Murray S. Davies

[1H, 15N] Heteronuclear Single Quantum Coherence NMR Study of the Mechanism of Aquation of Platinum(IV) Ammine Complexes

The aquation and hydrolysis of a series of platinum(IV) complexes of the general form cis, trans, cis-[PtCl 2(X) 2( (15)NH 3) 2] (X = Cl (-), O 2CCH 3 (-), OH (-)) have been followed by [ (1)H, (15)N] Heteronuclear Single Quantum Coherence NMR spectroscopy. Negligible aquation (<5%) is observed for the complexes where X = O 2CCH 3 (-) or OH (-) over 3-4 weeks. Aquation of cis-[PtCl 4( (15)NH 3) 2] ( 1) is observed, and the rate of aquation increases with increasing pH and upon the addition of 0.01 mol equiv of the platinum(II) complex cis-[PtCl 2( (15)NH 3) 2] (cisplatin). The first aquated species formed from cis-[PtCl 4(NH 3) 2] has one of the axial chloro groups (relative to the equatorial NH 3 ligands) replaced by an aqua/hydroxo ligand. The second observed substitution occurs in an equatorial position. Peaks that are consistent with five of the eight possible aquation species were observed in the NMR spectra.

Metal—ligand bonding in LM(CO)5 complexes (L = NMe3, PMe3, PCl3, PBr3 or AsMe3; M = Cr, Mo or W) from dielectric, electro-optic and spectroscopic evidence

Abstract A comparative study has been made of the electric dipole moments, optical polarisability anisotropies (from electric birefringence measurements), infrared carbonyl stretching frequencies and 13C NMR spectral shifts of LM(CO)5 complexes where L = NMe3, PMe3, PCl3, PBr3 or AsMe3 and M = Cr, Mo or W. Analysis of the polarisability anisotropies of the complexes provides direct, experimentally based evidence indicating a substantial π-component in the phosphorus—metal and arsenic—metal bonding in P(As)Me3M(CO)5 within a highly polarisable P(As)M(trans)CO delocalised π-electron system. The LM π-bonding appears not to be significantly affected by change of L from PMe3 to AsMe3 or by change of M within the chromium triad. It is shown that π-bonding between the phosphorus and the metal and electron delocalisation along the PM(trans)CO linkage are enhanced by electronegative halogen substituents in the phosphine ligand. The conclusions reached are in general accord with results from interpretation of the infrared and 13C NMR spectral and dipole moment data.

Studies on the Nature and Strength of Pt . . .H(-N) Interactions. The Crystal Structures of Chloro[N-(2-aminoethyl)-N-(2-ammonioethyl)ethane-1,2-diamine]platinum(II) Chloride and Dichloro[4,7-diaza-1-azoniacyclononane]platinum(II) Tetrachlor

Two complexes, namely, chloro[N-(2-aminoethyl)-N-(2-ammonioethyl)ethane-1,2-diamine]platinum(II) chloride {[PtCl(tren+H)]Cl2} and dichloro[4,7-diaza-1-azoniacyclononane]platinum(II) tetrachloroplatinate(II)–water (1/2) {[PtCl2(tacn+H)]2[PtCl4]·2H2O}, have been prepared and structurally characterized by single-crystal X-ray diffractometry as part of a study of the nature and strength of Pt···H(–N) interactions. Crystals of [PtCl(tren+H)]Cl2 are monoclinic, space group P21/c, a 8.293(2), b 14.396(6), c 11.305(3) A, β 107.34(2)o, Z 4, and the structure has been refined to a residual of 0.042 based on 1631 reflections. Crystals of [PtCl2(tacn+H)]2[PtCl4]·2H2O are monoclinic, space group P21/a, a 12.834(4), b 8.206(4), c 13.116(8) A, β 93.01(4)˚, Z 2, and the structure has been refined to a residual of 0.035 based on 1974 reflections. In [PtCl(tren+H)]2+, the protonated amine forms hydrogen bonds with chloride anions and no close contacts with the metal ion. In [PtCl2(tacn+H)]+, a short intramolecular contact is observed between the metal and the protonated amine and the results of molecular mechanics modelling are consistent with there being a Pt···H hydrogen bond. Molecular mechanics modelling of [PtCl(tren+H)]2+ and [PtCl2(dien+H)]+ shows that the protonated amines could readily form close contacts with the metal. It is concluded that there is evidence for the formation of Pt···H(–N) hydrogen bonds but these bonds are very weak, being similar or lower in energy than Cl···H(–NPt) hydrogen bonds.

Conformational studies of EPh3M(CO)5 complexes (E P, As or Sb; M Cr, Mo or W)

Abstract Studies are reported of the electro-optical Kerr effect, electric dipole moments and IR carbonyl stretching frequencies of the nine EPh 3 (CO) 5 complexes (E  P, As or Sb and M  Cr, Mo or W). The experimental results are applied in conjunction with molecular mechanics calculations and data from X-ray crystal structure analysis, to explore the stereostructural preferences of the EPh 3 M(CO) 5 molecules with regard to orientations about the ME bond and phenyl group rotations about EC ar . Evidence is drawn together and compared for EPh 3 M(CO) 5 in the solution and solid states and as isolated molecules. It is found that for all states, phenyl ring dispositions of like helicity are favoured for the coordinated EPh 3 ligands in these complexes.

Metal Template Synthesis of a Tripodal Tris(bipyridyl) Receptor that Encapsulates a Proton and an Iron(ii) Centre in a Pseudo Cage

The Fe(ii) template synthesis of the first member of a new category of tripodal tris-bipyridine ligands incorporating a nitrogen bridgehead is reported. The X-ray structure of the reaction product shows that the ligand adopts a pseudo cage-like structure that encapsulates both a proton and an Fe(ii) ion in its cavity. The complex shows an extended helical arrangement that is effectively ‘capped’ at its open end by a hydrogen bonded PF6– counter ion that is symmetrically aligned with the 3-fold axis of the helix. A 1H NMR study demonstrated that the encapsulated proton can be reversibly exchanged under acid/base conditions in CD3CN.

Steric control of stereoselective interactions between the platinum(II) complex [PtCl2(1,4-diazacycloheptane)] and DNA: comparison with cis-[PtCl2(NH3)2] and [PtCl2(ethane-1,2-diamine)] using DNA binding and molecular modeling studies.

The rate and extent of binding of [PtCl2(hpip)] (hpip=homopiperazine=1,4-diazacycloheptane) and cis-[PtCl2(NH3)2] to calf thymus DNA was measured using atomic absorption spectroscopy and it was found that [PtCl2(hpip)] bound both more rapidly and to a greater extent than did cis-[PtCl2(NH3)2]. The binding of [PtCl2(hpip)] and [PtCl2(en)] (en=ethane-1,2-diamine) to salmon sperm DNA and to synthetic, self-complementary 10-base-pair and 52-base-pair oligonucleotides was studied using enzymatic digestion and HPLC analysis of the products. [PtCl2(hpip)] forms approximately two-fold fewer GpG and ApG intrastrand adducts and concomitantly more monofunctional adducts than does [PtCl2(en)]. In the case of [PtCl2(hpip)], two GpG adducts, corresponding to the different orientations of the hpip ligand with respect to the DNA, were observed in a 1:3.3 ratio. The minor product corresponds to the orientation in which the bulkier propylene chain of the hpip ligand is adjacent to, and makes close contacts with, the floor of the major groove. When the reaction was repeated with a synthetic oligonucleotide decamer duplex, the ratio of the two forms was approximately 1:1.9 and with the 52-mer duplex it was 1:2.4, revealing an apparent systematic dependence of stereoselectivity on nucleotide size. Computer modeling of the two adducts formed by [PtCl2(hpip)] and those formed by [PtCl2(en)] and cis-[PtCl2(NH3)2] revealed that non-bonded interactions between the hpip ligand and the DNA were probably responsible for both the decreased proportion of GpG adducts formed by [PtCl2(hpip)] and the stereoselectivity exhibited in the formation of these adducts. This is the first case in which the stereoselectivity can be ascribed to steric factors alone.

Variable-temperature one- and two-dimensional 13C CP/MAS NMR studies of the dynamics of monohaptocyclopentadienyl rings of hafnium and titanium tetracyclopentadienyl in the solid state

Abstract Organometallic compounds with cyclopentadienyl ligands (C5H5) can undergo fluxional motion. We have studied the Group IVB transition metal complexes of the formula M(η5-C5H5)2(η1-C5H5)2, where M=Ti and Hf, in the solid state using variable-temperature 13C CP/MAS NMR spectroscopy. We present data which indicate that intramolecular rearrangement proceeds via a sigmatropic shift. Using two-dimensional (2D) exchange NMR, we can follow the rearrangement of the single bonded cyclopentadienyl ligands.

Crystal structures of [W(CO)5(PPh3)], [M(CO)5(AsPh3)] and [M(CO)5(SbPh3)](M = Mo or W): a comparative study of structure and bonding in [M(CO)5(EPh3)] complexes (E = P, as or Sb; M = Cr, Mo or W)

Crystal structures have been determined for [W(CO)5(PPh3)], [M(CO)5(AsPh3)] and [M(CO)5-(SbPh3)](M = Mo or W) as part of a systematic study of a series of nine [M(CO)5(EPh3)] complexes (M = Cr, Mo or W; E = P, As or Sb). Trends in bond lengths and angles are rationalised in terms of steric and electronic interactions between the bonded M(CO)5 and EPh3 fragments. Comparison is made between the solid-state geometry of the free and co-ordinated EPh3. Torsion angles defining the disposition of the EPh3 groups in relation to M(CO)5 show little variation within the [M(CO)5(EPh3)] series. For all nine complexes the EPh3 groups have propeller geometry with small deviations from symmetric C3 structures. The studies were extended to include other related [M(CO)5L] complexes. Trends in the structural parameters of 29 such compounds are related to the steric behaviour and π-acceptor capacity of the ligands L. It is shown that M–P bond dimensions are not adequately explained by hybridisation changes of the phosphorus atom in the ligand L.

Butyl methoxy dibenzoylmethane.

A comprehensive profile on Butyl methoxy dibenzoylmethane, one of the most commonly used ultraviolet (UV) filters in topical sunscreen products, is prepared. This UV filter, often referred to as Avobenzone, has its main absorbance in the UVA I region of the spectrum and is susceptible to photodegradation. The profile contains the following sections: general information, use and mechanism of action, method of preparation, physical characteristics, methods of analysis, stability, and toxicity. The physical characteristics section includes the melting range, differential scanning calorimetry, partition coefficient, ionization constant, solubility, and UV, infrared, nuclear magnetic resonance ((1)H NMR and (13)C NMR) and mass spectrometry and X-ray powder diffractometry. The method of analysis section in addition to compendial identification and purity and assay methods includes thin-layer gas and high-performance liquid chromatography. The photostability and photostabilization of Butyl methoxy dibenzoylmethane, in addition to its toxicity, are also documented.

Oxidation of [PtIICl2(ethane-1,2-diamine-N,N'-dicarboxylic Acid)] and Ligand Ring Closure in the Platinum(IV) Oxidation State

Oxidation of the dichloroplatinum(II) complex of the potentially tetradentate ligand ethane-1,2-diamine-N,N´-diacetic acid (H2enda) gives rise to a variety of products. A number of these species have been crystallographically characterized. [PtIVCl2(enda)] as the hemihydrate crystallizes in the monoclinic space group P21/a, with a 11.238(1), b 15.665(2), c 13.737(2) A, β 109.44(1)˚, and was refined to an R value of 0.030 on 3015F. [PtIVCl2(enda)] as the monohydrate crystallizes in the orthorhombic space group Pna21, with a 6.984(2), b 9.000(3), c 18.431(3) A, and was refined to an R value of 0.025 on 992F. [PtIVCl3(Henda)]·H2O crystallizes in the orthorhombic space group Pbca, with a 11.741(1), b 12.851(2), c 17.133(2) A, and was refined to an R value of 0.029 on 2015F. The major product is the ring-closed complex [PtIVCl2(enda)] and if the solution is heated under reflux for 24 h, this is the only product. In contrast, reaction of cis,trans-[PtIVCl2(OH)2(ethane-1,2-diamine)] with excess acetic acid was shown not to lead to displacement of the hydroxo ligands.