Mervyn K. Cooper

Metallation of the isopropenyl group by platinum(II): mechanism of formation of isomeric σ-allylic and σ-vinylic six-membered chelate rings. X-Ray structure of the σ-vinylic complex di-µ-acetato-bis-{[2-(o-diphenylarsinophenyl)propenyl–C′As]platinum(II)}

The (o-isopropenylphenyl)diphenylarsine (ipa) complex [Pt(ipa)(acac)][BF4](acac = acetylacetonate) reacts with nucleophiles including acetate to give [[graphic omitted]sPh2}(acac)](1) in which the ligand is bonded as a σ-allylic group. The complex [PtCl2(ipa)] reacts with silver acetate to give the complex [{[graphic omitted]sPh2}2(µ-O2CMe)2](2) shown from X-ray analysis to have the deprotonated olefin bonded as a σ-vinyl group. Crystals are monoclinic, space group C2/c, a= 31.633(5), b= 11.345(5), c= 18.450(5)A, β= 141.37(2)°, U= 4 133.6 A3, Z= 4, and R= 0.059 for 2 093 reflections. The σ-allylic complex (1) is converted to the σ-vinylic complex (2) by acetic acid. Mechanisms for the formation, protonation, and interconversion of the two isomeric forms of the metallated olefin have been deduced; carbonium ion complexes are strongly indicated as reactive intermediates. The σ-allylic and σ-vinylic forms appear to be the consequence of intermolecular and intramolecular attack respectively of a nucleophile on the co-ordinating olefin.

Isolation of the anions [M(CO)5(SH)]– and [M2(CO)10(µ-SH)]–(M = Cr, Mo, and W) as salts of the sodium (18-crown-6-ether) cation. X-Ray analysis of the sodium carbonyl linked ‘polymeric’ structures of the tungsten species

Ultraviolet irradiation has provided a convenient synthetic route to the anions [M(CO)5(SH)]– and [M2(CO)10(µ-SH)]–(M = Cr, Mo, and W) which have been isolated as their sodium (18-crown-6-ether) salts. X-Ray analysis of [Na(18-crown-6)][W(CO)5(SH)](1) and of [Na(18-crown-6)][W2(CO)10(µ-SH)](2) have shown them to be chain-polymeric in nature with sodium–carbonyl linkages between alternating cations and anions. The Na–O-(carbonyl) distances are in the range 2.41–2.47 A. In addition to the Na–O distances, compound (1) also shows a weaker Na–S interaction of 3.01 A. Crystals of (1) are orthorhombic, space group Pna21 with a= 16.484(3), b= 7.622(2), c= 19.220(3)A, and Z= 4. Crystals of (2) are triclinic, space group P, with a= 15.014(3), b= 11.874(2), c= 9.636(2)A, α= 102.28(2), β= 96.29(2), γ= 100.63(2)°, and Z= 2. Data were collected on a four-circle diffractometer using Mo-Kα radiation from a graphite monochromator. Blocked full-matrix refinement converged to R 0.044 for (1) and 0.031 for (2).

Electric dipole moments and anisotropic optical polarisabilities of methyl- and t-butyl-substituted (η6-benzene)tricarbonylchromium(0) complexes: Their relevance to the nature of the chromium-arene bond

Determinations of the electric dipole moments, carbonyl stretching frequencies and anisotropic optical polarisabilities are reported for [Cr(CO)3(η6-C6H6)] and for nine of its methyl- and t-butyl-substituted derivatives in cyclohexane solution. The effects of progressive substitution are approximately additive. For each complex, the molecular optical anisotropy from experiment is opposite in sign to that predicted from additivity of the anisotropies of the component arene and Cr(CO)3 fragments. Coordination between the fragments leads to a very large enhancement of polarisability along the Cr-arene axis while the polarisabilities perpendicular to that axis (parallel to the benzenoid ring) are lowered. The electron system constituting the Cr-arene bond is highly polarisable along the bond and provides a channel of relatively free electron movement between the arene and Cr(CO)3. The results are consistent with a postulated large magnetic anisotropy for the Cr-arene bond. The aromatic character of the complexed arene is diminished relative to that of the free ligand.

A study of the bonding between platinum(II) and the group VI donor ligand in the isostructural complexes chloropentafluorophenolato-o-vinyl-n, ndimethylanilineplatinum(II) and chloropentafluorothiophenolato-o-vinyl-N, Ndimethylanilineplatinum(II)

Abstract The molecular structures of Pt(VMN)Cl(OC 6 F 5 ), and Pt(VMN)Cl(SC 6 F 5 ), (VMN = o -Me 2 NC 6 H 4 CHCH 2 ) have been determined from single crystal X-ray diffraction data. Both complexes crystallize in the P 1 space group with lattice constants a 8.661(4), b 10.458(8), c 10.102(8) A, and a 8.724(3), b 10.385(5), c 10.414(8) A, respectively. Least squares refinements gave conventional R values of 0.033, and 0.045. The molecules are essentially isostructural and the coordination geometries have been used in conjunction with platinum—olefinic hydrogen coupling constants to reveal a small but significant degree of π-bonding between platinum(II) and the thiol sulphur.

The synthesis and characterisation of two novel cyclopentadienylberyllium compounds

Abstract The syntheses of pentamethylcyclopentadienylberyllium chloride (CpMe 5 BeCl) and the previously unreported pentamethylcyclopentadienylcyclopentadienylberyllium (CpMe 5 BeCp) are described. The NMR and IR spectra of the two compounds are reported and discussed in terms of the bonding of the latter compound. The reaction between pentamethylcyclopentadienylberyllium chloride and dicyclopentadienylberyllium (BeCp 2 ) is also described.

Reaction of [RhH(NH2C6H4PPh2-o)2Cl]Cl with air; characterisation of the products by X-ray structure analysis of cis-[Rh(NH2C6H4PPh2-o)(NHC6H4PPh2-o)Cl2] and trans-[Rh(NH2C6H4PPh2-o)2Cl2][p-MeC6H4SO3]·MeCN

The chlorohydridorhodium(III) complex of (o-diphenylphosphinophenyl)amine, [RhH(NH2C6H4PPh2-o)2Cl]Cl (1a), formed by oxidative addition of HCl to [Rh(NH2C6H4PPh2-o)2]BF4(2b), was found to react with air to give two products. These have been characterised by X-ray structure analysis as the cis-dichloro-complex [Rh(NH2C6H4PPh2-o)(NHC6H4PPh2-o)Cl2](6), containing an amino- and amido-donor group, and the trans-dichloro-complex [Rh(NH2C6H4PPh2-o)2Cl2][p-MeC6H4SO3](8). Crystals of (6) are monoclinic, space group P21/n, with a= 17.153(3), b= 18.667(3), c= 9.891(2)A, β= 91.77(3)°, and Z= 4. Blocked full-matrix refinement using 3 501 unique data [I 3σ(I), 3 ⩽θ⩽ 25°] gave R= 0.0487, R′= 0.0511. Complex (8) crystallises, with a molecule of acetonitrile as solvate, in the monoclinic space group I2/c with a= 18.394(4), b= 14.380(3), c= 16.378(3)A, β= 96.67(4)°, and Z= 4. Blocked full-matrix refinement of 2 741 reflections with I 3σ(I)(3 ⩽θ⩽ 25°) gave R= 0.0638 and R′= 0.0698. The cation of (8) has exact C2 symmetry. A mechanism for the reaction is proposed which involves peroxo- and hydrogenperoxo-species.

Transition metal-mediated discrimination between diastereoisomers of a new linear P2N2 ligand, L1; X-ray structure analysis of rac-L1, [Pt(rac-L1)Cl]Cl·2H2O, and an unusual RhI dimer [Rh2(rac-L1–H)2(CO)2]·2H2O

The new linear P2N2 ligand 1,3-bis{(o-aminophenyl)phenylphosphino}propane, L1, as syntheisised by reaction of (o-amonopheynyl)diphenylphosphine, L2, with lithium and 1,3-dichloropropane, forms racemic and meso isomer with distinctly different stereochemical requirements so that on reaction with PtCl2Y2(Y = dimethyl sulphoxide, DMSO, or benzonitrile) they bond in tridentate and tetradentate modes respectively to give the monocationic complex [Pt(rac-L1)Cl]+, (1), and the dicationic complex [Pt(meso-L1)]2+, (2); X-ray structure analysis of rac-L1, the chloride salt of (1), and the ligand bridged dimer [Rh2(rac-L1–H)2(CO)2], (3), has shown how the stereochemical requirements of this racemic ligand lead to unusual modes of co-ordination.

Synthesis of a new P2N2 ligand N,N′-bis[2-(diphenylphosphino)phenyl]propane-1,3-diamine, H2L2, and some of its complexes with elements of the nickel triad and rhodium: X-ray structure analyses of the neutral complex [NiL2] and the trans-spanned [Rh(CO)Cl(H2L2)]

The new multidentate phosphorus–nitrogen P2N2 hybrid ligand N,N′-bis[2-(diphenylphosphino)phenyl]propane-1,3-diamine, H2L2, has been prepared by demetallation of its neutral deprotonated nickel complex [NiL2],(1a), obtaibed from the metal-template catalysed condensation of bis(2-phenylphosphinophenylamido)nickel(II), [Ni(HL1)2], with 1,3-bis(toluene-p-sulphonyloxy)-propane in the presence of base. Under basic conditions, H2L2 forms complexes (1b) and (1c) analogous to (1a) with palladium(II) and platinum(II) in which the ligand is tetradentate around a square-planar metal ion. The complexes (1) may be protonated to form the corresponding dications [M(H2L2)]2+, (2a)–(2c). With rohodium(I), H2L2 forms both the monocation [Rh(H2L2)]+, (3), and the neutral square-planar complex [Rh(CO)Cl(H2L2)], (4), in which H2L2 behaves as a P2trans-spanning bidentate ligand. X-Ray crystal-structure analyses of both (1a) and (4) have been performed. Compound (1a) crystallises with a molecule of mesitylene as solvate in the tetragonal space group I/41/a with a= 35.246(6) and c= 13.190(2)A and Z= 16. Blocked full-matrix refinement of 2 837 unique reflections with I 3σ(I)(3.0 2.5σ(I)(1.0 < θ < 25.0°) gave R= 0.041 and R′= 0.047.

Preparation and characterization of chelating monoolefin-aniline ligands and their platinum(II) complexes

Abstract A number of new chelating monoolefin-aniline ligands have been prepared and treated with platinum(II). 1H NMR spectra of the ligands and their platinum(II) complexes have been recorded in order to investigate the bonding between the platinum and the olefin group. This has shown that all the olefins except o-vinyl-N,N-diphenylaniline bond to the platinum through both the olefin and the amine group to give complexes similar to those formed by the chelating monoolefin-phosphines and -arsines. Reaction of the complex Pt(IMN)Cl2 with a series of anionic ligands L gave complexes of the type Pt(IMN)ClL. Comparison of the 195Pt1H(olefin) coupling constants enabled a trans-influence series to be determined for this type of complex.

Anisotropic optical polarisabilities of the complexes LCr(CO)5 (L=PMe3, NMe3 or NH3): a study of π-back-bonding

Abstract Dipole moments and electric birefringences are reported for the complexes LCr(CO)5 where L is PMe3, NMe3 or NH3. Comparison of the molecular optical polarisability anisotropies of PMe3Cr(CO)5 and NMe3Cr(CO)5 shows a large enhancement of polarisability specifically in the L-Cr-(trans)CO direction for the phosphorus compound; the polarisabilities perpendicular to the symmetry axis are closely similar for the two complexes. The results are interpreted as direct evidence for a highly deformable π-component in PCr bonding. This work presents a new experimental approach to the study of π-back-bonding.