Kenneth Kite

Structural dependencies of pyramidal inversion at sulphur and selenium in thio- and seleno- ether complexes of palladium(II) and platinum(II): A nuclear magnetic resonance study

Abstract Total NMR band shape fitting methods have provided accurate energy data for inversion barriers at sulphur and selenium in complexes of types cis-[MX2L] (M = PdII, PtII; X = Cl, Br, I; L = MeS(CH2)2SMe, MeS(CH2)3SMe, o-(SMe)2C6H3Me, cis-MeSCH=CHSMe) and [PtXMe{MeE(CH2)2E′Me}] (E= E′= S or Se and E = S, E′= Se; X = Cl, Br, I). Barrier energies were found to decrease by 10–12 kJ mol−1 in going from aliphatic through aromatic to olefinic ligand back-bone. This can be explained in terms of (3p - 2p) π conjugation between the inverting centre and the ligand back-bone. The effects of ligand ring size, nature of halogen atom and the metal oxidation state on the barrier energies are discussed.

NMR studies of stereochemical non-rigidity in dinuclear thiolato-bridged complexes of platinum(IV) with platinum(II) and palladium(II): the structure of [Pt(dppe)(μ2-SMe)2PtClMe3]

Abstract The complexes [M(dppe)(μ2-SMe)2PtXMe3] [M = Pd or Pt; X = Cl, Br or I; dppe = 1,2-bis(diphenylphosphino)ethane] have been synthesized, and by means of 1H and 31P variable-temperature NMR studies are shown to have several different fluxional modes. Where possible, accurate activation parameters for the processes have been determined. The unexpected trends of these values demonstrate the consequences of the presence of the four-membered Pt(IV)SM(II)S ring. The structure of a representative member of this novel range of complexes, [Pt(dppe)(μ2-SMe)2PtClMe3], has been determined by X-ray diffraction methods.

Cationic complexes of trimethylplatinum(IV) with tridentate ligands. I: Preparation and characterization of complexes from a range of thio, seleno, thio-seleno, amino-thio and amino-seleno ligands

Abstract The new ionic complexes [PtMe3{MeE(CH2)nE′(CH2)nEMe}]+X− [n = 3; E = E′ = S : n = 2; E = Se or S; E′ = O, S, Se or SS: X = I, BPh4 or BF4] and [PtMe3(H2NCH2CH2)2E′]+BF−4 [E′ = O or SS] have been prepared and characterized by molar-conductivity measurements and 1H NMR spectroscopy. The hitherto unreported ligands [(MeE(CH2)n)2E′] (n = 3; E = E′ = S: n = 2; E = Se; E′ = O or S or Se: n = 2; E = S; E′ = Se] have been characterized by 1H NMR and 77Se NMR (where appropriate), and by mass spectroscopy.

The X-ray crystal structure of the organoplatinum bridging diselenide complex [(PtMe3I)2MeSeSeMe]

An X-ray crystal structure determination of the dinuclear complex [(PtMe3I)2MeSeSeMe] confirms the retention of the Se—Se bond and the presence of a bridging diselenide ligand.

Nuclear magnetic resonance study of pyramidal inversion and intramolecular rearrangements in complexes of trimethylplatinum(IV) halides with aliphatic and aromatic mixed thio–seleno-ethers

Mixed chalcogen ligand complexes of trimethylplatinum(IV) halides of general type [PtXMe3(MeSRSeMe)][R =(CH2)2 or o-C6H4] have been prepared and the energy barriers associated with the pyramidal inversions of the individual chalcogen atoms measured by total band-shape dynamic n.m.r. methods. At elevated temperatures an intramolecular scrambling of all of the Pt-methyls occurs, associated with a fluxional movement which apparently effects a 180° rotation of the bidentate ligand.

Complexes of trimethylplatinum(IV) halides with dithio- and diselenoethers, dimethyl disulphide, and dimethyl diselenide

Trimethylplatinum(IV) halides react with MeE(CH2)nEMe, E = S or Se, n= 2 or 3, to give mononuclear species [PtXMe3{MeE(CH2)n EMe}], X = Cl, Br or I. Under similar conditions the ligands L–L = MeECH2EMe, MeECH(Me)EMe, and MeEEMe, E = S or Se, give dinuclear complexes [(PtXMe3)2(L–L)] in which the S or Se donor ligand bridges the metal atoms. Structural asignments are based on 1H n.m.r. solution studies.

Dimeric complexes of trimethylplatinum(IV) with ethylacetoacetate, methylacetoacetate, dimethylmalonate and diethylmalonate, and their pyridine and 2,2′-bipyridyl adducts

Abstract An 1 H NMR study of the complexes [PtMe 3 (R 1 COCHCOR 2 )] 2 (R 1  CH 3 , R 2  OCH 3 ( 1 ) and R 1 ; CH 3 , R 2 ; OC 2 H 5 ( 2 ), R 1 ; R 2 ; OCH 3 ( 3 ) and R 1 ; R 2 ; OC 2 H 5 ( 4 )) shows that in solution 1–4 are non-fluxional at ambient temperature, in contrast to the complexes with R 1 ; R 2  alkyl. Incorporation of alkoxy groups into the β-dicarbonyl ligand strengthens the PtC bridge bond. The 1:1 adducts of 1–4 with pyridine and 2,2′-bipyridyl contain bidentate (O,O′bonded) and monodentate (Cbonded) dicarbonyl ligands, respectively. A correlation between 2 j (Pt-CH) and 2 j (Pt-CH) for compounds with a trans (CH 3 )-Pt-(CH) feature is demonstrated.

Cationic complexes of trimethylplatinum(IV) with tridentate ligands—II. Fluxional behaviour

Variable temperature 1H NMR studies on the ionic compounds [PtMe3{MeE(CH2)nE′(CH2)nEMe}]+X− (n = 3, E = E′ = S: n = 2, E = Se or S; E′ = O, S, Se: n = 2, E = S, E′ = SS: X = I, BPh4 or BF4) have shown that pyramidal inversion takes place only at the terminal chalcogen atoms. High-temperature studies on these complexes and [PtMe3{(H2NCH2CH2)2E′}]+BF4− (E′ = O or SS) show that only those with E′ = O undergo ligand scrambling processes. Computer simulation of the static and dynamic spectra gives accurate energy barriers for both fluxional processes.

Nuclear magnetic resonance investigations of configurational non-rigidity in dinuclear platinum(IV) complexes. Part 4. Ring reversal, pyramidal inversion, and novel fluxional rearrangements in [(PtXMe3)2(MeSCH2SeMe)] complexes

Dinuclear complexes of the type DL-[(PtXMe3)2(MeSCH2SeMe)] containing both PtIV–S and PtIV–Se bonds have been isolated. Detailed variable-temperature n.m.r. studies have established the existence of ligand ring reversal, pyramidal inversion of both S and Se atoms, ligand commutation (switching) between Pt atom pairs and scrambling of the platinum methyl environments which is considered to be a consequence of rapid ligand commutation producing a highly non-rigid seven-co-ordinate PtIV intermediate. Accurate energy barriers for these non-dissociative dynamic processes have been computed. Despite the probable non-synchronous nature of the S/Se double inversion, the spectra are shown to be sensitive only to Se inversion.

Cis-1,4-cyclohexadienebisepisulphide complexes of chromium, molybdenum and tungsten carbonyls: the x-ray crystal structure of

Abstract The first metal carbonyl derivatives of a coordinated episulphide ring are reported. Two classes of complex have been obtained wherein the bisepisulphide behaves either as a bridging ligand between two metal pentacarbonyl moieties as in for example , or as a chelating ligand in a mononuclear metal pentacarbonyl complex such as , for which the X-ray crystal structure is reported.