ALBERT

Notes: The bidentate diphosphine ligand, 3,3′-oxybis[(dipenylphosphino)methylbenzene] (1) forms monomeric, trans-square-planar complexes MX2(1) (M = Ni, Pd, Pt; X = Cl-, Br- I-, and, in part, N3-, NCS-, CN-, NO3-) as well as Pt(H)Cl(1), Pt(H)Br(1), and RhCl(CO)(1). Polymeric species have been observed with substitutionally inert metal centres: trans-[PtCl2(1)]2 and cis-[PtCl2(1)]n (mean value of n ≈ 4-5) 31P-NMR, and selected IR and UV/VIS parameters are reported. Ligand 1 shows a marked preference for trans-spanning and monomeric chelate formation, despite its various degrees of freedom of internal rotation in the lignad backbone. The readily available ligand 1 as well as analogues with other donor atoms, therefore, appear useful in most potential applications of trans-spanning chelate ligands. The crystal structure of AgCl(1)·0.5 (CH3)2C=O·0.39 C6H12 (space group C2/c,a = 21.02 Å, b = 14.57 Å, c = 24.79 Å, β = 99.77°, V = 7531.4 Å3, Z = 8) confirms the presence of three-coordinate Ag(I), with a coordination intermediate between a trigonal-planar and a T-shaped geometry (P-Ag-P = 145.61(8)°).

Notes: Base hydrolysis of optically pure mer-exo(H)- and mer-endo(H)-[CoCl(dien)(dapo)]2+ (A and B (X = Cl)), resp.; dien = N-(2-aminoethyl)ethane-1,2-damine; dapo = 1,3-diaminopopan-2-ol, kOH = (1.13 ±0.09)·105 M-1s-1 (A (X = Cl), kOH = (1.18 ± 0.11)·105M-1s-1 (B (X = Cl)); I = 1.0M (NaClO4 or NaN3)1, T = 298 K) is accompanied by retention of the mer-geometry and full racemization (99 ± 1%). It is shown this is not due to racemization of either reactants or products. This result, together with the fact that both A and B yield the same mer-exo(H)-product distribution, indicates the intermediacy of a pentacoordinate species II which is symmetrical (at least in the time average), viz. trigonal bipyramidal with a deprotonated (‘flat’) secondaryamine moiety. The H-exchange rates of the coordinated amine groups are consistent with this interpretation and indicate that loss of Cl- is the rate-determining step, in agreement with an SN1CB mechanism. The reactivity of the unsym-fac-exo(OH)- and unsy,-fac-endo(OH)-isomers C and D, respectively, is in sharp contrast: base hydrolysis is 3 orders of magnitue slower, and the reaction is accompanied by some change of coordination geometry (C, 23%; D, 10%, some inversion of configuration (C, 15%; D, 19%)); much lower acceleration of hydrolysis in base (106 vs. 1010). Azide competition during base hydrolysis of the mer-isomer A and B is quite large (R = [CoN3]∞/[CoOH]∞[N-3] = 1.4 ±0.2M-1, I= 1.0M, T = 298 K) and indicates that the coordinatively unsaturated intermediate II is highly selective. The ratios of exo(H)- and endo(H)-azide competition products A and B (X = N3), respectively, immediately after the substitution reaction (kinetic control) are independent of the engaged epierm A or B: 31.7 ± 0.9% of B (X = N3) and 68.3 ± 0.9% of A (X = N3, determined after ca. 10.t½ of the base hydrolysis). This is agreement with the effective site of deprotonation at the secondayr(central)-amine group of dien, cis to the leaving group X, and with a common set of intermediates. Epimerization of A and B (X = Cl, N3) is shown to proceed solely via the pentacoordinate (base hydrolysis) intermediate II, viz. the direct route involving a six-coordinate deprotonated intermediate is immeasurably slow. For the hydroxo products A and B (X = OH), the direct rotue may compete with the H2O-substitution(exchange) path which can occur by an internal conjugate-base process. The kinetically controlled distribution of complexes A/B (X = N3) is different from the quasi-thermodynamic one (19.1 ± 0.8% of B (X = N3) and 80.9 ± 0.8% of A (X = N3)). This is consistent with the differences in the base-hydrolysis rates of the reactants (kOh (A (X = N3))= (1.59 ± 0.04)·102M-1s-1; kOH (B (X = N3)) = (2.89 ± 0.22).102M-1s-1). Various aspects of the investigated reactions are discussed on the basis of the widely studied reaction of base hydrolysis of pentaaminecobalt(III) complexes. Also, the structure and reactivity of the pentacoordinate intermediate II are discussed in relation to various current models.

Notes: Comparative semi-empirical PM3 and ab initio STO 3-21G calculations on bornanesultam-derived dienophiles containing the structural moiety SO2—N—C(O)—X(α) = Y(β) suggest that, among the conformers of low energy, the thermodynamically less stable SO2/C(O)-syn,C(O)/X=Y-s-cis conformation is also reactive in terms of LUMO level and atomic coefficients. Furthermore, the X(α), Y(β) LUMO atomic coefficients are nonequivalent with respect to both X(α)-re and X(α)-si faces, and thus have, depending on the conformation, a matching or mismatching stereoelectronic influence with the co-operative steric effect. This dissymmetry is believed to result from the generalized anemone effect of the N lone pair, itself anomerically stabilized and directed, in the absence of crucial steric interactions, by the pseudo-axial anti-periplanar S=O bond. Five N-acyl-substituted bornanesultams arc discussed ((-)-1a: N-acryloyl, X=CH, Y=CH2; (-)-1b; N-crotonoyl, X=CH, Y=CHMe; (-)-1c: N-N′-fumaroyl, X=CH, Y=CH(C(O)-bornanesultam); 2a: N-glyoxyloyl, X=CH, Y=O; 2b: N-acylnitroso, X=N, Y=O). In this context, differences with toluenesultams 3 are pointed out. A previous report on N-(acylnitroso)-bornanesultam 2b is revisited, and the diastereoselectivity observed is shown to result from thermodynamic control.

Notes: The electrochemistry of potassium heptacyanorhenate(III) in aqueous solution was studied by cyclic and by rotating disk voltammetry at planar microelectrodes. The results are consistent with a single, reversible electron transfer: Re(CN)3-7 + e⇄Re(CN)4-7 with E′0 = 643 mV vs. NHE. A single protonation equilibrium is observed: Re(CN)4-7 + H+⇄ Re(CN)7H3- with pK = 1.31 determined from combined voltammetric and pH data. The Re-CN bond appears to be kinetically inert, and none of the cyano complexes in other oxidation states of Re claimed in the literature was found in the potential range - 2 V to + 1 V.

Notes: Oxygentation of aqueous solutions of CoIII in presence of stoichiometric amounts of N-(2-aminoethyl)ethane-1,2-diamine (dien) and 1,3-diaminopropan-2-ol (dapo) produces μ-peroxocobalt(III) dimers. Acid cleavage (HCI) yields mer-exo(H)-, mer-endo (H)-, unsym-fac-exo(OH)-, and unsym-fac-endo(OH)-[CoCl(dien)(dapo)]2+ (A-D)(X = Cl), resp. and unsym-fac-[Co-(dien)(dapo-N,N′,O)]3+ (G). Isomer seperation was achieved by fractional crystallization as ZnCl42- and ClO4- salts and by ion-exchange chromatography. The corresponding bromo, azido, nitrito-O, nitro-N, thiocyanato, hydroxo, and aqua complexes were also synthesized. Optically resolved samples were prepared for chiral compounds, and the complexes were structurally characterized by X-ray analyses (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-A (X = N3)), (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document}(-)436(CD)-B). (X = N3), \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document} (+)436(CD)-B by their chiroptical properties, and by 13C-NMR spectroscopy supported by 1H-NMR, IR, CD, and UV/VIS spectroscopy. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-mer-exo(H)-[Co(N3)(dien)(dapo)](hydrogen di-O-benzoyl-L-tartrate)2.4 H2O crystallizes in the orthorhombic space group P212121, a = 7.676(1) Å, b = 19.457(1) Å, c = 34.702(2) Å. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Lambda} \limits^ \to $\end{document}(-)436(CD)-mer-endo(H)-[Co(N3)(dien)(dapo)] (hydrogen di-O-benzoyl-L-tartrate)2.2.75 H2O crystallizes in the triclinic space group P1, a = 8.062(3) Å b = 10.296(1) Å, c = 15.056(2) Å, alpha = 80.55(1)°, β = 85.18(2)°, γ = 89.10(2)°. \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\it \Delta} \limits^ \to $\end{document}(+)436(CD)-mer-endo(H)-[Co(N3)(dien)(dapo)](hydrogen di-O-benzoyl-L-tartrate)2. 5.75 H2O crystallizes in the triclinic space group P1, a = 7.742(1) Å, b = 10.014(1) Å, c = 18.045(2) Å, α = 99.57(1)°, β = 92.87(1)°, γ = 102.56(1)°. The absolute configurations of the three cations were determined unambiguously. Interconversions of the various isomers and derivatives and structural, configurational, and spectroscopic aspects are discussed in detail.

Notes: Azide anation and racemization of optically pure mer-exo(H)- and mer-endo(H)-[Co(OH)(dien)(dapo)]2+ (A and B (X = OH), resp.; dien = N-(2-aminoethyl)ethane-1,2-diamine; dapo = 1,3-diaminopropan-2-ol) involve the same symmetrical pentacoordinate intermediate as the base hydrolyses of the corresponding mer-exo(H)- and mer-endo(H)-[CoX(dien)(dapo)]2+ species A and B, respectively, where X = Cl, Br, or N3. The kinetic parameters of the anation process are fully compatible with the independently measured competition ratio. The rate data reveal that substitution of OH- is unexpectedly fast, viz. it is not consistent with the usual sequence Br- 〉 Cl- 〉 H2O 〉 N3- 〉 OH-. This behavior is interpreted on the basis of an internal conjugate base mechanism which involves an amino-hydroxo/aminato-aqua tautomerism, viz. the reaction is actually an OH- -catalyzed substitution of [CoH2O(dien)(dapo)]3+ where deprotonation occurs effectively at the secondary-amine site NH of dien.

Notes: Some pentaamine complexes of Co(III) with 2,6-bis(aminomethyl)pyridine (bamp), a diamine ligand (or two ammonia ligands) and one unidentate ligand have been prepared (Table 1). In all these species, bamp remains coordinated meridionally under a variety of conditions as shown by 1H- and 13C-NMR. spectroscopy and correlations by stereoretentive reaction cycles. The rates of amine proton exchange and of spontaneous aquation, Hg2+-induced aquation and base hydrolysis of some chloropentaamine complexes have been determined. They essentially follow the patterns observed for complexes with purely aliphatic amine ligands; the presence of a pyridine donor in these complexes does not suggest deviations from the mechanistic schemes usually proposed for the solvolytic reactions investigated.

Notes: Acid hydrolysis of the ester function in Δ-(-)589-β2-(RR)-[Co (trien) (glyOEt) Cl]2+ ((-)-1) produces optically pure Δ-(-)589-(RR)-[Co (trien) (glyOH)Cl]2+ ((-)-4). Hg2+ induced removal of chloride in (-)-4 follows the rate law kobs = kHg [Hg2+] with kHg = (1.36 ± 0.03) × 10-2 M-1s-1, 25°, μ=1.0, and produces optically pure Δ-(-)589-β2-(RR)-[Co(trien) (glyO)]2+ ((-)-2). Competition by NO3- occurs in this reaction ([NO3-], 1M, 3%) indicating a path whereby external nucleophiles (Y=NO3-, H2O) compete with the intramolecular carboxylate function for an intermediate of reduced coordination number. Rapid ring closure to 2 must ensue for Y = H2O. Base hydrolysis of chloride in (±)-1 produces (±)-2 together with its diastereoisomer β2-(RS, SR)-[Co(trien) (glyO)]2+, ((±)-3), in which one secondary amine function has an inverted configuration. 2 and 3 incorporate 18O-labelled solvent into the Co-O position of the coordinated carboxylate moiety (2: 9.0%; 3: 12.3%) indicating that at least part of the product arises via intramolecular hydrolysis in β2-hydroxo ethylglycinate intermediates (Fig. 4). Base hydrolysis of (-)-4 follows the rate law Kobs = kOH[OH-] with kOH = (6.3 ± 0.6) × 10-4M-1 S-1, 25°, μ = 1.0 producing (-)-2 (37-45%) and (-)-3 (63-55%), the ratio being somewhat medium dependent. Competition by added N3- (1M) occurs using (±) -4 forming β2-(RR, SS)-[Co (trien) (glyO)N3]+ (∼2%) and β2-(RS, SR)-[Co (trien) (glyO)N3]+ (∼ 13%). Mutarotation at the secondary nitrogen centre is shown to occur after the rate determining loss of Cl- in 1 and 4 and before the formation of 2 and 3. It is concluded that this secondary nitrogen is the site of deprotonation in the reactive conjugate bases of 1 and 4, and possible mechanisms for the mutarotation process are considered.

Notes: The title cation ( = Ni2L+3) is formed in a variety of reactions (Schemes 1 and 2) in systems containing Ni2+ and (2-thiolatoethyl)-diphenylphosphine (= L-) in the absence of coordinating anions at Ni2+/L- ratios 〉 0.5 in apolar or moderately polar media. Solid [Ni2L3]CIO4 and [Ni2L3]BPh4 have been isolated. Job's plots confirm the Ni2L+3- stoichiometry in solution. 31P-NMR data are consistent with ≥ 97% Ni2L+3 (vs. ≤ 3% of hypothetical Ni3L2+4) at equilibrium and support the suggested configuration (Fig. 2). The equilibrium between NiL2 + NiL2Br2 and Ni2L+3 + Br- varies with the solvent composition in CH23Cl2/EtOH mixtures. The rate of formation of Ni2L2Br2 from Ni2L+3 and bromide (in high excess) in CH2Cl2 is first-order in [Ni2L+3]tot but depends on the ratio [Bu4NBr]tot/[Ni2L3 · ClO4]tot, even at a high excess of bromide. This is interpreted by efficient competition in ion-aggregate formation between the small perchlorate concentration introduced as the counterion of Ni2L+3, and the large excess of bromide.

Notes: The base hydrolysis of the optically active title compound proceeds with full racemization whilst the meridional arrangement of the diethylenetriamine ligand is fully retained. The optically active hydroxo complex prepared independently with retention of configuration racemizes ≳ 104 times slower. This unique result is discussed in terms of the classical π-stabilization hypothesis for the base hydrolysis mechanism.