Mohammed Mazid

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 2. Rhenium carbonyl halide complexes, fac-[ReX(CO)3(terpy)](X = Cl, Br or I): NMR studies of their solution dynamics, synthesis of cis-[ReBr(CO)2(terpy)] and the crystal structure of [ReBr(CO)3(terpy)]

Under mild conditions pentacarbonylhalogenorhenium(I) complexes react with 2,2′:6′,2″-terpyridine (terpy) to form stable octahedral tricarbonyl complexes fac-[ReX(CO)3(terpy)](X = Cl, Br or I) in which the terpyridine acts as a bidentate chelate ligand. Under more severe reaction conditions fac-[ReBr(CO)3(terpy)] can be converted to cis-[ReBr(CO)2(terpy)]. In solution the tricarbonyl complexes are fluxional with the terpyridine oscillating between equivalent bidentate bonding modes. At low temperatures rotation of the unco-ordinated pyridine ring is restricted and in CD2Cl2 solution two preferred rotamers exist in approximately equal abundances. Rotational energy barriers have been estimated for the X = Cl and I complexes. The X-ray crystal structure of fac-[ReBr(CO)3(terpy)] confirms the bidentate chelate bonding of terpy with a N–Re–N angle of 74.3°. The pendant pyridine ring is inclined at an angle of 52.9° to the adjacent co-ordinated ring and the unco-ordinated nitrogen is directed towards the axial carbonyl and trans to Br.

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 1. Trimethylplatinum(IV) halide complexes [PtXMe3(terpy)](X = Cl, Br or I): nuclear magnetic resonance studies of their solution dynamics and crystal structure of [PtIMe3(terpy)]

2,2′:6′,2″-Terpyridine (terpy) reacts with trimethylplatinum halides [(PtXMe3)4](X = Cl, Br or I) to form stable octahedral complexes fac-[PtXMe3(terpy)](X = Cl, Br or I) in which the terpy molecule is acting as a bidentate chelate ligand. In solution the complexes are fluxional with the ligand oscillating between equivalent bidentate bonding modes by a mechanism consisting of ‘tick-tock’ twists of the metal moiety through an angle equal to the N–Pt–N angle of the octahedral centre. At below-ambient temperatures rotation of the unco-ordinated pyridine ring is severely restricted with the most favoured rotamers having the plane of the pendant pyridine ring at an angle of ca. 52° with respect to the adjacent co-ordinated pyridine ring plane. The X-ray crystal structure of [PtIMe3(terpy)] depicts the pendant pyridine N atom cis to iodine and this is the predominant species in solution at low temperatures. At above-ambient temperatures the complexes exhibit intramolecular Pt–Me exchange of axial and equatorial environments. Energy data based on accurate dynamic NMR fittings are reported for the three dynamic processes, namely pendant pyridine rotation, 1,4-Pt–N metallotopic shifts and Pt–Me scramblings.

Nuclear magnetic resonance investigations of a novel intramolecular methylthio replacement process in palladium(II) and platinum(II) complexes of mixed sulfur–phosphine ligands

A series of palladium(II) and platinum(II) complexes with the mono- and bis-chelate ligands bis[o-(methylthio)phenyl]phosphine and tris[o-(methylthio)phenyl]phosphine have been prepared and characterised. Despite the potential tridenticity of the first ligand it acts as a P/S monochelate to form square-planar complexes of type [M{PPh(C6H4SMe-o)2}X2](M = Pd, X = Cl, Br or I; M = Pt, X = Cl). Variable-temperature one- and two-dimensional NMR spectroscopy showed that pyramidal inversion of the co-ordinated sulfur atoms was accompanied by an exchange of pendant and bound methylthio groups. The ΔG‡ values for both processes were in the range 43–69 kJ mol–1, being strongly metal and halogen dependent. The bis(chelate) complexes [M{P(C6H4SMe-o)3}2][ClO4]2 are also square planar with metal co-ordination involving one phosphorus and one sulfur of each ligand, the other two pairs of SMe groups being unco-ordinated. The X-ray crystal structure of [Pd{P(C6H4SMe-o)3}2][ClO4]2 shows the co-ordinated S-methyls to be mutually cis with respect to the metallocycle plane. In low-temperature solutions of this complex this cis form is assumed to be predominant. At higher solution temperatures a facile intramolecular exchange of all six methylthio groups occurs. The energy and probable mechanism of this fluxion are reported.

Platinum metal complexes of potentially chelating alkene–sulphur and alkene–selenium ligands. The synthesis by chalcogen dealkylation and X-ray structures of the dimeric complexes [{PtI(SCH2CH2CMeCH2)}2] and [{PtI(PPh3)(SCH2CH2CMeCH2)}2], and a dynamic nuclear magnetic resonance study of [{PtI(L)(SCH2CH2CMeCH2)}2][L = PPh3, PPh2Me, or As(CH2SiMe3)3]

The chelating ligands 2,8-dimethyl- 5-thianona-1,8-diene and 2,8-dimethyl-5-selenanona-1,8-diene have been found to undergo unusually facile chalcogen dealkylation on treatment with halide when co-ordinated to platinum(II). The resulting dimeric complexes contain chelating bridging alkenyl thiolato and alkenyl selenato ligands and have been fully characterised. An X-ray diffraction study of [{PtI(SCH2CH2CMeCH2)}2] is reported: the crystals are orthorhombic, space group Pbca with Z= 1 in a unit cell of dimensions a= 12.733(3), b= 15.288(2), and c= 16.904(3)A. The molecular structure involves a non-planar Pt2S2 ring, with square-planar co-ordination at each platinum being completed by the chelating alkene and iodide ligands. The principal internuclear distances are Pt(1)–I(1) 2.624(2), Pt(2)–I(2) 2.621(2), Pt(1)–S(1) 2.295(6), Pt(1)–S(2) 2.330(6), Pt(2)–S(1) 2.334(6), Pt(2)–S(2) 2.304(6), Pt(1)–C 2.216(25) and 2.21 (3), Pt(2)–C 2.207(24) and 2.155(23)A. The co-ordinated alkene functions are displaced by ligands containing Group 5A donor atoms yielding dimeric complexes which contain non-chelating bridging alkenyl thiolato and alkenyl selenato ligands and which have been fully characterised. Inversion of configuration at the bridging chalcogen atom is observed at moderate temperatures and has been studied by dynamic n.m.r. spectroscopy. An X-ray diffraction study of [{PtI(PPh3)-(SCH2CH2CMeCH2)}2] is reported: the crystals are triclinic, of space group P, with Z = 1 in a unit cell of dimensions a= 10.396(1), b= 11.250(5), and c= 13.348(2)A with α= 91.63(3)β= 94.53(1), and γ= 116.02(3)°. The molecular structure involves a planar Pt2S2 ring, with square-planar co-ordination at each platinum being completed by triphenylphosphine and iodide ligands. The molecule has a centre of inversion. The principal internuclear distances are Pt–I 2.621 (1), Pt–S 2.367(3), and Pt–P 2.267(3)A.

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.

Platinum metal complexes of potentially chelating alkene-thioether and -selenoether ligands: Synthesis of the trimeric complexes [RhCl{E(CH2CH2CHCH2)2}]3 (E S, Se) and the crystal structure of [RhCl{Se(CH2CH2CHCH2)2}]3

Reaction of [{RhCl(C 2 H 4 ) 2 } 2 ] with E(CH 2 CH 2 CHCH 2 ) 2 (E = S, affords the trimeric complexes [RhCl{E(CH 2 CH 2 CHCH 2 ) 2 }] 3 . The structure of the product with E = Se was established by X-ray diffraction. The coordination sphere at each rhodium atom consists of a distorted trigonal bipyramid with two alkene groups from the same selenoether in equatorial positions, one bridging selenium in the third equatorial position and the other in an axial site with a terminal chloride in the other axial site. One- and two-dimensional NMR studies of the compounds suggest that the solid state structure is retained in solution.

Cationic bis(cyclopentadienyl)titanium complexes. The synthesis and structure of [CP*2Ti(OH)(HNCPh2)]BPh4·Et2O

Abstract The oxidation of the titanium(III) ketimido complex, CP*2TiNCPh2 (Cp* = C5Me5), with AgBPh4 in the presence of traces of moisture gives the cationic ketimine complex [CP*2Ti(OH)(HNCPh2)]BPh4·Et2O (1). The structure of the complex has been determined by X-ray diffraction. The cation has a pseudo-tetrahedral structure. The TiOH distance is short [1.853(7) A], indicating TiO double bond character, while the diphenylketimine ligand acts as an N-donor, with a bent TiNC arrangement [145.1(5)°].

Dimethylplatinum complexes of polydentate alkene–sulfur and –selenium ligands

Interaction of [PtMe2(SMe2)2] with 1 equivalent of 5-selenanona-1,8-diene produces a monomeric complex containing the ligand chelating through one alkene moiety and the selenium atom. The unco-ordinated alkene moiety undergoes exchange with the co-ordinated alkene moiety which has been studied by dynamic NMR spectroscopy. Interaction of the same platinum(II) precursor with 0.5 mol equivalent of the dialkenyl chalcogenoether ligands E(CH2CH2CHCH2)2(E = S or Se) produced the novel dinuclear complexes [Pt2Me4{µ-E(CH2CH2CHCH2)2}] both of which have been characterised by X-ray crystallography and shown to be isostructural. The unit cells are of dimensions a= 10.850(2), b= 11.289(7) and c= 12.415(1)(E = S) and a= 11.056(1), b= 11.251(1) and c= 12.546(2)A, (E = Se). In each case the two metals are bridged by a tetrahedrally co-ordinated chalcogen atom, with one alkenyl group chelating to each platinum atom. The platinum–chalcogen distances are Pt–S 2.354(8) and Pt–Se 2.457(5)A.

Halogenotrimethylplatinum(IV) complexes of 2,6-bis(p-tolylthiomethyl)pyridine (L1): nuclear magnetic resonance studies of their solution state stereodynamics and the crystal structure of fac-[PtBrMe3L1]

Under mild conditions 2,6-bis(p-tolylthiomethyl) pyridine (L1) reacted with halogenotrimethylplatinum(IV) to afford complexes of the type fac-[PtXMe3L1](X = Cl or Br). This potentially terdentate ligand acts here in a five-membered S/N chelate bidentate fashion. Solution dynamic NMR studies revealed the presence of three fluxional processes: pyramidal inversion of the co-ordinated sulfur atom, S-S switching with correlated pyramidal inversion, and S-S switching. The mechanism for the S-S exchange process was elucidated by two-dimensional NMR exchange spectroscopy. The crystal structure of fac-[PtBrMe3L1] confirms the bidentate chelate nature of the ligand in the solid state, with a N-Pt-S(1) angle of 81.5°. IR data for the Pt-C, Pt-N and Pt-X stretching modes in these complexes are also presented.

Synthetic, dynamic nuclear magnetic resonance and crystallographic studies of platinum complexes containing silyl-substituted dialkenyl-thioether and -selenoether ligands

Potentially quadridentate di(silaalkenyl) chalcogenoether ligands have been observed to bind in a bidentate mode via an alkene moiety and a chacogen lone pair of electrons to platinum(II) and in a tridentate mode to rhodium(I) metal centres, via the chalcogen atom and both alkene moieties. Variable-temperature NMR studies established the occurrence of fluxional processes in these complexes, the energy barriers of which have been evaluated for the platinum systems. The crystal structures of two species have been determined: [PtI2{S(CH2SiMe2CHCH2)2}] forms monoclinic crystals of space group P21/a with a= 12.279(5), b= 8.961(3), c= 18.575(3)A, β= 108.49(2)° and Z= 4 and [{RhCl[S(CH2SiMe2CHCH2)2]}] forms triclinic crystals of space group P with a= 7.7178(12), b= 10.289(4), c= 10.5932(14)A, α= 92.56(2), β= 99.544(14), γ= 105.26(2)° and Z= 1. The platinum complex is monomeric and has a square-planar geometry with the iodine atoms in cis positions, whilst the rhodium complex is a centrosymmetric dimer with two chlorine atoms bridging a pair of rhodium atoms, both having trigonal-bipyramidal geometry.