Brian F. Taylor

Further investigations into tetrahedral M4L6 cage complexes containing guest anions: new structures and NMR spectroscopic studies

A series of ligands LPh, Lnaph and Lanth, which contain two bidentate pyrazolyl–pyridine termini separated by an aromatic (1,2-phenyl, 2,3-naphthyl or 2,3-anthracenyl, respectively) spacer have been used to prepare tetrahedral cage complexes of the form [M4L6]Xn, in which a bis-bidentate bridging ligand spans each of the six edges of the M4 tetrahedron and one anion is bound in the central cavity. Several new examples have been structurally characterised, including an example with a new ligand (Lanth), the first example with a second-row transition metal ion [Cd(II)], and the first example of a cage containing a dianionic guest (hexafluorosilicate). The series of structurally similar Co(II) complexes [Co4L6(BF4)](BF4)7 (L = LPh, Lnaph and Lanth) have been examined in detail by NMR spectroscopy. The 1H NMR spectra are highly shifted between −110 and +90 ppm, but the spectra can be completely assigned by correlation of measured T1 relaxation times with distances of the protons in the complexes from the paramagnetic Co(II) centres. 1H DOSY measurements have been used to estimate diffusion constants which confirm the structural integrity of the cages in solution, and 19F DOSY measurements on the anions show that (i) the trapped [BF4]− anion diffuses at the same rate as the cage superstructure surrounding it, indicating that it is trapped inside the cage cavity; and (ii) the ‘free’ [BF4]− anions have diffusion rates consistent with substantial retardation due to ion-pairing with the 7+ complex cation.

A reinvestigation of some triphenylphosphinesilver halide complexes and their reaction with stannous chloride: 119mSn Mössbauer and 31P FT NMR studies

Abstract Silver chloride reacts with triphenylphosphine to form either Ag(PPh 3 ) 2 Cl or Ag(PPh 3 ) 3 Cl, depending upon the solvent, whereas silver bromide and iodide afford the tris(triphenylphosphine)silver(I) halides. The reactions of these silverphosphinehalide complexes with anhydrous stannous halides are investigated and the structures of the isolated complexes, both in the solid state and in solution, are discussed in terms of their 31 P NMR and 119m Sn Mossbauer spectra and their molar conductivities.

The chemistry of heteroarylphosphorus compounds. Part 15. Phosphorus-31 nuclear magnetic resonance studies of the donor properties of heteroarylphosphines towards selenium and platinum(II)

The donor properties of a series of heteroarylphosphines (bearing 2- and 3-furyl, 2- and 3-thienyl, and 1-methylpyrrol-2-yl groups directly bound to phosphorus) towards selenium and platinum(II) acceptors have been investigated by 31P n.m.r. studies of the one-bond coupling constants 1J(77Se–31P) and 1J(195Pt–31P). It is shown that the respective coupling constants increase as the heteroaryl groups become more electron withdrawing, indicating an increased s character for the phosphorus lone pair. The implications of this for the relative donor properties of the heteroarylphosphines and PPh3 are considered.

The formation and characterisation of (η2-ethene)hydrido(η5-pentamethylcyclopentadienyl)(trisubstituted-silyl)rhodium complexes; intermediates in catalytic dehydrogenative silylation reactions

The complexes [(η5-C5Me5)Rh(H)(SiR3)(C2H4)][R = Et (4a) or Me (4b)] have been detected and characterised spectroscopically [including 103Rh n.m.r. spectra (via INEPT)] as intermediates in the thermal and photochemical reaction (i). Complex (4d)(R = OEt), which was isolated and fully [graphic omitted] characterised, and (4c)(R = Ph), were obtained from reaction of SiR3H and [(η5-C5Me5)Rh(C2H4)2]. Evidence for iridium analogues of (4) was obtained but more complex further reactions also occurred there. The complexes (4) were reasonably thermally robust; since (1) and (3) are active catalysts for the reaction, SiEt3H + C2H4→ CH2CHSiEt3+ SiEt4, this implies significant activation is required to reorganise the ligands in (4). The related reaction, of SiR3H (R = Me, Et, Ph, or OEt) and [(η5-C5Me5)Rh(CO)2], only proceeded as far as [(η5-C5Me5)Rh(H)(SiR3)(CO)]; this was very labile and lost SiR3H with the formation of blue [{(η5-C5Me5)Rh(CO)}2].

Thermal [1,5] sigmatropic rearrangements in (σ-7-cycloheptatrienyl)triphenyltin and (σ-5-cyclohepta-1,3-dienyl)triphenyltin: A 1H and 13C NMR reinvestigation

Abstract It has been confirmed by 1H and 13C NMR spectroscopies that Sn(σ-C7H7)Ph3 undergoes either 1,4- or 1,5-shifts of the SnPh3 moiety around the cycloheptatrienyl ring with ΔH‡ = 13.8 ± 0.4 kcal mol−1, ΔS‡ = −5.6 ± 1.2 cal mol−1 deg−1, and ΔG‡300 = 15.44 ± 0.14 kcal mol−1. Similarly, (σ-5-cyclohepta-1,3-dienyl)triphenyltin undergoes 1,5-shifts with ΔH‡ = 12.4 ± 0.6 kcal mol−1, ΔS‡ = −11.2 ± 1.8 cal mol−1 deg−1, and ΔG‡300 = 15.76 ± 0.13 kcal mol−1. It is therefore probable that Sn(σ-5-C5H5)R3 and Sn(σ-3-indenyl)R3 do not undergo 1,2-shifts as previously suggested but really undergo 1,5-shifts.

Determination of the magnitudes and signs of phosphorus–phosphorus coupling (2Jpp) by hydrogen-1{phosphorus-31} internuclear double resonance measurements on some gold(I), iridium(III), mercury(II), palladium(II), platinum-(II) and -(IV), and rhodium(III) complexes containing two, three, or four trialkylphosphine ligands

The application of 1H{31P} INDOR spectroscopy to the evaluation of P–P coupling in a number of complexes has been investigated. The sign of 2JPP(cis) for the complexes cis-[MX2(PMe3)2], cis-[MX2{P(OMe)3}2](M = Pd or Pt; X = Cl, Br, or I), and cis-[PtMe2(PMe3)2] has been determined by comparison of observed and calculated 1H{31P} INDOR spectra. The sign and magnitude of 2JPP(trans) in the complexes trans-[MX2(PMe3)2](M = Pd or Pt; X = Cl, Br, I, or CN), trans-[MX2(PEt3)2](M = Pd or Pt; X = Cl, Br, or I), trans-[PtX4(PMe3)2], [MX(PMe3)3]+(M = Pd or Pt), mer-[PtX3(PMe3)3]+, mer-[RhX3(PMe3)3], and trans-[PtX4(PEt3)2](X = Cl or Br), trans-[IrCl4(PMe3)2]–, mer-[IrCl3(PMe3)3], [Hg(PMe3)2]2+, [Au(PMe3)2]+, trans-[PtBr2(PPrn3)2], and trans-[Pdl2{P(OMe)3}2] have been obtained using increased irradiating powers. Signs and magnitudes of both 2JPP(cis) and 2JPP(trans) have similarly been determined for the complexes trans-[RhX2(PMe3)4]+ and trans-[IrX2(PMe3)4]+(X = Cl or Br), [Pt(PMe3)4]2+, and [Pt{P(OMe)3}4]2+. All the trans-couplings are positive and greater than 250 Hz, whilst the cis-couplings are much smaller and negative except for those of the complex cis-[PdX2{P(OMe)3}2]. Vibrational spectra of the latter complexes have been recorded and it is suggested that there may be something abnormal about their structure. The difference between the values of 2JPP in corresponding PMe3 and PEt3 complexes is discussed.

Preparation of alkynepentacarbonyltriphenylphosphinedicobalt complexes using ultra violet light

The preparation of alkynepentacarbonyltriphenylphosphinedicobalt complexes under mild conditions using linearly polarised ultra violet laser light is described. This method compares favourably with conventional thermal techniques and is superior when the alkyne contains reactive functional groups.

Carbene formation from CpM(SnPh3)(CO)2 (M = Fe, Ru). Crystal structures of CpFeI(CO){C(OEt)Ph}, CpRuI(CO){C(OEt)Ph} and CpRuI(CO){C(NHMe)Ph}

Addition of LiPh followed by [Et3O][BF4] to CpM(SnPh3)(CO)2 (M = Fe, Ru) gives the carbene complexes CpM(SnPh3)(CO){C(OEt)Ph}. These undergo aminolysis on treatment with EtNH2 or MeNH2 to form the amino carbenes CpFe(SnPh3)(CO){C(NHEt)Ph} and CpRu(SnPh3)(CO){C(NHMe)Ph}, respectively. All four compounds react with iodine, the SnPh3 group being replaced by I to give the new carbenes CpMI(CO){C(X)Ph} (M = Fe, Ru; X = OEt; M = Fe, X = NHEt; M = Ru, X = NHMe). The IR and NMR spectra show that the amino carbenes exist as single isomers while the ethoxy carbenes form fluxional isomeric mixtures. The compounds CpFeI(CO){C(OEt)Ph}, CpRuI(CO){C(OEt)Ph} and CpRuI(CO){C(NHMe)Ph} have been studied by X-ray diffraction. In each case the geometry about the metal is essentially conventional, with the carbene groups eclipsed by the MCO groups.

The synthesis and characterisation of dihydridobis-(trialkyltin)(pentamethylcyclopentadienyl)-rhodium(V) and iridium(V) complexes and related reactions

Abstract The dihydridobis(trialkylstannyl)-rhodium(V) and -iridium(V) complexes [C5-Me5M(H)2(SnR3)2] were made by reaction of R3SnH and [(C5Me5M)2Cl4] or [C5Me5M(C2H4)2]. An intermediate in the last reaction was spectroscopically identified as [C5Me5M(H)(SnR3)(C2H4)] (M  Ir, R Me), but the rhodium analogues could not be detected. The hydrido-carbonyl complexes, [C5Me5M(H)-(SnR3)(CO)] were readily obtained by reaction of R3SnH with [C5Me5M(CO)2]; they were more stable than their silyl analogues, but the rhodium complexes slowly decomposed. The complexes [C5Me5M(H)2(SnR3)2] were very resistant to attack by nucleophiles but the rhodium complexes slowly reacted with PPh3 to give [C5Me5Rh(PPh3)(SnR3)2]; this behaviour was in marked contrast to that shown by [C5Me5Rh(H)2(SiR3)2]. The complex [C5Me5Rh(H)2(SnMe3)2] was deprotonated by n-butyllithium to give [C5Me5Rh(H)(SnMe3)2] ; this was reversed on addition of methanol.

Activation energies for molecular tumbling and cyclopentadienyl rotation in [M(η5-C5H5)(η4-cod)](M = Rh or Ir; cod = cyclo-octa-1,5-diene) and the X-ray crystal structure of and bonding in [Rh(η5-C5H5)(η4-cod)]

The X-ray structure of [Rh(η5-C5H5)(η4-cod)](cod = cyclo-octa-1,5-diene) has been determined. The cyclopentadienyl ring is distorted in a manner consistent with an ‘allyl-ene’ structure. Carbon-13 and 103Rh n.m.r. studies have been used to determine the activation energies for molecular tumbling and cyclopentadienyl rotation in [M (η5-C5H5)(η4-cod)](M = Rh or Ir). Despite the ‘allyl-ene’ geometry, the activation energy for cyclopentadienyl rotation is the same as for ferrocene derivatives. The 13C and 103Rh chemical shift anisotropies were also determined.