Equilibria in complexes of N-heterocyclic molecules,part XII. The reaction of hydroxide and alkoxide Ions with platinum(II) complexes of 5-nitro-1,10-phenanthroline and 2,2′-bipyridyl

Summary Bis-(5-nitro-1,10-phenanthroline)platinum(II) dichloride and diperchlorate have been prepared. The reaction between the parent cation and hydroxide ion has been studied using 1 FI n.m.r. spectroscopy and found to involve attack at the ligand. The bis-(2,2-bipyridyl)platinum(II) ion has been shown to be highly reactive towards methoxide ion. The dissociation of a 2,2-bipyridyl ligand is preceded by attack at the ligand.Part XI: R. D. Gillard, t.. A. P. Kane-Maguire and P. A. Williams,Transition Met. Chem., 2, 47 (1977).On leave from the University of Baghdad, Iraq.     

Molecular orbital calculations of iron(II) complexes of diimine ligands

Summary Molecular orbital calculations using-, the INDO method have been carried out fm the [FeL(CN)₄]² and [FeLH(CN)₄] complexes, as well as for the tree ligands, with L 2 × pyridine, 1,10-phenanthroline.2,2-bipyridyl. 2,2-rimidine, 2, 3,3-bipyridazine and 4.4-bipyrimidine. Calculations of residual charge at carbon atoms in the ligand rings. correlating with relative nucleophilicity of the compounds, corresponds with observed differences of rate of reaction of the complex [FeI;]² With nucleophiles.     

Kinetics of nucleophilic attack on coordinated organic moieties. XVIII. Nucleophilicity of anions towards the tricarbonyl-(η-benzene) manganese (I) cation.

Kinetic results for the addition of OH^? to [Mn(CO)₃(η-C₆H₆)]⁺ (I) in water (eq. 1, X  OH) obey the expression k_obs  k_OH[OH^?], and give a k_OH value of 290 mol^?1 dm³ s^?1 at 20.0°C and ionic strength of 0.25 mol dm^?3. The analogous reaction of NaCN with I in water fits the two-term expression k_obs = k_OH[OH^?] + k_CN[CN^?], and leads to a k_CN value of 0.8 mol^?1 dm³ s^?1 at 20.0°C and ionic strength of 0.25 mol dm^?3. Interestingly, the related reaction (eq. 1, X  N₃) is too rapid to follow by stopped-flow spectrophotometry, indicating the overall rate trend N₃^? » OH^? » CN^?. This unusual nucleophilicity order, unexpected on the basis of both basicity and polarizability, is similar to that previously observed for anion addition to free carbonium ions.     

Chiral separations of transition metal complexes using capillary zone electrophoresis.

Several buffer additives that may facilitate chiral separation for optically active transition metal (TM) systems are investigated using capillary zone electrophoresis. The TM complexes evaluated exhibit considerable heterogeneity with respect to total complex charge (0 to 4+), ligand type, and identity of the central metal including Ru2+, Ni2+, Cr3+, and Co3+, threo-D[+]-Isocitrate, potassium antimonyl-d-tartrate and dibenzoyl-L-tartrate are identified as the most efficient chiral selectors. Interestingly, TM complexes exhibiting a (3+) total complex charge exhibit a reversal of enantiomer elution order versus all other complexes when separated using the tartrate additives. Operating parameters including pH, temperature, and capillary length are discussed, and chiral separations of complex mixtures are demonstrated.     

Equilibria in complexes ofN-heterocyclic molecules,part IX. Circular dichroism study of nucleophilic attack at tris-(5-nitro1,10-phenanthroline)ruthenium(II)

Summary The reactions between Ho^–, CN^–, MeO^– and EtO^– and -(-)-tris-(5-vitro-1,10-phenantliroline)ruthenium(II) ion in solution were followed by c.d. measurements. The results support the earlier findings that these reactions proceed through the formation of pseudo-bases with the ligand.Part VIII: R. D. Gillard, L. A. P. Kane-Maguire and P. A. Williams,J. Chem. Soc. Dalton Trans. in press.     

Field desorption mass spectra of [M(CO)3(η-arene)]X (MMn,Re; XBF4, PF6) salts

Field desorption mass spectra are reported for a range of [M(CO)₃(η-arene)]X (MMn or Re, XBF₄ or PF₆) salts. In most cases the spectra are simple, being dominated by molecular, [M]^+·, [M + 1]⁺, and [MCO]⁺ ions for the cationic part of their structure. However, with the π-chloroarene complexes [Mn(CO)₃(η-ClC₆H₅)]PF₆ and [Mn(CO)₃(η-1-Cl, 4-MeC₆H₄)]PF₆, facile loss of the chloro substituent and further fragmentation leads to unusually complex spectra, which include strong peaks arising from recombination of fragment species. Cluster ions are also noted in several cases, allowing identification of the anion.     

Electronic energy self-exchange with macrocyclic chromium(III) complexes

The luminescence lifetimes of N-deuterated Cr(III) complexes of macrocyclic tetraamine ligands, trans-CrN(4)X(2)(n)()(+), are substantially longer than those of their undeuterated counterparts in room temperature solution. Thus, excited-state emission quenching of the longer lived species by the shorter lived species may be studied by analyzing the decay profile following pulsed excitation. Flash photolysis experiments were carried out for three deuterated/undeuterated pairs of trans-CrN(4)X(2)(n)()(+) complexes (where X = CN-, NH(3), and F-). For the trans-Cr(cyclam)(CN)(2)(+) system in H(2)O, it was determined that energy transfer was occurring between the deuterated and undeuterated species. Although the rate constant of energy transfer was too fast to measure explicitly, it could be bracketed as k(et) >7 x 10(6) M(-1) s(-1). For this reaction it was possible to measure an equilibrium constant which was very near 1.0. For trans-Cr(cyclam)(NH(3))(2)(3+) in DMSO, it was also established that energy transfer was occurring and rate constants of 2.4 x 10(6) M(-1) s(-1) (mu = 0.1) and 9.7 x 10(6) M(-1) s(-1) (mu = 1.0) were determined by a Stern-Volmer analysis. For trans-Cr(tet a)F(2+) in H(2)O, no energy transfer was observed, which implies that the rate constant is <3 x 10(5) M(-1) s(-1). Because these energy-transfer reactions represent self-exchange energy transfer and are thus thermoneutral, we are able to analyze the results using Marcus theory and draw some conclusions about the relative importance of nuclear reorganization and electronic factors in the overall rate.     

Photobehavior of (alpha-diimine)dimesitylplatinum(II) complexes

The photobehavior of complexes of the type Pt(diimine)(mes)2 is investigated (where diimine = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), and 4,7-diphenyl-1,10-phenanthroline (dpp) and mes = the mesityl (2,4,6-trimethylphenyl) anion). For all compounds studied, solution RT emission is observed to be weak and excited-state lifetimes are found to be short (< or = 20 ns) regardless of solvent choice. Evidence is presented for energy-transfer quenching of Pt(dpp)(mes)2 luminescence in toluene by dissolved O2 (primarily producing singlet oxygen) with an observed quenching rate constant of kq > or = 1.3 x 10(9) M-1 s-1. Electron-transfer quenching is also observed in the presence of 3,5-dinitrobenzonitrile, yielding a quenching rate constant of kq > or = 1.6 x 10(9) M-1 s-1. The latter observation suggests that phase Pt(II) systems may have future value as excited-state reductants. All of the complexes display a much more intense and longer-lived luminescence in the solid state at room temperature. Several possible explanations for this dependence on phase are proposed, with the most probable mechanism involving radiationless deactivation in solution via rotation of the o-methyl groups of the mesityl ligands.     

Kinetics of nucleophilic attack on coordinated organic moieties : VI. Mechanism of addition of tri-n-butylphosphine to [(C7H7)M(CO)3]BF4 (M = Cr, Mo, W) and related cations

Phosphonium adduct formation via attack of tri-n-butylphosphine on the cations [(C₇H₇)M(CO)₃]⁺ (M = Cr, Mo, W) obeys the rate law, Rate = k [complex] [PBu₃]. The very similar rate constants for the Cr, Mo and W complexes confirm the similar electrophilicities of the tropylium rings in these cations, and also support the view that there is direct addition to the rings. The related complexes [(C₆H₇)Fe(CO)₃]BF₄ and [(C₆H₆)Mn(CO)₃]BF₄ also form adducts with PBu₃, and the quantitative reactivity order [(C₆H₇)Fe(CO)₃]⁺ > [(C₇H₇)Cr(CO)₃]⁺ » [(C₆H₆)Mn(CO)₃]⁺ (160:60:1) has been established.