The preparation and ligating properties of S-oxygenated derivatives of a macrobinucleating hexaazadithiophenolate macrocycle H 2 L 1 of the Robson type towards nickel(II) and zinc(II) ions are reported. Nickel complexes of the hexaazadi-

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.

The preparation and characterization of mononuclear complexes of the dinucleating 24-membered hexazadithiophenolate macrocycles H2L2 and H2L3 and their open-chain N3S2 analogues H2L4 and H2L5 are reported. The highly crystalline compounds [Ni(L4)] (4), [Ni(L5)] (5), [Co(L5)] (6), [NiH2(L2)]2+ (7), [ZnH2(L2)]2+ (8), and [NiH2(L3)]2+ (9) could be readily prepared by stoichiometric complexation reactions of the hydrochlorides of the free ligands with the corresponding metal(II) dichlorides and NEt3 in methanolic solution. All complexes were characterized by X-ray crystallography. Monometallic complexes 4-6 of the pentadentate ligands H2L4 and H2L5 feature distorted square pyramidal MN3S2 structures (tau = 0.01 to 0.44). Similar coordination geometries are observed for the macrocyclic complexes 7-9 of the octadentate ligands H2L2 and H2L3. The two hydrogen atoms in 7-9 are attached to the noncoordinating benzylic amine functions and are hydrogen bonded to the metal-bound thiophenolate functions. A comparison of the structures of 4-9 reveals that the macrocycles L2 and L3 have a rather flexible ligand backbone that do not confer unusual coordination geometries on the metal ions. We also report on the ability of the monometallic complexes 7 and 8 to serve as starting materials for the preparation of dinuclear complexes.

The effect of de‐tert‐butylation on the coordinating properties of the 24‐membered hexaazadithiophenolate macrocycle 13,27‐bis(tert‐butyl)‐3,6,9,17,20,23‐hexaazatricyclo[23.3.1.11.15]triaconta‐1(28),11,13,15(30),25,26‐hexaene‐29,30‐dithiol (H2L1) has been examined. For this purpose, a series of mixed‐ligand NiII and ZnII complexes of the de‐tert‐butylated hexaaminedithiophenolate macrocycle H2L2were prepared and characterized, namely, [NiII2L2(Cl)]+(1b), [ZnII2L2(OAc)]+ (2b), [NiII2L2(O2CCH=CHPh)]+ (3b), [ZnII2L2(O2CCH=CHPh)]+ (4b), [NiII2L2(O2CC14H17)]+ (5b), [ZnII2L2(O2CC14H17)]+ (6b, in which C14H17CO2– =3,4‐dimethyl‐6‐phenylcyclohex‐3‐enecarboxylate), [NiII2L2(O2CC6H4‐3‐OMe)]+ (7b), and [ZnII2L2(O2CC6H4‐3‐OMe)]+ (8b). The synthesis and characterization data for complexes [NiII2L4(O2CC6H4‐3‐OMe)]+ (7d) and [ZnII2L4(O2CC6H4‐3‐OMe)]+ (8d), in which H2L4 represents the S‐oxygenated (bis‐sulfonate) derivative of H2L2 are also reported. The de‐tert‐butylated macrocycles H2L2 (and H2L4) behave essentially in the same fashion as H2L1 (and H2L3) producing dinuclear mixed‐ligand [M2L(μ‐L′)]+ complexes with analogous bioctahedral core structures in similar good yields and reaction times. The spectroscopic features of the [M2L2(μ‐L′)]+ and [M2L4(μ‐L′)]+ complexes resemble those of theanalogous complexes supported by the tert‐butylated derivatives H2L1 and H2L3. One major difference between the [M2L1,3(μ‐L′)]+ and [M2L2,4(μ‐L′)]+ complexes concerns the depth of the binding pocket of the compounds, which is significantly reduced upon removing the tert‐butyl substituents. Another significant difference associated with removal of the tert‐butyl substituent concerns the less pronounced differences of the relative stability constants for the carboxylato‐bridged [M2L2(μ‐O2CR)]+ complexes {as compared to the [M2L1(μ‐O2CR)]+ complexes}. These stability differences can be qualitatively explained in terms of less pronounced intramolecular CH···π and/or van der Waals interactions in the de‐tert‐butylated complex systems.

The regioselectivity of the Diels–Alder reaction between ω‐substituted dienoates and unsymmetrical dienophiles can be strictly controlled by “calixarene‐like” metal complexes of type A (see scheme). The reaction of the dienoate coligand in A with acrylonitrile leads to the exclusive formation of the regioisomer adduct I, which is in striking contrast to the low regioselectivity of the background reaction.