monodentate) complexes of general formulae fac-[PtXMe3L2](X = Cl, Br or I) and fac-[ReX(CO)3L2](X = Cl, Br or I). These complexes in above-ambient temperature solutions exhibit 1,2-fluxional shifts between the nitrogen donor pairs of each ring. All linkage isomers of the pydz complexes are equivalent whereas three NMR-distinct linkage isomers, namely (1,1), (1,2)/(2,1) and (2,2) species, occur in solutions of the 4Me-pydz complexes. Fluxional exchange kinetics have been measured by variable-temperature 1H NMR bandshape analysis and two-dimensional exchange spectroscopy (EXSY). Platinum-195 NMR data have been obtained for the complexes [PtXMe3(4Me-pydz)2](X = Br or I) and their fluxional dynamics investigated by 195Pt two-dimensional EXSY and total bandshape analysis. Energy barriers, ΔG‡(298.15 K) for the 1,2-M–N fluxion are in the ranges 69–74 kJ mol–1 for the PtIV complexes and 84–90 kJ mol–1 for the ReI complexes. The crystal structure of [PtClMe3(pydz)2] shows the cis pydz rings oriented in a propeller arrangement with their unco-ordinated nitrogens oriented away from the cis positioned chlorine.

1,2-Metallotropic shifts in tricarbonylrhenium(I) complexes of pyridazine (pydz): a dynamic NMR investigation of the effects of cis-chelating ligands

Abstract Complexes of general formula fac-[Re(CO)3(L–L)(pydz)][BF4] (L–L=neutral bidentate chelate ligand; pydz=pyridazine) were prepared in high yield from fac-[ReBr(CO)3(L–L)]. The pyridazine ligand coordinates to the metal moiety in a monodentate fashion, and undergoes a facile intramolecular 1,2-Re–N shift. The kinetics of the 1,2-metallotropic shift were measured by either one-dimensional NMR bandshape analysis or two-dimensional exchange spectroscopy. The free energies of activation, ΔG≠ (298 K), were found to be dependent on the nature of the chelate ligand, and were in the range 77–87 kJ mol−1. The origins of the chelate ligand effects are discussed.

Synthesis and reactivity of N,N,N′,N′-tetramethyldiaminomethane complexes of tricarbonylrhenium(I). X-ray molecular structures of [ReBr(CO)3(TMDM)] and [{Re(bipy)(CO)3}2(μ-OH)][SbF6]

N,N,N′,N′-Tetramethyldiaminomethane (TMDM) is known to act as a source of Me₂NCH in carbonyl substitution reactions, but the reaction of TMDM with the neutral halogenopentacarbonylrhenium(I) compounds gave unexpectedly fac-[ReX(CO)₃(TMDM)] (X=Cl, Br or I), in which the intact TMDM ligand acts in a chelating fashion. The complexes are stable both in the solid-state and in solution, but rapidly decompose on dehalogenation, yielding Re metal. Under anaerobic conditions, the reaction of TMDM with [Re(CO)₃(bipy)]⁺also leads to decomposition. In the presence of oxygen the system is stable. Three Re(bipy) containing species were identified in the reaction mixture: [{Re(CO)₃(bipy)}₂(μ-OH)][SbF₆] (1), which was characterised by X-ray crystallography, [{Re(CO)₃(bipy)}₂(μOH)₂][SbF₆]₂(2) and [Re(OH)(CO)₃(bipy)] (3). Graphical Abstract Reaction of neutral [ReX(CO)₅] (X=Cl, Br or I) with N,N,N′,N′-tetramethyldiaminomethane ((TMDM)) gave unexpectedly fac-[ReX(CO)₃(TMDM)] (X=Cl, Br or I), in which the intact TMDM ligand acts in a chelating fashion. Reaction of TMDM with [Re(CO)₃(bipy)]⁺ under aerobic conditions yields three complexes: [{Re(CO)₃(bipy)}₂(μ-OH)][SbF₆] (1), which was characterised by X-ray crystallography, [{Re(CO)₃(bipy)}₂(μOH₂)][SbF₆]₂(2) and [Re(OH)(CO)₃(bipy)] (3).

Dynamic stereochemical rearrangements in ‘chiral-at-ligand’ complexes. Tricarbonylhalogenorhenium( I ) and halogenotrimethylplatinum( IV ) complexes of 2,6-bis[4-(S)-methyloxazolin-2-yl]pyridine

Enantiomerically pure 2,6-bis[4-(S)-methyloxazolin-2-yl]pyridine, L, reacted with the pentacarbonylhalogenorhenium(I) and halogenotrimethylplatinum(IV) metal moieties to afford complexes of general formulae fac-[ReX(CO) 3 L] and fac-[PtXMe 3 L] (X = Cl, Br or I) in moderate yield. The potentially terdentate ligand acts here in a bidentate bonding mode, and undergoes a dynamic structural rearrangement which exchanges the pendant and co-ordinated oxazole rings. The bidentate bonding mode and absolute configuration of the ligand were confirmed by the crystal structure of the complex [ReCl(CO) 3 L]. The chiral centres on the ligand provide an excellent spectroscopic handle on the mechanism of the rearrangement, and two independent fluxional pathways are apparent. The energetics of the rearrangement in the complexes [ReX(CO) 3 L] (X = Cl, Br or I) was measured by standard 1 H NMR band-shape analysis; ΔG ‡ (average) (298 K) is 74.3 kJ mol -1 for the ‘tick-tock twist’ mechanism and 84.0 kJ mol -1 for the ‘rotation’ mechanism. Platinum-195 NMR data are reported for the complexes [PtXMe 3 L] (X = Cl, Br or I).

Isolation and characterization of the pyridazine (pydz) bridged halogenotrimethylplatinum(IV) complexes [PtXMe3)2(μ-pydz)] (X = Cl, Br, I). X-ray crystal structure of [(PtIMe3)2(μ-pydz)]

Abstract The bridged dinuclear platinum(IV) complexes [(PtXMe3)2(μ-pydz)] (X = Cl, Br, I) were isolated as minor products from the reaction between pyridazine (pydz) and the halogenotrimethylplatinum(IV) tetramers. The X-ray crystal structure of the iodo complex reveals both a double halide bridge and a pyridazine bridged structure with a Pt⋯Pt non-bonded distance of 3.5937(5) A. The platinum atoms show only a slight deviation from an idealized octahedral geometry, but the structure is folded in the equatorial plane by 51.5° to accommodate the iodines between the two platinum moieties.

A dynamic NMR study of 1,2-metallotropic shifts in trimethylplatinum(IV) halide complexes fo 3-methylpyridazine

Abstract 3-Methylpyridazine (3-Mepydz) reacts with halogenotrimethylplatinum(IV), [PtXMe3)4], to afford complexes of type fac-[PtXMe3(3-Mepydz)2] (X = Cl, Br or I). In solution these complexes undergo 1,2-metallotropic shifts between the contiguous nitrogen donors producing different linkage isomers. Solution abundances of these ismers are strongly influenced by the steric effects of the 3-methyl group on the pyridazine ring, with the (1,1)-isomer always being predominant (≈ 95%). Activation energies for the fluxion were determined by variable temperature 1H NMR spectroscopy, values of the (1,1) → (1,2) isomer shift being in the range 74–78 kJ mol−1.

2,6-Bis(diphenylphosphinosulfide)pyridine (L) as a facial terdentate ligand: synthesis and characterisation of the tricarbonylrhenium(I) complexes fac-[Re(CO)3L]+ [Re2(CO)6(μ-X)3]− (X=Cl, Br or I) and fac-[Re(CO)3L]+ [SbF6]−

The halogenopentacarbonylrhenium(I) compounds react with 2,6-bis(diphenylphosphinosulfide) pyridine (L) under mild conditions to yield ionic complexes of general formulae, fac-[Re₂(CO)₃L]⁺ [Re2(CO) ₆(μ-X) )₃]⁻ (X=Cl, Br or I), in which the ligand adopts a facial terdentate bonding mode. A synthesis of [Re(CO)₃L]⁺ [SbF₆]⁻ was carried out to establish the presence of the cation, fac-[Re(CO)₃L]⁺, in the complexes. The character of the anions was confirmed by negative ion MALDI-TOF mass spectrometry. The cation is fluxional; the P–phenyl rings oriented towards the metal moiety exhibit restricted rotation at low temperature. The free energy of activation, ΔG †, for hindered rotation is ca. 47 kJ mol⁻¹ for all complexes. Solid-state₃ ¹P NMR data are reported for the free ligand and for the complexes, [Re(CO)₃L][SbF₆] and [Re(CO)₃L][Re₂(CO)₆(μ-X)₃] (X=Cl, Br or I).

Trimethylplatinum(IV) complexes of anionic O/O and N/O donor ligands: synthesis, NMR and fluxional behaviour

Reaction of pentane-2,4-dione, pyridine-2-carboxylic acid or pyridine-2,6-dicarboxylic acid with trimethylplatinum(IV) gives dimeric complexes of general formulate fac-[PtMe3L](2), in which the ionised ligand acts in a chelating and a bridging fashion. High-resolution solid-state Pt-195 NMR data shows that the two platinum atoms are equivalent; the chemical shielding anisotropy and the principal components of the shielding tensor are reported. The complexes are soluble in co-ordinating solvents, yielding monomeric species of general formulae fac-[PtMe3L(solvent)], which are fluxional. The pyridine adducts, fac-[PtMe3L(py)] (L = pentane-2,4-dionato or pyridine-2-carboxylato), are also stereochemically non-rigid. The energetics of the dynamic processes have been studied by standard H-1 NMR band shape analysis techniques; Delta G( double dagger) (298 K) is in the range 69-86 kJ mol(-1). Solid-state C-13, and solution-state C-13 and Pt-195 NMR data are also reported

Synthesis and detailed NMR study of tricarbonylrhenium(I) and trimethylplatinum(IV) halide complexes of 2-methylthiomethyl-4-(S)-methyl-1,3-oxazoline (L). X-ray crystal structure of fac-[ReBr(CO)3L]

Abstract 2-Methylthiomethyl-4-(S)-methyl-1,3-oxazoline (L) reacts with the halogenopentacarbonylrhenium(I) and halgenotrimethylplatinum(IV) metal moieties, to form complexes of general formulae fac-[ReX(CO)3L] and fac-[PtXMe3L] (X = Cl, Br or I) in good yield. Detailed NMR studies reveal the presence of four solution-state diasteroisomers, which differ according to the orientation of the SMe and oxazole-methyl groups with respect to the halogen. Above ambient temperature, inversion at the S atom causes the epimerisation of pairs of diastereoisomers. The energetics of S inversion in the complexes [ReX(CO)3L](X = Cl, Br or I) were measured by standard 1H band shape analysis of the variable temperature spectra; energy barriers, ΔG‡ (298 K), are in the range 67–70 kJ mol−1. Atropisomerisation occurs over a period of several hours at ca. 350 K, and several weeks at ca. 273 K. Platinum-195 NMR data are reported for the complexes [PtXMe3L](X = Cl, Br or I).

A detailed NMR study of the solution stereodynamics in tricarbonylrhenium(I) halide complexes of the non-racemic chiral ligand 2,6-bis[(4R,5R)-dimethyl-1,3-dioxan-2-yl]pyridine (L1) and the molecular structure of fac-[ReBr(CO)3(L1)]†

1 Tricarbonylrhenium(I) halide complexes of the non-racemic chiral ligand 2,6-bis[(4R, 5R)-dimethyl-1,3-dioxan-2-yl]pyridine (L¹), namely fac-[ReX(CO)₃(L¹)] (X = Cl, Br or I), have been prepared. In these complexes the ligand is bound in a bidentate fashion, with the N atom of the pyridine ring and an O atom of one of the acetal rings co-ordinated to the octahedral metal centre. The bidentate mode is confirmed by the X-ray structure of fac-[ReBr(CO)₃(L¹)]. There are four possible diastereoisomers, depending on the configuration at the metal centre and at the acetal-carbon atom of the co-ordinated ring; the X-ray structure of fac-[ReBr(CO)₃(L¹)] shows that the SR diastereoisomer is present in the solid state. In solution, three of the four possible diastereoisomers are observed, namely SR, RR and RS; their relative populations are in the order SR > RR > SS. Above ambient temperature the complexes are stereochemically non-rigid. The fluxional kinetics have been measured by a combination of standard band shape analysis and selective inversion experiments. Two distinct processes are present: an acetal ring flip and exchange of the pendant and co-ordinated acetal rings. The latter process occurs via two independent mechanisms, namely tick-tock and rotation pathways. The activation energies for the stereodynamics are in the ranges 72 – 73 kJ mol⁻¹ (tick-tock), 77 – 78 kJ mol⁻¹ (acetal ring flip) and 83 – 90 kJ mol⁻¹ (rotation) at 298 K.