Assembly reactions that can prepare reliably regioselective metallamacrocyclic complexes have been a target in the development of metallacrowns. To this end, a series of mixed ligand and mixed ligand/mixed metal metallacrowns have been synthesized in high yield and structurally characterized. Two distinct connectivities have been observed in these types of metallacrowns. The monomeric, vacant metallacrown with mixed ligand composition [12-MC(Ni(II)N(Hshi)2(pko)2-4)] (1a) shows the connectivity pattern [-O-Ni-O-N-Ni-N-]2 while the other Ni metallacrowns, [12-MC(Ni(II)N(shi)2(pko)2-4)] (2a) and the coupled [12-MC(Ni(II)N(shi))2(pko)2-4)][12-MC(Ni(II)N(shi))3(pko)-4)] (3a) fused metallacrowns as well as the mixed metal Mn-Ni metallacrown [12-MC(Ni(II)Mn(III)N(shi)2(pko)2-4)] (4a), follow the pattern [-Ni-O-N-]4. Also, three distinct arrangements of the chelate rings around the metal ions have been observed. The syntheses are completely general, allowing for the substitution of different ligands into the metallacrown core. Compounds 1 and 4 show the 6-5-6-5-6-5-6-5 arrangement, compounds 2 and 3(1) the 6-6-5-5-6-6-5-5, and the 3(2) component the 6-6-5-5-6-5-6-5. The obtained structures can be rationalized by balancing the charge at each metal site in the metallacrown. Variable temperature magnetic susceptibility measurements show that exchange interactions for all the compounds are weak and dominantly antiferromagnetic (e.g., 2a gives an exchange coupling of J = -1.2 cm(-1) with g = 2.2). In solution, the metallacrowns are shown to be stable both to decomposition and ligand exchange.
The reaction of 1-chloro-1-boracyclohexa-2,5-diene with diisopropylamine or N-benzyl-N-methylamine followed by reaction with LDA in THF affords lithium N,N-diisopropyl-1-aminoboratabenzene (9b) or lithium N-benzyl-N-methyl-1-aminoboratabenzene (9c), respectively. The reaction of 9b with FeCl2 affords bis(N,N-diisopropyl-1-aminoboratabenzene)iron (18b), while the reaction of 9b or 9c with Mn(CO)3(CH3CN)3PF6 affords tricarbonyl[N,N-diisopropyl-1-aminoboratabenzene)manganese (19b) or tricarbonyl-1-(N-benzyl-N-methylamino) boratabenzene manganese (19c), respectively. Photochemical displacement of CO by PMe3 from 19b affords dicarbonyl(trimethylphosphine) (N-benzyl-N-methyl-1-aminoboratabenzene)manganese (20b). The rates of bond rotation about the B−N bonds of 9c, 18b, 19b,c, and 20b have been determined using variable-temperature NMR spectroscopy. The rates depend markedly on the electron-withdrawing power of the coordinating metal group. The boron atom is weakly coordinated to manganese (B−Mn = 2.485(3) Å) and strongly bound to nitrogen (B−N = 1.417 (3) Å).
Hydrolysis of Cp*SiCl 3 affords the silanetriol Cp*Si(OH) 3 (1) as an amorphous solid. Reaction of 1 with Me 3 SiCl/NEt 3 and with N(SnMe 3 ) 3 leads to Cp*Si-(OSiMe 3 ) 3 ( 2) and Cp*Si(OSnMe 3 ) 3 (3), respectively. From a concentrated solution of 1 in diethyl ether, the hemihydrate Cp*Si(OH) 3 ‚0.5 H 2 O ( 4) is obtained as colorless crystals. An X-ray crystal structure analysis of 4 reveals that Cp*Si(OH) 3 and water molecules are hydrogen-bonded to form a multilayer arrangement with the pentamethylcyclopentadienyl groups forming the hydrophobic outer sheets and the silanetriol groups together with the water molecules forming the hydrophilic inner sheets.
Novel oligomeric titanasiloxanes have been synthesized in good yields by reaction of sterically demanding organosilanetriols with titanium alkoxides. The silanetriols tBu2(Me3Si)FlSi(OH)3 (5), (Me3Si)FlSi(OH)3 (6), and MeFlSi(OH)3 (7) and the titanium alkoxides Ti(OEt)4, Ti(OiPr)4, and Ti(OiPr)2(acac)2 have been used as starting materials (Fl = fluorenyl). Quite different structures are obtained by only small modifications of the organic substituents of the substrates. Thus, the condensation reactions result in the formation of the polyhedral titanasiloxanes [tBu2(Me3Si)FlSi]4O12[TiOEt]4 (8), [(Me3Si)FlSi]2O5[Ti(OEt)]4[μ2-OEt]6[μ4-O] (9), ([tBu2(Me3Si)FlSi]3O10[Ti(OiPr)]4[μ2-OiPr]2[μ3-O]Ti)2O (10), and [MeFlSi]2O8[Ti(OiPr)]6[μ2-OiPr]4[μ3-O]2[PhNH2]2 (11) and the cyclic titanasiloxane [MeFlSi(OiPr)]2O4[Ti(acac)2]2 (12). A 1:1 stoichiometry of the starting materials leads to 8 and 12 in quantitative yield, while 9−11 are isolated in minor quantities. If the appropriate substrate ratio is used, the latter compounds can also be obtained in high yields. All titanasiloxanes have been characterized by X-ray crystallography, NMR, IR, and elemental analysis.
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