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Under anaerobic conditions, the reactions of cobalt(II) and nickel(II) acetate tetrahydrate with 2,6-pyridinedimethanol (H2L2, 3) in anhydrous acetonitrile afforded two tetranuclear metal(II) complexes [MII4(HL2)4(OAc)4] (4; MII = Co2+, Ni2+) with a [M4(μ3-O)4]4+ cubane core. X-ray structural analyses revealed that both MII cubanes 4a·2CH3OH and 4b·2CH3OH are isostructural and crystallize in the tetragonal space group I41/acd with eight molecules in the unit cell. In the solid state, the orientation of the cubane cores of 4 and the formation of a 3D framework were controlled by π–π interactions as well as intra- and intermolecular O–H···O hydrogen bonds. Variable-temperature magnetic susceptibility measurements revealed that the cubanes 4 show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for both complexes. Core-level X-ray photoelectron spectroscopy confirmed that the Co and Ni ions in 4a and 4b are in a divalent state. X-ray magnetic circular dichroism was performed to extract the spin and orbital contributions to the Co and Ni magnetic moments. We compared the experimental results of the local electronic structures around the Co2+ ions in 4a and the Ni2+ ions in 4b with charge-transfer multiplet simulations.

The coordination chemistry of copper complexes with theligand L1 [L1 = {7E}-N1-benzylidene-N2-{(E)-2-(benzylideneamino)ethyl}ethane-1,2-diamine] has been investigated. For copper(I) complexes of L1, the counterion determines the molecular structure in the solid state. The reaction of [Cu(CH3CN)4]PF6 with L1 yielded the mononuclear complex [Cu(L1)(CH3CN)]PF6 (1), whereas dinuclear helical [Cu2(L1)2](ClO4)2 (2) resulted from a similar reaction with [Cu(CH3CN)4]ClO4. Both compounds have been structurally characterized, and their solution behaviour investigated. Structurally characterized [Cu(L1)(PPh3)]ClO4 (3) has been synthesized by reacting 2 with PPh3. Exposure of a solution of 1 towards dioxygen in CH3OH and CH2Cl2 yielded the dinuclear complexes [Cu2(L1)2(OCH3)2](PF6)2 (4) and [Cu2(L1)2(OH)2](PF6)2 (5), respectively. Both compounds have been fully characterized. During the oxidation reaction, no hydroxylation of L1 occurred. The oxidation reaction of 1 has been studied by a chemical approach and by UV/Vis spectroscopy, indicating the formation of a peroxido-bridged species during the reaction. Furthermore, by reduction of the imine groups in L1 the ligand L2 [L2 = N1-benzyl-N2-{2-(benzylamino)ethyl}ethane-1,2-diamine] was obtained and the dinuclear copper(II) complex [Cu2(L2)2Cl3]PF6·2MeOH (6) has been structurally characterized.

Reaction of bis(1,3-diketone) H 2 L 1 in the presence of cesium acetate with magnesium acetate yielded crystalline one-dimensional coordination polymer rac-(2) n . The {2}-metallacryptand core [Mg 2 (L 1 ) 3 ] 2- is composed of two magnesium centres linked through three bis(1,3-diketo) dianions (L 1 ) 2 -. These {2}-metallacryptands are homochiral with either (A,A)-iac or (Λ,Λ)-fac stereochemistry at the magnesium centres, and they are capable to host a cesium ion in the cavity. Charge compensation of the thus formed {2}-metallacryptates (Cs⊂(Mg 2 (L 1 ) 3 ]) - is achieved through extra external cesium ions to give the neutral self-complementary building blocks [{Cs⊂[(Δ,Δ)/(Λ, Λ ) -Mg 2 (L 1 ) 3 ]}Cs], which aggregate end-on across the external cesium ions to give the homochiral one-dimensional strings [{Cs⊂[(Δ,Δ )-Mg 2 (L 1 ) 3 ]}Cs] n [Δ-(2) n ] and [{Cs⊂[(Λ,Λ)-Mg 2 (L 1 ) 3 ]}Cs) n [A-(2) n ], which are packed in the crystal in alternating homochiral layers. However, reaction of bulkier phenyl-substituted bis(1,3-diketone) H 2 L 2 instead of methyl-substituted H 2 L 1 with cesium or rubidium acetate and magnesium, cobalt or zinc acetate yielded the meandering polymer meso-{[({M 1 ⊂[(Δ,Δ)-M 2 2 -(L 2 ) 3 ]}M 1 end) ({M 1 ⊂[Λ,Λ]-M 2 2 (L 2 ) 3 ]}M 1 side )][({M 1 ⊂[(Λ,Λ)-M 2 2 (L 2 ) 3 ]}M 1 end )({M 1 end )([(Δ,Δ)-M 2 2 (L 2 ) 3 ]}M 1 side )]} n [meso-(3) n ] (M 1 = Cs + , Rb+; M 2 = Mg 2+ , Co 2+ , Zn 2+ ). In this case, the (2)-metallacryptates (M 1 ⊂ [(Δ,Δ/Λ,Λ)-M 2 2 (L 2 ) 3 ]}- are linked by only one cesium ion end-on to give the fragments meso-[({M 1 ⊂[(A,A)-M22(L2)3]}M 1 end )((MlC[(A,A)-M 2 2 (L 2 )3]}M 1 side )], which are connected by the second cesium ions side-on. The one-dimensional meander strands of isostructural mesa-(3) n are packed in the crystal in parallel. Reaction of 4 equiv. of zinc acetate and 1 equiv. of cesium or rubidium acetate with 2 equiv. of H 2 L 2 afforded the {M 1 ⊂[Zn 2 (L 2 ) 2 OAc)) cryptates 4a,b (M 1 = Cs + , Rb + ).

N,N,N',N'-Tetrakis(2-pyridylmethyl)benzene-1,3-diamine (1,3-tpbd), a bis(tridentate) ligand, its protonated derivative, [1,3-tpbdH 2 ] 2+ , and a series of new dinuclear complexes (Fe 2 (1,3-tpbd)(CH 3 CN) 6 ](ClO 4 ) 4 ·(CH 3 CN) 2 ·(H 2 O) 0.5 (1), [Fe 2 (1,3-tpbd)(DMF) 6 )(ClO 4 ) 4 (2), [Ni2(1,3-tpbd)(DMF) 6 ](ClO 4 )4 (3), [Zn 2 (1,3-tpbd)(CH3CN)2(SO 3 CF 3 ) 2 (H 2 O)](SO 3 CF 3 )2 (4), [Zn 2 (1,3-tpbd)-Cl 4 ]·H 2 O (5), [CuZn(1,3-tpbd)Cl 4 ] (7) and the tetranuclear copper(II) complex [Cu2(1,3-tpbd)2(H20)2](ClO 4 ) 4 ·2H 2 O (8) have been prepared and structurally characterized. Complex 8, a so called "dimetallocyclophane", interestingly only formed in the presence of zinc ions and not when copper(II) ions were mixed stoichiometrically (1:1 mixtures) under aerobic conditions. Theoretical calculations provide evidence for the formation of a side-on dinuclear peroxido copper complex during the oxidation of the (1,3-tpbd)copper(I) complex. A possible reaction product, the dinuclear copper complex [Cu 2 (2,6-tpcd)(H 2 O)-(Cl)](ClO 4 ) 2 .2H 2 O (9) of a phenolate derivative of 1,3-tpbd was synthesized and structurally characterized independently from oxidation reactions from copper(II) perchlorate and the ligand 2,6-bis[bis(2-pyridylmethyl)amino]-p-cresol.

Reactions of enantiopure (S)-[(η 5 -C 5 H 5 )Re(NO)(PPh 3 )-(=CH 2 )] + PF 6 - [(S)-21 and PH 2 CH 2 (CH 2 ) n CH 2 PH 2 (0.5 equiv.) give (S R e S R e )-[(η 5 -C 5 H 5 )Re(NO)(PPh 3 )(CH 2 PH 2 CH 2 (CH 2 ) n -CH 2 PH 2 CH 2 }(Ph 3 P)(ON)Re(η 5 -C 5 H 5 )] 2 + 2PF 6 - [n = 0/1, (S R e S R e )-3/4; 65-62/77-58%]. Reaction of racemic 2 (BF 4 - salt) and PH 2 (CH 2 ) 2 PH 2 (0.5 equiv.) gives the meso and rac diastereomers of 3 (BF 4 - salts) in 28% and 38% yields after crystallization. Treatments of (S R e S R e )-3/4 with tBuOK and then (S)-2 give the tetrarhenium complexes (S R e S R e S R e S R e )[{(η 5 -C 5 H 5 )Re(NO)(PPh 3 )(CH 2 )} 2 {PHCH 2 (CH 2 ) n -CH 2 PH}{(CH 2 )(Ph 3 P)(ON)Re(η 5 -C 5 H 5 )} 2 ] 2 + 2PF 6 - [n = 0/1, (S R e S R e S R e S R e )-7/8; 89-88/98-87%]. The crystal structure of (S R e S R e S R e S R e )-7 is determined and its conformation analyzed. Reactions of (S R e S R e S R e S R e )-7/8 and tBuOK give air-sensitive diphosphanes (S R e S R e S R e S R e )-{(η 5 -C 5 H 5 )Re(NO)-(PPh 3 )(CH 2 )} 2 (PCH 2 (CH 2 ) n CH 2 P}{(CH 2 )(Ph 3 P)(ON)Re(η 5 -C 5 H 5 )} 2 [n = 0/1, (S R e S R e S R e S R e )-9/10; 92/62%]. Additions of (a) PhIO give the corresponding dioxides (72/62%), and (b) [Rh(NBD) 2 ] + PF 6 - give the corresponding chelates [(P-P)-Rh(NBD)] + PF 6 - (75/82%) (NBD = norbornadiene). These catalyze hydrogenations of protected dehydroamino acids and hydrosilylations of propiophenone with only modest enantioselectivities. Similar results are obtained when (S R e S R e S R e S R e )-9/10 are applied in rhodium-catalyzed conjugate additions of aryl boronic acids, or palladium-catalyzed allylic alkylations.

Cleavage of the all-iron(III)μ 2 -O 2 - -linked dimer [Fe I I I 3 O(L) 2 -(OAc) 4 ] 2 O (3) with lithium chloride yields [Fe I I I 3 O(L) 2 -(OAc) 4 ]Cl (4) and with sodium benzoate, in combination with complete acetate-to-benzoate coligand exchange, gives [Fe I I I 3 O(L) 2 -(OBz) 4 ]OBz (5). Reduction of the all-Fe I I I complex 5 [Fe/L/OBz = 3:2:(4+1)] with sodium iodide affords the homonuclear mixed-valent cluster [Fe I I Fe I I I 2 O(L) 3 (OBz) 3 ] (6) (Fe/L/OBz = 1:1:1) and requires fundamental coligand-to-ligand exchange. Likewise, when the all-Fe I I I dimer [Fe I I I 3 O-(L) 2 (OAC) 4 ] 2 O (3) (Fe/L/OAc = 3:2:4) is cleaved with nickel acetate, the mixed-valent heteronuclear complex [Ni I I Fe I I I 2 -O(L) 3 (OAC) 3 ] (7) (M/L/OAc = 1:1:1) is formed.

Upon reaction of N-substituted diethanolamines H2L2–4 (4, 6, 7) with cesium carbonate and bis(tetraethylammonium) tetrachloromanganate(II) in acetonitrile in the presence of air, the metal-centered mixed-valent manganese wheels [NEt4]{MnII⊂[MnII3MnIII3Cl6(L2–4)6]} (8–10) were generated. X-ray crystallographic structure analyses revealed, that 8–10 are principally isostructural and consist of an alternating ring of three MnII and three MnIII ions, centered by an additional MnII ion. The cyclic voltammograms of 8 and 10 displayed three quasi-reversible oxidation processes, which are attributed to the subsequent one electron-oxidations of the three peripheral MnII ions to MnIII. Oxidation of the central MnII ion is not observed within the applied potential. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The homochiral, dimeric biphenolate alkyllanthanum complex [La{(R)-Biphen}{CH(SiMe3)2}]2 can be prepared by facile alkane elimination starting from [La{CH(SiMe3)2}3] and enantiopure (R)-3,3′-di-tert-butyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diol [H2{(R)-Biphen}]. Single-crystal X-ray diffraction revealed that the two La{(R)-Biphen}{CH(SiMe3)2} fragments are connected through bridging phenolate groups of the biphenolate ligands. The two different phenolate groups undergo an intramolecular exchange process in solution leading to their equivalence on the NMR timescale. The biphenolate alkyl complex shows high catalytic activity for hydroamination/cyclization of aminoalkenes, similar to previously known lanthanocene catalysts, but only low enantioselectivity. Addition of THF to [La{(R)-Biphen}{CH(SiMe3)2}]2 leads to a monomeric tris-THF adduct [La{(R)-Biphen}{CH(SiMe3)2}(THF)3] with higher catalytic activity than the THF-free homochiral dimer in the cyclization of 2,2-dimethylpent-4-enylamine, suggesting that the dimeric structure of the catalyst system prevails under catalytic conditions in the absence of THF. Addition of HN(SiHMe2)2 to [La{(R)-Biphen}{CH(SiMe3)2}(THF)3] results in the formation of [La{(R)-Biphen}{N(SiHMe2)2}(THF)3] which is in equilibrium with its homochiral dimer [La{(R)-Biphen}{N(SiHMe2)2}(THF)]2 at elevated temperatures. The biphenolate alkyl complexes exhibit good catalytic activity and diastereoselectivity in the hydrosilylation of styrene. Hydrosilylation of 1-hexene and norbornene also proceeds with high diastereoselectivity but rather low activity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

To study the interplay between the steric demand of the guest and the space available at the host, we have prepared the tetraammonium complexes {(NH4)4∩[Mg4(L1/2)6]} 1, tetrakis(methylammonium) complexes {(Me-NH3)4∩[Mg4(L1/2)6]} 2, tetrakis(ethylammonium) complex {(Et-NH3)4∩[Mg4(L1)6]} 3, and mixed sodium tris(ethylammonium) complex {Na(Et-NH3)3∩[Mg4(L2)6]} 4. The tetrahemispheraplexes 1−4 were available in one-pot syntheses. The tetrakis(alkylammonium) clusters {(R1−NH3)4∩[Mg4(L1)6]} 5 and the mixed diammonium-bis(p-methoxybenzylammonium) cluster {(NH4)2(R2−NH3)2∩[Mg4(L1)6]} 6, however, were prepared by exchange of the ammonium ions of 1a by alkylammonium ions. Similarly, exchange of the four ammonium ions of 1b by alkaline metal cations afforded the tetraalkaline metal tetrahemispheraplexes {M4∩[Mg4(L2)6]} 7. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Reaction of methanolic copper(II) acetate solution with oxazolidine 21 (HL7) led to the formation of the one-dimensional coordination polymer 1D-∞1[CuL27] 23. On the contrary, reaction of copper(II) acetate in methanol with pyrrolidine 24 (HL8) yielded the two-dimensional coordination polymer 2D-∞2[CuL28] 26. A common feature of 23 and 26 are the C2h-symmetric coordinatively unsaturated building blocks 22 and 25. In 1D-∞1[CuL27] 23, the cyano groups are linked to copper in a side-on fashion and the monomers 22 are oriented parallel to one another, whereas in 2D-∞2[CuL28] 26 the cyano groups are bound to copper in the end-on mode and the monomers 25 are oriented at an angle of 117° to one another. In both 1D-23 and 2D-26, copper has a distorted octahedral coordination sphere. On the other hand, reaction of methanolic copper(II) acetate solution with enantiomerically pure (5S)-pyrrolidine 27 (HL9(S)) led to the formation of the diastereomeric helical strands (M)-/(P)-1D-∞1[CuL29] 29. (M)- and (P)-29 are present in pairs in the infinite unit cell. In helical 1D-29, copper is tetragonal-pyramidally coordinated and the C2-symmetric monomers 28 (CuL29) are linked through only one cyano group. Moreover, it has been shown that the reaction of chiral racemic pyrrolidine 30 (HL10(R,S)) with copper(II) acetate via the intermediate Ci-symmetric building blocks 31 (CuL10(R)L10(S)) furnishes one-dimensional 1D-∞1[CuL10(R)L10(S)] 32. Single-crystal X-ray diffraction analyses of the supramolecular species 23, 26, 29, and 32 unequivocally establish the structures of these coordination polymers.